How to draw text using only OpenGL methods

Question

I don t have the option to use but OpenGL methods  that is glxxx   methods   I need to draw text using gl methods only  After reading the red book  I understand that it is possible only through the glBitmap   method  If this is the only possible way  then can any one help me with the pixel array information for all the characters  Is there is any other way to draw text

User · Answer

Drawing text in plain OpenGL isn t a straigth-forward task  You should probably have a look at libraries for doing this  either by using a library or as an example implementation    Some good starting points could be GLFont  OpenGL Font Survey and NeHe Tutorial for Bitmap Fonts  Windows    Note that bitmaps are not the only way of achieving text in OpenGL as mentioned in the font survey

User · Answer

This article describes how to render text in OpenGL using various techniques   With only using opengl  there are several ways    using glBitmap using textures using display lists

User · Answer

Use glutStrokeCharacter GLUT STROKE ROMAN  myCharString    An example  A STAR WARS SCROLLER    include  lt windows h gt   include  lt string h gt   include  lt GL glut h gt   include  lt iostream h gt   include  lt fstream h gt   GLfloat UpwardsScrollVelocity   -10 0  float view 20 0   char quote 6  80   int numberOfQuotes 0 i                                                        glutIdleFunc timeTick                                                                       void timeTick void        if  UpwardsScrollVelocity lt  -600          view- 0 000011      if view  lt  0   view 20  UpwardsScrollVelocity   -10 0           exit 0       UpwardsScrollVelocity -  0 015    glutPostRedisplay                                                             printToConsoleWindow                                                                     void printToConsoleWindow         int l lenghOfQuote  i       for   l 0 l lt numberOfQuotes l                  lenghOfQuote    int strlen quote l             for  i   0  i  lt  lenghOfQuote  i                          cout lt  lt quote l  i                         out lt  lt endl                                                                RenderToDisplay                                                                            void RenderToDisplay         int l lenghOfQuote  i       glTranslatef 0 0  -100  UpwardsScrollVelocity       glRotatef -20  1 0  0 0  0 0       glScalef 0 1  0 1  0 1          for   l 0 l lt numberOfQuotes l                  lenghOfQuote    int strlen quote l            glPushMatrix            glTranslatef - lenghOfQuote 37   - l 200   0 0           for  i   0  i  lt  lenghOfQuote  i                          glColor3f  UpwardsScrollVelocity 10  300  l 10   UpwardsScrollVelocity 10  300  l 10  0 0               glutStrokeCharacter GLUT STROKE ROMAN  quote l  i                      glPopMatrix                                                                 glutDisplayFunc myDisplayFunction                                                            void myDisplayFunction void      glClear GL COLOR BUFFER BIT     glLoadIdentity      gluLookAt 0 0  30 0  100 0  0 0  0 0  0 0  0 0  1 0  0 0     RenderToDisplay      glutSwapBuffers                                                          glutReshapeFunc reshape                                                                    void reshape int w  int h      glViewport 0  0  w  h     glMatrixMode GL PROJECTION     glLoadIdentity      gluPerspective 60  1 0  1 0  3200     glMatrixMode GL MODELVIEW                                                          int main                                                                                      int main         strcpy quote 0   Luke  I am your father          strcpy quote 1   Obi-Wan has taught you well          strcpy quote 2   The force is strong with this one          strcpy quote 3   Alert all commands  Calculate every possible destination along their last known trajectory          strcpy quote 4   The force is with you  young Skywalker  but you are not a Jedi yet         numberOfQuotes 5       glutInitDisplayMode GLUT DOUBLE   GLUT RGB   GLUT DEPTH       glutInitWindowSize 800  400       glutCreateWindow  StarWars scroller        glClearColor 0 0  0 0  0 0  1 0       glLineWidth 3        glutDisplayFunc myDisplayFunction       glutReshapeFunc reshape       glutIdleFunc timeTick       glutMainLoop         return 0

User · Answer

Load an image with characters as texture and draw the part of that texture depending on what character you want  You can create that texture using a paint program  hardcode it or use a window component to draw to an image and retrieve that image for an exact copy of system fonts   No need to use Glut or any other extension  just basic OpenGL operability  It gets the job done  not to mention that its been done like this for decades by professional programmers in very succesfull games and other applications

