OpenGL Blit layered frame buffers

OpenGL OpenGL: Advanced Coding
1

I have a simple question that I find pretty hard to find information online. How can I blit layered frame buffers? I have the following:

glGenFramebuffers(1, &MSAAFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, MSAAFramebuffer);

// generate texture
glGenTextures(4, msaaColorBuffers);
for (int i = 0; i < 4; ++i)
{
	glBindTexture(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, msaaColorBuffers[i]);
	if (i == 1) glTexImage3DMultisample(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, msaaSamples, GL_R11F_G11F_B10F, renderWidth, renderHeight, 2, GL_TRUE);
	else glTexImage3DMultisample(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, msaaSamples, GL_RGBA8, renderWidth, renderHeight, 2, GL_TRUE);
	// attach it to currently bound framebuffer object
	glFramebufferTextureMultiviewOVR(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, msaaColorBuffers[i], 0, 0, 2);
}

glGenTextures(1, &depthTextureMS);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, depthTextureMS);
glTexImage3DMultisample(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, msaaSamples, GL_DEPTH_COMPONENT32F, renderWidth, renderHeight, 2, GL_TRUE);
glFramebufferTextureMultiviewOVR(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthTextureMS, 0, 0, 2);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE_ARRAY, 0);

GLuint resolvedTextAttachments[4] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 , GL_COLOR_ATTACHMENT3 };
glDrawBuffers(4, resolvedTextAttachments);

if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
	Log::error("ERROR::FRAMEBUFFER:: Off screen render Framebuffer is not complete!");

// bind again the default frame buffer
glBindFramebuffer(GL_FRAMEBUFFER, 0);

And trying to blit like this:

	glBindFramebuffer(GL_READ_FRAMEBUFFER, gBufferMSAA);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, MSAAFramebuffer);

	for (int layer = 0; layer < 2; ++layer) {
		glFramebufferTexture3D(GL_READ_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D_MULTISAMPLE_ARRAY, depthTextureArrayMS, 0, layer);
		glFramebufferTexture3D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D_MULTISAMPLE_ARRAY, depthTextureMS, 0, layer);
		glBlitFramebuffer(0, 0, renderWidth, renderHeight, 0, 0, renderWidth, renderHeight,	GL_DEPTH_BUFFER_BIT, GL_NEAREST);
	}

During initializing the frame buffer I get no errors and everything works as expected. During blit and if I use “glFramebufferTexture3D” or “glFramebufferTextureLayer” I get frame buffer bindings are incomplete. Any ideas here?

2

Hi there! I’m pretty sure you can’t dynamically reattach a single layer (using glFramebufferTexture3D or glFramebufferTextureLayer) to a multiview FBO that was originally created to handle multiple layers at once. The OpenGL spec requires that the framebuffer’s attachments remain consistent in type and number of layers. This is why you get an incomplete framebuffer error.

To blit layered framebuffers, you may either:
– Resolve each layer using a dedicated FBO with a single-layer attachment
– Perform the resolve in a shader

This should give you a complete framebuffer configuration for each blit and avoid the incomplete FBO error :wink: