CODEWITHSUNDEEP
c++opengl
Anne Quinn
Anne Quinn

Reputation: 13002

OpenGL: Acquiring only a stencil buffer and no depth buffer?

I would like to acquire a stencil buffer, but not suffer the overhead of an attached depth buffer if it's possible, since I wouldn't be using it. Most of the resources I've found suggest that while the stencil buffer is optional (excluding it in favour of gaining more depth buffer precision, for example) I have not seen any code that requests and successfully gets only the 8-bit stencil buffer. The most common configuration I've seen being 24 bit depth buffers with an 8 bit stencil buffer.

Is it possible to request only a stencil buffer with a color buffer?

If it is possible, Is it likely the request would be granted by most OpenGL implementations?

The OpenGL version I'm using is 2.0

edit:

The API I'm using to call OpenGL is SFML, which normally doesn't support stencil allocation for it's FBO wrapper objects, though it allows it for the display surface's framebuffer. I edited the functionality in myself, though that's where I'm stuck. 

glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH24_STENCIL8_EXT, width, height));

This line decides the storage type I assume. However, GL_DEPTH24_STENCIL8_EXT is the only define I've found that specifies a stencil buffer's creation. (there's no GL_STENCIL8 or anything similar at least)

Upvotes: 4

Views: 1351

Answers (1)

Anne Quinn
Anne Quinn

Reputation: 13002

Researching GL_STENCIL_INDEX8 that was mentioned in the comments, I came across the following line in the the official OpenGL wiki, http://www.opengl.org/wiki/Framebuffer_Object_Examples#Stencil

NEVER EVER MAKE A STENCIL buffer. All GPUs and all drivers do not support an independent stencil buffer. If you need a stencil buffer, then you need to make a Depth=24, Stencil=8 buffer, also called D24S8.

Stress testing the two different allocation schemes, GL_STENCIL_INDEX8_EXT vs GL_DEPTH24_STENCIL8_EXT, the results were roughly equal, both in terms of memory usage and performance. I suspect that it padded the stencil buffer with 24bits anyway. So for sake of portability, going to just use the depth and stencil packed scheme.

Upvotes: 1

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