Native bindings to the OES_packed_depth_stencil extension.

Many OpenGL implementations have chosen to interleave the depth and stencil buffers into one buffer, often with 24 bits of depth precision and 8 bits of stencil data. 32 bits is more than is needed for the depth buffer much of the time; a 24-bit depth buffer, on the other hand, requires that reads and writes of depth data be unaligned with respect to power-of-two boundaries. On the other hand, 8 bits of stencil data is more than sufficient for most applications, so it is only natural to pack the two buffers into a single buffer with both depth and stencil data. OpenGL never provides direct access to the buffers, so the OpenGL implementation can provide an interface to applications where it appears the one merged buffer is composed of two logical buffers.

One disadvantage of this scheme is that OpenGL lacks any means by which this packed data can be handled efficiently. For example, when an application reads from the 24-bit depth buffer, using the type GL_UNSIGNED_SHORT will lose 8 bits of data, while GL_UNSIGNED_INT has 8 too many. Both require expensive format conversion operations. A 24-bit format would be no more suitable, because it would also suffer from the unaligned memory accesses that made the standalone 24-bit depth buffer an unattractive proposition in the first place.

If OES_depth_texture is supported, a new data format, GL_DEPTH_STENCIL_OES, as well as a packed data type, UNSIGNED_INT_24_8_OES, together can be used with glTex[Sub]Image2D. This provides an efficient way to supply data for a 24-bit depth texture. When a texture with DEPTH_STENCIL_OES data is bound for texturing, only the depth component is accessible through the texture fetcher.

This extension also provides a new sized internal format, DEPTH24_STENCIL8_OES, which can be used for renderbuffer storage. When a renderbuffer or texture image with a DEPTH_STENCIL_OES base internal format is attached to both the depth and stencil attachment points of a framebuffer object, then it becomes both the depth and stencil buffers of the framebuffer. This fits nicely with hardware that interleaves both depth and stencil data into a single buffer.