ebitencp

ebiten-chipmunk

ebiten-chipmunk is an implementation of the cp.Drawer interface from jakecoffman/cp/v2. This implementation utilizes hajimehoshi/ebiten/v2, making it possible to run across multiple platforms.

Usage

Within your Draw() method, invoke the cp.DrawSpace() function, passing in both a *cp.Space and a *ebitencp.Drawer as parameters.

type Game struct {
	space  *cp.Space
	drawer *ebitencp.Drawer
}
func main() {
    // ...
	game := &Game{}
	game.space = space
	game.drawer = ebitencp.NewDrawer(screenWidth, screenHeight)
    // ...
}
func (g *Game) Draw(screen *ebiten.Image) {
	// Drawing with Ebitengine/v2
	cp.DrawSpace(g.space, g.drawer.WithScreen(screen))
}

If you want to enable dragging, call the HandleMouseEvent() function within the Update method, passing the *cp.Space object. This will allow objects to be dragged using a mouse or touch device.

func (g *Game) Update() error {
	// Handling dragging
	g.drawer.HandleMouseEvent(g.space)
	g.space.Step(1 / 60.0)
	return nil
}

Below is a simple example that demonstrates the implementation in action.

package main

import (
	_ "image/png"
	"log"

	"github.com/demouth/ebitencp"
	"github.com/hajimehoshi/ebiten/v2"

	"github.com/jakecoffman/cp/v2"
)

const (
	screenWidth   = 640
	screenHeight  = 480
	hScreenWidth  = screenWidth / 2
	hScreenHeight = screenHeight / 2
)

type Game struct {
	space  *cp.Space
	drawer *ebitencp.Drawer
}

func (g *Game) Update() error {
	// Handling dragging
	g.drawer.HandleMouseEvent(g.space)
	g.space.Step(1 / 60.0)
	return nil
}

func (g *Game) Draw(screen *ebiten.Image) {
	// Drawing with Ebitengine/v2
	g.drawer.Screen = screen
	cp.DrawSpace(g.space, g.drawer)
}

func (g *Game) Layout(outsideWidth, outsideHeight int) (int, int) {
	return screenWidth, screenHeight
}

func main() {
	// Initialising Chipmunk
	space := cp.NewSpace()
	space.SleepTimeThreshold = 0.5
	space.SetGravity(cp.Vector{X: 0, Y: -100})
	walls := []cp.Vector{
		{X: -hScreenWidth, Y: -hScreenHeight}, {X: -hScreenWidth, Y: hScreenHeight},
		{X: hScreenWidth, Y: -hScreenHeight}, {X: hScreenWidth, Y: hScreenHeight},
		{X: -hScreenWidth, Y: -hScreenHeight}, {X: hScreenWidth, Y: -hScreenHeight},
		{X: -hScreenWidth, Y: hScreenHeight}, {X: hScreenWidth, Y: hScreenHeight},
		{X: -100, Y: -100}, {X: 100, Y: -80},
	}
	for i := 0; i < len(walls)-1; i += 2 {
		shape := space.AddShape(cp.NewSegment(space.StaticBody, walls[i], walls[i+1], 0))
		shape.SetElasticity(0.5)
		shape.SetFriction(0.5)
	}
	addBall(space, 0, 0, 50)
	addBall(space, 0, 100, 20)

	// Initialising Ebitengine/v2
	game := &Game{}
	game.space = space
	game.drawer = ebitencp.NewDrawer(screenWidth, screenHeight)
	ebiten.SetWindowSize(screenWidth, screenHeight)
	ebiten.SetWindowTitle("ebiten-chipmunk - ball")
	if err := ebiten.RunGame(game); err != nil {
		log.Fatal(err)
	}
}

func addBall(space *cp.Space, x, y, radius float64) {
	mass := radius * radius / 100.0
	body := space.AddBody(cp.NewBody(mass, cp.MomentForCircle(mass, 0, radius, cp.Vector{})))
	body.SetPosition(cp.Vector{X: x, Y: y})
	shape := space.AddShape(cp.NewCircle(body, radius, cp.Vector{}))
	shape.SetElasticity(0.5)
	shape.SetFriction(0.5)
}

Additional examples can be found in the examples/ directory. These examples can help you adapt the implementation to your own projects.

Using Ebitengine

You can correct the coordinate system by setting FlipYAxis to true.

Example:

  func main() {
	// ...
  	game.drawer = ebitencp.NewDrawer(screenWidth, screenHeight)
+ 	game.drawer.FlipYAxis = true
+	// Set the camera offset to the center of the screen
+	drawer.GeoM.Translate(-screenWidth/2, -screenHeight/2)
	// ...
  }