Collision Detection between two images in Java

Question

I have two characters displayed in a game I am writing  the player and the enemy  defined as such   public void player Graphics g        g drawImage plimg  x  y  this      public void enemy Graphics g        g drawImage enemy  200  200  this       Then called with   player g   enemy g     I am able to move player   around with the keyboard  but I am at a loss when trying to detect a collision between the two  A lot of people have said to use Rectangles  but being a beginner I cannot see how I would link this into my existing code  Can anyone offer some advice for me

User · Answer

No need to use rectangles     compare the coordinates of  2 players constantly   like  if x1   x amp  amp y1  y   remember to increase the range of x when ur comparing   if ur rectangle width is 30 take as if  x1 gt x amp  amp x2 gt x 30   likewise y

User · Answer

Since Java doesn t have an intersect function  really    you can do collision detection by simply comparying the X and Y  Width and Height values of the bounding boxes  rectangle  for each of the objects that could potentially collide   So     in the base object of each colliding object    i e  if your player and enemy have a common base you can put a simple Rectangle object called something like BoundingBox   If the common base is a built in Java class then you ll need to create a class that extends the build in class and have the player and enemy objects extend your new class or are instances of that class   At creation  and each tick or update  you ll need to set the BoundingBox paremeters for both your player and enemy   I don t have the Rectangle class infront of me but its most likely something like X  Y  Width and finally Height   X and Y are that objects location in your game world   The width and height are self explanatory I think   They ll most likely come out from the right of the players location though so  if the X and Y were bothe at 0 and your Width and Height were both at 256 you wouldn t see anything because the character would be at the top left outside of the screen   Anyways    to detect a collision  you ll want to compare the attributes of the player and enemy BoundingBoxes   So something like this      if  Player BoundingBox X   Enemy BoundingBox X  amp  amp  If  Player BoundingBox Y   Enemy BoundingBox Y              Oh noes   The enemy and player are on top of eachother       The logic can get sort of complicated but you ll need to compare the distances between each BoundingBox and compare locations

User · Answer

Use a rectangle to surround each player and enemy  the height and width of the rectangles should correspond to the object you re surrounding  imagine it being in a box only big enough to fit it   Now  you move these rectangles the same as you do the objects  so they have a  bounding box   I m not sure if Java has this  but it might have a method on the rectangle object called  intersects   so you d do if rectangle1 intersectS rectangle2  to check to see if an object has collided with another   Otherwise you can get the x and y co-ordinates of the boxes and using the height width of them detect whether they ve intersected yourself   Anyway  you can use that to either do an event on intersection  make one explode  or whatever  or prevent the movement from being drawn   revert to previous co-ordinates   edit  here we go  boolean         intersects Rectangle r               Determines whether or not this Rectangle and the specified   Rectangle intersect    So I would do  and don t paste this code  it most likely won t work  not done java for a long time and I didn t do graphics when I did use it    Rectangle rect1   new Rectangle player x  player y  player width  player height    Rectangle rect2   new Rectangle enemy x  enemy y  enemy width  enemy height      detects when the two rectangles hit if rect1 intersects rect2      System out println  game over  g        obviously you d need to fit that in somewhere

