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Juicemonger

OpenGL Mipmaps and FBOs

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I am having a hell of a time generating mipmaps for my FBO texture. My mipmaps just aren't being generated properly. I render a grid to the FBO on every frame, and try to generate a full set of mipmaps immediately. Then I draw my FBO texture to the screen: When I move the camera back from the render position, the grid disappears completely within my black quad. Obviously, the renderer is trying to use my mipmaps to render my quad to the screen, but those mipmap texture levels haven't been generated. My FBO texture is 1024x1024. I'm using OpenGL Version 3.2 on an nVidia Quadro 4800 card, Windows 7. Here is my code for creating my FBO:

	texData.width = w;
	texData.height = h;
	texData.bFlipTexture = true;
	texData.glType = GL_RGB;

	this->autoClear = autoClear;

	// create & setup texture
	glGenTextures(1, (GLuint *)texData.textureName);   // could be more then one, but for now, just one

	glEnable(GL_TEXTURE_2D);

	const GLubyte* ver = glGetString(GL_VERSION);
	glBindTexture(GL_TEXTURE_2D, (GLuint)texData.textureName[0]);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);//);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);		//GL_LINEAR

	//glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap - when I include this line and draw my texture
	//at a small scale, I see the imagery, but it does not appear to be mipmapped -- it looks like a typical (jagged) linear shrinkage. (See image below)

	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8 , texData.tex_w, texData.tex_h, 0, /*texData.glType*/ GL_RGB, GL_UNSIGNED_BYTE, 0);

	// when I use glGenerateMipmapEXT(), I see proper transitions between mipmap levels as I scale down my texture, but every mipmap level
	//is just black with no imagery. (See image above.) Level 0 crossfades to black as it reaches a 50% scale.
	glGenerateMipmapEXT(GL_TEXTURE_2D);  //Allocate necessary space for mipmaps

	glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

	// create & setup FBO
	glGenFramebuffersEXT(1, &fbo);
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);

	// attach it to the FBO so we can render to it
	glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, (GLuint)texData.textureName[0], 0);

	glGenRenderbuffersEXT(1, &depthBuffer);
	glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthBuffer);
	glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, texData.tex_w, texData.tex_h);

	// Attach the depth render buffer to the FBO as it's depth attachment
	glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthBuffer);

	GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
	if(status != GL_FRAMEBUFFER_COMPLETE_EXT) {
		cout<<"glBufferTexture failed to initialize. Perhaps your graphics card doesnt support the framebuffer extension? If you are running osx prior to system 10.5, that could be the cause"<<endl;
		std::exit(1);
	}


In the code above, you may notice the commented line in which I set: glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); ...if I use this call instead of glGenerateMipmapEXT(), then I can see my entire FBO texture rendered in my quad, but it is obviously NOT mipmapped: Anyway, when it's time to actually render to my FBO texture, here is my pseudocode:

	glBindTexture(GL_TEXTURE_2D, 0);
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); 

	//DRAW to FBO

	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); //unbind the FBO

	glBindTexture(GL_TEXTURE_2D, (GLuint)texData.textureName);
	//glEnable(GL_TEXTURE_2D); //I'm told I need this on an ATI card, but not necessary for nVidia?
	glGenerateMipmapEXT(GL_TEXTURE_2D);


I have tried lots of combinations of tiny tweaks to the different calls, especially glTexImage2D, but haven't gotten anywhere. I've tried to mimic every example usage of glGenerateMipmapEXT() I can find online. I'd rather not deal with gluBuild2DMipmaps(), and I don't know why it should work where these other methods fail. Please help! I've been stuck on this for two days!

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Perhaps the 3.2 profile isn't working too well. Can you try it with GL 2 since you are calling glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
and using the glGenerateMipmapEXT (the FBO_EXT version)

//glEnable(GL_TEXTURE_2D); //I'm told I need this on an ATI card, but not necessary for nVidia?
That's for regular texture on ATI. For FBO texture, you don't need it even on ATI. Also, it was for really old drivers. Perhaps it is already fixed.

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V-man,

Using the 2.0 or 2.1 profile is something I hadn't thought of. I'd love to try, but I have no idea how to do this. I can use glGetString(GL_VERSION) to see which version I'm using, but I can't find a reference online for how to specify an older version/profile. I don't know if it means using a different nVidia driver, gl_.dll, setting preprocessor constants... Where do I start?

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Making an old context is done with the old fashion way. Look at any code such as at Nehe. Of course, the version will always say 3.0 even if you have old profile.

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You suggested that I try 2.0 because I was using glGenerateMipmapEXT and a lot of other EXT function pointers. I have since updated glee.h and am now using glGenerateMipmap(). Should that make a difference? My results on screen are the same.

I'm using a fairly large code base that does not easily lend itself to being pushed backwards. I don't think that it is worth trying to revert everything to an older version of OpenGL. Is there anything in more recent versions that might work better?

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