Can I trigger a breakpoint on OpenGL errors in Xcode 4? - iphone

Question

Is there any way I can set a symbolic breakpoint that will trigger when any OpenGL function call sets any state other than GL_NO_ERROR? Initial evidence suggests opengl_error_break is intended to to serve just that purpose, but it doesn't break.

Answer 1

Based on Lars' approach you can achieve this tracking of errors automatically, it is based on some preprocessor magic and generating stub functions.
I wrote a small Python script which processes the OpenGL header (I used the Mac OS X one in the example, but it should also work with the one of iOS).
The Python script generates two files, a header to include in your project everywhere where you call OpenGL like this (you can name the header however you want):
#include "gl_debug_overwrites.h"
The header contains macros and function declarations after this scheme:
#define glGenLists _gl_debug_error_glGenLists
GLuint _gl_debug_error_glGenLists(GLsizei range);
The script also produces a source file in the same stream which you should save separately, compile and link with your project.
This will then wrap all gl* functions in another function which is prefixed with _gl_debug_error_ which then checks for errors similar to this:
GLuint _gl_debug_error_glGenLists(GLsizei range) {
GLuint var = glGenLists(range);
CHECK_GL_ERROR();
return var;
}

Answer 2

Wrap your OpenGL calls to call glGetError after every call in debug mode. Within the wrapper method create a conditional breakpoint and check if the return value of glGetError is something different than GL_NO_ERROR.
Details:
Add this macro to your project (from OolongEngine project):
#define CHECK_GL_ERROR() ({ GLenum __error = glGetError(); if(__error) printf("OpenGL error 0x%04X in %s\n", __error, __FUNCTION__); (__error ? NO : YES); })
Search for all your OpenGL calls manually or with an appropriate RegEx. Then you have two options exemplary shown for the glViewport() call:
Replace the call with glViewport(...); CHECK_GL_ERROR()
Replace the call with glDebugViewport(...); and implement glDebugViewport as shown in (1).

Answer 3

I think that what could get you out of the problem is to capture OpenGL ES Frames (scroll down to "Capture OpenGL ES Frames"), which is now supported by Xcode. At least this is how I am debugging my OpenGL Games.
By capturing the frames when you know an error is happening you could identify the issue in the OpenGL Stack without too much effort.
Hope it helps!