Test looping over all styles' background colors

m/styling.go

@@ -55,11 +55,7 @@ func twinStyleFromChroma(chromaStyle *chroma.Style, chromaFormatter *chroma.Form
 	return &cells[0].Style
 }
 
-func backgroundStyleFromChroma(chromaStyle *chroma.Style) *twin.Style {
-	if chromaStyle == nil {
-		return nil
-	}
-
+func backgroundStyleFromChroma(chromaStyle chroma.Style) twin.Style {
 	backgroundEntry := chromaStyle.Get(chroma.Background)
 
 	if !backgroundEntry.Background.IsSet() {
@@ -92,7 +88,7 @@ func backgroundStyleFromChroma(chromaStyle *chroma.Style) *twin.Style {
 		returnMe = returnMe.WithAttr(twin.AttrUnderline)
 	}
 
-	return &returnMe
+	return returnMe
 }
 
 // consumeLessTermcapEnvs parses LESS_TERMCAP_xx environment variables and
@@ -128,9 +124,8 @@ func styleUi(chromaStyle *chroma.Style, chromaFormatter *chroma.Formatter, statu
 	if standoutStyle != nil {
 		statusbarStyle = *standoutStyle
 	} else if statusbarOption == STATUSBAR_STYLE_INVERSE {
-		styleBackground := backgroundStyleFromChroma(chromaStyle)
-		if styleBackground != nil {
-			statusbarStyle = styleBackground.WithAttr(twin.AttrReverse)
+		if chromaStyle != nil {
+			statusbarStyle = backgroundStyleFromChroma(*chromaStyle).WithAttr(twin.AttrReverse)
 		} else {
 			statusbarStyle = twin.StyleDefault.WithAttr(twin.AttrReverse)
 		}

m/styling_test.go

@@ -4,15 +4,30 @@ import (
 	"testing"
 
 	"github.com/alecthomas/chroma/v2/styles"
+	"github.com/walles/moar/twin"
 	"gotest.tools/v3/assert"
 )
 
 func TestBackgroundStyleFromChromaGithub(t *testing.T) {
-	style := backgroundStyleFromChroma(styles.Get("github"))
-	assert.Check(t, style != nil)
+	style := backgroundStyleFromChroma(*styles.Get("github"))
 
 	assert.Equal(t, style.String(), "Default color on #ffffff")
 }
 
-// FIXME: Add a parameterized test looping over all styles and checking that the
-// contrast we get in backgroundStyleFromChroma is good enough.
+// Test looping over all styles and checking that the contrast we get in
+// backgroundStyleFromChroma is good enough.
+func TestBackgroundStyleContrast(t *testing.T) {
+	for _, style := range styles.Registry {
+		t.Run(style.Name, func(t *testing.T) {
+			backgroundStyle := backgroundStyleFromChroma(*style)
+			assert.Check(t, backgroundStyle.Background().ColorType() == twin.ColorType24bit)
+
+			if backgroundStyle.Foreground().ColorType() == twin.ColorTypeDefault {
+				return
+			}
+
+			distance := backgroundStyle.Background().Distance(backgroundStyle.Foreground())
+			assert.Check(t, distance > 0.5, "distance=%f", distance)
+		})
+	}
+}

twin/colors.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 
+	"github.com/alecthomas/chroma/v2"
 	"github.com/lucasb-eyer/go-colorful"
 )
 
@@ -14,7 +15,7 @@ type ColorType uint8
 
 const (
 	// Default foreground / background color
-	colorTypeDefault ColorType = iota
+	ColorTypeDefault ColorType = iota
 
 	// https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
 	//
@@ -33,7 +34,7 @@ const (
 )
 
 // Reset to default foreground / background color
-var ColorDefault = newColor(colorTypeDefault, 0)
+var ColorDefault = newColor(ColorTypeDefault, 0)
 
 // From: https://en.wikipedia.org/wiki/ANSI_escape_code#3-bit_and_4-bit
 var colorNames16 = map[int]string{
@@ -77,7 +78,7 @@ func NewColorHex(rgb uint32) Color {
 	return newColor(ColorType24bit, rgb)
 }
 
-func (color Color) colorType() ColorType {
+func (color Color) ColorType() ColorType {
 	return ColorType(color >> 24)
 }
 
@@ -94,13 +95,13 @@ func (color Color) ansiString(foreground bool, terminalColorCount ColorType) str
 		fgBgMarker = "4"
 	}
 
-	if color.colorType() == colorTypeDefault {
+	if color.ColorType() == ColorTypeDefault {
 		return fmt.Sprint("\x1b[", fgBgMarker, "9m")
 	}
 
 	color = color.downsampleTo(terminalColorCount)
 
-	if color.colorType() == ColorType16 {
+	if color.ColorType() == ColorType16 {
 		value := color.colorValue()
 		if value < 8 {
 			return fmt.Sprint("\x1b[", fgBgMarker, value, "m")
@@ -113,14 +114,14 @@ func (color Color) ansiString(foreground bool, terminalColorCount ColorType) str
 		}
 	}
 
