Native bindings to the NV_sample_locations extension.

This extension allows an application to modify the locations of samples within a pixel used in multisample rasterization. Additionally, it allows applications to specify different sample locations for each pixel in a group of adjacent pixels, which may increase antialiasing quality (particularly if a custom resolve shader is used that takes advantage of these different locations).

It is common for implementations to optimize the storage of depth values by storing values that can be used to reconstruct depth at each sample location, rather than storing separate depth values for each sample. For example, the depth values from a single triangle can be represented using plane equations. When the depth value for a sample is needed, it is automatically evaluated at the sample location. Modifying the sample locations causes the reconstruction to no longer evaluate the same depth values as when the samples were originally generated. This extension provides a command to "resolve" and store per-sample depth values using the currently programmed sample locations, which allows the application to manage this issue if/when necessary.

The programmable sample locations are used during rasterization and for evaluation of depth functions during normal geometric rendering. The programmable locations are associated with a framebuffer object rather than an individual depth buffer, so if the depth buffer is used as a texture the texture sampling may be done at the standard sample locations. Additionally, commands that do not render geometric primitives (e.g. ReadPixels, BlitFramebuffer, CopyTexSubImage2D, etc.) may use the standard sample locations to resolve depth functions rather than the programmable locations. If a single depth buffer is used at different times with different sample locations, the depth functions may be interpreted using the current sample locations.