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pixel: implement RGB555 pixel format as used by the GameBoy Advance #621

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merged 1 commit into from
Nov 24, 2023
Merged

pixel: implement RGB555 pixel format as used by the GameBoy Advance #621

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33 changes: 32 additions & 1 deletion pixel/pixel.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ import (
// particular display. Each pixel is at least 1 byte in size.
// The color format is sRGB (or close to it) in all cases.
type Color interface {
RGB888 | RGB565BE | RGB444BE
RGB888 | RGB565BE | RGB555 | RGB444BE

BaseColor
}
Expand Down Expand Up @@ -46,6 +46,8 @@ func NewColor[T Color](r, g, b uint8) T {
return any(NewRGB888(r, g, b)).(T)
case RGB565BE:
return any(NewRGB565BE(r, g, b)).(T)
case RGB555:
return any(NewRGB555(r, g, b)).(T)
case RGB444BE:
return any(NewRGB444BE(r, g, b)).(T)
default:
Expand Down Expand Up @@ -140,6 +142,35 @@ func (c RGB565BE) RGBA() color.RGBA {
return color
}

// Color format used on the GameBoy Advance among others.
//
// Colors are stored as native endian values, with bits 0bbbbbgg_gggrrrrr (red
// is least significant, blue is most significant).
type RGB555 uint16

func NewRGB555(r, g, b uint8) RGB555 {
return RGB555(r)>>3 | (RGB555(g)>>3)<<5 | (RGB555(b)>>3)<<10
}

func (c RGB555) BitsPerPixel() int {
// 15 bits per pixel, but there are 16 bits when stored
return 16
}

func (c RGB555) RGBA() color.RGBA {
color := color.RGBA{
R: uint8(c>>10) << 3,
G: uint8(c>>5) << 3,
B: uint8(c) << 3,
A: 255,
}
// Correct color rounding, so that 0xff roundtrips back to 0xff.
color.R |= color.R >> 5
color.G |= color.G >> 5
color.B |= color.B >> 5
return color
}

// Color format that is supported by the ST7789 for example.
// It may be a bit faster to use than RGB565BE on very slow SPI buses.
//
Expand Down