94 lines
2.5 KiB
Go
94 lines
2.5 KiB
Go
// Provides a [color.Color] type for dealing with premultiplied linear RGBA colours.
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package lrgba
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import (
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"image/color"
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"math"
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"smariot.com/color/internal/helper"
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)
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// Color is a pre-multiplied linear RGBA [color.Color].
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type Color struct {
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R, G, B, A float64
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}
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func sqr(a float64) float64 {
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return a * a
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}
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// DistanceSqr returns the maximum possible euclidean distance squared between two colours,
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// accounting for the possible backgrounds they might be composited over.
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func DistanceSqr(a, b Color) float64 {
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dR := a.R - b.R
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dG := a.G - b.G
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dB := a.B - b.B
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dA := a.A - b.A
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return max(sqr(dR), sqr(dR+dA)) + max(sqr(dG), sqr(dG+dA)) + max(sqr(dB), sqr(dB+dA))
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}
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// Distance returns the maximum possible euclidean distance between two colours,
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// accounting for the possible backgrounds they might be composited over.
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//
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// If you just want to compare relative distances, use [DistanceSqr] instead.
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func Distance(a, b Color) float64 {
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return math.Sqrt(DistanceSqr(a, b))
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}
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// RGBA converts to premultiplied RGBA, implementing the [color.Color] interface.
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func (c Color) RGBA() (r, g, b, a uint32) {
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return helper.NLRGBAtoRGBA(c.NLRGBA())
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}
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// NRGBA converts to non-premultiplied RGBA.
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func (c Color) NRGBA() (r, g, b, a uint32) {
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return helper.NLRGBAtoNRGBA(c.NLRGBA())
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}
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// NLRGBA converts to non-premultiplied linear RGBA.
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func (c Color) NLRGBA() (r, g, b, a float64) {
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if c.A <= 0 {
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return 0, 0, 0, 0
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}
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return c.R / c.A, c.G / c.A, c.B / c.A, c.A
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}
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// NXYZA converts to non-premultiplied XYZ+Alpha.
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func (c Color) NXYZA() (x, y, z, a float64) {
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if c.A <= 0 {
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return 0, 0, 0, 0
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}
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x, y, z = helper.LRGBtoXYZ(c.R/c.A, c.G/c.A, c.B/c.A)
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return x, y, z, c.A
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}
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// NOkLabA converts to non-premultiplied OkLab+Alpha.
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func (c Color) NOkLabA() (lightness, chromaA, chromaB, a float64) {
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if c.A <= 0 {
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return 0, 0, 0, 0
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}
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lightness, chromaA, chromaB = helper.LMStoOkLab(helper.LRGBtoLMS(c.R/c.A, c.G/c.A, c.B/c.A))
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return lightness, chromaA, chromaB, c.A
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}
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// Convert converts an arbitrary colour type to a premultiplied linear RGBA [Color].
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func Convert(c color.Color) Color {
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if c, ok := c.(Color); ok {
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return c
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}
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r, g, b, a := helper.ColorToNLRGBA(c)
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return Color{r * a, g * a, b * a, a}
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}
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// A [color.Model] for converting arbitrary colours to a premultiplied linear RGBA [Color].
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//
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// Wraps the [Convert] function, returning a [color.Color] interface rather than the [Color] type.
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var Model = helper.Model(Convert)
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// Type assertion.
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var _ color.Color = Color{}
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