HP b2600 Reference Manual page 34

B
glBlendFunc
Parameters
Table 2-1
Parameter
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_SRC_ALPHA_SATURATE
In the table,
i = min(A
To determine the blended RGBA values of a pixel when drawing in RGBA mode, the
system uses the following equations:
R
G
d
B
d
A
d
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 sfactor is
GL_SRC_ALPHA, dfactor is GL_ONE_MINUS_SRC_ALPHA, and A
equations reduce to simple replacement:
R
d
G
d
B
d
A
d
34
, k - A ) / k
s A d A
= min(k , R s + R
d R s R d
= min(k , G s + G
G s G d
= min(k , B s + B d
B s B d
= min(k , A s + A d
A s A d
= R
s
= G
s
= B
s
= A
s
(f , f , f
R G B
(0, 0, 0, 0)
(1, 1, 1, 1)
(R /k , G
s R s
(1,1,1,1) - (R
(R /k , G
d R d
(1, 1, 1, 1) - (R
(A /k , A
s A s
(1, 1, 1, 1) - (A
(A /k , A
d A d
(1, 1, 1, 1) - (A
(i, i, i,1)
d )
R
d )
G
)
B
)
A
, f )
A
/k , B /k , A /k )
G s B s A
/k , G /k , B /k , A
s R s G s B
/k , B /k , A /k )
G d B d A
/k , G /k , B /k , A
d R d G d B
/k , A /k , A /k )
A s A s A
/k , A /k , A /k , A
s A s A s A
/k ,A /k ,A /k )
A d A d A
/k , A /k ,A /k ,A
d A d A d A
is equal to k
s
/k )
s A
/k )
d A
/k )
s A
/k )
d A
, the
A
Chapter 2