palette

Documentation

Overview

Package palette provides basic color palette handling.

Index

• Variables
• type ColorMap
  • func Reverse(c ColorMap) ColorMap
• type DivergingColorMap
• type DivergingPalette
  • func Radial(colors int, start, end Hue, alpha float64) DivergingPalette
• type HSVA
  • func (c HSVA) RGBA() (r, g, b, a uint32)
• type Hue
  • func (h Hue) Complement() Hue
• type Palette
  • func Heat(colors int, alpha float64) Palette
  • func Rainbow(colors int, start, end Hue, sat, val, alpha float64) Palette

Examples

• Reverse
• Reverse (Palette)

Variables

var (
	// ErrOverflow is the error returned by ColorMaps when the specified
	// value is greater than the maximum value.
	ErrOverflow = errors.New("palette: specified value > maximum")

	// ErrUnderflow is the error returned by ColorMaps when the specified
	// value is less than the minimum value.
	ErrUnderflow = errors.New("palette: specified value < minimum")

	// ErrNaN is the error returned by ColorMaps when the specified
	// value is NaN.
	ErrNaN = errors.New("palette: specified value == NaN")
)

var HSVAModel = color.ModelFunc(hsvaModel)

HSVAModel converts any color.Color to an HSVA color.

Types

type ColorMap

type ColorMap interface {
	// At returns the color associated with the given value.
	// If the value is not between Max() and Min(), an error is returned.
	At(float64) (color.Color, error)

	// Max returns the current maximum value of the ColorMap.
	Max() float64

	// SetMax sets the maximum value of the ColorMap.
	SetMax(float64)

	// Min returns the current minimum value of the ColorMap.
	Min() float64

	// SetMin sets the minimum value of the ColorMap.
	SetMin(float64)

	// Alpha returns the opacity value of the ColorMap.
	Alpha() float64

	// SetAlpha sets the opacity value of the ColorMap. Zero is transparent
	// and one is completely opaque. The default value of alpha should be
	// expected to be one. The function should be expected to panic
	// if alpha is not between zero and one.
	SetAlpha(float64)

	// Palette creates a Palette with the specified number of colors
	// from the ColorMap.
	Palette(colors int) Palette
}

A ColorMap maps scalar values to colors.

func Reverse

func Reverse(c ColorMap) ColorMap

Reverse reverses the direction of ColorMap c.

Example

This example creates a color bar and a second color bar where the direction of the colors are reversed.

package main

import (
	"log"

	"github.com/elamre/plot"
	"github.com/elamre/plot/palette"
	"github.com/elamre/plot/palette/moreland"
	"github.com/elamre/plot/plotter"
)

func main() {
	p, err := plot.New()
	if err != nil {
		log.Panic(err)
	}
	l := &plotter.ColorBar{ColorMap: moreland.Kindlmann()}
	l2 := &plotter.ColorBar{ColorMap: palette.Reverse(moreland.Kindlmann())}
	l.ColorMap.SetMin(0.5)
	l.ColorMap.SetMax(2.5)
	l2.ColorMap.SetMin(2.5)
	l2.ColorMap.SetMax(4.5)

	p.Add(l, l2)
	p.HideY()
	p.X.Padding = 0
	p.Title.Text = "A ColorMap and its Reverse"

	if err = p.Save(300, 48, "testdata/reverse.png"); err != nil {
		log.Panic(err)
	}
}

Example (Palette)

This example creates a color palette from a reversed ColorMap.

package main

import (
	"fmt"
	"log"

	"github.com/elamre/plot"
	"github.com/elamre/plot/palette"
	"github.com/elamre/plot/palette/moreland"
	"github.com/elamre/plot/plotter"
)

func main() {
	p, err := plot.New()
	if err != nil {
		log.Panic(err)
	}
	thumbs := plotter.PaletteThumbnailers(palette.Reverse(moreland.Kindlmann()).Palette(10))
	for i, t := range thumbs {
		p.Legend.Add(fmt.Sprint(i), t)
	}
	p.HideAxes()
	p.X.Padding = 0
	p.Y.Padding = 0

	if err = p.Save(35, 120, "testdata/reverse_palette.png"); err != nil {
		log.Panic(err)
	}
}

type DivergingColorMap

type DivergingColorMap interface {
	ColorMap

	// SetConvergePoint sets the value where the diverging colors
	// should meet. The default value should be expected to be
	// (Min() + Max()) / 2. It should be expected that calling either
	// SetMax() or SetMin() will set a new default value, so for a
	// custom convergence point this function should be called after
	// SetMax() and SetMin(). The function should be expected to panic
	// if the value is not between Min() and Max().
	SetConvergePoint(float64)

	// ConvergePoint returns the value where the diverging colors meet.
	ConvergePoint() float64
}

DivergingColorMap maps scalar values to colors that diverge from a central value.

type DivergingPalette

type DivergingPalette interface {
	Palette

	// CriticalIndex returns the indices of the lightest
	// (median) color or colors in the DivergingPalette.
	// The low and high index values will be equal when
	// there is a single median color.
	CriticalIndex() (low, high int)
}

DivergingPalette is a collection of colors ordered into a palette with a critical class or break in the middle of the color range.

func Radial

func Radial(colors int, start, end Hue, alpha float64) DivergingPalette

Radial return a diverging palette across the specified range, through white and with the specified alpha.

type HSVA

type HSVA struct {
	H, S, V, A float64
}

HSVA represents a Hue/Saturation/Value/Alpha color. H, S, V and A are valid within [0, 1].

func (HSVA) RGBA

func (c HSVA) RGBA() (r, g, b, a uint32)

RGBA allows HSVAColor to satisfy the color.Color interface.

type Hue

type Hue float64

Hue represents a hue in HSV color space. Valid Hues are within [0, 1].

const (
	Red Hue = Hue(iota) / 6
	Yellow
	Green
	Cyan
	Blue
	Magenta
)

func (Hue) Complement

func (h Hue) Complement() Hue

Complement returns the complementary hue of a Hue.

type Palette

type Palette interface {
	Colors() []color.Color
}

Palette is a collection of colors ordered into a palette.

func Heat

func Heat(colors int, alpha float64) Palette

Heat returns a red to yellow palette with the specified number of colors and alpha.

func Rainbow

func Rainbow(colors int, start, end Hue, sat, val, alpha float64) Palette

Rainbow returns a rainbow palette with the specified number of colors, saturation value and alpha, and hues in the specified range.