Simplify picking contrasting label text color

Pick between white and black depending on which one is the first to
satisfy the contrast ratio of 7.0 (or 4.5 as fallback).

commands/issue.go

@@ -606,38 +606,32 @@ func colorizeLabel(label github.IssueLabel, color *utils.Color) string {
 		fgColorCode, bgColorCode, label.Name)
 }
 
+type contrastCandidate struct {
+	color    *utils.Color
+	contrast float64
+}
+
 func pickHighContrastTextColor(color *utils.Color) *utils.Color {
-	var candidates [12]*utils.Color
-	hsl := color.ToHsl()
-	a := hsl.ScaleLightness(0.5)
-	candidates[0] = a.ToRgb()
-	candidates[1] = a.ScaleLightness(0.25).ToRgb()
-	candidates[2] = a.ScaleSaturation(-0.25).ToRgb()
-	b := hsl.ScaleSaturation(0.75)
-	candidates[3] = b.ToRgb()
-	candidates[4] = b.ScaleLightness(0.25).ToRgb()
-	candidates[5] = b.ScaleSaturation(-0.25).ToRgb()
-	c := hsl.ScaleLightness(-0.5)
-	candidates[6] = c.ToRgb()
-	candidates[7] = c.ScaleLightness(-0.25).ToRgb()
-	candidates[8] = c.ScaleSaturation(-0.25).ToRgb()
-	d := hsl.ScaleSaturation(-0.75)
-	candidates[9] = d.ToRgb()
-	candidates[10] = d.ScaleLightness(-0.25).ToRgb()
-	candidates[11] = d.ScaleSaturation(-0.25).ToRgb()
-
-	foundContrastRatio := -999.0
-	ix := -1
-	for i := 0; i < 12; i++ {
-		contrastRatio := color.ContrastRatio(candidates[i])
-		if contrastRatio > foundContrastRatio {
-			ix = i
-			foundContrastRatio = contrastRatio
+	candidates := []contrastCandidate{}
+	appendCandidate := func(c *utils.Color) {
+		candidates = append(candidates, contrastCandidate{
+			color:    c,
+			contrast: color.ContrastRatio(c),
+		})
+	}
+
+	appendCandidate(utils.White)
+	appendCandidate(utils.Black)
+
+	for _, candidate := range candidates {
+		if candidate.contrast >= 7.0 {
+			return candidate.color
 		}
 	}
-	if foundContrastRatio >= 7.0 {
-		return candidates[ix]
-	} else {
-		return candidates[11]
+	for _, candidate := range candidates {
+		if candidate.contrast >= 4.5 {
+			return candidate.color
+		}
 	}
+	return utils.Black
 }

commands/issue_test.go

@@ -66,7 +66,7 @@ func TestFormatIssue(t *testing.T) {
 			},
 			format:   format,
 			colorize: true,
-			expect:   "\033[32m     #42\033[m  An issue with labels  \033[38;2;64;64;64;48;2;128;0;0m bug \033[m \033[38;2;0;0;0;48;2;85;255;85m reproduced \033[m\n",
+			expect:   "\033[32m     #42\033[m  An issue with labels  \033[38;2;255;255;255;48;2;128;0;0m bug \033[m \033[38;2;0;0;0;48;2;85;255;85m reproduced \033[m\n",
 		},
 		{
 			name: "not colorized",
@@ -181,7 +181,7 @@ func TestFormatIssue_customFormatString(t *testing.T) {
 			issue:    issue,
 			format:   "%l",
 			colorize: true,
-			expect:   "\033[38;2;68;68;68;48;2;136;0;0m bug \033[m \033[38;2;68;68;68;48;2;0;136;0m feature \033[m",
+			expect:   "\033[38;2;255;255;255;48;2;136;0;0m bug \033[m \033[38;2;255;255;255;48;2;0;136;0m feature \033[m",
 		},
 		{
 			name:     "label not colorized",

utils/color.go

@@ -7,8 +7,14 @@ import (
 	"strconv"
 )
 
+var (
+	Black, White *Color
+)
+
 func init() {
 	initColorCube()
+	Black, _ = NewColor("000000")
+	White, _ = NewColor("ffffff")
 }
 
 type Color struct {
@@ -38,12 +44,6 @@ func NewColor(hex string) (*Color, error) {
 	}, nil
 }
 