User · Answer

Here s the main class from my collision detection program  You can see it run at  http   www youtube com watch v JIXhCvXgjsQ             author Tyler Griffin     import java awt    import javax swing    import java awt event    import java awt GraphicsDevice    import java util ArrayList  import java awt Graphics  import java awt geom Line2D    public class collision extends JFrame implements KeyListener  MouseMotionListener  MouseListener       ArrayList everything new ArrayList lt tile gt          int time 0  x  y  width  height  up 0  down 0  left 0  right 0  mouse1 0  mouse2 0      int mouseX  mouseY       GraphicsEnvironment environment   GraphicsEnvironment getLocalGraphicsEnvironment        GraphicsDevice screen   environment getDefaultScreenDevice        DisplayMode displayMode   screen getDisplayMode           private BufferStrategy strategy       JLayeredPane pane   new JLayeredPane          tile Tile       circle Circle       rectangle Rectangle            textPane text       public collision                 setUndecorated screen isFullScreenSupported             setDefaultCloseOperation JFrame EXIT ON CLOSE           setVisible true           setLayout null           setResizable false           screen setFullScreenWindow this             width displayMode getWidth            height displayMode getHeight                Circle new circle - int Math round  double height 7 2  - int Math round  double height 7 2   int Math round  double height 7  85  this             Rectangle new rectangle - int Math round  double height 7 1 5  - int Math round  double height 7 1 5   int Math round  double height 7 1 5   int Math round  double height 7 1 5  this             Tile Circle            Tile move mouseX-Tile width 2  mouseY-Tile height 2                     text new textPane 0 0 width height this              everything add new circle  int Math round  double width 100 75   int Math round  double height 100 15   int Math round  double width 100 10  this                      everything add new rectangle  int Math round  double width 100 70   int Math round  double height 100 60   int Math round  double width 100 20   int Math round  double height 100 20  this                        everything add new line 750 250 750 750 this                        everything add new line width 700 419 height 700 68 width 700 495 height 700 345 this                      everything add new line width 700 495 height 700 345 width 700 749 height 700 350 this                      everything add new line width 700 749 height 700 350 width 700 549 height 700 519 this                      everything add new line width 700 549 height 700 519 width 700 624 height 700 800 this                      everything add new line width 700 624 height 700 800 width 700 419 height 700 638 this                      everything add new line width 700 419 height 700 638 width 700 203 height 700 800 this                      everything add new line width 700 203 height 700 800 width 700 279 height 700 519 this                      everything add new line width 700 279 height 700 519 width 700 76 height 700 350 this                      everything add new line width 700 76 height 700 350 width 700 333 height 700 345 this                      everything add new line width 700 333 height 700 345 width 700 419 height 700 68 this                       everything add new line width 950 419 height 700 68 width 950 624 height 700 800 this                      everything add new line width 950 419 height 700 68 width 950 203 height 700 800 this                      everything add new line width 950 76 height 700 350 width 950 624 height 700 800 this                      everything add new line width 950 203 height 700 800 width 950 749 height 700 350 this                      everything add new rectangle width 950 76 height 700 350 width 950 673 1 this                         everything add new line  int Math round  double width 1350 419   int Math round  double height 1000 68   int Math round  double width 1350 624   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 419   int Math round  double height 1000 68   int Math round  double width 1350 203   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 76   int Math round  double height 1000 350   int Math round  double width 1350 624   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 203   int Math round  double height 1000 800   int Math round  double width 1350 749   int Math round  double height 1000 350  this                      everything add new rectangle  int Math round  double width 1350 76   int Math round  double height 1000 350   int Math round  double width 1350 673  1 this              addKeyListener this           addMouseMotionListener this           addMouseListener this              public void keyReleased KeyEvent e                Object source e getSource             int released e getKeyCode             if  released  KeyEvent VK A  left 0           if  released  KeyEvent VK W  up 0           if  released  KeyEvent VK D  right 0           if  released  KeyEvent VK S  down 0          end keyReleased       public void keyPressed KeyEvent e                Object source e getSource             int pressed e getKeyCode             if  pressed  KeyEvent VK A  left 1           if  pressed  KeyEvent VK W  up 1           if  pressed  KeyEvent VK D  right 1           if  pressed  KeyEvent VK S  down 1            if  pressed  KeyEvent VK PAUSE amp  amp pressed  KeyEvent VK P                          if  paused  0  paused 1                 else paused 0                   end keyPressed      public void keyTyped KeyEvent e                                                                                                            public void mouseDragged MouseEvent e                mouseX  e getX             mouseY  e getY                  run               public void mouseMoved MouseEvent e                mouseX  e getX             mouseY  e getY                  run                                                                                                                  public void mousePressed MouseEvent e                if e getX    0  amp  amp  e getY    0  System exit 0         mouseX  e getX   x           mouseY  e getY   y            if Tile instanceof circle                            Circle move 0-Circle width  0-Circle height                   Circle setBounds Circle x  Circle y  Circle width  Circle height                   Tile Rectangle                    else                           Rectangle move 0-Rectangle width  0-Rectangle height                   Rectangle setBounds Rectangle x  Rectangle y  Rectangle width  Rectangle height                   Tile Circle                     Tile move mouseX-Tile width 2  mouseY-Tile height 2              public void mouseReleased MouseEvent e                   run               public void mouseEntered MouseEvent e        public void mouseExited MouseEvent e         public void mouseClicked MouseEvent e                                                                                                            public void run    run collision detection               while  this    this                        Tile move Tile x     mouseX -  Tile x    Tile width   2      10   Tile y     mouseY -  Tile y    Tile height   2      10                  Tile move  mouseX - Tile width   2   mouseY -  Tile height   2                 for  int i   0  i  lt  everything size    i                                  tile Temp    tile  everything get i                    if  Temp x  lt   Tile x   Tile width   amp  amp   Temp x   Temp width   gt  Tile x  amp  amp  Temp y  lt   Tile y   Tile height   amp  amp   Temp y   Temp height   gt  Tile y   rectangles collided                                       if  Temp instanceof rectangle                                                if  Tile instanceof rectangle  rectangleRectangle Temp                            else  circleRectangle Temp     Tile instanceof circle                                           else                                               if  Temp instanceof circle                                                        if  Tile instanceof rectangle   rectangleCircle Temp                                else  circleCircle Temp                                                      else  line                                                       if  Tile instanceof rectangle  rectangleLine Temp                                else circleLine Temp                                                                       end if                end for              try  Thread sleep 16L                catch  Exception e                  Tile setBounds Tile x  Tile y  Tile width  Tile height                 Rectangle setBounds x  y  width  height                 Circle setBounds x  y  width  height               repaint                 text out                 end while loop        end run                                           special collision detection handling functions                                                      void rectangleRectangle tile Temp                int lapTop  lapBot  lapLeft  lapRight  small  scootX 0  scootY 0           lapTop  Temp y Temp height -Tile y          lapBot  Tile y Tile height -Temp y          lapLeft  Temp x Temp width -Tile x          lapRight  Tile x Tile width -Temp x           small 999999999           if  lapTop lt small  small lapTop  scootX 0  scootY lapTop           if  lapBot lt small  small lapBot  scootX 0  scootY lapBot -1                   if  lapLeft lt small  small lapLeft  scootX lapLeft  scootY 0                   if  lapRight lt small  small lapRight  scootX lapRight -1  scootY 0            Tile move Tile x scootX  Tile y scootY  text out  collision detected                 void circleRectangle tile Temp                if  Tile x Tile width 2 lt  Temp x Temp width  amp  amp  Tile x Tile width 2 gt  Temp x    Tile y Tile height 2 gt  Temp y  amp  amp  Tile y Tile height 2 lt  Temp y Temp height                         rectangleRectangle Temp                     else  push from nearest corner                       int x y              if Tile x Tile width 2 gt Temp x Temp width  amp  amp  Tile y Tile height 2 lt Temp y  x Temp x Temp width  y Temp y               else if Tile x Tile width 2 lt Temp x  amp  amp  Tile y Tile height 2 lt Temp y  x Temp x  y Temp y               else if Tile x Tile width 2 gt Temp x Temp width  amp  amp  Tile y Tile height 2 gt Temp y Temp height  x Temp x Temp width  y Temp y Temp height               else  x Temp x  y Temp y Temp height                double distance   Math sqrt Math pow Tile x  Tile width 2  - x  2    Math pow Tile y  Tile height 2  - y  2                 if  int Math round distance  lt Tile height 2                                             double normY     Tile y  Tile height 2  - y    distance                                double normX     Tile x  Tile width 2  - x    distance                                Tile move x-Tile width 2  int Math round normX   Tile width 2      y-Tile height 2  int Math round normY   Tile height 2     text out  collision detected                                         