How to hook OpenGL extensions?

[phuongtran7]

Hi,

I'm trying to hook into some of the OpenGL extensions, especially the glCreateShader and glShaderSource to try and implement some shader manipulation for a game. There is an example on how to hook OpenGL API in the sample folder, but it seems that it can only hook OpenGL 1.1 calls. Anything beyond that I would need to call wglGetProcAddress to get the address.

However, in order for wglGetProcAddress to work, I need to correctly set the pixel format and create a device context first. If I let the application run first to do all that then I can't hook into it like normal. And from #256 it seems that hooking into already running process is rather involved.

Is there anyway to hook into those OpenGL extensions without having to go into hooking already running process?

Thank you so much for your time and help.

[phuongtran7]

Took awhile but I'm finally able to answer my own question. Using apitrace I noticed that the call to wglMakeCurrent to at the almost very top of the application I want to hook into, and it's one of the few API that Detours can hook. So I just hooked into it, made context as current, then used Glew to finally find all the other functions', that I wanted to hook into, addresses. And that worked like a charm.

Something like this if I want to hook into glShaderSource:

static BOOL(* TruewglMakeCurrent)(HDC, HGLRC) = wglMakeCurrent;
static void(*TrueglShaderSource)(GLuint, GLsizei, const GLchar* const*, const GLint*) = nullptr;
void CustomglShaderSource(GLuint, GLsizei, const GLchar* const*, const GLint*);

BOOL CustomwglMakeCurrent(HDC unnamedParam1, HGLRC unnamedParam2)
{
	const auto result = TruewglMakeCurrent(unnamedParam1, unnamedParam2);
	if (result)
	{
                if (glewInit())
		{
			// Can't init glew. Handle error
                        return result;
		}

                TrueglShaderSource = glShaderSource;
                
               // Detour attach like normal here and everything else
               DetourAttach(&(PVOID&)TrueglShaderSource, CustomglShaderSource);
	}

	return result;
}