83 lines
2.3 KiB
Go
83 lines
2.3 KiB
Go
// Provides a [color.Color] type for dealing with linear grayscale colours without alpha.
|
|
package lgray
|
|
|
|
import (
|
|
"image/color"
|
|
"math"
|
|
|
|
"smariot.com/color/internal/helper"
|
|
)
|
|
|
|
// Color is a linear grayscale [color.Color].
|
|
type Color struct {
|
|
Y float64
|
|
}
|
|
|
|
// DistanceSqr returns the euclidean distance squared between two colours.
|
|
func DistanceSqr(a, b Color) float64 {
|
|
dY := a.Y - b.Y
|
|
return dY * dY
|
|
}
|
|
|
|
// Distance returns the euclidean distance between two colours,
|
|
//
|
|
// If you just want to compare relative distances, use [DistanceSqr] instead.
|
|
func Distance(a, b Color) float64 {
|
|
return math.Abs(a.Y - b.Y)
|
|
}
|
|
|
|
// RGBA converts to premultiplied RGBA, implementing the [color.Color] interface.
|
|
func (c Color) RGBA() (r, g, b, a uint32) {
|
|
_y := helper.Delinearize(c.Y)
|
|
return _y, _y, _y, 0xffff
|
|
}
|
|
|
|
// NRGBA converts to non-premultiplied RGBA.
|
|
func (c Color) NRGBA() (r, g, b, a uint32) {
|
|
_y := helper.Delinearize(c.Y)
|
|
return _y, _y, _y, 0xffff
|
|
}
|
|
|
|
// NLRGBA converts to non-premultiplied linear RGBA.
|
|
func (c Color) NLRGBA() (r, g, b, a float64) {
|
|
return c.Y, c.Y, c.Y, 1
|
|
}
|
|
|
|
// NXYZA converts to non-premultiplied XYZ+Alpha.
|
|
func (c Color) NXYZA() (x, y, z, a float64) {
|
|
x, y, z = helper.LRGBtoXYZ(c.Y, c.Y, c.Y)
|
|
return x, y, z, 1
|
|
}
|
|
|
|
// NOkLabA converts to non-premultiplied OkLab+Alpha.
|
|
func (c Color) NOkLabA() (lightness, chromaA, chromaB, a float64) {
|
|
lightness, chromaA, chromaB = helper.LMStoOkLab(helper.LRGBtoLMS(c.Y, c.Y, c.Y))
|
|
return lightness, chromaA, chromaB, 1
|
|
}
|
|
|
|
// Convert converts an arbitrary colour type to a linear RGB [Color].
|
|
func Convert(c color.Color) Color {
|
|
if c, ok := c.(Color); ok {
|
|
return c
|
|
}
|
|
|
|
r, g, b, _ := helper.ColorToNLRGBA(c)
|
|
|
|
// the color.Gray16Model documents that it uses the coefficients 0.299, 0.5867, and 0.114.
|
|
// however, it does this using integer arithmetic, so the actual coefficients are effectively rounded to the nearest 1/0x10000.
|
|
|
|
return Color{Y: helper.DelinearizeF(
|
|
helper.LinearizeF(r)*0x0.4c8bp0 +
|
|
helper.LinearizeF(g)*0x0.9646p0 +
|
|
helper.LinearizeF(b)*0x0.1d2fp0,
|
|
)}
|
|
}
|
|
|
|
// A [color.Model] for converting arbitrary colours to a linear RGB [Color].
|
|
//
|
|
// Wraps the [Convert] function, returning a [color.Color] interface rather than the [Color] type.
|
|
var Model = helper.Model(Convert)
|
|
|
|
// Type assertion.
|
|
var _ color.Color = Color{}
|