8.5.11 Blending
The last step before the pixel will be written to the framebuffer is to blend the pixel
with the data that has already been written to the framebuffer. If blending is
activated the framebuffer, which is here referred to as DST, must be read. SRC is
the output from the colourization unit.
The following blend modes are supported:
•
SRC_ZERO
•
SRC_ONE
•
SRC_ALPHA
•
SRC_ONE_MINUS_ALPHA
•
DST_ZERO
•
DST_ONE
•
DST_ALPHA
•
DST_ONE_MINUS_ALPHA
The selection of the blend modes is done with the following flags.
•
BSF: blend source factor is alpha
•
BSI: blend source factor invert
•
BDF: blend destination factor is alpha
•
BDI: blend destination factor invert
The formula for the blending is:
D
S
f
dst
f
src
dst
⋅
+
⋅
=
1
0
,
0
=
⇒
=
=
S
f
BSI
BSF
α
=
⇒
=
=
S
f
BSI
BSF
0
,1
0
1
,
0
=
⇒
=
=
S
f
BSI
BSF
α
−
=
⇒
=
=
1
0
,1
S
f
BSI
BSF
1
0
,
0
=
⇒
=
=
D
f
BDI
BDF
α
=
⇒
=
=
D
f
BDI
BDF
0
,1
0
1
,
0
=
⇒
=
=
D
f
BDI
BDF
α
−
=
⇒
=
=
1
0
,1
D
f
BDI
BDF
Drawing Engine
Chapter 8
Preliminary User's Manual S19203EE1V3UM00
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