how to get support for GL_ARB_debug_output

[vamsee]

Hi all,

I was trying to check out the "GL_ARB_debug_output" extension.
When i ran the 'glewInfo.exe' it gave me the below result for this extension

GL_ARB_debug_output:                                           OK [MISSING]
--------------------
  glDebugMessageCallbackARB:                                   OK
  glDebugMessageControlARB:                                    OK
  glDebugMessageInsertARB:                                     OK
  glGetDebugMessageLogARB:                                     OK

Why des it say 'OK' and also 'Missing' ??

Also when i checked in code with

glewIsSupported("GL_ARB_debug_output")

it returned false.

Im using Nvidia GTX 460M , with driver version 304.48 (open gl version 4.2)
does this mean that i cannot enable this extension at all??

or are there any ways of getting this extension to work?

[Aleksandar]

I'm not sure how GLEW implements that, but what you have to do is to:
- create a debugging GL context, and
- grab pointers for needed functions.
I can bet 304.xx drivers support debug_output.

[vamsee]

hmmmn ... for creating debug context im passing these attribs

int attribs[] =
	{
		WGL_CONTEXT_MAJOR_VERSION_ARB, 4,
		WGL_CONTEXT_MINOR_VERSION_ARB, 2,
		WGL_CONTEXT_FLAGS_ARB, 
		WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB | [COLOR="#0000FF"]WGL_CONTEXT_DEBUG_BIT_ARB[/COLOR] ,
		WGL_CONTEXT_PROFILE_MASK_ARB, WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
		0
	};

And while creating the context im using this :

PFNWGLCREATECONTEXTATTRIBSARBPROC my_wglCreateContextAttribsARB = NULL;
		my_wglCreateContextAttribsARB = (PFNWGLCREATECONTEXTATTRIBSARBPROC) wglGetProcAddress("wglCreateContextAttribsARB");
 
		if(my_wglCreateContextAttribsARB!=NULL)
		{
			wglMakeCurrent(NULL,NULL);
			wglDeleteContext(tempContext);
 
			glrc = my_wglCreateContextAttribsARB(hDC,0, attribs);
 
			wglMakeCurrent(hDC, glrc);
		}

So, is this correct for creating a debug context? and also how do i confirm that i have/can create a debug context??

is there any command that i can issue to check if debug context is indeed created ??

And if the above is correct, then can you point me at how i can get the address of the debug functions?

[Aleksandar]

Looks OK.

The only purpose of debugging context is to enable debugging. So if you can call debug_output functions you certainly have a debug context.
Is glrc context is valid? Try to debug and take a look at the value of that handle.

[vamsee]

yeah the handle is valid, i can draw primitives and all ....

but, i cant make any debug functions to work!

[Alfonse Reinheart]

how do i confirm that i have/can create a debug context?

If you have GL 4.3, you can query `GL_CONTEXT_FLAGS` and test the result against `GL_CONTEXT_FLAG_DEBUG_BIT`. But if you don't, you can't.

However, if you have reasonably up-to-date drivers, creating a debug context will cause NVIDIA's drivers to spam error messages to standard out. So if you don't get that spam, you probably didn't do it right.

[vamsee]

So for earlier versions of openGL there is no way of confirming that debug context is enabled??
thats sad!

im on the latest drivers for my card(not the beta drivers though). I still dont see any error messages.
but im working on my laptop with a mobile graphic card, so may be that could be a problem.

Can any one share with me any code snippet that works on your machine for setting a debug context?

[Alfonse Reinheart]

So for earlier versions of openGL there is no way of confirming that debug context is enabled??
thats sad!

Why? Until KHR_debug (the core extension that introduced debug output), there was no behavior in OpenGL that changed based on it. An implementation does not have to offer ARB_debug_output if you use a debug context. An implementation does not have to remove ARB_debug_output if you don't ask for a debug context.

So being able to check for a debug context never mattered before KHR_debug. Which is why it is KHR_debug that adds the `GL_CONTEXT_FLAG_DEBUG_BIT`.

[vamsee]

sorry but i dont understand where did KHR_debug came in between ARB_debug, arent they like different implementations or something??
(i also checked for the KHR_debug, that also is shown as missing in glew output)

may be im going off topic here, so coming back to what i was asking for

what is the solution to this problem ? (how do i make sure my current drivers have arb_debug_output supported?)

[Alfonse Reinheart]

how do i make sure my current drivers have arb_debug_output supported?

You cannot.

You can set the debug flag in your context creation logic. But if the implementation doesn't want to expose ARB_debug_output, that is its right. Just like you can't force support for ARB_tessellation_shader or any other extension.

That being said, the easiest way to test this is really simple: use someone else's context creation code. Download FreeGLUT and make a simple application with it, using the GLUT_DEBUG flag. If that gets you ARB_debug_output, then clearly the issue is with your context creation code. If it doesn't, then your implementation doesn't support ARB_debug_output.