feat: support convert rgb to 16-color code. close: #31

README.md

@@ -24,9 +24,9 @@ Now, 256 colors and RGB colors have also been supported to work in Windows CMD a
 ## Features
 
   - Simple to use, zero dependencies
-  - Supports rich color output: 16-color, 256-color, true color (24-bit, RGB)
+  - Supports rich color output: 16-color (4-bit), 256-color (8-bit), true color (24-bit, RGB)
     - 16-color output is the most commonly used and most widely supported, working on any Windows version
-    - Since `v1.2.4` **the 256-color, true color (24-bit) support windows CMD and PowerShell**
+    - Since `v1.2.4` **the 256-color (8-bit), true color (24-bit) support windows CMD and PowerShell**
     - See [this gist](https://gist.github.com/XVilka/8346728) for information on true color support
   - Generic API methods: `Print`, `Printf`, `Println`, `Sprint`, `Sprintf`
   - Supports HTML tag-style color rendering, such as `<green>message</>`. Support working on windows `cmd` `powerShell`

_examples/ref/cmd_color.go

@@ -1,3 +1,5 @@
+//+build windows
+
 package main
 
 import (

color_16.go

@@ -40,6 +40,12 @@ func (o Opts) String() string {
  * Basic 16 color definition
  *************************************************************/
 
+// Base value for foreground/background color
+const (
+	FgBase uint8 = 30
+	BgBase uint8 = 40
+)
+
 // Foreground colors. basic foreground colors 30 - 37
 const (
 	FgBlack Color = iota + 30

color_rgb.go

@@ -173,9 +173,10 @@ func (c RGBColor) C256() Color256 {
 }
 
 // C16 returns the closest approximate 256 (8 bit) color
-// func (c RGBColor) C16() Color {
-// 	return Color()
-// }
+// refer https://github.com/radareorg/radare2/blob/master/libr/cons/rgb.c#L249-L271
+func (c RGBColor) C16() Color {
+	return Color(RgbToAnsi(c[0], c[1], c[2], c[3] == AsBg))
+}
 
 /*************************************************************
  * RGB Style

color_rgb_test.go

@@ -2,6 +2,8 @@ package color
 
 import (
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func testRgbToC256Color(t *testing.T, name string, c RGBColor, expected uint8) {
@@ -45,3 +47,11 @@ func TestRgbToC256Background(t *testing.T) {
 		t.Errorf("background color didn't have background prefix: %v", prefix)
 	}
 }
+
+func TestRGBColor_C16(t *testing.T) {
+	rgb := RGB(57, 187, 226)
+	assert.Equal(t, "36", rgb.C16().String())
+
+	rgb = RGB(57, 187, 226, true)
+	assert.Equal(t, "46", rgb.C16().String())
+}

go.mod

@@ -2,4 +2,6 @@ module github.com/gookit/color
 
 go 1.12
 
-require github.com/stretchr/testify v1.3.0
+require (
+	github.com/stretchr/testify v1.3.0
+)

utils.go

@@ -171,7 +171,7 @@ func HexToRgb(hex string) (rgb []int) {
 // Rgb2hex alias of the RgbToHex()
 func Rgb2hex(rgb []int) string { return RgbToHex(rgb) }
 
-// RgbToHex convert RGB to hex code
+// RgbToHex convert RGB-code to hex-code
 // Usage:
 //	hex := RgbToHex([]int{170, 187, 204}) // hex: "aabbcc"
 func RgbToHex(rgb []int) string {
@@ -183,6 +183,51 @@ func RgbToHex(rgb []int) string {
 	return strings.Join(hexNodes, "")
 }
 
+// Rgb2ansi alias of the RgbToAnsi()
+func Rgb2ansi(r, g, b uint8, isBg bool) uint8  {
+	return RgbToAnsi(r, g, b, isBg)
+}
+
+// RgbToAnsi convert RGB-code to 16-code
+func RgbToAnsi(r, g, b uint8, isBg bool) uint8  {
+	var bright, c, k uint8
+
+	base := compareVal(isBg, BgBase, FgBase)
+
+	// eco bright-specific
+	if r == 0x80 && g == 0x80 && b == 0x80 { // 0x80=128
+		bright = 53
+	} else if r == 0xff || g == 0xff || b == 0xff { // 0xff=255
+		bright = 60
+	} // else bright = 0
+
+	if r == g && g == b {
+		// 0x7f=127
+		// r = (r > 0x7f) ? 1 : 0;
+		r = compareVal(r > 0x7f, 1, 0)
+		g = compareVal(g > 0x7f, 1, 0)
+		b = compareVal(b > 0x7f, 1, 0)
+	} else {
+		k = (r + g + b) / 3;
+
+		// r = (r >= k) ? 1 : 0;
+		r = compareVal(r >= k, 1, 0)
+		g = compareVal(g >= k, 1, 0)
+		b = compareVal(b >= k, 1, 0)
+	}
+
+	// c = (r ? 1 : 0) + (g ? (b ? 6 : 2) : (b ? 4 : 0))
+	c = compareVal(r > 0, 1, 0)
+
+	if g > 0 {
+		c += compareVal(b > 0, 6, 2)
+	} else {
+		c += compareVal(b > 0, 4, 0)
+	}
+
+	return base + bright + c
+}
+
 /*************************************************************
  * print methods(will auto parse color tags)
  *************************************************************/
@@ -308,6 +353,14 @@ func Text(s string) string {
 // 	return runtime.GOOS == "windows"
 // }
 
+// equals: return ok ? val1 : val2
+func compareVal(ok bool, val1, val2 uint8) uint8 {
+	if ok {
+		return val1
+	}
+	return val2
+}
+
 func saveInternalError(err error) {
 	if err != nil {
 		errors = append(errors, err)

utils_test.go

@@ -1,6 +1,7 @@
 package color
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -43,3 +44,37 @@ func TestRgbToHex(t *testing.T) {
 		assert.Equal(t, Rgb2hex(item.given), item.want)
 	}
 }
+
+func TestRgbToAnsi(t *testing.T) {
+	tests := []struct {
+		want uint8
+		rgb  []uint8
+		isBg bool
+	}{
+		{40, []uint8{102, 102, 102}, true},
+		{37, []uint8{204, 204, 204}, false},
+		{47, []uint8{170, 78, 204}, true},
+		{37, []uint8{170, 153, 245}, false},
+		{30, []uint8{127, 127, 127}, false},
+		{40, []uint8{127, 127, 127}, true},
+		{90, []uint8{128, 128, 128}, false},
+		{97, []uint8{34, 56, 255}, false},
+		{31, []uint8{134, 56, 56}, false},
+		{30, []uint8{0, 0, 0}, false},
+		{40, []uint8{0, 0, 0}, true},
+		{97, []uint8{255, 255, 255}, false},
+		{107, []uint8{255, 255, 255}, true},
+	}
+
+	for _, item := range tests {
+		r, g, b := item.rgb[0], item.rgb[1], item.rgb[2]
+
+		assert.Equal(
+			t,
+			item.want,
+			RgbToAnsi(r, g, b, item.isBg),
+			fmt.Sprint("rgb=", item.rgb, ", is bg? ", item.isBg),
+		)
+		assert.Equal(t, item.want, Rgb2ansi(r, g, b, item.isBg))
+	}
+}