GL_TEXTURE_3D color and stencil FBO attachments

Question

I am doing a layered rendering to an offscreen FBO using OpenGL 4.3.I used GL_TEXTURE_3D with several layers as COLOR attachment.Then I use geometry shader to index into different layers when writing the output.It works ok.Now I need also stencil attachment for stencil test I am performing during the rendering.First I tried just to attach a render buffer as in the case with 2D attachments.

glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT,
GL_RENDERBUFFER, _stencilBuffer)

In this case,when checking FBO for completeness I am getting frame buffer error:

GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS_ARB

Then I assumed that if the color attachment is 3D so the stencil attachment also must be 3D.And because there is no 3D render buffer I tried to attach a 3D texture for depth stencil slot of the FBO.

glTexImage3D(GL_TEXTURE_3D, 0, GL_DEPTH24_STENCIL8, width, height, depth,
0, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8);

Where width - texture width,height-texture height,depth-number of layers inside texture 3D.

//Attach to FBO:
 
 glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, texId, 0));

Doing it this way I am getting:

GL_FRAMEBUFFER_INCOMPLETE

INVALID_OPERATION

I have searched any possible example to find how such a setup should be done,but found nothing.I also tried to use GL_TEXTURE_2D_ARRAY instead,but same problem. (for some reason this actually fixed the problem which persisted in my earlier tests)

UPDATE

My fault as got confused with some of my findings during the debug.Basically half of what I wrote above can be discarded.But because other people may get into the same issues I will explain what happened.

At first,when I attached a 3d texture to COLOR attachment of FBO I created a render buffer for GL_DEPTH_STENCIL attachment.And yes,on completeness check I got:

GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS_ARB

Next,I tried instead:

glTexImage3D(GL_TEXTURE_3D, 0, GL_DEPTH24_STENCIL8, width, height, depth,
0, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8);

which thrown:

INVALID_OPERATION

Now,instead of GL_TEXTURE_3D target I tried GL_TEXTURE_2D_ARRAY which finally caused the FBO to be complete.So,while I would still like to understand why GL_TEXTURE_3D causes INVALID_OPERATION(feel free to post an answer),this change has solved the problem.

Answer 1

Based on the spec, GL_FRAMEBUFFER_INCOMPLETE_LAYER_TARGETS means (quoted from OpenGL 4.5 spec):

If any framebuffer attachment is layered, all populated attachments must be layered. Additionally, all populated color attachments must be from textures of the same target (three-dimensional, one- or two-dimensional array, cube map, or cube map array textures).

Based on the first part of this, your initial attempt of using a single layer stencil attachment with a layered 3D texture color attachment was clearly illegal.

The second part sounds somewhat unclear to me. Since it only talks about "color attachments", it suggests that using a GL_TEXTURE_3D color attachment and a GL_TEXTURE_2D_ARRAY stencil attachment would be legal. But I'm not convinced that this is actually the intention. Unfortunately I couldn't find additional confirmation of this in the rest of the spec.

Using GL_TEXTURE_3D for a stencil or depth/stencil texture is a non-starter. There's no such thing as a 3D stencil texture. From the 4.5 spec, pages 191-192 in section "8.5 Texture Image Specification"

Textures with a base internal format of DEPTH_COMPONENT, DEPTH_STENCIL, or STENCIL_INDEX are supported by texture image specification commands only if target is TEXTURE_1D, TEXTURE_2D, TEXTURE_2D_MULTISAMPLE, TEXTURE_1D_ARRAY, TEXTURE_2D_ARRAY, TEXTURE_2D_MULTISAMPLE_ARRAY, TEXTURE_RECTANGLE, TEXTURE_CUBE_MAP, TEXTURE_CUBE_MAP_ARRAY, PROXY_TEXTURE_1D, PROXY_TEXTURE_2D, PROXY_TEXTURE_2D_MULTISAMPLE, PROXY_TEXTURE_1D_ARRAY, PROXY_TEXTURE_2D_ARRAY, PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY, PROXY_TEXTURE_RECTANGLE, PROXY_TEXTURE_CUBE_MAP, or PROXY_TEXTURE_CUBE_MAP_ARRAY.

That's a long list, but TEXTURE_3D is not in it.

Based on this, I believe that what you found to be working is the only option. You need to use textures with target GL_TEXTURE_2D_ARRAY for both the color and stencil attachment.