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// SPDX-License-Identifier: Unlicense OR MIT
package f32color
import (
"image/color"
"math"
)
// RGBA is a 32 bit floating point linear space color.
type RGBA struct {
R, G, B, A float32
}
// Array returns rgba values in a [4]float32 array.
func (rgba RGBA) Array() [4]float32 {
return [4]float32{rgba.R, rgba.G, rgba.B, rgba.A}
}
// Float32 returns r, g, b, a values.
func (col RGBA) Float32() (r, g, b, a float32) {
return col.R, col.G, col.B, col.A
}
// SRGBA converts from linear to sRGB color space.
func (col RGBA) SRGB() color.RGBA {
return color.RGBA{
R: uint8(linearTosRGB(col.R)*255 + .5),
G: uint8(linearTosRGB(col.G)*255 + .5),
B: uint8(linearTosRGB(col.B)*255 + .5),
A: uint8(col.A*255 + .5),
}
}
// Opaque returns the color without alpha component.
func (col RGBA) Opaque() RGBA {
col.A = 1.0
return col
}
// RGBAFromSRGB converts from SRGBA to RGBA.
func RGBAFromSRGB(col color.RGBA) RGBA {
r, g, b, a := col.RGBA()
return RGBA{
R: sRGBToLinear(float32(r) / 0xffff),
G: sRGBToLinear(float32(g) / 0xffff),
B: sRGBToLinear(float32(b) / 0xffff),
A: float32(a) / 0xFFFF,
}
}
// linearTosRGB transforms color value from linear to sRGB.
func linearTosRGB(c float32) float32 {
// Formula from EXT_sRGB.
switch {
case c <= 0:
return 0
case 0 < c && c < 0.0031308:
return 12.92 * c
case 0.0031308 <= c && c < 1:
return 1.055*float32(math.Pow(float64(c), 0.41666)) - 0.055
}
return 1
}
// sRGBToLinear transforms color value from sRGB to linear.
func sRGBToLinear(c float32) float32 {
// Formula from EXT_sRGB.
if c <= 0.04045 {
return c / 12.92
} else {
return float32(math.Pow(float64((c+0.055)/1.055), 2.4))
}
}
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