Name SGIX_tag_sample_buffer Name Strings GL_SGIX_tag_sample_buffer Version $Date: 1995/10/31 00:11:43 $ $Revision: 1.2 $ Number 58 Dependencies SGIS_multisample is required. Overview The extensions defines a special purpose fast multisample clear. This clear can be used with some restrictions as a significantly faster alternative to Clear(DEPTH_BUFFER_BIT). The extension is based on the RealityEngine architecture and will probably never be supported by any other architecture. New Procedures and Functions void TagSampleBufferSGIX(void); New Tokens None. Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation) None. Additions to Chapter 3 of the 1.0 Specification (Rasterization) None. Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Frame Buffer) The specification of the sample buffer tagging operation is added to the GL Specification in section 4.2.3 "Clearing the Buffers". Each sample in the multisample buffer carries a tag that can be either set or cleared. When a tag of a sample is set, a depth test against that sample always succeeds. Note, however, that the stencil test (if enabled) still uses the stencil value that is stored at the sample. When a color is written into a sample, its tag is cleared. Depth tests against a sample with a cleared tag use the depth value stored at the sample. Initially the state of the tags of all samples is undefined. Clearing the main color buffer clears all the tags. For a given pixel, the color values stored in the sample buffer are resolved into the main color buffer only when the tags of all samples of that pixel are cleared. The tags of all the samples can be set by calling TagSampleBuffer. When using TagSampleBuffer, it is the responsibility of the application to ensure that the tags of all samples are cleared (i.e., that a color is stored into each sample least once) before the frame is completed, as color values are only resolved for pixels for which all tags are cleared. The result of blending a color into a sample whose tag is set is undefined. When SAMPLE_BUFFER_SGIS is 0, TagSampleBuffer has no effect. Additions to Chapter 5 of the 1.0 Specification (Special Functions) None. Additions to Chapter 6 of the 1.0 Specification (State and State Requests) None. Additions to the GLX Specification None. Errors INVALID_OPERATION is generated if TagSampleBufferSGIX is called between the execution of Begin and the execution of the corresponding End. New State None. New Implementation Dependent State None.