// +build example

package main

import (
        "fmt"
        "image"
        "image/color"
        "log"
        "math"

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

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        count       int
        brushImage  *ebiten.Image
        canvasImage *ebiten.Image
)

func init() {
        const (
                a0 = 0x40
                a1 = 0xc0
                a2 = 0xff
        )
        pixels := []uint8{
                a0, a1, a1, a0,
                a1, a2, a2, a1,
                a1, a2, a2, a1,
                a0, a1, a1, a0,
        }
        brushImage, _ = ebiten.NewImageFromImage(&image.Alpha{
                Pix:    pixels,
                Stride: 4,
                Rect:   image.Rect(0, 0, 4, 4),
        }, ebiten.FilterDefault)

        canvasImage, _ = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterDefault)
        canvasImage.Fill(color.White)
}

// paint draws the brush on the given canvas image at the position (x, y).
func paint(canvas *ebiten.Image, x, y int) {
        op := &ebiten.DrawImageOptions{}
        op.GeoM.Translate(float64(x), float64(y))
        // Scale the color and rotate the hue so that colors vary on each frame.
        op.ColorM.Scale(1.0, 0.50, 0.125, 1.0)
        theta := 2.0 * math.Pi * float64(count%ebiten.FPS) / ebiten.FPS
        op.ColorM.RotateHue(theta)
        canvas.DrawImage(brushImage, op)
}

func update(screen *ebiten.Image) error {
        drawn := false

        // Paint the brush by mouse dragging
        mx, my := ebiten.CursorPosition()
        if ebiten.IsMouseButtonPressed(ebiten.MouseButtonLeft) {
                paint(canvasImage, mx, my)
                drawn = true
        }

        // Paint the brush by touches
        for _, t := range ebiten.Touches() {
                x, y := t.Position()
                paint(canvasImage, x, y)
                drawn = true
        }
        if drawn {
                count++
        }

        if ebiten.IsRunningSlowly() {
                return nil
        }

        screen.DrawImage(canvasImage, nil)

        msg := fmt.Sprintf("(%d, %d)", mx, my)
        for _, t := range ebiten.Touches() {
                x, y := t.Position()
                msg += fmt.Sprintf("\n(%d, %d) touch %d", x, y, t.ID())
        }
        ebitenutil.DebugPrint(screen, msg)
        return nil
}

func main() {
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Paint (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}