void rectangleCircle tile Temp                if  Temp x Temp width 2 lt  Tile x Tile width  amp  amp  Temp x Temp width 2 gt  Tile x    Temp y Temp height 2 gt  Tile y  amp  amp  Temp y Temp height 2 lt  Tile y Tile height                         rectangleRectangle Temp                     else  push from nearest corner                       int x y              if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 lt Tile y  x Tile x Tile width  y Tile y               else if Temp x Temp width 2 lt Tile x  amp  amp  Temp y Temp height 2 lt Tile y  x Tile x  y Tile y               else if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 gt Tile y Tile height  x Tile x Tile width  y Tile y Tile height               else  x Tile x  y Tile y Tile height                double distance   Math sqrt Math pow Temp x  Temp width 2  - x  2    Math pow Temp y  Temp height 2  - y  2                 if  int Math round distance  lt Temp height 2                             double normY     Temp y  Temp height 2  - y    distance                double normX     Temp x  Temp width 2  - x    distance                 if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 lt Tile y  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2   -Tile width  Temp y Temp height 2 - int Math round normY   Temp height 2     text out  collision detected                     else if Temp x Temp width 2 lt Tile x  amp  amp  Temp y Temp height 2 lt Tile y  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2     Temp y Temp height 2 - int Math round normY   Temp height 2     text out  collision detected                     else if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 gt Tile y Tile height  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2   -Tile width  Temp y Temp height 2 - int Math round normY   Temp height 2   -Tile height  text out  collision detected                     else  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2     Temp y Temp height 2 - int Math round normY   Temp height 2   -Tile height  text out  collision detected                                           void circleCircle tile Temp                double distance   Math sqrt Math pow  Tile x  Tile width 2   -  Temp x  Temp width 2   2    Math pow  Tile y  Tile height 2   -  Temp y  Temp height 2    2             if  int distance lt  Tile width 2 Temp width 2                                     double normX     Tile x  Tile width 2   -  Temp x  Temp width 2      distance                          double normY     Tile y  Tile height 2   -  Temp y  Temp height 2      distance               Tile move  Temp x  Temp width 2    int Math round normX  Tile width 2 Temp width 2  - Tile width 2     Temp y  Temp height 2    int Math round normY  Tile height 2 Temp height 2  - Tile height 2   text out  collision detected                           void circleLine tile Temp                    line Line  line Temp               if  Line x1  lt   Tile x   Tile width   amp  amp   Line x1   gt  Tile x  amp  amp  Line y1  lt   Tile y   Tile height   amp  amp  Line y1  gt  Tile y   circle may be hitting one of the end points                               rectangle rec new rectangle Line x1  Line y1  1  1  this                   circleRectangle rec                   remove rec                              if  Line x2  lt   Tile x   Tile width   amp  amp   Line x2   gt  Tile x  amp  amp  Line y2  lt   Tile y   Tile height   amp  amp  Line y2  gt  Tile y   circle may be hitting one of the end points                               rectangle rec new rectangle Line x2  Line y2  1  1  this                   circleRectangle rec                   remove rec                               int x1 0  y1 0  x2 Tile x  Tile width 2   y2 Tile y  Tile height 2                x1 Tile x  Tile width 2 -Line height    int Math round Line xNorm 1000               x2 Tile x  Tile width 2  Line height              if Line posSlope                                y1 Tile y  Tile height 2 -Line width                  y2 Tile y  Tile height 2  Line width                            else                               y1 Tile y  Tile height 2  Line width                  y2 Tile y  Tile height 2 -Line width                             Point point intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection              if  point x  lt   Line x   Line width   amp  amp  point x  gt  Line x  amp  amp  point y  lt   Line y   Line height   amp  amp  point y  gt  Line y   line intersects within line segment                                 if point  null  System out println point x     point y                    double distance   Math sqrt Math pow  Tile x  Tile width 2   - point x 2    Math pow  Tile y  Tile width 2   - point y  2                     if  int distance lt Tile width 2                                          System out println  hit                        double normX     Tile x  Tile width 2   - point x    distance                      double normY     Tile y  Tile height 2   - point y    distance                       Tile move  point x   int Math round normX  Tile width 2  - Tile width 2     point y   int Math round normY  Tile height 2  - Tile height 2   text out  collision detected                          System out println point x     point y                                                  new bullet this   int Math round tryX    int Math round tryY                   void rectangleLine tile Temp                    line Line  line Temp              if new Line2D Double Line x1 Line y1 Line x2 Line y2  intersects new Rectangle Tile x Tile y Tile width Tile height                                  if  Line x1  lt   Tile x   Tile width   amp  amp   Line x1   gt  Tile x  amp  amp  Line y1  lt   Tile y   Tile height   amp  amp  Line y1  gt  Tile y   circle may be hitting one of the end points                                       rectangle rec new rectangle Line x1  Line y1  1  1  this                       rectangleRectangle rec                       remove rec                                      if  Line x2  lt   Tile x   Tile width   amp  amp   Line x2   gt  Tile x  amp  amp  Line y2  lt   Tile y   Tile height   amp  amp  Line y2  gt  Tile y   circle may be hitting one of the end points                                       rectangle rec new rectangle Line x2  Line y2  1  1  this                       rectangleRectangle rec                       remove rec                                      if Line posSlope   positive sloped line                                         first we ll do the top left corner                     int x1 Tile x-Line height                      int x2 Tile x Line height                      int y1 Tile y-Line width                      int y2 Tile y Line width                      Point topPoint new Point -99 -99   botPoint new Point -99 -99                       double topDistance 0  botDistance 0                       topPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      topDistance   Math sqrt Math pow Tile x - topPoint x 2    Math pow Tile y - topPoint y  2                           new let s do the bottom right corner                     x1 Tile x Tile width-Line height                      x2 Tile x Tile width Line height                      y1 Tile y Tile height-Line width                      y2 Tile y Tile height Line width                       botPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      botDistance   Math sqrt Math pow  Tile x Tile width  - botPoint x 2    Math pow  Tile y Tile height  - botPoint y  2                          if topDistance lt botDistance                                                if new Rectangle Tile x Tile y Tile width Tile height  contains topPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains topPoint                                                         Tile move topPoint x topPoint y  text out  collision detected                                                                        else                                               if new Rectangle Tile x Tile y Tile width Tile height  contains botPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains botPoint                                                         Tile move botPoint x-Tile width botPoint y-Tile height  text out  collision detected                                                                                      else  negative sloped lne                                         first we ll do the top right corner                     int x1 Tile x Tile width-Line height                      int x2 Tile x Tile width Line height                      int y1 Tile y Line width                      int y2 Tile y-Line width                      Point topPoint new Point -99 -99   botPoint new Point -99 -99                       double topDistance 0  botDistance 0                       topPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      topDistance   Math sqrt Math pow Tile x   Tile width - topPoint x 2    Math pow Tile y - topPoint y  2                           new let s do the bottom left corner                     x1 Tile x-Line height                      x2 Tile x Line height                      y1 Tile y Tile height Line width                      y2 Tile y Tile height-Line width                       botPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      botDistance   Math sqrt Math pow Tile x - botPoint x 2    Math pow  Tile y Tile height  - botPoint y  2                          if topDistance lt botDistance                                                if new Rectangle Tile x Tile y Tile width Tile height  contains topPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains topPoint                                                         Tile move topPoint x-Tile width topPoint y  text out  collision detected                                                                        else                                               if new Rectangle Tile x Tile y Tile width Tile height  contains botPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains botPoint                                                         Tile move botPoint x botPoint y-Tile height  text out  collision detected                                                                                                  public Point intersection double x1  double y1  double x2  double y2 double x3  double y3  double x4  double y4   I didn t write this  got it from http   www ahristov com tutorial geometry-games intersection-lines html  I altered it                       double d    x1 - x2     y3 - y4  -  y1 - y2     x3 - x4                double xi     x3 - x4     x1   y2 - y1   x2  -  x1 - x2     x3   y4 - y3   x4     d              double yi     y3 - y4     x1   y2 - y1   x2  -  y1 - y2     x3   y4 - y3   x4     d               int x  int Math round xi               int y  int Math round yi                return new Point x  y                                                                                                             public static void main String   args                final collision Collision new collision              Collision run           end main    end class

