OpenGL Programming/Debugging
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Mesa
[edit | edit source]If you are using the Mesa OpenGL implementation you can set the following environment variables:
- LIBGL_ALWAYS_SOFTWARE=1 : use the software implementation, without using the graphic card at all. This help when:
- you suspect a bug in a driver,
- you want to try an alternative implementation (as if you were using a different graphic card),
- you want to check whether a graphic glitch is due to unitialized memory or to a programming mistake
- MESA_DEBUG=1 : will output diagnostic messages in erroneous situations (e.g. assigning a uniform when the program is not linked)
See also Mesa's debugging and environment variables pages.
Common mistakes
[edit | edit source]If you manually draw lines or triangles, and nothing appears:
- check that your 4th coordinate is 1 and not 0
- check that you properly set glEnableVertexAttribArray / glBindBuffer / glVertexAttribPointer
- double-check that you used the right variables (bad copy/paste...) - avoid global variables to help this
- triple-check your
glUniform*
calls, including the type (3fv, 4fv...) - OpenGL is unforgiving and silent - beware that glDrawElements' 4th and last parameter (
indices
) is expressed in byte offset from the start, not in number of elements from the start, even when working with IBOs
Error reporting
[edit | edit source]OpenGL uses glGetError() to report errors:
switch (glGetError()) {
case GL_NO_ERROR:
cerr << "GL_NO_ERROR" << endl;
break;
case GL_INVALID_ENUM:
cerr << "GL_INVALID_ENUM" << endl;
break;
case GL_INVALID_VALUE:
cerr << "GL_INVALID_VALUE" << endl;
break;
case GL_INVALID_OPERATION:
cerr << "GL_INVALID_OPERATION" << endl;
break;
case GL_INVALID_FRAMEBUFFER_OPERATION:
cerr << "GL_INVALID_FRAMEBUFFER_OPERATION" << endl;
break;
case GL_OUT_OF_MEMORY:
cerr << "GL_OUT_OF_MEMORY" << endl;
break;
}
Stencil buffer
[edit | edit source]For tips on how to debug the stencil buffer, you can check the Stencil buffer section.
Links
[edit | edit source]- Debugging of Shaders in the GLSL wikibooks (about debugging with colors)
- Debugging Android NDK for debugging OpenGL NDK application on Android
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