// +build example

package main

import (
        "fmt"
        "image"
        "log"

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

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        noiseImage *image.RGBA
)

type rand struct {
        x, y, z, w uint32
}

func (r *rand) next() uint32 {
        // math/rand is too slow to keep 60 FPS on web browsers.
        // Use Xorshift instead: http://en.wikipedia.org/wiki/Xorshift
        t := r.x ^ (r.x << 11)
        r.x, r.y, r.z = r.y, r.z, r.w
        r.w = (r.w ^ (r.w >> 19)) ^ (t ^ (t >> 8))
        return r.w
}

var theRand = &rand{12345678, 4185243, 776511, 45411}

func update(screen *ebiten.Image) error {
        // Generate the noise with random RGB values.
        const l = screenWidth * screenHeight
        for i := 0; i < l; i++ {
                x := theRand.next()
                noiseImage.Pix[4*i] = uint8(x >> 24)
                noiseImage.Pix[4*i+1] = uint8(x >> 16)
                noiseImage.Pix[4*i+2] = uint8(x >> 8)
                noiseImage.Pix[4*i+3] = 0xff
        }

        if ebiten.IsRunningSlowly() {
                return nil
        }

        screen.ReplacePixels(noiseImage.Pix)
        ebitenutil.DebugPrint(screen, fmt.Sprintf("FPS: %f", ebiten.CurrentFPS()))
        return nil
}

func main() {
        noiseImage = image.NewRGBA(image.Rect(0, 0, screenWidth, screenHeight))
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Noise (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}