User · Answer

Since Java doesn t have an intersect function  really    you can do collision detection by simply comparying the X and Y  Width and Height values of the bounding boxes  rectangle  for each of the objects that could potentially collide   So     in the base object of each colliding object    i e  if your player and enemy have a common base you can put a simple Rectangle object called something like BoundingBox   If the common base is a built in Java class then you ll need to create a class that extends the build in class and have the player and enemy objects extend your new class or are instances of that class   At creation  and each tick or update  you ll need to set the BoundingBox paremeters for both your player and enemy   I don t have the Rectangle class infront of me but its most likely something like X  Y  Width and finally Height   X and Y are that objects location in your game world   The width and height are self explanatory I think   They ll most likely come out from the right of the players location though so  if the X and Y were bothe at 0 and your Width and Height were both at 256 you wouldn t see anything because the character would be at the top left outside of the screen   Anyways    to detect a collision  you ll want to compare the attributes of the player and enemy BoundingBoxes   So something like this      if  Player BoundingBox X   Enemy BoundingBox X  amp  amp  If  Player BoundingBox Y   Enemy BoundingBox Y              Oh noes   The enemy and player are on top of eachother       The logic can get sort of complicated but you ll need to compare the distances between each BoundingBox and compare locations

User · Answer

You don t want to have the collision check code inside the painting code   The painting needs to be fast   Collision can go in the game loop   Therefore you need an internal representation of the objects independent of their sprites

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First  use the bounding boxes as described by Jonathan Holland to find if you may have a collision   From the  multi-color  sprites  create black and white versions  You probably already have these if your sprites are transparent  i e  there are places which are inside the bounding box but you can still see the background   These are  masks    Use Image getRGB   on the mask to get at the pixels  For each pixel which isn t transparent  set a bit in an integer array  playerArray and enemyArray below   The size of the array is height if width  lt   32 pixels   width 31  32 height otherwise  The code below is for width  lt   32   If you have a collision of the bounding boxes  do this      Find the first line where the two sprites might overlap int linePlayer  lineEnemy  if  player y  lt   enemy y        linePlayer   enemy y - player y      lineEnemy   0    else       linePlayer   0      lineEnemy   player y - enemy y    int line   Math max linePlayer  lineEnemy       Get the shift between the two x   player x - enemy x  int maxLines   Math max player height  enemy height   for   line  lt  maxLines  line              if width  gt  32  then you need a second loop here     long playerMask   playerArray linePlayer       long enemyMask   enemyArray lineEnemy          Reproduce the shift between the two sprites     if  x  lt  0  playerMask  lt  lt   -x       else enemyMask  lt  lt  x         If the two masks have common bits  binary AND will return    0     if   playerMask  amp  enemyMask     0               Contact             Links  JGame  Framework for Small Java Games

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Here s a useful of an open source game that uses a lot of collisions  http   robocode sourceforge net    You may take a look at the code and complement with the answers written here

User · Answer

Use a rectangle to surround each player and enemy  the height and width of the rectangles should correspond to the object you re surrounding  imagine it being in a box only big enough to fit it   Now  you move these rectangles the same as you do the objects  so they have a  bounding box   I m not sure if Java has this  but it might have a method on the rectangle object called  intersects   so you d do if rectangle1 intersectS rectangle2  to check to see if an object has collided with another   Otherwise you can get the x and y co-ordinates of the boxes and using the height width of them detect whether they ve intersected yourself   Anyway  you can use that to either do an event on intersection  make one explode  or whatever  or prevent the movement from being drawn   revert to previous co-ordinates   edit  here we go  boolean         intersects Rectangle r               Determines whether or not this Rectangle and the specified   Rectangle intersect    So I would do  and don t paste this code  it most likely won t work  not done java for a long time and I didn t do graphics when I did use it    Rectangle rect1   new Rectangle player x  player y  player width  player height    Rectangle rect2   new Rectangle enemy x  enemy y  enemy width  enemy height      detects when the two rectangles hit if rect1 intersects rect2      System out println  game over  g        obviously you d need to fit that in somewhere

User · Answer

Since Java doesn t have an intersect function  really    you can do collision detection by simply comparying the X and Y  Width and Height values of the bounding boxes  rectangle  for each of the objects that could potentially collide   So     in the base object of each colliding object    i e  if your player and enemy have a common base you can put a simple Rectangle object called something like BoundingBox   If the common base is a built in Java class then you ll need to create a class that extends the build in class and have the player and enemy objects extend your new class or are instances of that class   At creation  and each tick or update  you ll need to set the BoundingBox paremeters for both your player and enemy   I don t have the Rectangle class infront of me but its most likely something like X  Y  Width and finally Height   X and Y are that objects location in your game world   The width and height are self explanatory I think   They ll most likely come out from the right of the players location though so  if the X and Y were bothe at 0 and your Width and Height were both at 256 you wouldn t see anything because the character would be at the top left outside of the screen   Anyways    to detect a collision  you ll want to compare the attributes of the player and enemy BoundingBoxes   So something like this      if  Player BoundingBox X   Enemy BoundingBox X  amp  amp  If  Player BoundingBox Y   Enemy BoundingBox Y              Oh noes   The enemy and player are on top of eachother       The logic can get sort of complicated but you ll need to compare the distances between each BoundingBox and compare locations

User · Answer

Use a rectangle to surround each player and enemy  the height and width of the rectangles should correspond to the object you re surrounding  imagine it being in a box only big enough to fit it   Now  you move these rectangles the same as you do the objects  so they have a  bounding box   I m not sure if Java has this  but it might have a method on the rectangle object called  intersects   so you d do if rectangle1 intersectS rectangle2  to check to see if an object has collided with another   Otherwise you can get the x and y co-ordinates of the boxes and using the height width of them detect whether they ve intersected yourself   Anyway  you can use that to either do an event on intersection  make one explode  or whatever  or prevent the movement from being drawn   revert to previous co-ordinates   edit  here we go  boolean         intersects Rectangle r               Determines whether or not this Rectangle and the specified   Rectangle intersect    So I would do  and don t paste this code  it most likely won t work  not done java for a long time and I didn t do graphics when I did use it    Rectangle rect1   new Rectangle player x  player y  player width  player height    Rectangle rect2   new Rectangle enemy x  enemy y  enemy width  enemy height      detects when the two rectangles hit if rect1 intersects rect2      System out println  game over  g        obviously you d need to fit that in somewhere

User · Answer

is there a problem with   Rectangle box1   new Rectangle 100 100 100 100   Rectangle box2   new Rectangle 200 200 100 100       what this means is if any pixel in box2 enters  hits  box1 if  box1 contains box2              collision occurred       your code for moving the boxes      this can also be applied to circles    Ellipse2D Double ball1   new Ellipse2D Double 100 100 200 200   Ellipse2D Double ball2   new Ellipse2D Double 400 100 200 200       what this means is if any pixel on the circumference in ball2 touches  hits     ball1     if  ball1 contains ball2                      collision occurred               your code for moving the balls    to check whether youve hit the edge of a screen you could use the following    Rectangle screenBounds   jpanel getBounds    Ellipse2D Double ball   new Ellipse2D Double 100 100 200 200       diameter 200 Rectangle ballBounds   ball getBounds     if   screenBounds contains ballBounds        the ball touched the edge of the screen

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I think your problem is that you are not using good OO design for your player and enemies  Create two classes   public class Player       int X      int Y      int Width      int Height          Getters and Setters    public class Enemy       int X      int Y      int Width      int Height          Getters and Setters     Your Player should have X Y Width and Height variables   Your enemies should as well   In your game loop  do something like this  C     foreach  Enemy e in EnemyCollection        Rectangle r   new Rectangle e X e Y e Width e Height       Rectangle p   new Rectangle player X player Y player Width player Height           Assuming there is an intersect method  otherwise just handcompare the values     if  r Intersects p                   A Collision            we know which enemy  e   so we can call e DoCollision           e DoCollision              To speed things up  don t bother checking if the enemies coords are offscreen

