gradientgen.go

Documentation: github.com/lucasb-eyer/go-colorful/doc/gradientgen

     1  package main
     2  
     3  import (
     4  	"image"
     5  	"image/draw"
     6  	"image/png"
     7  	"os"
     8  	"strconv"
     9  
    10  	"github.com/lucasb-eyer/go-colorful"
    11  )
    12  
    13  // This table contains the "keypoints" of the colorgradient you want to generate.
    14  // The position of each keypoint has to live in the range [0,1]
    15  type GradientTable []struct {
    16  	Col colorful.Color
    17  	Pos float64
    18  }
    19  
    20  // This is the meat of the gradient computation. It returns a HCL-blend between
    21  // the two colors around `t`.
    22  // Note: It relies heavily on the fact that the gradient keypoints are sorted.
    23  func (gt GradientTable) GetInterpolatedColorFor(t float64) colorful.Color {
    24  	for i := 0; i < len(gt)-1; i++ {
    25  		c1 := gt[i]
    26  		c2 := gt[i+1]
    27  		if c1.Pos <= t && t <= c2.Pos {
    28  			// We are in between c1 and c2. Go blend them!
    29  			t := (t - c1.Pos) / (c2.Pos - c1.Pos)
    30  			return c1.Col.BlendHcl(c2.Col, t).Clamped()
    31  		}
    32  	}
    33  
    34  	// Nothing found? Means we're at (or past) the last gradient keypoint.
    35  	return gt[len(gt)-1].Col
    36  }
    37  
    38  // This is a very nice thing Golang forces you to do!
    39  // It is necessary so that we can write out the literal of the colortable below.
    40  func MustParseHex(s string) colorful.Color {
    41  	c, err := colorful.Hex(s)
    42  	if err != nil {
    43  		panic("MustParseHex: " + err.Error())
    44  	}
    45  	return c
    46  }
    47  
    48  func main() {
    49  	// The "keypoints" of the gradient.
    50  	keypoints := GradientTable{
    51  		{MustParseHex("#9e0142"), 0.0},
    52  		{MustParseHex("#d53e4f"), 0.1},
    53  		{MustParseHex("#f46d43"), 0.2},
    54  		{MustParseHex("#fdae61"), 0.3},
    55  		{MustParseHex("#fee090"), 0.4},
    56  		{MustParseHex("#ffffbf"), 0.5},
    57  		{MustParseHex("#e6f598"), 0.6},
    58  		{MustParseHex("#abdda4"), 0.7},
    59  		{MustParseHex("#66c2a5"), 0.8},
    60  		{MustParseHex("#3288bd"), 0.9},
    61  		{MustParseHex("#5e4fa2"), 1.0},
    62  	}
    63  
    64  	h := 1024
    65  	w := 40
    66  
    67  	if len(os.Args) == 3 {
    68  		// Meh, I'm being lazy...
    69  		w, _ = strconv.Atoi(os.Args[1])
    70  		h, _ = strconv.Atoi(os.Args[2])
    71  	}
    72  
    73  	img := image.NewRGBA(image.Rect(0, 0, w, h))
    74  
    75  	for y := h - 1; y >= 0; y-- {
    76  		c := keypoints.GetInterpolatedColorFor(float64(y) / float64(h))
    77  		draw.Draw(img, image.Rect(0, y, w, y+1), &image.Uniform{c}, image.Point{}, draw.Src)
    78  	}
    79  
    80  	outpng, err := os.Create("gradientgen.png")
    81  	if err != nil {
    82  		panic("Error storing png: " + err.Error())
    83  	}
    84  	defer outpng.Close()
    85  
    86  	png.Encode(outpng, img)
    87  }
    88
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