1package main
2
3import "github.com/lucasb-eyer/go-colorful"
4import "image"
5import "image/draw"
6import "image/png"
7import "os"
8import "strconv"
9
10// This table contains the "keypoints" of the colorgradient you want to generate.
11// The position of each keypoint has to live in the range [0,1]
12type GradientTable []struct {
13	Col colorful.Color
14	Pos float64
15}
16
17// This is the meat of the gradient computation. It returns a HCL-blend between
18// the two colors around `t`.
19// Note: It relies heavily on the fact that the gradient keypoints are sorted.
20func (self GradientTable) GetInterpolatedColorFor(t float64) colorful.Color {
21	for i := 0; i < len(self)-1; i++ {
22		c1 := self[i]
23		c2 := self[i+1]
24		if c1.Pos <= t && t <= c2.Pos {
25			// We are in between c1 and c2. Go blend them!
26			t := (t - c1.Pos) / (c2.Pos - c1.Pos)
27			return c1.Col.BlendHcl(c2.Col, t).Clamped()
28		}
29	}
30
31	// Nothing found? Means we're at (or past) the last gradient keypoint.
32	return self[len(self)-1].Col
33}
34
35// This is a very nice thing Golang forces you to do!
36// It is necessary so that we can write out the literal of the colortable below.
37func MustParseHex(s string) colorful.Color {
38	c, err := colorful.Hex(s)
39	if err != nil {
40		panic("MustParseHex: " + err.Error())
41	}
42	return c
43}
44
45func main() {
46	// The "keypoints" of the gradient.
47	keypoints := GradientTable{
48		{MustParseHex("#9e0142"), 0.0},
49		{MustParseHex("#d53e4f"), 0.1},
50		{MustParseHex("#f46d43"), 0.2},
51		{MustParseHex("#fdae61"), 0.3},
52		{MustParseHex("#fee090"), 0.4},
53		{MustParseHex("#ffffbf"), 0.5},
54		{MustParseHex("#e6f598"), 0.6},
55		{MustParseHex("#abdda4"), 0.7},
56		{MustParseHex("#66c2a5"), 0.8},
57		{MustParseHex("#3288bd"), 0.9},
58		{MustParseHex("#5e4fa2"), 1.0},
59	}
60
61	h := 1024
62	w := 40
63
64	if len(os.Args) == 3 {
65		// Meh, I'm being lazy...
66		w, _ = strconv.Atoi(os.Args[1])
67		h, _ = strconv.Atoi(os.Args[2])
68	}
69
70	img := image.NewRGBA(image.Rect(0, 0, w, h))
71
72	for y := h - 1; y >= 0; y-- {
73		c := keypoints.GetInterpolatedColorFor(float64(y) / float64(h))
74		draw.Draw(img, image.Rect(0, y, w, y+1), &image.Uniform{c}, image.ZP, draw.Src)
75	}
76
77	outpng, err := os.Create("gradientgen.png")
78	if err != nil {
79		panic("Error storing png: " + err.Error())
80	}
81	defer outpng.Close()
82
83	png.Encode(outpng, img)
84}
85