Circle drawing with SVG s arc path

Question

Short question  using SVG path  we can draw 99 99  of a circle and it shows up  but when it is 99 99999999  of a circle  then the circle won t show up  How can it be fixed   The following SVG path can draw 99 99  of a circle     try it on http   jsfiddle net DFhUF 1381  and see if you see 4 arcs or only 2 arcs  but note that if it is IE  it is rendered in VML  not SVG  but have the similar issue   M 100 100 a 50 50 0 1 0 0 00001 0   But when it is 99 99999999  of a circle  then nothing will show at all   M 100 100 a 50 50 0 1 0 0 00000001 0       And that s the same with 100  of a circle  it is still an arc  isn t it  just a very complete arc   M 100 100 a 50 50 0 1 0 0 0    How can that be fixed   The reason is I use a function to draw a percentage of an arc  and if I need to  special case  a 99 9999  or 100  arc to use the circle function  that d be kind of silly   Again  a test case on jsfiddle using RaphaelJS is at http   jsfiddle net DFhUF 1381   and if it is VML on IE 8  even the second circle won t show    you have to change it to 0 01     Update   This is because I am rendering an arc for a score in our system  so 3 3 points get 1 3 of a circle   0 5 gets half a circle  and 9 9 points get 99  of a circle   But what if there are scores that are 9 99 in our system   Do I have to check whether it is close to 99 999  of a circle  and use an arc function or a circle function accordingly   Then what about a score of 9 9987   Which one to use   It is ridiculous to need to know what kind of scores will map to a  too complete circle  and switch to a circle function  and when it is  a certain 99 9   of a circle or a 9 9987 score  then use the arc function

User · Answer

For those like me who were looking for an ellipse attributes to path conversion    const ellipseAttrsToPath    rx cx ry cy    gt   M  cx-rx    cy a  rx    ry  0 1 0   rx 2  0a  rx    ry  0 1 0 -  rx 2  0

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It s a good idea that using two arc command to draw a full circle   usually  I use ellipse or circle element to draw a full circle

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Written as a function  it looks like this   function getPath cx cy r     return  M    cx         cy    m     -r      0a    r         r     0 1 0      r   2      0a    r         r     0 1 0      -r   2      0

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I know it s a bit late in the game  but I remembered this question from when it was new and I had a  similar dillemma  and I accidently found the  quot right quot  solution  if anyone is still looking for one   lt path      d  quot      M cx cy     m -r  0     a r r 0 1 0  r   2  0     a r r 0 1 0 - r   2  0      quot    gt   In other words  this   lt circle cx  quot 100 quot  cy  quot 100 quot  r  quot 75 quot    gt   can be achieved as a path with this     lt path          d  quot          M 100  100         m -75  0         a 75 75 0 1 0 150 0         a 75 75 0 1 0 -150 0          quot      gt   The trick is to have two arcs  the second one picking up where the first left off and using the negative diameter to get back to the original arc start point  The reason it can t be done as a full circle in one arc  and I m just speculating  is because you would be telling it to draw an arc from itself  let s say 150 150  to itself  150 150   which it renders as  quot oh  I m already there  no arc necessary  quot   The benefits of the solution I m offering are   it s easy to translate from a circle directly to a path  and there is no overlap in the two arc lines  which may cause issues if you are using markers or patterns  etc    It s a clean continuous line  albeit drawn in two pieces   None of this would matter if they would just allow textpaths to accept shapes  But I think they are avoiding that solution since shape elements like circle don t technically have a  quot start quot  point  jsfiddle demo  http   jsfiddle net crazytonyi mNt2g  Update  If you are using the path for a textPath reference and you are wanting the text to render on the outer edge of the arc  you would use the exact same method but change the sweep-flag from 0 to 1 so that it treats the outside of the path as the surface instead of the inside  think of 1 0 as someone sitting at the center and drawing a circle around themselves  while 1 1 as someone walking around the center at radius distance and dragging their chalk beside them  if that s any help    Here is the code as above but with the change   lt path      d  quot      M cx cy     m -r  0     a r r 0 1 1  r   2  0     a r r 0 1 1 - r   2  0      quot    gt

User · Answer

In reference to Anthony   s solution  here is a function to get the path   function circlePath cx  cy  r       return  M   cx     cy   m -  r    0 a   r     r   0 1 0    r 2    0 a   r     r   0 1 0 -   r 2    0

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Same for XAML s arc  Just close the 99 99  arc with a Z and you ve got a circle

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A totally different approach   Instead of fiddling with paths to specify an arc in svg  you can also take a circle element and specify a stroke-dasharray  in pseudo code   with  score between 0  1  and pi   3 141592653589793238   length    score   2   pi    r  max   7    r   i e  well above 2 pi r    lt circle r   r  stroke-dasharray   length  max    gt    Its simplicity is the main advantage over the multiple-arc-path method  e g  when scripting you only plug in one value and you re done for any arc length   The arc starts at the rightmost point  and can be shifted around using a rotate transform   Note  Firefox has an odd bug where rotations over 90 degrees or more are ignored  So to start the arc from the top  use    lt circle r   r  transform  rotate -89 9   stroke-dasharray   length  max    gt

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Building upon Anthony and Anton s answers I incorporated the ability to rotate the generated circle without affecting it s overall appearance  This is useful if you re using the path for an animation and you need to control where it begins   function cx  cy  r  deg       var theta   deg Math PI 180          dx   r Math cos theta           dy   -r Math sin theta       return  M   cx     cy  m   dx     dy  a   r     r   0 1 0   -2 dx     -2 dy  a   r     r   0 1 0   2 dx     2 dy

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Adobe Illustrator uses bezier curves like SVG  and for circles it creates four points  You can create a circle with two elliptical arc commands   but then for a circle in SVG I would use a  lt circle   gt

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Another way would be to use two Cubic Bezier Curves  That s for iOS folks using pocketSVG which doesn t recognize svg arc parameter   C x1 y1  x2 y2  x y  or c dx1 dy1  dx2 dy2  dx dy     The last set of coordinates here  x y  are where you want the line to end  The other two are control points   x1 y1  is the control point for the start of your curve  and  x2 y2  for the end point of your curve    lt path d  M25 0 C60 0  60 50  25 50 C-10 50  -10 0  25 0    gt

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i made a jsfiddle to do it in here   function polarToCartesian centerX  centerY  radius  angleInDegrees    var angleInRadians    angleInDegrees-90    Math PI   180 0   return   x  centerX    radius   Math cos angleInRadians    y  centerY    radius   Math sin angleInRadians         function describeArc x  y  radius  startAngle  endAngle    var start   polarToCartesian x  y  radius  endAngle   var end   polarToCartesian x  y  radius  startAngle    var largeArcFlag   endAngle - startAngle  lt   180    0     1    var d          M   start x  start y        A   radius  radius  0  largeArcFlag  0  end x  end y   join        return d           console log describeArc 255 255 220 134 136     link  all you need to do is to change the input of console log and get the result in console

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These answers are much too complicated   A simpler way to do this without creating two arcs or convert to different coordinate systems    This assumes your canvas area has width w and height h    M  w 0 5   radius    h 0 5   A  radius    radius  0 1 0   w 0 5   radius    h 0 5001     Just use the  long arc  flag  so the full flag is filled  Then make the arcs 99 9999  the full circle  Visually it is the same  Avoid the sweep flag by just starting the circle at the rightmost point in the circle  one radius directly horizontal from the center

[svg] Circle drawing with SVG's arc path

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