HP c3700 - Workstation, Reference Manual, Page: 33 / 486

B
glBlendFunc
Chapter 2
33
glBlendFunc
glBlendFunc
: specify pixel arithmetic.
C Specification
void glBlendFunc(
GLenum sfactor,
GLenum dfactor)
Parameters
sfactor Specifies how the red, green, blue, and alpha source blending factors
are computed. Nine symbolic constants are accepted:
GL_ZERO, GL_ONE, GL_DST_COLOR,
GL_ONE_MINUS_DST_COLOR, GL_SRC_ALPHA,
GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA,
GL_ONE_MINUS_DST_ALPHA, and GL_SRC_ALPHA_SATURATE.
The initial value is GL_ONE.
dfactor Specifies how the red, green, blue, and alpha destination blending
factors are computed. Eight symbolic constants are accepted:
GL_ZERO, GL_ONE, GL_SRC_COLOR,
GL_ONE_MINUS_SRC_COLOR, GL_SRC_ALPHA,
GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA, and
GL_ONE_MINUS_DST_ALPHA.
The initial value is GL_ZERO.
Description
In RGBA mode, 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.
glBlendFunc defines the operation of blending when it is enabled. sfactor specifies which
of nine methods is used to scale the source color components. dfactor specifies which of
eight methods is used to scale the destination color components. The eleven 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, 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
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
).
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].