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I think your problem is that you are not using good OO design for your player and enemies  Create two classes   public class Player       int X      int Y      int Width      int Height          Getters and Setters    public class Enemy       int X      int Y      int Width      int Height          Getters and Setters     Your Player should have X Y Width and Height variables   Your enemies should as well   In your game loop  do something like this  C     foreach  Enemy e in EnemyCollection        Rectangle r   new Rectangle e X e Y e Width e Height       Rectangle p   new Rectangle player X player Y player Width player Height           Assuming there is an intersect method  otherwise just handcompare the values     if  r Intersects p                   A Collision            we know which enemy  e   so we can call e DoCollision           e DoCollision              To speed things up  don t bother checking if the enemies coords are offscreen

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Here s a useful of an open source game that uses a lot of collisions  http   robocode sourceforge net    You may take a look at the code and complement with the answers written here

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You don t want to have the collision check code inside the painting code   The painting needs to be fast   Collision can go in the game loop   Therefore you need an internal representation of the objects independent of their sprites

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Here s the main class from my collision detection program  You can see it run at  http   www youtube com watch v JIXhCvXgjsQ             author Tyler Griffin     import java awt    import javax swing    import java awt event    import java awt GraphicsDevice    import java util ArrayList  import java awt Graphics  import java awt geom Line2D    public class collision extends JFrame implements KeyListener  MouseMotionListener  MouseListener       ArrayList everything new ArrayList lt tile gt          int time 0  x  y  width  height  up 0  down 0  left 0  right 0  mouse1 0  mouse2 0      int mouseX  mouseY       GraphicsEnvironment environment   GraphicsEnvironment getLocalGraphicsEnvironment        GraphicsDevice screen   environment getDefaultScreenDevice        DisplayMode displayMode   screen getDisplayMode           private BufferStrategy strategy       JLayeredPane pane   new JLayeredPane          tile Tile       circle Circle       rectangle Rectangle            textPane text       public collision                 setUndecorated screen isFullScreenSupported             setDefaultCloseOperation JFrame EXIT ON CLOSE           setVisible true           setLayout null           setResizable false           screen setFullScreenWindow this             width displayMode getWidth            height displayMode getHeight                Circle new circle - int Math round  double height 7 2  - int Math round  double height 7 2   int Math round  double height 7  85  this             Rectangle new rectangle - int Math round  double height 7 1 5  - int Math round  double height 7 1 5   int Math round  double height 7 1 5   int Math round  double height 7 1 5  this             Tile Circle            Tile move mouseX-Tile width 2  mouseY-Tile height 2                     text new textPane 0 0 width height this              everything add new circle  int Math round  double width 100 75   int Math round  double height 100 15   int Math round  double width 100 10  this                      everything add new rectangle  int Math round  double width 100 70   int Math round  double height 100 60   int Math round  double width 100 20   int Math round  double height 100 20  this                        everything add new line 750 250 750 750 this                        everything add new line width 700 419 height 700 68 width 700 495 height 700 345 this                      everything add new line width 700 495 height 700 345 width 700 749 height 700 350 this                      everything add new line width 700 749 height 700 350 width 700 549 height 700 519 this                      everything add new line width 700 549 height 700 519 width 700 624 height 700 800 this                      everything add new line width 700 624 height 700 800 width 700 419 height 700 638 this                      everything add new line width 700 419 height 700 638 width 700 203 height 700 800 this                      everything add new line width 700 203 height 700 800 width 700 279 height 700 519 this                      everything add new line width 700 279 height 700 519 width 700 76 height 700 350 this                      everything add new line width 700 76 height 700 350 width 700 333 height 700 345 this                      everything add new line width 700 333 height 700 345 width 700 419 height 700 68 this                       everything add new line width 950 419 height 700 68 width 950 624 height 700 800 this                      everything add new line width 950 419 height 700 68 width 950 203 height 700 800 this                      everything add new line width 950 76 height 700 350 width 950 624 height 700 800 this                      everything add new line width 950 203 height 700 800 width 950 749 height 700 350 this                      everything add new rectangle width 950 76 height 700 350 width 950 673 1 this                         everything add new line  int Math round  double width 1350 419   int Math round  double height 1000 68   int Math round  double width 1350 624   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 419   int Math round  double height 1000 68   int Math round  double width 1350 203   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 76   int Math round  double height 1000 350   int Math round  double width 1350 624   int Math round  double height 1000 800  this                      everything add new line  int Math round  double width 1350 203   int Math round  double height 1000 800   int Math round  double width 1350 749   int Math round  double height 1000 350  this                      everything add new rectangle  int Math round  double width 1350 76   int Math round  double height 1000 350   int Math round  double width 1350 673  1 this              addKeyListener this           addMouseMotionListener this           addMouseListener this              public void keyReleased KeyEvent e                Object source e getSource             int released e getKeyCode             if  released  KeyEvent VK A  left 0           if  released  KeyEvent VK W  up 0           if  released  KeyEvent VK D  right 0           if  released  KeyEvent VK S  down 0          end keyReleased       public void keyPressed KeyEvent e                Object source e getSource             int pressed e getKeyCode             if  pressed  KeyEvent VK A  left 1           if  pressed  KeyEvent VK W  up 1           if  pressed  KeyEvent VK D  right 1           if  pressed  KeyEvent VK S  down 1            if  pressed  KeyEvent VK PAUSE amp  amp pressed  KeyEvent VK P                          if  paused  0  paused 1                 else paused 0                   end keyPressed      public void keyTyped KeyEvent e                                                                                                            public void mouseDragged MouseEvent e                mouseX  e getX             mouseY  e getY                  run               public void mouseMoved MouseEvent e                mouseX  e getX             mouseY  e getY                  run                                                                                                                  public void mousePressed MouseEvent e                if e getX    0  amp  amp  e getY    0  System exit 0         mouseX  e getX   x           mouseY  e getY   y            if Tile instanceof circle                            Circle move 0-Circle width  0-Circle height                   Circle setBounds Circle x  Circle y  Circle width  Circle height                   Tile Rectangle                    else                           Rectangle move 0-Rectangle width  0-Rectangle height                   Rectangle setBounds Rectangle x  Rectangle y  Rectangle width  Rectangle height                   Tile Circle                     Tile move mouseX-Tile width 2  mouseY-Tile height 2              public void mouseReleased MouseEvent e                   run               public void mouseEntered MouseEvent e        public void mouseExited MouseEvent e         public void mouseClicked MouseEvent e                                                                                                            public void run    run collision detection               while  this    this                        Tile move Tile x     mouseX -  Tile x    Tile width   2      10   Tile y     mouseY -  Tile y    Tile height   2      10                  Tile move  mouseX - Tile width   2   mouseY -  Tile height   2                 for  int i   0  i  lt  everything size    i                                  tile Temp    tile  everything get i                    if  Temp x  lt   Tile x   Tile width   amp  amp   Temp x   Temp width   gt  Tile x  amp  amp  Temp y  lt   Tile y   Tile height   amp  amp   Temp y   Temp height   gt  Tile y   rectangles collided                                       if  Temp instanceof rectangle                                                if  Tile instanceof rectangle  rectangleRectangle Temp                            else  circleRectangle Temp     Tile instanceof circle                                           else                                               if  Temp instanceof circle                                                        if  Tile instanceof rectangle   rectangleCircle Temp                                else  circleCircle Temp                                                      else  line                                                       if  Tile instanceof rectangle  rectangleLine Temp                                else circleLine Temp                                                                       end if                end for              try  Thread sleep 16L                catch  Exception e                  Tile setBounds Tile x  Tile y  Tile width  Tile height                 Rectangle setBounds x  y  width  height                 Circle setBounds x  y  width  height               repaint                 text out                 end while loop        end run                                           special collision detection handling functions                                                      void rectangleRectangle tile Temp                int lapTop  lapBot  lapLeft  lapRight  small  scootX 0  scootY 0           lapTop  Temp y Temp height -Tile y          lapBot  Tile y Tile height -Temp y          lapLeft  Temp x Temp width -Tile x          lapRight  Tile x Tile width -Temp x           small 999999999           if  lapTop lt small  small lapTop  scootX 0  scootY lapTop           if  lapBot lt small  small lapBot  scootX 0  scootY lapBot -1                   if  lapLeft lt small  small lapLeft  scootX lapLeft  scootY 0                   if  lapRight lt small  small lapRight  scootX lapRight -1  scootY 0            Tile move Tile x scootX  Tile y scootY  text out  collision detected                 void circleRectangle tile Temp                if  Tile x Tile width 2 lt  Temp x Temp width  amp  amp  Tile x Tile width 2 gt  Temp x    Tile y Tile height 2 gt  Temp y  amp  amp  Tile y Tile height 2 lt  Temp y Temp height                         rectangleRectangle Temp                     else  push from nearest corner                       int x y              if Tile x Tile width 2 gt Temp x Temp width  amp  amp  Tile y Tile height 2 lt Temp y  x Temp x Temp width  y Temp y               else if Tile x Tile width 2 lt Temp x  amp  amp  Tile y Tile height 2 lt Temp y  x Temp x  y Temp y               else if Tile x Tile width 2 gt