Go: HSV to RGB

hsv.go

package bake

import (
	"errors"
	"image/color"
	"math"
)

// https://en.wikipedia.org/wiki/HSL_and_HSV#Converting_to_RGB
func HSVToRGBA(h float64, s float64, v float64) (*color.RGBA, error) {
	if h < 0.0 || h > 1.0 {
		return nil, errors.New("hue must be in [0.0, 1.0]")
	}
	if s < 0.0 || s > 1.0 {
		return nil, errors.New("saturation must be in [0.0, 1.0]")
	}
	if v < 0.0 || v > 1.0 {
		return nil, errors.New("lightness must be in [0.0, 1.0]")
	}
	c := v * s
	h_prime := h * 6.0
	x := c * (1 - math.Abs(math.Mod(h_prime, 2.0)-1.0))
	var r, g, b float64
	switch {
	case 0 <= h_prime && h_prime < 1:
		r, g, b = c, x, 0
	case 1 <= h_prime && h_prime < 2:
		r, g, b = x, c, 0
	case 2 <= h_prime && h_prime < 3:
		r, g, b = 0, c, x
	case 3 <= h_prime && h_prime < 4:
		r, g, b = 0, x, c
	case 4 <= h_prime && h_prime < 5:
		r, g, b = x, 0, c
	case 5 <= h_prime && h_prime < 6:
		r, g, b = c, 0, x
	}
	m := v - c
	return &color.RGBA{
		uint8((r + m) * 255),
		uint8((g + m) * 255),
		uint8((b + m) * 255),
		255,
	}, nil
}