GLBLENDFUNCSEPARATE - Online Linux Manual Page

Section : 3G
Updated : 01/20/2022
Source : [FIXME: source]
Note : [FIXME: manual]

NAME

glBlendFuncSeparate − specify pixel arithmetic for RGB and alpha components separately

C SPECIFICATION

void glBlendFuncSeparate(GLenum

srcRGB

, GLenum

dstRGB

, GLenum

srcAlpha

, GLenum

dstAlpha

);

void glBlendFuncSeparatei(GLuint

buf

, GLenum

srcRGB

, GLenum

dstRGB

, GLenum

srcAlpha

, GLenum

dstAlpha

);

PARAMETERS

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

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.

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 R s0 G s0 B s0 A s0, R s1 G s1 B s1 A s1, and R d G d B d A d, respectively. The color specified by glBlendColor

(

) is referred to as R c G c B c A c. They are understood to have integer values between 0 and k R k G k B k A, where

k c = 2 m c − 1

and m R m G m B m A is the number of red, green, blue, and alpha bitplanes.

Source and destination scale factors are referred to as s R s G s B s A and d R d G d B d A. All scale factors have range 0 1.

Parameter	RGB Factor	Alpha Factor
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 − R s0 k R G s0 k G B s0 k B	1 − 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 − R d k R G d k G B d k B	1 − 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 − A s0 k A A s0 k A A s0 k A	1 − 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 − A d k A A d k A A d k A	1 − A d k A
GL_CONSTANT_COLOR	R c G c B c	A c
GL_ONE_MINUS_CONSTANT_COLOR	1 1 1 − R c G c B c	1 − A c
GL_CONSTANT_ALPHA	A c A c A c	A c
GL_ONE_MINUS_CONSTANT_ALPHA	1 1 1 − A c A c A c	1 − 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	1 − 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 − A s1 k A A s1 k A A s1 k A	1 − A s1 k A

In the table,

i = min ⁡ A s 1 − A d

To determine the blended RGBA values of a pixel, the system uses the following equations:

R d = min ⁡ k R R s ⁢ s R + R d ⁢ d R G d = min ⁡ k G G s ⁢ s G + G d ⁢ d G B d = min ⁡ k B B s ⁢ s B + B d ⁢ d B A d = min ⁡ k A A s ⁢ s A + A d ⁢ d A

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

GL_SRC_ALPHA

dstRGB

GL_ONE_MINUS_SRC_ALPHA

, and A s is equal to k A, the equations reduce to simple replacement:

R d = R s G d = G s B d = B s A d = A s

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

GL_INVALID_ENUM

is generated if either

srcRGB

dstRGB

is not an accepted value.

GL_INVALID_VALUE

is generated by

glBlendFuncSeparatei

buf

is greater than or equal to the value of

GL_MAX_DRAW_BUFFERS

ASSOCIATED GETS

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

VERSION SUPPORT

	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	−	−	−	−	−	−	✔	✔	✔	✔	✔	✔