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Name Strings
$Date: 1995/10/31 00:11:43 $ $Revision: 1.2 $
SGIS_multisample is required.
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
Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation)
Additions to Chapter 3 of the 1.0 Specification (Rasterization)
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
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
When SAMPLE_BUFFER_SGIS is 0, TagSampleBuffer has no effect.
Additions to Chapter 5 of the 1.0 Specification (Special Functions)
Additions to Chapter 6 of the 1.0 Specification (State and State Requests)
Additions to the GLX Specification
INVALID_OPERATION is generated if TagSampleBufferSGIX is called
between the execution of Begin and the execution of the
corresponding End.
New State
New Implementation Dependent State