add example/infinitescroll (#255)

This resolved #254

examples/infinitescroll/main.go

@@ -0,0 +1,147 @@
+// Copyright 2016 The Ebiten Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	_ "image/png"
+	"log"
+	"math"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+)
+
+const (
+	screenWidth  = 320
+	screenHeight = 240
+)
+
+var (
+	theViewport     = &viewport{}
+	bgImage         *ebiten.Image
+	repeatedBgImage *ebiten.Image
+	groundImage     *ebiten.Image
+)
+
+type viewport struct {
+	x16 int
+	y16 int
+}
+
+func round(x float64) float64 {
+	return math.Floor(x + 0.5)
+}
+
+func (p *viewport) Move() {
+
+	w, h := bgImage.Size()
+	mx := w * 16
+	my := h * 16
+
+	p.x16 += w / 32
+	p.y16 += h / 32
+
+	for mx <= p.x16 {
+		p.x16 -= mx
+	}
+	for my <= p.y16 {
+		p.y16 -= my
+	}
+	for p.x16 < 0 {
+		p.x16 += mx
+	}
+	for p.y16 < 0 {
+		p.y16 += my
+	}
+}
+
+func (p *viewport) Position() (int, int) {
+	return p.x16, p.y16
+}
+
+func updateGroundImage(ground *ebiten.Image) error {
+
+	if err := ground.Clear(); err != nil {
+		return err
+	}
+
+	x16, y16 := theViewport.Position()
+	op := &ebiten.DrawImageOptions{}
+	op.GeoM.Translate(float64(-x16)/16, float64(-y16)/16)
+	if err := ground.DrawImage(repeatedBgImage, op); err != nil {
+		return err
+	}
+	return nil
+}
+
+func drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) error {
+
+	op := &ebiten.DrawImageOptions{}
+	if err := screen.DrawImage(ground, op); err != nil {
+		return err
+	}
+	return nil
+}
+
+func update(screen *ebiten.Image) error {
+
+	theViewport.Move()
+
+	if err := updateGroundImage(groundImage); err != nil {
+		return err
+	}
+	if err := drawGroundImage(screen, groundImage); err != nil {
+		return err
+	}
+
+	msg := fmt.Sprintf("FPS: %0.2f", ebiten.CurrentFPS())
+	if err := ebitenutil.DebugPrint(screen, msg); err != nil {
+		return err
+	}
+	return nil
+}
+
+func main() {
+
+	var err error
+	bgImage, _, err = ebitenutil.NewImageFromFile("tile.png", ebiten.FilterNearest)
+	if err != nil {
+		log.Fatal(err)
+	}
+	w, h := bgImage.Size()
+	const repeat = 5
+	repeatedBgImage, err = ebiten.NewImage(w*repeat, h*repeat, ebiten.FilterNearest)
+	if err != nil {
+		log.Fatal(err)
+	}
+	for j := 0; j < repeat; j++ {
+		for i := 0; i < repeat; i++ {
+			op := &ebiten.DrawImageOptions{}
+			op.GeoM.Translate(float64(w*i), float64(h*j))
+			if err := repeatedBgImage.DrawImage(bgImage, op); err != nil {
+				log.Fatal(err)
+			}
+		}
+	}
+	groundImage, err = ebiten.NewImage(screenWidth, screenHeight, ebiten.FilterNearest)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if err := ebiten.Run(update, screenWidth, screenHeight, 2, "infinite scroll"); err != nil {
+		log.Fatal(err)
+	}
+}