Temp x Temp width  amp  amp  Tile y Tile height 2 gt Temp y Temp height  x Temp x Temp width  y Temp y Temp height               else  x Temp x  y Temp y Temp height                double distance   Math sqrt Math pow Tile x  Tile width 2  - x  2    Math pow Tile y  Tile height 2  - y  2                 if  int Math round distance  lt Tile height 2                                             double normY     Tile y  Tile height 2  - y    distance                                double normX     Tile x  Tile width 2  - x    distance                                Tile move x-Tile width 2  int Math round normX   Tile width 2      y-Tile height 2  int Math round normY   Tile height 2     text out  collision detected                                         void rectangleCircle tile Temp                if  Temp x Temp width 2 lt  Tile x Tile width  amp  amp  Temp x Temp width 2 gt  Tile x    Temp y Temp height 2 gt  Tile y  amp  amp  Temp y Temp height 2 lt  Tile y Tile height                         rectangleRectangle Temp                     else  push from nearest corner                       int x y              if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 lt Tile y  x Tile x Tile width  y Tile y               else if Temp x Temp width 2 lt Tile x  amp  amp  Temp y Temp height 2 lt Tile y  x Tile x  y Tile y               else if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 gt Tile y Tile height  x Tile x Tile width  y Tile y Tile height               else  x Tile x  y Tile y Tile height                double distance   Math sqrt Math pow Temp x  Temp width 2  - x  2    Math pow Temp y  Temp height 2  - y  2                 if  int Math round distance  lt Temp height 2                             double normY     Temp y  Temp height 2  - y    distance                double normX     Temp x  Temp width 2  - x    distance                 if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 lt Tile y  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2   -Tile width  Temp y Temp height 2 - int Math round normY   Temp height 2     text out  collision detected                     else if Temp x Temp width 2 lt Tile x  amp  amp  Temp y Temp height 2 lt Tile y  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2     Temp y Temp height 2 - int Math round normY   Temp height 2     text out  collision detected                     else if Temp x Temp width 2 gt Tile x Tile width  amp  amp  Temp y Temp height 2 gt Tile y Tile height  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2   -Tile width  Temp y Temp height 2 - int Math round normY   Temp height 2   -Tile height  text out  collision detected                     else  Tile move  Temp x Temp width 2 - int Math round normX   Temp width 2     Temp y Temp height 2 - int Math round normY   Temp height 2   -Tile height  text out  collision detected                                           void circleCircle tile Temp                double distance   Math sqrt Math pow  Tile x  Tile width 2   -  Temp x  Temp width 2   2    Math pow  Tile y  Tile height 2   -  Temp y  Temp height 2    2             if  int distance lt  Tile width 2 Temp width 2                                     double normX     Tile x  Tile width 2   -  Temp x  Temp width 2      distance                          double normY     Tile y  Tile height 2   -  Temp y  Temp height 2      distance               Tile move  Temp x  Temp width 2    int Math round normX  Tile width 2 Temp width 2  - Tile width 2     Temp y  Temp height 2    int Math round normY  Tile height 2 Temp height 2  - Tile height 2   text out  collision detected                           void circleLine tile Temp                    line Line  line Temp               if  Line x1  lt   Tile x   Tile width   amp  amp   Line x1   gt  Tile x  amp  amp  Line y1  lt   Tile y   Tile height   amp  amp  Line y1  gt  Tile y   circle may be hitting one of the end points                               rectangle rec new rectangle Line x1  Line y1  1  1  this                   circleRectangle rec                   remove rec                              if  Line x2  lt   Tile x   Tile width   amp  amp   Line x2   gt  Tile x  amp  amp  Line y2  lt   Tile y   Tile height   amp  amp  Line y2  gt  Tile y   circle may be hitting one of the end points                               rectangle rec new rectangle Line x2  Line y2  1  1  this                   circleRectangle rec                   remove rec                               int x1 0  y1 0  x2 Tile x  Tile width 2   y2 Tile y  Tile height 2                x1 Tile x  Tile width 2 -Line height    int Math round Line xNorm 1000               x2 Tile x  Tile width 2  Line height              if Line posSlope                                y1 Tile y  Tile height 2 -Line width                  y2 Tile y  Tile height 2  Line width                            else                               y1 Tile y  Tile height 2  Line width                  y2 Tile y  Tile height 2 -Line width                             Point point intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection              if  point x  lt   Line x   Line width   amp  amp  point x  gt  Line x  amp  amp  point y  lt   Line y   Line height   amp  amp  point y  gt  Line y   line intersects within line segment                                 if point  null  System out println point x     point y                    double distance   Math sqrt Math pow  Tile x  Tile width 2   - point x 2    Math pow  Tile y  Tile width 2   - point y  2                     if  int distance lt Tile width 2                                          System out println  hit                        double normX     Tile x  Tile width 2   - point x    distance                      double normY     Tile y  Tile height 2   - point y    distance                       Tile move  point x   int Math round normX  Tile width 2  - Tile width 2     point y   int Math round normY  Tile height 2  - Tile height 2   text out  collision detected                          System out println point x     point y                                                  new bullet this   int Math round tryX    int Math round tryY                   void rectangleLine tile Temp                    line Line  line Temp              if new Line2D Double Line x1 Line y1 Line x2 Line y2  intersects new Rectangle Tile x Tile y Tile width Tile height                                  if  Line x1  lt   Tile x   Tile width   amp  amp   Line x1   gt  Tile x  amp  amp  Line y1  lt   Tile y   Tile height   amp  amp  Line y1  gt  Tile y   circle may be hitting one of the end points                                       rectangle rec new rectangle Line x1  Line y1  1  1  this                       rectangleRectangle rec                       remove rec                                      if  Line x2  lt   Tile x   Tile width   amp  amp   Line x2   gt  Tile x  amp  amp  Line y2  lt   Tile y   Tile height   amp  amp  Line y2  gt  Tile y   circle may be hitting one of the end points                                       rectangle rec new rectangle Line x2  Line y2  1  1  this                       rectangleRectangle rec                       remove rec                                      if Line posSlope   positive sloped line                                         first we ll do the top left corner                     int x1 Tile x-Line height                      int x2 Tile x Line height                      int y1 Tile y-Line width                      int y2 Tile y Line width                      Point topPoint new Point -99 -99   botPoint new Point -99 -99                       double topDistance 0  botDistance 0                       topPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      topDistance   Math sqrt Math pow Tile x - topPoint x 2    Math pow Tile y - topPoint y  2                           new let s do the bottom right corner                     x1 Tile x Tile width-Line height                      x2 Tile x Tile width Line height                      y1 Tile y Tile height-Line width                      y2 Tile y Tile height Line width                       botPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      botDistance   Math sqrt Math pow  Tile x Tile width  - botPoint x 2    Math pow  Tile y Tile height  - botPoint y  2                          if topDistance lt botDistance                                                if new Rectangle Tile x Tile y Tile width Tile height  contains topPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains topPoint                                                         Tile move topPoint x topPoint y  text out  collision detected                                                                        else                                               if new Rectangle Tile x Tile y Tile width Tile height  contains botPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains botPoint                                                         Tile move botPoint x-Tile width botPoint y-Tile height  text out  collision detected                                                                                      else  negative sloped lne                                         first we ll do the top right corner                     int x1 Tile x Tile width-Line height                      int x2 Tile x Tile width Line height                      int y1 Tile y Line width                      int y2 Tile y-Line width                      Point topPoint new Point -99 -99   botPoint new Point -99 -99                       double topDistance 0  botDistance 0                       topPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      topDistance   Math sqrt Math pow Tile x   Tile width - topPoint x 2    Math pow Tile y - topPoint y  2                           new let s do the bottom left corner                     x1 Tile x-Line height                      x2 Tile x Line height                      y1 Tile y Tile height Line width                      y2 Tile y Tile height-Line width                       botPoint intersection  double x1  double y1  double x2  double y2  double Line x1  double Line y1  double Line x2  double Line y2    find intersection                      botDistance   Math sqrt Math pow Tile x - botPoint x 2    Math pow  Tile y Tile height  - botPoint y  2                          if topDistance lt botDistance                                                if new Rectangle Tile x Tile y Tile width Tile height  contains topPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains topPoint                                                         Tile move topPoint x-Tile width topPoint y  text out  collision detected                                                                        else                                               if new Rectangle Tile x Tile y Tile width Tile height  contains botPoint   amp  amp  new Rectangle Line x Line y Line width Line height  contains botPoint                                                         Tile move botPoint x botPoint y-Tile height  text out  collision detected                                                                                                  public Point intersection double x1  double y1  double x2  double y2 double x3  double y3  double x4  double y4   I didn t write this  got it from http   www ahristov com tutorial geometry-games intersection-lines html  I altered it                       double d    x1 - x2     y3 - y4  -  y1 - y2     x3 - x4                double xi     x3 - x4     x1   y2 - y1   x2  -  x1 - x2     x3   y4 - y3   x4     d              double yi     y3 - y4     x1   y2 - y1   x2  -  y1 - y2     x3   y4 - y3   x4     d               int x  int Math round xi               int y  int Math round yi                return new Point x  y                                                                                                             public static void main String   args                final collision Collision new collision              Collision run           end main    end class

