examples: Add physics example (#572)

examples/physics/main.go

@@ -0,0 +1,153 @@
+// 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 (
+	"fmt"
+	"image/color"
+	"math/rand"
+	"os"
+
+	"github.com/hajimehoshi/ebiten"
+	"github.com/hajimehoshi/ebiten/ebitenutil"
+	"github.com/jakecoffman/cp"
+)
+
+const (
+	imageWidth     = 188
+	imageHeight    = 35
+	imageRowLength = 24
+)
+
+var (
+	space *cp.Space
+)
+
+func main() {
+	space = cp.NewSpace()
+	space.Iterations = 1
+
+	// The space will contain a very large number of similarly sized objects.
+	// This is the perfect candidate for using the spatial hash.
+	// Generally you will never need to do this.
+	space.UseSpatialHash(2.0, 10000)
+
+	var body *cp.Body
+	var shape *cp.Shape
+
+	for y := 0; y < imageHeight; y++ {
+		for x := 0; x < imageWidth; x++ {
+			if getPixel(uint(x), uint(y)) == 0 {
+				continue
+			}
+
+			xJitter := 0.05 * rand.Float64()
+			yJitter := 0.05 * rand.Float64()
+
+			shape = makeBall(2.0*(float64(x)+imageWidth/2+xJitter)-75, 2*(imageHeight/2.0+float64(y)+yJitter)+150)
+			space.AddBody(shape.Body())
+			space.AddShape(shape)
+		}
+	}
+
+	body = space.AddBody(cp.NewBody(1e9, cp.INFINITY))
+	body.SetPosition(cp.Vector{-1000, 225})
+	body.SetVelocity(400, 0)
+
+	shape = space.AddShape(cp.NewCircle(body, 8, cp.Vector{}))
+	shape.SetElasticity(0)
+	shape.SetFriction(0)
+
+	err := ebiten.Run(update, 600, 480, 1, "Ebiten")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+	}
+}
+
+func getPixel(x, y uint) int {
+	return (imageBitmap[(x>>3)+y*imageRowLength] >> (^x & 0x7)) & 1
+}
+
+func update(screen *ebiten.Image) error {
+	space.Step(1. / 60.)
+	if ebiten.IsRunningSlowly() {
+		return nil
+	}
+
+	screen.Fill(color.Black)
+	dot, _ := ebiten.NewImage(1, 1, ebiten.FilterNearest)
+	dot.Fill(color.White)
+
+	op := &ebiten.DrawImageOptions{}
+	op.ColorM.Scale(200./255., 200./255., 200./255., 1)
+
+	space.EachBody(func(body *cp.Body) {
+		op.GeoM.Reset()
+		op.GeoM.Translate(body.Position().X, body.Position().Y)
+		screen.DrawImage(dot, op)
+	})
+
+	ebitenutil.DebugPrint(screen, fmt.Sprint(ebiten.CurrentFPS()))
+	return nil
+}
+
+func makeBall(x, y float64) *cp.Shape {
+	body := cp.NewBody(1.0, cp.INFINITY)
+	body.SetPosition(cp.Vector{x, y})
+
+	shape := cp.NewCircle(body, 0.95, cp.Vector{})
+	shape.SetElasticity(0)
+	shape.SetFriction(0)
+
+	return shape
+}
+
+var imageBitmap = []int{
+	15, -16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, -64, 15, 63, -32, -2, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 31, -64, 15, 127, -125, -1, -128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 127, -64, 15, 127, 15, -1, -64, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, -64, 15, -2,
+	31, -1, -64, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, -64, 0, -4, 63, -1, -32, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, -64, 15, -8, 127, -1, -32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	1, -1, -64, 0, -8, -15, -1, -32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -31, -1, -64, 15, -8, -32,
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+	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 31, -15, -1, -64, 0, -15, -32, -1, -32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 63, -7, -1, -64, 9, -29, -32, 127, -61, -16, 63, 15, -61, -1, -8, 31, -16, 15, -8, 126, 7, -31,
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+	-97, -25, -8, 0, 63, -61, -61, -4, 127, -1, -29, -4, 127, -64, 15, -8, 0, 0, 55, -1, -1, -121, -8,
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+	63, 15, -61, -16, 0, 31, -127, -127, -8, 31, -1, -127, -8, 31, -128, 7, -128, 0, 0,
+}