examples: Add wheel example

examples/wheel/main.go

@@ -0,0 +1,67 @@
+// Copyright 2018 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.
+
+// +build example jsgo
+
+package main
+
+import (
+	"image/color"
+	"log"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+)
+
+var pointerImage *ebiten.Image
+
+func init() {
+	pointerImage, _ = ebiten.NewImage(4, 4, ebiten.FilterDefault)
+	pointerImage.Fill(color.RGBA{0xff, 0, 0, 0xff})
+}
+
+const (
+	screenWidth  = 320
+	screenHeight = 240
+)
+
+var (
+	x = 0.0
+	y = 0.0
+)
+
+func update(screen *ebiten.Image) error {
+	dx, dy := ebiten.Wheel()
+	x += dx
+	y += dy
+
+	if ebiten.IsDrawingSkipped() {
+		return nil
+	}
+
+	op := &ebiten.DrawImageOptions{}
+	op.GeoM.Translate(x, y)
+	op.GeoM.Translate(screenWidth/2, screenHeight/2)
+	screen.DrawImage(pointerImage, op)
+
+	ebitenutil.DebugPrint(screen, "Move the red point by mouse wheeling")
+
+	return nil
+}
+
+func main() {
+	if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Wheel (Ebiten Demo)"); err != nil {
+		log.Fatal(err)
+	}
+}