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is there a problem with   Rectangle box1   new Rectangle 100 100 100 100   Rectangle box2   new Rectangle 200 200 100 100       what this means is if any pixel in box2 enters  hits  box1 if  box1 contains box2              collision occurred       your code for moving the boxes      this can also be applied to circles    Ellipse2D Double ball1   new Ellipse2D Double 100 100 200 200   Ellipse2D Double ball2   new Ellipse2D Double 400 100 200 200       what this means is if any pixel on the circumference in ball2 touches  hits     ball1     if  ball1 contains ball2                      collision occurred               your code for moving the balls    to check whether youve hit the edge of a screen you could use the following    Rectangle screenBounds   jpanel getBounds    Ellipse2D Double ball   new Ellipse2D Double 100 100 200 200       diameter 200 Rectangle ballBounds   ball getBounds     if   screenBounds contains ballBounds        the ball touched the edge of the screen

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I think your problem is that you are not using good OO design for your player and enemies  Create two classes   public class Player       int X      int Y      int Width      int Height          Getters and Setters    public class Enemy       int X      int Y      int Width      int Height          Getters and Setters     Your Player should have X Y Width and Height variables   Your enemies should as well   In your game loop  do something like this  C     foreach  Enemy e in EnemyCollection        Rectangle r   new Rectangle e X e Y e Width e Height       Rectangle p   new Rectangle player X player Y player Width player Height           Assuming there is an intersect method  otherwise just handcompare the values     if  r Intersects p                   A Collision            we know which enemy  e   so we can call e DoCollision           e DoCollision              To speed things up  don t bother checking if the enemies coords are offscreen

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Use a rectangle to surround each player and enemy  the height and width of the rectangles should correspond to the object you re surrounding  imagine it being in a box only big enough to fit it   Now  you move these rectangles the same as you do the objects  so they have a  bounding box   I m not sure if Java has this  but it might have a method on the rectangle object called  intersects   so you d do if rectangle1 intersectS rectangle2  to check to see if an object has collided with another   Otherwise you can get the x and y co-ordinates of the boxes and using the height width of them detect whether they ve intersected yourself   Anyway  you can use that to either do an event on intersection  make one explode  or whatever  or prevent the movement from being drawn   revert to previous co-ordinates   edit  here we go  boolean         intersects Rectangle r               Determines whether or not this Rectangle and the specified   Rectangle intersect    So I would do  and don t paste this code  it most likely won t work  not done java for a long time and I didn t do graphics when I did use it    Rectangle rect1   new Rectangle player x  player y  player width  player height    Rectangle rect2   new Rectangle enemy x  enemy y  enemy width  enemy height      detects when the two rectangles hit if rect1 intersects rect2      System out println  game over  g        obviously you d need to fit that in somewhere

