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compositor: Fix blending functions

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Correctly calculate alpha in a few places by dividing by 255,
not 256.

Fix the argb and bgra blending functions to avoid an off-by-one
error in the calculations, so painting with alpha = 0xff doesn't
ever bleed through from behind
This commit is contained in:
Jan Schmidt 2015-03-16 00:22:14 +11:00
parent 875e5c0320
commit 6a1f97cd50
1 changed files with 29 additions and 12 deletions
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41
gst/compositor/compositororc.orc
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@ -35,6 +35,7 @@ convsuswb d1, t2
.source 4 s guint8
.param 2 alpha
.temp 4 t
.temp 4 t2
.temp 2 tw
.temp 1 tb
.temp 4 a
@ -49,14 +50,26 @@ convwb tb, tw
splatbl a, tb
x4 convubw a_wide, a
x4 mullw a_wide, a_wide, alpha
x4 shruw a_wide, a_wide, 8
x4 div255w a_wide, a_wide
# dest pixel into t2
loadl t2, d
# t = s - d (as bytes)
x4 subb t, t, t2
# s_wide = (uint16)(t) * alpha
x4 convubw s_wide, t
loadl t, d
x4 convubw d_wide, t
x4 subw s_wide, s_wide, d_wide
x4 mullw s_wide, s_wide, a_wide
# s_wide /= 255
x4 div255w s_wide, s_wide
# d_wide = (uint16)(dest) + s_wide
x4 convubw d_wide, t2
x4 addw d_wide, d_wide, s_wide
# Set output alpha to 0xff and store
x4 convwb t, d_wide
orl t, t, a_alpha
storel d, t
@ -83,13 +96,17 @@ convwb tb, tw
splatbl a, tb
x4 convubw a_wide, a
x4 mullw a_wide, a_wide, alpha
x4 shruw a_wide, a_wide, 8
x4 div255w a_wide, a_wide
loadl t2, d
# t = s - d (as bytes)
x4 subb t, t, t2
x4 convubw s_wide, t
loadl t, d
x4 convubw d_wide, t
x4 subw s_wide, s_wide, d_wide
x4 mullw s_wide, s_wide, a_wide
x4 div255w s_wide, s_wide
x4 convubw d_wide, t2
x4 addw d_wide, d_wide, s_wide
x4 convwb t, d_wide
orl t, t, a_alpha
@ -114,14 +131,14 @@ storel d, t
.const 4 a_alpha 0x000000ff
.const 4 a_alpha_inv 0xffffff00
# calc source alpha as alpha_s = alpha_s * alpha / 256
# calc source alpha as alpha_s = alpha_s * alpha / 255
loadl t, s
convlw tw, t
convwb tb, tw
splatbl a, tb
x4 convubw alpha_s, a
x4 mullw alpha_s, alpha_s, alpha
x4 shruw alpha_s, alpha_s, 8
x4 div255w alpha_s, alpha_s
x4 convubw s_wide, t
x4 mullw s_wide, s_wide, alpha_s
@ -175,7 +192,7 @@ storel d, t
.const 4 a_alpha 0xff000000
.const 4 a_alpha_inv 0x00ffffff
# calc source alpha as alpha_s = alpha_s * alpha / 256
# calc source alpha as alpha_s = alpha_s * alpha / 255
loadl t, s
shrul t2, t, 24
convlw tw, t2
@ -183,7 +200,7 @@ convwb tb, tw
splatbl a, tb
x4 convubw alpha_s, a
x4 mullw alpha_s, alpha_s, alpha
x4 shruw alpha_s, alpha_s, 8
x4 div255w alpha_s, alpha_s
x4 convubw s_wide, t
x4 mullw s_wide, s_wide, alpha_s