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OpenGL 4.2 (Compatibility Profile) - April 27, 2012

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3.4. POINTS 225<br />

any other variables not qualified with sample in need not be evaluated independently<br />

for each sample.<br />

If the sample locations differ per pixel, they should be aligned to window, not<br />

screen, boundaries. Otherwise rendering results will be window-position specific.<br />

The invariance requirement described in section 3.2 is relaxed for all multisample<br />

rasterization, because the sample locations may be a function of pixel location.<br />

Sample Shading<br />

Sample shading can be used to specify a minimum number of unique samples to<br />

process for each fragment. Sample shading is controlled by calling Enable or<br />

Disable with the symbolic constant SAMPLE_SHADING.<br />

If MULTISAMPLE or SAMPLE_SHADING is disabled, sample shading has no<br />

effect. Otherwise, an implementation must provide a minimum of<br />

max(⌈mss × samples⌉, 1)<br />

unique color values and sets of texture coordinates for each fragment, where mss<br />

is the value of MIN_SAMPLE_SHADING_VALUE and samples is the number of<br />

samples (the value of SAMPLES). These are associated with the samples in an<br />

implementation-dependent manner. The value of MIN_SAMPLE_SHADING_VALUE<br />

is specified by calling<br />

void MinSampleShading( float value );<br />

with value set to the desired minimum sample shading fraction. value is clamped<br />

to [0, 1] when specified. The sample shading fraction may be queried by calling<br />

GetFloatv with the symbolic constant MIN_SAMPLE_SHADING_VALUE.<br />

When the sample shading fraction is 1.0, a separate set of colors and other<br />

associated data are evaluated for each sample, and each set of values is evaluated<br />

at the sample location.<br />

3.4 Points<br />

A point is drawn by generating a set of fragments in the shape of a square or circle<br />

centered around the vertex of the point. Each vertex has an associated point size<br />

that controls the size of that square or circle.<br />

If no vertex, tessellation control, tessellation evaluation, or geometry shader is<br />

active, then the rasterization of points is controlled with<br />

void PointSize( float size );<br />

<strong>OpenGL</strong> <strong>4.2</strong> (<strong>Compatibility</strong> <strong>Profile</strong>) - <strong>April</strong> <strong>27</strong>, <strong>2012</strong>

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