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pixel: add NewImageFromBytes function (#713)

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* pixel: add NewImageFromBytes() function to allow creating image from existing slice

Signed-off-by: deadprogram <ron@hybridgroup.com>

* pixel: correct and clarify code for monochrome get/set pixels

Signed-off-by: deadprogram <ron@hybridgroup.com>

---------

Signed-off-by: deadprogram <ron@hybridgroup.com>
This commit is contained in:
Ron Evans
2024-10-27 23:59:39 +00:00
committed by GitHub
parent f12454d4f7
commit 4fb5d7a0e5
2 changed files with 134 additions and 16 deletions
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pixel/image.go
+42 -6
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@@ -43,6 +43,40 @@ func NewImage[T Color](width, height int) Image[T] {
}
}
// NewImageFromBytes creates a new image of the given size using an existing data slice of bytes.
func NewImageFromBytes[T Color](width, height int, buf []byte) Image[T] {
if width < 0 || height < 0 || int(int16(width)) != width || int(int16(height)) != height {
// The width/height are stored as 16-bit integers and should never be
// negative.
panic("NewImageFromBytes: width/height out of bounds")
}
var zeroColor T
var data unsafe.Pointer
switch {
case zeroColor.BitsPerPixel()%8 == 0:
// Typical formats like RGB888 and RGB565.
// Each color starts at a whole byte offset from the start.
if len(buf) != width*height*int(unsafe.Sizeof(zeroColor)) {
panic("NewImageFromBytes: data slice size mismatch")
}
data = unsafe.Pointer(&buf[0])
default:
// Formats like RGB444 that have 12 bits per pixel.
// We access these as bytes, so allocate the buffer as a byte slice.
bufBits := width * height * zeroColor.BitsPerPixel()
bufBytes := (bufBits + 7) / 8
if len(buf) != bufBytes {
panic("NewImageFromBytes: data slice size mismatch")
}
data = unsafe.Pointer(&buf[0])
}
return Image[T]{
width: int16(width),
height: int16(height),
data: data,
}
}
// Rescale returns a new Image buffer based on the img buffer.
// The contents is undefined after the Rescale operation, and any modification
// to the returned image will overwrite the underlying image buffer in undefined
@@ -105,14 +139,15 @@ func (img Image[T]) setPixel(index int, c T) {
case zeroColor.BitsPerPixel() == 1:
// Monochrome.
x := index % int(img.width)
y := index / int(img.width)
offset := x + (y/8)*int(img.width)
offset := index / 8
ptr := (*byte)(unsafe.Add(img.data, offset))
if c != zeroColor {
*((*byte)(ptr)) |= 1 << uint8(y%8)
*((*byte)(ptr)) |= (1 << (7 - uint8(x%8)))
} else {
*((*byte)(ptr)) &^= 1 << uint8(y%8)
*((*byte)(ptr)) &^= (1 << (7 - uint8(x%8)))
}
return
case zeroColor.BitsPerPixel()%8 == 0:
// Each color starts at a whole byte offset.
@@ -166,9 +201,10 @@ func (img Image[T]) Get(x, y int) T {
case zeroColor.BitsPerPixel() == 1:
// Monochrome.
var c Monochrome
offset := x + (y/8)*int(img.width)
offset := index / 8
bits := index - (offset * 8)
ptr := (*byte)(unsafe.Add(img.data, offset))
c = (*ptr >> uint8(y%8) & 0x1) == 1
c = ((*ptr >> (7 - uint8(bits))) & 0x1) > 0
return any(c).(T)
case zeroColor.BitsPerPixel()%8 == 0:
// Colors like RGB565, RGB888, etc.