-func (c *Color) Brightness() float32 {
-	return (0.299*float32(c.Red) +
-		0.587*float32(c.Green) +
-		0.114*float32(c.Blue)) / 255
-}
-
 func (c *Color) Distance(other *Color) float64 {
 	return math.Sqrt(float64(math.Pow(float64(c.Red-other.Red), 2) +
 		math.Pow(float64(c.Green-other.Green), 2) +
@@ -78,86 +78,6 @@ func (c *Color) ContrastRatio(other *Color) float64 {
 	return ratio
 }
 
-type HslColor struct {
-	Hue        float64
-	Saturation float64
-	Lightness  float64
-}
-
-func (c *Color) ToHsl() *HslColor {
-	rPrime := float64(c.Red) / 255
-	gPrime := float64(c.Green) / 255
-	bPrime := float64(c.Blue) / 255
-	cMax := math.Max(rPrime, math.Max(gPrime, bPrime))
-	cMin := math.Min(rPrime, math.Min(gPrime, bPrime))
-	delta := cMax - cMin
-
-	var H float64
-	if delta == 0 {
-		H = 0
-	} else if cMax == rPrime {
-		H = 60 * math.Mod((gPrime-bPrime)/delta, 6)
-	} else if cMax == gPrime {
-		H = 60 * (((bPrime - rPrime) / delta) + 2)
-	} else {
-		H = 60 * (((rPrime - gPrime) / delta) + 4)
-	}
-	var L float64
-	L = (cMax + cMin) / 2
-	var S float64
-	if delta == 0 {
-		S = 0
-	} else {
-		S = delta / (1 - math.Abs((2*L)-1))
-	}
-
-	return &HslColor{H, S, L}
-}
-
-func (c *HslColor) ToRgb() *Color {
-	C := (1 - math.Abs(2*c.Lightness-1)) * c.Saturation
-	X := C * (1 - math.Abs(math.Mod(c.Hue/60, 2)-1))
-	m := c.Lightness - (C / 2)
-	var rPrime, gPrime, bPrime float64
-	switch {
-	case c.Hue < 60.0:
-		rPrime, gPrime, bPrime = C, X, 0
-	case c.Hue < 120.0:
-		rPrime, gPrime, bPrime = X, C, 0
-	case c.Hue < 180.0:
-		rPrime, gPrime, bPrime = 0, C, X
-	case c.Hue < 240.0:
-		rPrime, gPrime, bPrime = 0, X, C
-	case c.Hue < 300.0:
-		rPrime, gPrime, bPrime = X, 0, C
-	case c.Hue < 360.0:
-		rPrime, gPrime, bPrime = C, 0, X
-	}
-	R := uint8((rPrime + m) * 255)
-	G := uint8((gPrime + m) * 255)
-	B := uint8((bPrime + m) * 255)
-
-	return &Color{R, G, B}
-}
-
-func (c *HslColor) ScaleLightness(x float64) *HslColor {
-	newLightness := round(math.Min(math.Max(0, c.Lightness*(1.0+x)), 1.0))
-	return &HslColor{c.Hue, c.Saturation, newLightness}
-}
-
-func (c *HslColor) ScaleSaturation(x float64) *HslColor {
-	newSaturation := round(math.Min(math.Max(0, c.Lightness*(1.0+x)), 1.0))
-	return &HslColor{c.Hue, newSaturation, c.Lightness}
-}
-
-func round(n float64) float64 {
-	i := math.Trunc(n)
-	if math.Abs(n-i) >= 0.5 {
-		return i + math.Copysign(1, n)
-	}
-	return i
-}
-
 var x6colorIndexes = [6]uint8{0, 95, 135, 175, 215, 255}
 var x6colorCube [216]Color
 

utils/color_test.go

-package utils
-
-import (
-	"github.com/bmizerany/assert"
-	"testing"
-)
-
-func TestColorBrightness(t *testing.T) {
-	c, err := NewColor("880000")
-	assert.Equal(t, nil, err)
-	actual := c.Brightness()
-	assert.Equal(t, float32(0.15946665406227112), actual)
-}
-
-func TestRoundDown(t *testing.T) {
-	assert.Equal(t, 3.0, round(3.0))
-	assert.Equal(t, 3.0, round(3.01))
-	assert.Equal(t, 3.0, round(3.49))
-}
-
-func TestRoundUp(t *testing.T) {
-	assert.Equal(t, 3.0, round(2.5))
-	assert.Equal(t, 3.0, round(2.51))
-	assert.Equal(t, 3.0, round(2.99))
-}
-
-func TestRoundNegative(t *testing.T) {
-	assert.Equal(t, -2.0, round(-2.49))
-	assert.Equal(t, -3.0, round(-2.5))
-	assert.Equal(t, -3.0, round(-2.51))
-}