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much faster toStraightAlpha

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This commit is contained in:
Ryan Oldenburg 2022-06-14 17:54:02 -05:00
parent 104cfb03d6
commit 1e6070c150
1 changed files with 14 additions and 7 deletions
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21
src/pixie/internal.nim
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@ -81,16 +81,23 @@ proc fillUnsafe*(
for j in i ..< start + len: for j in i ..< start + len:
data[j] = rgbx data[j] = rgbx
const straightAlphaTable = block:
var table: array[256, array[256, uint8]]
for a in 0 ..< 256:
let multiplier = if a > 0: (255 / a.float32) else: 0
for c in 0 ..< 256:
table[a][c] = min(round((c.float32 * multiplier)), 255).uint8
table
proc toStraightAlpha*(data: var seq[ColorRGBA | ColorRGBX]) {.raises: [].} = proc toStraightAlpha*(data: var seq[ColorRGBA | ColorRGBX]) {.raises: [].} =
## Converts an image from premultiplied alpha to straight alpha. ## Converts an image from premultiplied alpha to straight alpha.
## This is expensive for large images. ## This is expensive for large images.
for c in data.mitems: for i in 0 ..< data.len:
if c.a == 0 or c.a == 255: var c = data[i]
continue c.r = straightAlphaTable[c.a][c.r]
let multiplier = ((255 / c.a.float32) * 255).uint32 c.g = straightAlphaTable[c.a][c.g]
c.r = ((c.r.uint32 * multiplier) div 255).uint8 c.b = straightAlphaTable[c.a][c.b]
c.g = ((c.g.uint32 * multiplier) div 255).uint8 data[i] = c
c.b = ((c.b.uint32 * multiplier) div 255).uint8
proc toPremultipliedAlpha*(data: var seq[ColorRGBA | ColorRGBX]) {.raises: [].} = proc toPremultipliedAlpha*(data: var seq[ColorRGBA | ColorRGBX]) {.raises: [].} =
## Converts an image to premultiplied alpha from straight alpha. ## Converts an image to premultiplied alpha from straight alpha.