wglMakeCurrent

OpenGL OpenGL: Basic Coding
1

Why would calling:
wglMakeCurrent( NULL, NULL );

return GL_INVALID_OPERATION, when the previous GL command returned no error?

And it didn’t just return one error, it returned thousands of GL_INVALID_OPERATION error messages.

Is there a limit to how many error codes that glGetError() can store? How would I reset it if I wanted to?

[edit]
I just looked at it again, and it’s returning an ENDLESS loop of GL_INVALID_OPERATION error messages.
Why would it do something like this? I thought this removes them:


GLenum error;
while ((error = glGetError()) != GL_NO_ERROR) {
   // display error
}
2

Woohoo! I figured it out. You can’t call glGetError() when there is no active rendering context,
otherwise you will get stuck in an infinite loop of GL_INVALID_OPERATION errors.

Here’s my fix, that’s working great now:


if(wglGetCurrentContext() != NULL) {
   GLenum error;
   while ((error = glGetError()) != GL_NO_ERROR) {
      // display error
   }
}

I couldn’t figure out why my program was crashing all the time!
I know why now!

3

Here’s some better code. Probably better to check each time in case some sneaky thread tries to clear
out the active context while I’m digging through GL errors:


if(wglGetCurrentContext() != NULL) {
   GLenum error;
   while ((error = glGetError()) != GL_NO_ERROR) {
      // display error
      if(wglGetCurrentContext() != NULL) break;
   }
}
4

What is the purpose of the while loop in the first place? Shouldn’t is be an “if” statement?

5

There may be more than one error returned.

Although it’s probably safer to just check for one error and skip the entire while loop all together! It’s a bloody trap waiting to happen. It’ll crash your app if you’re not careful. :slight_smile:

IMHO, kinda ridiculous if you ask me. Querying for error information causes your app to crash.

Anybody know if OpenGL 3.0 does this too?