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First  use the bounding boxes as described by Jonathan Holland to find if you may have a collision   From the  multi-color  sprites  create black and white versions  You probably already have these if your sprites are transparent  i e  there are places which are inside the bounding box but you can still see the background   These are  masks    Use Image getRGB   on the mask to get at the pixels  For each pixel which isn t transparent  set a bit in an integer array  playerArray and enemyArray below   The size of the array is height if width  lt   32 pixels   width 31  32 height otherwise  The code below is for width  lt   32   If you have a collision of the bounding boxes  do this      Find the first line where the two sprites might overlap int linePlayer  lineEnemy  if  player y  lt   enemy y        linePlayer   enemy y - player y      lineEnemy   0    else       linePlayer   0      lineEnemy   player y - enemy y    int line   Math max linePlayer  lineEnemy       Get the shift between the two x   player x - enemy x  int maxLines   Math max player height  enemy height   for   line  lt  maxLines  line              if width  gt  32  then you need a second loop here     long playerMask   playerArray linePlayer       long enemyMask   enemyArray lineEnemy          Reproduce the shift between the two sprites     if  x  lt  0  playerMask  lt  lt   -x       else enemyMask  lt  lt  x         If the two masks have common bits  binary AND will return    0     if   playerMask  amp  enemyMask     0               Contact             Links  JGame  Framework for Small Java Games

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You don t want to have the collision check code inside the painting code   The painting needs to be fast   Collision can go in the game loop   Therefore you need an internal representation of the objects independent of their sprites

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You don t want to have the collision check code inside the painting code   The painting needs to be fast   Collision can go in the game loop   Therefore you need an internal representation of the objects independent of their sprites

User · Answer

No need to use rectangles     compare the coordinates of  2 players constantly   like  if x1   x amp  amp y1  y   remember to increase the range of x when ur comparing   if ur rectangle width is 30 take as if  x1 gt x amp  amp x2 gt x 30   likewise y

User · Answer

First  use the bounding boxes as described by Jonathan Holland to find if you may have a collision   From the  multi-color  sprites  create black and white versions  You probably already have these if your sprites are transparent  i e  there are places which are inside the bounding box but you can still see the background   These are  masks    Use Image getRGB   on the mask to get at the pixels  For each pixel which isn t transparent  set a bit in an integer array  playerArray and enemyArray below   The size of the array is height if width  lt   32 pixels   width 31  32 height otherwise  The code below is for width  lt   32   If you have a collision of the bounding boxes  do this      Find the first line where the two sprites might overlap int linePlayer  lineEnemy  if  player y  lt   enemy y        linePlayer   enemy y - player y      lineEnemy   0    else       linePlayer   0      lineEnemy   player y - enemy y    int line   Math max linePlayer  lineEnemy       Get the shift between the two x   player x - enemy x  int maxLines   Math max player height  enemy height   for   line  lt  maxLines  line              if width  gt  32  then you need a second loop here     long playerMask   playerArray linePlayer       long enemyMask   enemyArray lineEnemy          Reproduce the shift between the two sprites     if  x  lt  0  playerMask  lt  lt   -x       else enemyMask  lt  lt  x         If the two masks have common bits  binary AND will return    0     if   playerMask  amp  enemyMask     0               Contact             Links  JGame  Framework for Small Java Games

User · Answer

First  use the bounding boxes as described by Jonathan Holland to find if you may have a collision   From the  multi-color  sprites  create black and white versions  You probably already have these if your sprites are transparent  i e  there are places which are inside the bounding box but you can still see the background   These are  masks    Use Image getRGB   on the mask to get at the pixels  For each pixel which isn t transparent  set a bit in an integer array  playerArray and enemyArray below   The size of the array is height if width  lt   32 pixels   width 31  32 height otherwise  The code below is for width  lt   32   If you have a collision of the bounding boxes  do this      Find the first line where the two sprites might overlap int linePlayer  lineEnemy  if  player y  lt   enemy y        linePlayer   enemy y - player y      lineEnemy   0    else       linePlayer   0      lineEnemy   player y - enemy y    int line   Math max linePlayer  lineEnemy       Get the shift between the two x   player x - enemy x  int maxLines   Math max player height  enemy height   for   line  lt  maxLines  line              if width  gt  32  then you need a second loop here     long playerMask   playerArray linePlayer       long enemyMask   enemyArray lineEnemy          Reproduce the shift between the two sprites     if  x  lt  0  playerMask  lt  lt   -x       else enemyMask  lt  lt  x         If the two masks have common bits  binary AND will return    0     if   playerMask  amp  enemyMask     0               Contact             Links  JGame  Framework for Small Java Games

User · Answer

I think your problem is that you are not using good OO design for your player and enemies  Create two classes   public class Player       int X      int Y      int Width      int Height          Getters and Setters    public class Enemy       int X      int Y      int Width      int Height          Getters and Setters     Your Player should have X Y Width and Height variables   Your enemies should as well   In your game loop  do something like this  C     foreach  Enemy e in EnemyCollection        Rectangle r   new Rectangle e X e Y e Width e Height       Rectangle p   new Rectangle player X player Y player Width player Height           Assuming there is an intersect method  otherwise just handcompare the values     if  r Intersects p                   A Collision            we know which enemy  e   so we can call e DoCollision           e DoCollision              To speed things up  don t bother checking if the enemies coords are offscreen

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Since Java doesn t have an intersect function  really    you can do collision detection by simply comparying the X and Y  Width and Height values of the bounding boxes  rectangle  for each of the objects that could potentially collide   So     in the base object of each colliding object    i e  if your player and enemy have a common base you can put a simple Rectangle object called something like BoundingBox   If the common base is a built in Java class then you ll need to create a class that extends the build in class and have the player and enemy objects extend your new class or are instances of that class   At creation  and each tick or update  you ll need to set the BoundingBox paremeters for both your player and enemy   I don t have the Rectangle class infront of me but its most likely something like X  Y  Width and finally Height   X and Y are that objects location in your game world   The width and height are self explanatory I think   They ll most likely come out from the right of the players location though so  if the X and Y were bothe at 0 and your Width and Height were both at 256 you wouldn t see anything because the character would be at the top left outside of the screen   Anyways    to detect a collision  you ll want to compare the attributes of the player and enemy BoundingBoxes   So something like this      if  Player BoundingBox X   Enemy BoundingBox X  amp  amp  If  Player BoundingBox Y   Enemy BoundingBox Y              Oh noes   The enemy and player are on top of eachother       The logic can get sort of complicated but you ll need to compare the distances between each BoundingBox and compare locations

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Here s a useful of an open source game that uses a lot of collisions  http   robocode sourceforge net    You may take a look at the code and complement with the answers written here

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Here s a useful of an open source game that uses a lot of collisions  http   robocode sourceforge net    You may take a look at the code and complement with the answers written here

[java] Collision Detection between two images in Java

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