-	if color.colorType() == ColorType256 {
+	if color.ColorType() == ColorType256 {
 		value := color.colorValue()
 		if value <= 255 {
 			return fmt.Sprint("\x1b[", fgBgMarker, "8;5;", value, "m")
 		}
 	}
 
-	if color.colorType() == ColorType24bit {
+	if color.ColorType() == ColorType24bit {
 		value := color.colorValue()
 		red := (value & 0xff0000) >> 16
 		green := (value & 0xff00) >> 8
@@ -129,7 +130,7 @@ func (color Color) ansiString(foreground bool, terminalColorCount ColorType) str
 		return fmt.Sprint("\x1b[", fgBgMarker, "8;2;", red, ";", green, ";", blue, "m")
 	}
 
-	panic(fmt.Errorf("unhandled color type=%d %s", color.colorType(), color.String()))
+	panic(fmt.Errorf("unhandled color type=%d %s", color.ColorType(), color.String()))
 }
 
 func (color Color) ForegroundAnsiString(terminalColorCount ColorType) string {
@@ -143,8 +144,8 @@ func (color Color) BackgroundAnsiString(terminalColorCount ColorType) string {
 }
 
 func (color Color) String() string {
-	switch color.colorType() {
-	case colorTypeDefault:
+	switch color.ColorType() {
+	case ColorTypeDefault:
 		return "Default color"
 
 	case ColorType16:
@@ -160,15 +161,15 @@ func (color Color) String() string {
 		return fmt.Sprintf("#%06x", color.colorValue())
 	}
 
-	panic(fmt.Errorf("unhandled color type %d", color.colorType()))
+	panic(fmt.Errorf("unhandled color type %d", color.ColorType()))
 }
 
 func (color Color) downsampleTo(terminalColorCount ColorType) Color {
-	if color.colorType() == colorTypeDefault || terminalColorCount == colorTypeDefault {
+	if color.ColorType() == ColorTypeDefault || terminalColorCount == ColorTypeDefault {
 		panic(fmt.Errorf("downsampling to or from default color not supported, %s -> %#v", color.String(), terminalColorCount))
 	}
 
-	if color.colorType() <= terminalColorCount {
+	if color.ColorType() <= terminalColorCount {
 		// Already low enough
 		return color
 	}
@@ -177,7 +178,7 @@ func (color Color) downsampleTo(terminalColorCount ColorType) Color {
 	var targetR float64
 	var targetG float64
 	var targetB float64
-	if color.colorType() == ColorType24bit {
+	if color.ColorType() == ColorType24bit {
 		targetR = float64(color.colorValue()>>16) / 255.0
 		targetG = float64(color.colorValue()>>8&0xff) / 255.0
 		targetB = float64(color.colorValue()&0xff) / 255.0
@@ -227,3 +228,31 @@ func (color Color) downsampleTo(terminalColorCount ColorType) Color {
 		return NewColor256(uint8(bestMatch))
 	}
 }
+
+// Wrapper for Chroma's color distance function.
+//
+// That one says it uses this formula: https://www.compuphase.com/cmetric.htm
+//
+// The result from this function has been scaled to 0.0-1.0, where 1.0 is the
+// distance between black and white.
+func (c Color) Distance(other Color) float64 {
+	if c.ColorType() != ColorType24bit {
+		panic(fmt.Errorf("contrast only supported for 24 bit colors, got %s vs %s", c.String(), other.String()))
+	}
+
+	baseColor := chroma.NewColour(
+		uint8(c.colorValue()>>16&0xff),
+		uint8(c.colorValue()>>8&0xff),
+		uint8(c.colorValue()&0xff),
+	)
+
+	otherColor := chroma.NewColour(
+		uint8(other.colorValue()>>16&0xff),
+		uint8(other.colorValue()>>8&0xff),
+		uint8(other.colorValue()&0xff),
+	)
+
+	// Magic constant comes from testing
+	maxDistance := 764.8333151739665
+	return baseColor.Distance(otherColor) / maxDistance
+}

twin/colors_test.go

@@ -40,3 +40,17 @@ func TestAnsiStringDefault(t *testing.T) {
 		"\x1b[39m",
 	)
 }
+
+func TestDistance(t *testing.T) {
+	// Black -> white
+	assert.Equal(t,
+		NewColor24Bit(0, 0, 0).Distance(NewColor24Bit(255, 255, 255)),
+		1.0,
+	)
+
+	// White -> black
+	assert.Equal(t,
+		NewColor24Bit(255, 255, 255).Distance(NewColor24Bit(0, 0, 0)),
+		1.0,
+	)
+}

twin/styles.go

@@ -117,6 +117,14 @@ func (attr AttrMask) has(attrs AttrMask) bool {
 	return attr&attrs != 0
 }
 
+func (style Style) Background() Color {
+	return style.bg
+}
+
+func (style Style) Foreground() Color {
+	return style.fg
+}
+
 func (style Style) WithBackground(color Color) Style {
 	return Style{
 		fg:           style.fg,