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pixel: add Grayscale2bit color (#817)

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* pixel: add GrayScale2bit color
* pixel: fix spelling of 'GrayScale' to 'Grayscale'
This commit is contained in:
sago35
2025-11-15 17:02:55 +09:00
committed by GitHub
parent c710cc8236
commit 253f8e3220
3 changed files with 115 additions and 1 deletions
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pixel/image.go
+21
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@@ -149,6 +149,20 @@ func (img Image[T]) setPixel(index int, c T) {
}
return
case zeroColor.BitsPerPixel() == 2:
// Grayscale2bit.
offset := index / 4 // 4 pixels per byte
shift := 6 - (index%4)*2 // bits: 6, 4, 2, 0
ptr := (*byte)(unsafe.Add(img.data, offset))
raw := *(*uint8)(unsafe.Pointer(&c))
gray := raw & 0b11
mask := byte(0b11 << shift)
*ptr = (*ptr &^ mask) | (gray << shift)
return
case zeroColor.BitsPerPixel()%8 == 0:
// Each color starts at a whole byte offset.
// This is the easy case.
@@ -206,6 +220,13 @@ func (img Image[T]) Get(x, y int) T {
ptr := (*byte)(unsafe.Add(img.data, offset))
c = ((*ptr >> (7 - uint8(bits))) & 0x1) > 0
return any(c).(T)
case zeroColor.BitsPerPixel() == 2:
// Grayscale2bit.
offset := index / 4 // 4 pixels per byte
shift := 6 - (index%4)*2 // bits: 6, 4, 2, 0
ptr := (*byte)(unsafe.Add(img.data, offset))
value := ((*ptr) >> shift) & 0b11
return any(Grayscale2bit(value)).(T)
case zeroColor.BitsPerPixel()%8 == 0:
// Colors like RGB565, RGB888, etc.
offset := index * int(unsafe.Sizeof(zeroColor))