glBlendFuncSeparateEXT

NAME

C SPECIFICATION

void glBlendFuncSeparateEXT(GLenum sfactorRGB,
                             GLenum dfactorRGB,
                             GLenum sfactorAlpha,
                             GLenum dfactorAlpha)

PARAMETERS

DESCRIPTION

For some blend equations (see glBlendEquationEXT), glBlendFuncSeparateEXT specifies separate operations for red, green, and blue (RGB) and alpha when blending is enabled. sfactorRGB specifies which of the thirteen methods is used to scale the source red, green, and blue components. sfactorAlpha specifies which of the methods is used to scale the source alpha component. dfactorRGB specifies which of the methods is used to scale the destination red, green, and blue components. dfactorAlpha specifies which of the methods is used to scale the destination alpha component. All of the possible methods are described in the following tables.

In the table and in subsequent equations, source and destination color components are referred to as (R_s, G_s, B_s, A_s) and (R_d, G_d, B_d, A_d). They are understood to have integer values between 0 and (k_R,k_G,k_B,k_A), where

k_c = 2^mc - 1

and (m_R,m_G,m_B,m_A) is the number of red, green, blue, and alpha bitplanes.

Constant color components are referred to as (R_c, G_c, B_c, A_c). The components are not scaled by (k_R,k_G,k_B,k_A) since they are already in the range [0,1].

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). The scale factors described in the table, denoted (f_R, f_G, f_B, f_A), represent either source or destination factors. All scale factors have range [0,1].

Parameter	(fR, fG, fB)	fA
GL_ZERO	(0,0,0)	0
GL_ONE	(1,1,1)	1
GL_SRC_COLOR	(Rs/kR, Gs/kG, Bs/kB)	As/kA
GL_ONE_MINUS_SRC_COLOR	(1,1,1) - (Rs/kR, Gs/kG, Bs/kB)	1 - As/kA
GL_DST_COLOR	(Rd/kR, Gd/kG, Bd/kB)	Ad/kA
GL_ONE_MINUS_DST_COLOR	(1,1,1) - (Rd/kR, Gd/kG, Bd/kB)	1 - Ad/kA
GL_SRC_ALPHA	(As/kA, As/kA, As/kA)	As/kA
GL_ONE_MINUS_SRC_ALPHA	(1,1,1) - (As/kA, As/kA, As/kA)	1 - As/kA
GL_DST_ALPHA	(Ad/kA, Ad/kA, Ad/kA)	Ad/kA
GL_ONE_MINUS_DST_ALPHA	(1,1,1) - (Ad/kA, Ad/kA, Ad/kA)	1 - Ad/kA
GL_SRC_ALPHA_SATURATE	(i,i,i)	1
GL_CONSTANT_COLOR_EXT	(Rc, Gc, Bc)	Ac
GL_ONE_MINUS_CONSTANT_COLOR_EXT	(1,1,1) - (Rc, Gc, Bc)	1 - Ac
GL_CONSTANT_ALPHA_EXT	(Ac, Ac, Ac)	Ac
GL_ONE_MINUS_CONSTANT_ALPHA_EXT	(1,1,1) - (Ac, Ac, Ac)	1 - Ac

In the table,

i = min(A_s, k_A -A_d) / k_A

To determine the blended RGBA values of a pixel when drawing in RGBA mode, the system uses the following equations (if the blend equation extension is not supported):

R_d = min(k_R, R_ss_R+R_dd_R)
G_d = min(k_G, G_ss_G+G_dd_R)
B_d = min(k_B, B_ss_B+B_dd_B)
A_d = min(k_A, A_ss_B+A_dd_A)

If the blend equation extension is supported, the blended RGBA values of a pixel are computed based on the current blend equation (see glBlendEquationEXT.

NOTES

When more than one color buffer is enabled for drawing, blending is done separately for each enabled buffer, using the contents of that buffer for destination color. (See glDrawBuffer.)

Blending affects only RGBA rendering. It is ignored by color index renderers.

For backward compatibility, calling glGet with the arguments GL_BLEND_SRC or GL_BLEND_DST returns the RGB blend factors.

EXTENSIONS

GL_EXT_blend_func_separate

glBlendFuncSeparateEXT is part of the EXT_blend_func_separate extension.

GL_EXT_blend_color

GL_CONSTANT_COLOR_EXT, GL_ONE_MINUS_CONSTANT_COLOR_EXT, GL_CONSTANT_ALPHA_EXT, and GL_ONE_MINUS_CONSTANT_ALPHA_EXT are part of the EXT_blend_color extension.

ERRORS

GL_INVALID_OPERATION is generated if glBlendFunc is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

SEE ALSO