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Theory  Why it is hard  Popular font formats like TrueType and OpenType are vector outline formats  they use Bezier curves to define the boundary of the letter     Image source   Transforming those formats into arrays of pixels  rasterization  is too specific and out of OpenGL s scope  specially because OpenGl does not have non-straight primitives  e g  see Why is there no circle or ellipse primitive in OpenGL    The easiest approach is to first raster fonts ourselves on the CPU  and then give the array of pixels to OpenGL as a texture   OpenGL then knows how to deal with arrays of pixels through textures very well   Texture atlas  We could raster characters for every frame and re-create the textures  but that is not very efficient  specially if characters have a fixed size   The more efficient approach is to raster all characters you plan on using and cram them on a single texture   And then transfer that to the GPU once  and use it texture with custom uv coordinates to choose the right character   This approach is called a texture atlas and it can be used not only for textures but also other repeatedly used textures  like tiles in a 2D game or web UI icons   The Wikipedia picture of the full texture  which is itself taken from freetype-gl  illustrates this well     I suspect that optimizing character placement to the smallest texture problem is an NP-hard problem  see  What algorithm can be used for packing rectangles of different sizes into the smallest rectangle possible in a fairly optimal way   The same technique is used in web development to transmit several small images  like icons  at once  but there it is called  CSS Sprites   https   css-tricks com css-sprites  and are used to hide the latency of the network instead of that of the CPU   GPU communication    Non-CPU raster methods  There also exist methods which don t use the CPU raster to textures   CPU rastering is simple because it uses the GPU as little as possible  but we also start thinking if it would be possible to use the GPU efficiency further    This FOSDEM 2014 video explains other existing techniques    tesselation  convert the font to tiny triangles  The GPU is then really good at drawing triangles  Downsides    generates a bunch of triangles O n log n  CPU calculation of the triangles  calculate curves on shaders  A 2005 paper by Blinn-Loop put this method on the map  Downside  complex  See  Resolution independent cubic bezier drawing on GPU  Blinn Loop  direct hardware implementations like OpenVG  Downside  not very widely implemented for some reason  See    OpenGL  OpenVG  Draw text  OpenVG implementation     Fonts inside of the 3D geometry with perspective  Rendering fonts inside of the 3D geometry with perspective  compared to an orthogonal HUD  is much more complicated  because perspective could make one part of the character much closer to the screen and larger than the other  making an uniform CPU discretization  e g  raster  tesselation  look bad on the close part  This is actually an active research topic    What is state-of-the-art for text rendering in OpenGL as of version 4 1  http   www valvesoftware com publications 2007 SIGGRAPH2007 AlphaTestedMagnification pdf     Distance fields are one of the popular techniques now   Implementations  The examples that follow were all tested on Ubuntu 15 10   Because this is a complex problem as discussed previously  most examples are large  and would blow up the 30k char limit of this answer  so just clone the respective Git repositories to compile   They are all fully open source however  so you can just RTFS   FreeType solutions  FreeType looks like the dominant open source font rasterization library  so it would allow us to use TrueType and OpenType fonts  making it the most elegant solution    https   github com rougier freetype-gl  Was a set of examples  OpenGL and freetype  but is more or less evolving into a library that does it and exposes a decent API   In any case  it should already be possible to integrate it on your project by copy pasting some source code   It provides both texture atlas and distance field techniques out of the box   Demos under  https   github com rougier freetype-gl tree master demos  Does not have a Debian package  and it a pain to compile on Ubuntu 15 10  https   github com rougier freetype-gl issues 82 issuecomment-216025527  packaging issues  some upstream   but it got better as of 16 10   Does not have a nice installation method  https   github com rougier freetype-gl issues 115   Generates beautiful outputs like this demo    libdgx https   github com libgdx libgdx tree 1 9 2 extensions gdx-freetype   Examples   tutorials    a NEHE tutorial  http   nehe gamedev net tutorial freetype fonts in opengl 24001  http   learnopengl com   In-Practice Text-Rendering mentions it  but I could not find runnable source code SO questions    OpenGL font rendering using Freetype2 Text not rendering correctly - OpenGL using FreeType2    Other font rasterizers  Those seem less good than FreeType  but may be more lightweight    https   github com nothings stb blob master stb truetype h http   www angelcode com products bmfont    Anton s OpenGL 4 Tutorials example 26  Bitmap fonts    tutorial  http   antongerdelan net opengl  source  https   github com capnramses antons opengl tutorials book blob 9a117a649ae4d21d68d2b75af5232021f5957aac 26 bitmap fonts main cpp   The font was created by the author manually and stored in a single  png file  Letters are stored in an array form inside the image   This method is of course not very general  and you would have difficulties with internationalization   Build with   make -f Makefile linux64   Output preview     opengl-tutorial chapter 11  2D fonts    tutorial  http   www opengl-tutorial org intermediate-tutorials tutorial-11-2d-text  source  https   github com opengl-tutorials ogl blob 71cad106cefef671907ba7791b28b19fa2cc034d tutorial11 2d fonts tutorial11 cpp   Textures are generated from DDS files   The tutorial explains how the DDS files were created  using CBFG and Paint Net   Output preview     For some reason Suzanne is missing for me  but the time counter works fine  https   github com opengl-tutorials ogl issues 15  FreeGLUT  GLUT has glutStrokeCharacter and FreeGLUT is open source    https   github com dcnieho FreeGLUT blob FG 3 0 0 src fg font c L255  OpenGLText  https   github com tlorach OpenGLText  TrueType raster  By NVIDIA employee  Aims for reusability  Haven t tried it yet   ARM Mali GLES SDK Sample  http   malideveloper arm com resources sample-code simple-text-rendering  seems to encode all characters on a PNG  and cut them from there    SDL ttf    Source  https   github com cirosantilli cpp-cheat blob d36527fe4977bb9ef4b885b1ec92bd0cd3444a98 sdl ttf c  Lives in a separate tree to SDL  and integrates easily   Does not provide a texture atlas implementation however  so performance will be limited  How to render fonts and text with SDL2 efficiently   Related threads   How to do OpenGL live text-rendering for a GUI  Text font rendering in OpenGLES 2  iOS - CoreText   - options and best practice

User · Answer

I think that the best solution for drawing text in OpenGL is texture fonts  I work with them for a long time  They are flexible  fast and nice looking  with some rear exceptions   I use special program for converting font files   ttf for example  to texture  which is saved to file of some internal  font  format  I ve developed format and program based on http   content gpwiki org index php OpenGL Tutorials Font System though my version went rather far from the original supporting Unicode and so on   When starting the main app  fonts are loaded from this  internal  format  Look link above for more information   With such approach the main app doesn t use any special libraries like FreeType  which is undesirable for me also  Text is being drawn using standard OpenGL functions

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