OpenGL.GL.NV.copy_depth_to_color

OpenGL extension NV.copy_depth_to_color

This module customises the behaviour of the OpenGL.raw.GL.NV.copy_depth_to_color to provide a more Python-friendly API

Overview (from the spec)

Some applications, especially systems for distributed OpenGL rendering, would like to have a fast way of copying their depth buffer into a color buffer; for example, this allows the depth buffer to be scanned out, allowing downstream compositing operations.

To do this operation in unextended OpenGL, the app must use glReadPixels of GL_DEPTH_COMPONENT data, followed by glDrawPixels of RGBA data. However, this typically will not provide adequate performance.

This extension provides a way to copy the depth data directly into the color buffer, by adding two new options for the "type" parameter of glCopyPixels: GL_DEPTH_STENCIL_TO_RGBA_NV and GL_DEPTH_STENCIL_TO_BGRA_NV.

Typically, OpenGL implementations support many more bits of depth precision than color precision per channel. On many PC platforms, it is common, for example, to have 24 bits of depth, 8 bits of stencil, and 8 bits of red, green, blue, and alpha.

In such a framebuffer configuration, the most effective way to copy the data without this extension would be to perform a glReadPixels of GL_UNSIGNED_INT_24_8_NV/GL_DEPTH_STENCIL_NV (using the existing NV_packed_depth_stencil extension), followed by a glDrawPixels of GL_UNSIGNED_INT_8_8_8_8/GL_RGBA or GL_BGRA data. This places the depth data in the color channels and the stencil data in the alpha channel.

This extension's new operations concatenates these two operations, providing a CopyPixels command that does both of these steps in one. This provides a large performance speedup, since no pixel data must be transfered across the bus.

The official definition of this extension is available here: http://www.opengl.org/registry/specs/NV/copy_depth_to_color.txt