glBlendFuncSeparate — specify pixel arithmetic for RGB and alpha components separately
void glBlendFuncSeparate(
|
GLenum srcRGB, |
| GLenum dstRGB, | |
| GLenum srcAlpha, | |
GLenum dstAlpha); |
void glBlendFuncSeparatei(
|
GLuint buf, |
| GLenum srcRGB, | |
| GLenum dstRGB, | |
| GLenum srcAlpha, | |
GLenum dstAlpha); |
buf
For glBlendFuncSeparatei, specifies the index of the draw
buffer for which to set the blend functions.
srcRGB
Specifies how the red, green, and blue blending factors are computed.
The initial value is GL_ONE.
dstRGB
Specifies how the red, green, and blue destination blending factors are
computed.
The initial value is GL_ZERO.
srcAlpha
Specified how the alpha source blending factor is computed.
The initial value is GL_ONE.
dstAlpha
Specified how the alpha destination blending factor is computed.
The initial value is GL_ZERO.
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.
glBlendFuncSeparate defines the operation of blending for all draw buffers when it is enabled.
glBlendFuncSeparatei defines the operation of blending for a single draw buffer
specified by buf when enabled for that draw buffer.
srcRGB specifies which method is used to scale the
source RGB-color components.
dstRGB specifies which method is used to scale the
destination RGB-color components.
Likewise, srcAlpha specifies which method is used to scale the source alpha
color component, and dstAlpha specifies which method is used to scale the
destination alpha component.
The possible methods are described in the following table.
Each method defines four scale factors,
one each for red, green, blue, and alpha.
In the table and in subsequent equations, first source, second source and destination
color components are referred to as
and
Source and destination scale factors are referred to as
| Parameter | RGB Factor | Alpha Factor |
|---|---|---|
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 |
||
GL_ONE_MINUS_CONSTANT_ALPHA |
||
GL_SRC_ALPHA_SATURATE |
||
GL_SRC1_COLOR |
||
GL_ONE_MINUS_SRC1_COLOR |
||
GL_SRC1_ALPHA |
||
GL_ONE_MINUS_SRC1_ALPHA |
In the table,
To determine the blended RGBA values of a pixel, the system uses the following equations:
Despite the apparent precision of the above equations, blending arithmetic
is not exactly specified, because blending operates with imprecise integer
color values. However, a blend factor that should be equal to 1 is
guaranteed not to modify its multiplicand, and a blend factor equal to 0
reduces its multiplicand to 0. For example, when srcRGB is
GL_SRC_ALPHA, dstRGB is GL_ONE_MINUS_SRC_ALPHA, and
Incoming (source) alpha is correctly thought of as a material opacity,
ranging from 1.0
(
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.
GL_INVALID_ENUM is generated if either srcRGB or dstRGB is not an
accepted value.
GL_INVALID_VALUE is generated by glBlendFuncSeparatei if buf is greater
than or equal to the value of GL_MAX_DRAW_BUFFERS.
glGet with argument GL_BLEND_SRC_RGB
glGet with argument GL_BLEND_SRC_ALPHA
glGet with argument GL_BLEND_DST_RGB
glGet with argument GL_BLEND_DST_ALPHA
glIsEnabled with argument GL_BLEND
| OpenGL Version | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5 |
glBlendFuncSeparate
|
✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
glBlendFuncSeparatei
|
- | - | - | - | - | - | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
glBlendColor, glBlendFunc, glBlendEquation, glClear, glDrawBuffer, glEnable, glLogicOp, glStencilFunc
Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2018 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.