Ebiten example - hsv

// +build example

package main

import (
        "fmt"
        _ "image/jpeg"
        "log"
        "math"

        "github.com/hajimehoshi/ebiten"
        "github.com/hajimehoshi/ebiten/ebitenutil"
)

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        hueInt        = 0
        saturationInt = 128
        valueInt      = 128
        gophersImage  *ebiten.Image
)

func clamp(v, min, max int) int {
        if min > max {
                panic("min must <= max")
        }
        if v < min {
                return min
        }
        if max < v {
                return max
        }
        return v
}

func update(screen *ebiten.Image) error {
        if ebiten.IsKeyPressed(ebiten.KeyQ) {
                hueInt--
        }
        if ebiten.IsKeyPressed(ebiten.KeyW) {
                hueInt++
        }
        if ebiten.IsKeyPressed(ebiten.KeyA) {
                saturationInt--
        }
        if ebiten.IsKeyPressed(ebiten.KeyS) {
                saturationInt++
        }
        if ebiten.IsKeyPressed(ebiten.KeyZ) {
                valueInt--
        }
        if ebiten.IsKeyPressed(ebiten.KeyX) {
                valueInt++
        }
        hueInt = clamp(hueInt, -256, 256)
        saturationInt = clamp(saturationInt, 0, 256)
        valueInt = clamp(valueInt, 0, 256)

        w, h := gophersImage.Size()
        op := &ebiten.DrawImageOptions{}
        op.GeoM.Translate(float64(screenWidth-w)/2, float64(screenHeight-h)/2)
        hue := float64(hueInt) * 2 * math.Pi / 128
        saturation := float64(saturationInt) / 128
        value := float64(valueInt) / 128
        op.ColorM.ChangeHSV(hue, saturation, value)
        screen.DrawImage(gophersImage, op)

        msg := fmt.Sprintf(`Hue:        %0.2f [Q][W]
Saturation: %0.2f [A][S]
Value:      %0.2f [Z][X]`, hue, saturation, value)
        ebitenutil.DebugPrint(screen, msg)
        return nil
}

func main() {
        var err error
        gophersImage, _, err = ebitenutil.NewImageFromFile("_resources/images/gophers.jpg", ebiten.FilterNearest)
        if err != nil {
                log.Fatal(err)
        }
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "HSV (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}