GLSAMPLECOVERAGEARB(3gl)GLSAMPLECOVERAGEARB(3gl)NAMEglSampleCoverageARB - Specify parameters for coverage calculation
C SPECIFICATION
void glSampleCoverageARB( GLclampf value,
GLboolean invert )
PARAMETERS
value Specifies the value for GL_SAMPLE_COVERAGE_VALUE_ARB. The value
is clamped [0,1]; 0 implies no coverage, and 1 implies full
coverage. The initial value is 1.
invert Specifies GL_SAMPLE_COVERAGE_INVERT_ARB flag. The initial
value is GL_FALSE.
DESCRIPTION
Multisampling works by sampling primitives multiple times at different
locations at each pixel, in effect collecting subpixel information. The
results is an image that has fewer aliasing artifacts. If GL_SAM‐
PLE_BUFFERS_ARB is 1, multisample rasterlization can be enabled/dis‐
abled by enabling/disabling GL_MULTISAMPLE_ARB; otherwise it is always
a single-sample rasterization. The primitives are sampled at the loca‐
tion defined by a sample pattern, which produces a fragment coverage
value. This coverage value is modified as described below before it is
used.
GL_SAMPLE_ALPHA_TO_COVERAGE_ARB, GL_SAMPLE_ALPHA_TO_ONE_ARB, and
GL_SAMPLE_COVERAGE_ARB are enabled/disbale for calculation of a cover‐
age value for multisampling.
If GL_SAMPLE_ALPHA_TO_COVERAGE_ARB is enbaled, the fragment alpha value
is used to generate a temporay coverage value, which is then ANDed with
the fragment coverage value. Otherwise the fragment coverage value is
unchanged.
If GL_SAMPLE_ALPHA_TO_ONE_ARB is enabled, fragment alpha is replaced by
the maximum representable alpha value. Otherwise the fragment coverage
value is unchanged.
When GL_SAMPLE_COVERAGE_ARB is enabled, the fragment coverage is ANDed
with a temporary coverage. This temporary coverage is generated in the
same manner as described in GL_SAMPLE_ALPHA_TO_COVERAGE_ARB, but as a
function of the value of GL_SAMPLE_COVERAGE_VALUE_ARB. If GL_SAM‐
PLE_COVERAGE_INVERT_ARB is GL_TRUE, the temporary coverage is inverted
(all bit values are inverted) before it is ANDed with the fragment cov‐
erage.
NOTESglSampleCoverageARB is available only if the GL version is 1.2.2 or
greater.
ERRORSSEE ALSO
glXChooseVisual, glXGetConfig, glEnable, glGet
7 June 01 GLSAMPLECOVERAGEARB(3gl)