hub/utils/color.go

package utils

import (
	"fmt"
	"math"
	"os"
	"strconv"
)

var (
	Black *Color
	White *Color
)

func init() {
	initColorCube()
	Black, _ = NewColor("000000")
	White, _ = NewColor("ffffff")
}

type Color struct {
	Red   uint8
	Green uint8
	Blue  uint8
}

func NewColor(hex string) (*Color, error) {
	red, err := strconv.ParseUint(hex[0:2], 16, 8)
	if err != nil {
		return nil, err
	}
	green, err := strconv.ParseUint(hex[2:4], 16, 8)
	if err != nil {
		return nil, err
	}
	blue, err := strconv.ParseUint(hex[4:6], 16, 8)
	if err != nil {
		return nil, err
	}

	return &Color{
		Red:   uint8(red),
		Green: uint8(green),
		Blue:  uint8(blue),
	}, nil
}

func (c *Color) Distance(other *Color) float64 {
	return math.Sqrt(math.Pow(float64(c.Red-other.Red), 2) +
		math.Pow(float64(c.Green-other.Green), 2) +
		math.Pow(float64(c.Blue-other.Blue), 2))
}

func rgbComponentToBoldValue(component uint8) float64 {
	srgb := float64(component) / 255
	if srgb <= 0.03928 {
		return srgb / 12.92
	}
	return math.Pow(((srgb + 0.055) / 1.055), 2.4)
}

func (c *Color) Luminance() float64 {
	return 0.2126*rgbComponentToBoldValue(c.Red) +
		0.7152*rgbComponentToBoldValue(c.Green) +
		0.0722*rgbComponentToBoldValue(c.Blue)
}

func (c *Color) ContrastRatio(other *Color) float64 {
	L := c.Luminance()
	otherL := other.Luminance()
	var L1, L2 float64
	if L > otherL {
		L1, L2 = L, otherL
	} else {
		L1, L2 = otherL, L
	}
	ratio := (L1 + 0.05) / (L2 + 0.05)
	return ratio
}

var x6colorIndexes = [6]uint8{0, 95, 135, 175, 215, 255}
var x6colorCube [216]Color

func initColorCube() {
	i := 0
	for iR := 0; iR < 6; iR++ {
		for iG := 0; iG < 6; iG++ {
			for iB := 0; iB < 6; iB++ {
				x6colorCube[i] = Color{
					x6colorIndexes[iR],
					x6colorIndexes[iG],
					x6colorIndexes[iB],
				}
				i++
			}
		}
	}
}

func ditherTo256ColorCode(color *Color) (code int) {
	iMatch := -1
	minDistance := float64(99999)
	for i := 0; i < 216; i++ {
		distance := color.Distance(&x6colorCube[i])
		if distance < minDistance {
			iMatch = i
			minDistance = distance
		}
	}
	return iMatch + 16
}

var non24bitColorTerms = []string{
	"Apple_Terminal",
}
var isTerm24bitColorCapableCache bool
var isTerm24bitColorCapableCacheIsInit bool = false

func isTerm24bitColorCapable() bool {
	if !isTerm24bitColorCapableCacheIsInit {
		isTerm24bitColorCapableCache = true
		myTermProg := os.Getenv("TERM_PROGRAM")
		for _, brokenTerm := range non24bitColorTerms {
			if myTermProg == brokenTerm {
				isTerm24bitColorCapableCache = false
				break
			}
		}
		isTerm24bitColorCapableCacheIsInit = true
	}
	return isTerm24bitColorCapableCache
}

func RgbToTermColorCode(color *Color) string {
	if isTerm24bitColorCapable() {
		return fmt.Sprintf("2;%d;%d;%d", color.Red, color.Green, color.Blue)
	}
	intCode := ditherTo256ColorCode(color)
	return fmt.Sprintf("5;%d", intCode)
}