GL instance of hidden GLCanvas invalid?

OpenGL Development JOGL Development
#1

Hi,

I’d like to do some things for which I do not need a visible GLCanvas (get the maximum size of a texture).
But:

GLCanvas c = new GLCanvas();
c.getGL().glGetIntegerv(GL.GL_MAX_TEXTURE_SIZE, intBuffer);
//...

returns 0! But, when the GLCanvas is visible, and I do the same in the init()-method, it works (returns 2048).
Is this normal? Is there no way to do things without a visible surface?

Thanks :slight_smile:

Andi

#2

The GLCanvas must be visible in order for its OpenGL context to be valid. You can use a 1x1 GLPbuffer (see GLDrawableFactory.canCreateGLPbuffer(), createGLPbuffer() for this purpose. You’ll need to call display() once on the GLPbuffer to cause its OpenGL context to be created.

#3

This doesn’t work too:

GLDrawableFactory f = GLDrawableFactory.getFactory();
//yes, f.canCreateGLPbuffer() returns true
GLPbuffer b = f.createGLPbuffer(new GLCapabilities(), null, 1, 1, null);
b.display();
b.getGL().glGetIntegerv(...);
//...

It returns 0 again… Must I register a GLEventListener and call the method within the init()-method?

#4

Yes. Either that or you need to call b.getContext().makeCurrent() (checking the return value), then call your OpenGL functions, and then call b.getContext().release().

#5

Now it works. Ken, thank you very much for your quick responses :slight_smile: