Is it possible to set breakpoint at OpenGL functions?

Question

Sometimes I need to find out which part of the code call a certain OpenGL function, so I try this:

b glEnableVertexAttribArray
----------------------------
Breakpoint 3 at 0x7ffff0326c80 (2 locations)

But it doesn't work, is there any way to make this work?

I'm using gdb in ubuntu18.04, my GPU is GeForce GTX 1050 Ti

Does your program use an OpenGL loader like GLAD or GLEW by any chance? — Botje
– Botje, Commented Dec 19, 2019 at 14:52
@Botje I have tried GLAD c-debug generator, it works nicely. How to do it with GLEW? — dedowsdi
– dedowsdi, Commented Dec 20, 2019 at 3:17

Botje · Accepted Answer · 2019-12-20 15:09:02Z

3

If you look at your GL/glew.h header, you will see that it contains lines similar to the following:

#define GLEW_GET_FUN(x) x
#define glCopyTexSubImage3D GLEW_GET_FUN(__glewCopyTexSubImage3D)
#define glDrawRangeElements GLEW_GET_FUN(__glewDrawRangeElements)
#define glTexImage3D GLEW_GET_FUN(__glewTexImage3D)
#define glTexSubImage3D GLEW_GET_FUN(__glewTexSubImage3D)

When you call glewInit, these __glew* variables are populated with pointers extracted from your OpenGL implementation. In your case, you should set a breakpoint on the contents of such a pointer, so *__glewEnableVertexAttribArray.

For GLAD you will have to put a breakpoint on *glad_glEnableVertexAttribArray. Note the * in both cases: that tells your debugger to dereference the pointer and put the breakpoint at the correct location.

edited Dec 20, 2019 at 15:09

answered Dec 20, 2019 at 13:49

Botje

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2 Comments

dedowsdi Over a year ago

The same approach doesn't work on GLAD, gdb doesn't let me set breakpoint on functions populated with OpenGL implementation, I can only set breakpont on glad_debug_impl_*, which is real function that calls populated function. I havn't try it with glew, it looks suspicious, I will try it later.

Botje Over a year ago

Can't you put a breakpoint on *glad_glEnableVertexAttribArray after GLAD has loaded all the pointers? (note the *)

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