table of contents
GLBLENDFUNC(3G) | [FIXME: manual] | GLBLENDFUNC(3G) |
NAME¶
glBlendFunc - specify pixel arithmeticC SPECIFICATION¶
void
glBlendFunc(GLenum sfactor,
GLenum dfactor);
void
glBlendFunci(GLuint buf, GLenum sfactor,
GLenum dfactor);
PARAMETERS¶
bufFor glBlendFunci, specifies the index
of the draw buffer for which to set the blend function.
sfactor
Specifies how the red, green, blue, and alpha
source blending factors are computed. The initial value is
GL_ONE.
dfactor
Specifies how the red, green, blue, and alpha
destination blending factors are computed. The following symbolic constants
are accepted: GL_ZERO, GL_ONE, GL_SRC_COLOR,
GL_ONE_MINUS_SRC_COLOR, GL_DST_COLOR,
GL_ONE_MINUS_DST_COLOR, GL_SRC_ALPHA,
GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA,
GL_ONE_MINUS_DST_ALPHA. GL_CONSTANT_COLOR,
GL_ONE_MINUS_CONSTANT_COLOR, GL_CONSTANT_ALPHA, and
GL_ONE_MINUS_CONSTANT_ALPHA. The initial value is GL_ZERO.
DESCRIPTION¶
Pixels can be drawn using a function that blends the incoming (source) RGBA values with the RGBA values that are already in the frame buffer (the destination values). Blending is initially disabled. Use glEnable() and glDisable() with argument GL_BLEND to enable and disable blending.Parameter | f R f G f B f A |
GL_ZERO | 0 0 0 0 |
GL_ONE | 1 1 1 1 |
GL_SRC_COLOR | R s0 k R G s0 k G B s0 k B A s0 k A |
GL_ONE_MINUS_SRC_COLOR | 1 1 1 1 - R s0 k R G s0 k G B s0 k B A s0 k A |
GL_DST_COLOR | R d k R G d k G B d k B A d k A |
GL_ONE_MINUS_DST_COLOR | 1 1 1 1 - R d k R G d k G B d k B A d k A |
GL_SRC_ALPHA | A s0 k A A s0 k A A s0 k A A s0 k A |
GL_ONE_MINUS_SRC_ALPHA | 1 1 1 1 - A s0 k A A s0 k A A s0 k A A s0 k A |
GL_DST_ALPHA | A d k A A d k A A d k A A d k A |
GL_ONE_MINUS_DST_ALPHA | 1 1 1 1 - A d k A A d k A A d k A A d k A |
GL_CONSTANT_COLOR | R c G c B c A c |
GL_ONE_MINUS_CONSTANT_COLOR | 1 1 1 1 - R c G c B c A c |
GL_CONSTANT_ALPHA | A c A c A c A c |
GL_ONE_MINUS_CONSTANT_ALPHA | 1 1 1 1 - A c A c A c A c |
GL_SRC_ALPHA_SATURATE | i i i 1 |
GL_SRC1_COLOR | R s1 k R G s1 k G B s1 k B A s1 k A |
GL_ONE_MINUS_SRC1_COLOR | 1 1 1 1 - R s1 k R G s1 k G B s1 k B A s1 k A |
GL_SRC1_ALPHA | A s1 k A A s1 k A A s1 k A A s1 k A |
GL_ONE_MINUS_SRC1_ALPHA | 1 1 1 1 - A s1 k A A s1 k A A s1 k A A s1 k A |
EXAMPLES¶
Transparency is best implemented using blend function ( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) with primitives sorted from farthest to nearest. Note that this transparency calculation does not require the presence of alpha bitplanes in the frame buffer. Blend function ( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) is also useful for rendering antialiased points and lines in arbitrary order. Polygon antialiasing is optimized using blend function ( GL_SRC_ALPHA_SATURATE, GL_ONE) with polygons sorted from nearest to farthest. (See the glEnable(), glDisable() reference page and the GL_POLYGON_SMOOTH argument for information on polygon antialiasing.) Destination alpha bitplanes, which must be present for this blend function to operate correctly, store the accumulated coverage.NOTES¶
Incoming (source) alpha is correctly thought of as a material opacity, ranging from 1.0 (K A), representing complete opacity, to 0.0 (0), representing complete transparency. When more than one color buffer is enabled for drawing, the GL performs blending separately for each enabled buffer, using the contents of that buffer for destination color. (See glDrawBuffer().) When dual source blending is enabled (i.e., one of the blend factors requiring the second color input is used), the maximum number of enabled draw buffers is given by GL_MAX_DUAL_SOURCE_DRAW_BUFFERS, which may be lower than GL_MAX_DRAW_BUFFERS.ERRORS¶
ASSOCIATED GETS¶
SEE ALSO¶
COPYRIGHT¶
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.05/30/2012 | [FIXME: source] |