README.md

colorgrad

Go (Golang) color scales library for data visualization, charts, games, maps, generative art and others.

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Index

• Custom Gradient
• Preset Gradients
• Using the Gradient
• Examples
• Playground

import "github.com/mazznoer/colorgrad"

Custom Gradient

Basic

grad, err := colorgrad.NewGradient().Build()

Custom Colors

grad, err := colorgrad.NewGradient().
    Colors(
        colorgrad.Rgb8(0, 206, 209, 255),
        colorgrad.Rgb8(255, 105, 180, 255),
        colorgrad.Rgb(0.274, 0.5, 0.7, 1),
        colorgrad.Hsv(50, 1, 1, 1),
        colorgrad.Hsv(348, 0.9, 0.8, 1),
    ).
    Build()

Using Web Color Format

HtmlColors() method accepts named colors, hexadecimal (#rgb, #rgba, #rrggbb, #rrggbbaa), rgb(), rgba(), hsl(), hsla(), hwb(), and hsv().

grad, err := colorgrad.NewGradient().
    HtmlColors("#C41189", "#00BFFF", "#FFD700").
    Build()

grad, err := colorgrad.NewGradient().
    HtmlColors("gold", "hotpink", "darkturquoise").
    Build()

grad, err := colorgrad.NewGradient().
    HtmlColors(
        "rgb(125,110,221)",
        "rgb(90%,45%,97%)",
        "hsl(229,79%,85%)",
    ).
    Build()

Domain & Color Position

Default domain is [0..1].

grad, err := colorgrad.NewGradient().
    HtmlColors("deeppink", "gold", "seagreen").
    Build()

Set the domain to [0..100].

grad, err := colorgrad.NewGradient().
    HtmlColors("deeppink", "gold", "seagreen").
    Domain(0, 100).
    Build()

Set the domain to [-1..1].

grad, err := colorgrad.NewGradient().
    HtmlColors("deeppink", "gold", "seagreen").
    Domain(-1, 1).
    Build()

Set exact position for each color. The domain is [0..1].

grad, err := colorgrad.NewGradient().
    HtmlColors("deeppink", "gold", "seagreen").
    Domain(0, 0.7, 1).
    Build()

Set exact position for each color. The domain is [15..80].

grad, err := colorgrad.NewGradient().
    HtmlColors("deeppink", "gold", "seagreen").
    Domain(15, 30, 80).
    Build()

Blending Mode

grad, err := colorgrad.NewGradient().
    HtmlColors("#FFF", "#00F").
    Mode(colorgrad.BlendRgb).
    Build()

Interpolation Mode

grad, err := colorgrad.NewGradient().
    HtmlColors("#C41189", "#00BFFF", "#FFD700").
    Interpolation(colorgrad.InterpolationLinear).
    Build()

InterpolationLinear

InterpolationCatmullRom

InterpolationBasis

Preset Gradients

See PRESET.md

Parsing GIMP Gradient

import "os"

foreground := colorgrad.Rgb(0, 0, 0, 1)
background := colorgrad.Rgb(1, 1, 1, 1)
file, err := os.Open("Abstract_1.ggr")

if err != nil {
	panic(err)
}

defer file.Close()
grad, name, err2 := colorgrad.ParseGgr(file, foreground, background)
fmt.Println(name) // Abstract 1

Using the Gradient

Get the domain

grad := colorgrad.Rainbow()

fmt.Println(grad.Domain()) // 0 1

Get single color at certain position

grad := colorgrad.Rainbow()

fmt.Println(grad.At(0.0).HexString()) // #6e40aa
fmt.Println(grad.At(0.5).HexString()) // #aff05b
fmt.Println(grad.At(1.0).HexString()) // #6e40aa

Get n colors evenly spaced across gradient

grad := colorgrad.Rainbow()

for _, c := range grad.Colors(10) {
    fmt.Println(c.HexString())
}

Output:

#6e40aa
#c83dac
#ff5375
#ff8c38
#c9d33a
#7cf659
#5dea8d
#48b8d0
#4775de
#6e40aa

Hard-Edged Gradient

Convert gradient to hard-edged gradient with 11 segments and 0 smoothness.

grad := colorgrad.Rainbow().Sharp(11, 0)

This is the effect of different smoothness.

Examples

Gradient Image

package main

import (
    "image"
    "image/png"
    "os"

    "github.com/mazznoer/colorgrad"
)

func main() {
    grad, _ := colorgrad.NewGradient().
        HtmlColors("#C41189", "#00BFFF", "#FFD700").
        Build()

    w := 1500
    h := 70
    fw := float64(w)

    img := image.NewRGBA(image.Rect(0, 0, w, h))

    for x := 0; x < w; x++ {
        col := grad.At(float64(x) / fw)
        for y := 0; y < h; y++ {
            img.Set(x, y, col)
        }
    }

    file, err := os.Create("gradient.png")
    if err != nil {
        panic(err.Error())
    }
    defer file.Close()
    png.Encode(file, img)
}

Example output:

Colored Noise

package main

import (
    "image"
    "image/png"
    "os"

    "github.com/mazznoer/colorgrad"
    "github.com/ojrac/opensimplex-go"
)

func main() {
    w := 600
    h := 350
    scale := 0.02

    grad := colorgrad.Rainbow().Sharp(7, 0.2)
    noise := opensimplex.NewNormalized(996)
    img := image.NewRGBA(image.Rect(0, 0, w, h))

    for y := 0; y < h; y++ {
        for x := 0; x < w; x++ {
            t := noise.Eval2(float64(x)*scale, float64(y)*scale)
            img.Set(x, y, grad.At(t))
        }
    }

    file, err := os.Create("noise.png")
    if err != nil {
        panic(err.Error())
    }
    defer file.Close()
    png.Encode(file, img)
}

Example output:

Playground

• Basic
• Random colors

Dependencies

• csscolorparser

Inspirations

• chroma.js
• d3-scale-chromatic
• colorful's gradientgen.go

Links

• colorgrad-rs - Rust port of this library