step

examples/physics/chipmunk/main.go

@@ -0,0 +1,163 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"math/rand"
+
+	rl "github.com/gen2brain/raylib-go/raylib"
+	"github.com/jakecoffman/cp"
+)
+
+var grabbableMaskBit uint = 1 << 31
+var grabFilter = cp.ShapeFilter{
+	cp.NO_GROUP, grabbableMaskBit, grabbableMaskBit,
+}
+
+func randUnitCircle() cp.Vector {
+	v := cp.Vector{X: rand.Float64()*2.0 - 1.0, Y: rand.Float64()*2.0 - 1.0}
+	if v.LengthSq() < 1.0 {
+		return v
+	}
+	return randUnitCircle()
+}
+
+var simpleTerrainVerts = []cp.Vector{
+	{350.00, 425.07}, {336.00, 436.55}, {272.00, 435.39}, {258.00, 427.63}, {225.28, 420.00}, {202.82, 396.00},
+	{191.81, 388.00}, {189.00, 381.89}, {173.00, 380.39}, {162.59, 368.00}, {150.47, 319.00}, {128.00, 311.55},
+	{119.14, 286.00}, {126.84, 263.00}, {120.56, 227.00}, {141.14, 178.00}, {137.52, 162.00}, {146.51, 142.00},
+	{156.23, 136.00}, {158.00, 118.27}, {170.00, 100.77}, {208.43, 84.00}, {224.00, 69.65}, {249.30, 68.00},
+	{257.00, 54.77}, {363.00, 45.94}, {374.15, 54.00}, {386.00, 69.60}, {413.00, 70.73}, {456.00, 84.89},
+	{468.09, 99.00}, {467.09, 123.00}, {464.92, 135.00}, {469.00, 141.03}, {497.00, 148.67}, {513.85, 180.00},
+	{509.56, 223.00}, {523.51, 247.00}, {523.00, 277.00}, {497.79, 311.00}, {478.67, 348.00}, {467.90, 360.00},
+	{456.76, 382.00}, {432.95, 389.00}, {417.00, 411.32}, {373.00, 433.19}, {361.00, 430.02}, {350.00, 425.07},
+}
+
+// creates a circle with random placement
+func addCircle(space *cp.Space, radius float64) {
+	mass := radius * radius / 25.0
+	body := space.AddBody(cp.NewBody(mass, cp.MomentForCircle(mass, 0, radius, cp.Vector{})))
+	body.SetPosition(randUnitCircle().Mult(180))
+
+	shape := space.AddShape(cp.NewCircle(body, radius, cp.Vector{}))
+	shape.SetElasticity(0)
+	shape.SetFriction(0.9)
+}
+
+// creates a simple terrain to contain bodies
+func simpleTerrain() *cp.Space {
+	space := cp.NewSpace()
+	space.Iterations = 10
+	space.SetGravity(cp.Vector{0, -100})
+	space.SetCollisionSlop(0.5)
+
+	offset := cp.Vector{X: -320, Y: -240}
+	for i := 0; i < len(simpleTerrainVerts)-1; i++ {
+		a := simpleTerrainVerts[i]
+		b := simpleTerrainVerts[i+1]
+		space.AddShape(cp.NewSegment(space.StaticBody, a.Add(offset), b.Add(offset), 0))
+	}
+
+	return space
+}
+
+func main() {
+	const width, height = 800, 450
+	const physicsTickrate = 1.0 / 60.0
+
+	rl.SetConfigFlags(rl.FlagVsyncHint)
+	rl.InitWindow(width, height, "raylib [physics] example - chipmunk")
+
+	offset := rl.Vector2{X: width / 2, Y: height / 2}
+	// since the example ported from elsewhere, flip the camera 180 and offset to center it
+	camera := rl.NewCamera2D(offset, rl.Vector2{}, 180, 1)
+
+	space := simpleTerrain()
+	for i := 0; i < 1000; i++ {
+		addCircle(space, 5)
+	}
+	mouseBody := cp.NewKinematicBody()
+	var mouse cp.Vector
+	var mouseJoint *cp.Constraint
+
+	var accumulator, dt float32
+	lastTime := rl.GetTime()
+	for !rl.WindowShouldClose() {
+		// calculate dt
+		now := rl.GetTime()
+		dt = float32(now - lastTime)
+		lastTime = now
+
+		// update the mouse position
+		mousePos := rl.GetMousePosition()
+		// alter the mouse coordinates based on the camera position, rotation
+		mouse.X = float64(mousePos.X-camera.Offset.X) * -1
+		mouse.Y = float64(mousePos.Y-camera.Offset.Y) * -1
+		// smooth mouse movements to new position
+		newPoint := mouseBody.Position().Lerp(mouse, 0.25)
+		mouseBody.SetVelocityVector(newPoint.Sub(mouseBody.Position()).Mult(60.0))
+		mouseBody.SetPosition(newPoint)
+
+		// handle grabbing
+		if rl.IsMouseButtonPressed(rl.MouseLeftButton) {
+			result := space.PointQueryNearest(mouse, 5, grabFilter)
+			if result.Shape != nil && result.Shape.Body().Mass() < cp.INFINITY {
+				var nearest cp.Vector
+				if result.Distance > 0 {
+					nearest = result.Point
+				} else {
+					nearest = mouse
+				}
+
+				// create a new constraint where the mouse is to draw the body towards the mouse
+				body := result.Shape.Body()
+				mouseJoint = cp.NewPivotJoint2(mouseBody, body, cp.Vector{}, body.WorldToLocal(nearest))
+				mouseJoint.SetMaxForce(50000)
+				mouseJoint.SetErrorBias(math.Pow(1.0-0.15, 60.0))
+				space.AddConstraint(mouseJoint)
+			}
+		} else if rl.IsMouseButtonReleased(rl.MouseLeftButton) && mouseJoint != nil {
+			space.RemoveConstraint(mouseJoint)
+			mouseJoint = nil
+		}
+
+		// perform a fixed rate physics tick
+		accumulator += dt
+		for accumulator >= physicsTickrate {
+			space.Step(physicsTickrate)
+			accumulator -= physicsTickrate
+		}
+
+		rl.BeginDrawing()
+		rl.ClearBackground(rl.RayWhite)
+		rl.BeginMode2D(camera)
+
+		// this is a generic way to iterate over the shapes in a space,
+		// to avoid the type switch just keep a pointer to the shapes when they've been created
+		space.EachShape(func(s *cp.Shape) {
+			switch s.Class.(type) {
+			case *cp.Segment:
+				segment := s.Class.(*cp.Segment)
+				a := segment.A()
+				b := segment.B()
+				rl.DrawLineV(v(a), v(b), rl.Black)
+			case *cp.Circle:
+				circle := s.Class.(*cp.Circle)
+				pos := circle.Body().Position()
+				rl.DrawCircleV(v(pos), float32(circle.Radius()), rl.Red)
+			default:
+				fmt.Println("unexpected shape", s.Class)
+			}
+		})
+
+		rl.EndMode2D()
+		rl.DrawFPS(0, 0)
+		rl.EndDrawing()
+	}
+
+	rl.CloseWindow()
+}
+
+func v(v cp.Vector) rl.Vector2 {
+	return rl.Vector2{X: float32(v.X), Y: float32(v.Y)}
+}