platformer

README

Platformer Demo

What does it do?

Stars fall from the sky. You can collect the stars and get points for each one you collect.

What are the important aspects of the code?

Adding your Player to the systems

	dudeBodyDef := box2d.NewB2BodyDef()
	dudeBodyDef.Type = box2d.B2BodyType.B2_dynamicBody
	dudeBodyDef.Position = engoBox2dSystem.Conv.ToBox2d2Vec(dude.SpaceComponent.Center())
	dudeBodyDef.Angle = engoBox2dSystem.Conv.DegToRad(dude.SpaceComponent.Rotation)
	dudeBodyDef.FixedRotation = true
	dude.Box2dComponent.Body = engoBox2dSystem.World.CreateBody(dudeBodyDef)
	var dudeBodyShape box2d.B2PolygonShape
	dudeBodyShape.SetAsBox(engoBox2dSystem.Conv.PxToMeters(dude.SpaceComponent.Width/2),
		engoBox2dSystem.Conv.PxToMeters(dude.SpaceComponent.Height/2))
	dudeFixtureDef := box2d.B2FixtureDef{
		Shape:    &dudeBodyShape,
		Density:  1.0,
		Friction: 0.1,
	}
	dude.Box2dComponent.Body.CreateFixtureFromDef(&dudeFixtureDef)

	for _, system := range w.Systems() {
		switch sys := system.(type) {
		case *common.RenderSystem:
			sys.Add(&dude.BasicEntity, &dude.RenderComponent, &dude.SpaceComponent)
		case *engoBox2dSystem.PhysicsSystem:
			sys.Add(&dude.BasicEntity, &dude.SpaceComponent, &dude.Box2dComponent)
		case *controlSystem:
			sys.Add(&dude.BasicEntity, &dude.Box2dComponent)
		case *engoBox2dSystem.CollisionSystem:
			sys.Add(&dude.BasicEntity, &dude.SpaceComponent, &dude.Box2dComponent)
		case *starCollectionSystem:
			sys.Add(dude.BasicEntity, &dude.Box2dComponent, true)
		}
	}

Adding the floors

	grassBodyDef := box2d.NewB2BodyDef()
	grassBodyDef.Position = engoBox2dSystem.Conv.ToBox2d2Vec(grass.SpaceComponent.Center())
	grassBodyDef.Angle = engoBox2dSystem.Conv.DegToRad(grass.SpaceComponent.Rotation)
	grass.Box2dComponent.Body = engoBox2dSystem.World.CreateBody(grassBodyDef)
	var grassBodyShape box2d.B2PolygonShape
	grassBodyShape.SetAsBox(engoBox2dSystem.Conv.PxToMeters(grass.SpaceComponent.Width/2),
		engoBox2dSystem.Conv.PxToMeters(grass.SpaceComponent.Height/2))
	grassFixtureDef := box2d.B2FixtureDef{Shape: &grassBodyShape}
	grass.Box2dComponent.Body.CreateFixtureFromDef(&grassFixtureDef)

	// Add it to appropriate systems
	for _, system := range w.Systems() {
		switch sys := system.(type) {
		case *common.RenderSystem:
			sys.Add(&grass.BasicEntity, &grass.RenderComponent, &grass.SpaceComponent)
		case *engoBox2dSystem.PhysicsSystem:
			sys.Add(&grass.BasicEntity, &grass.SpaceComponent, &grass.Box2dComponent)
		}
	}

Adding Walls so you can't leave the play area

	leftWallBodyDef := box2d.NewB2BodyDef()
	leftWallBodyDef.Position = engoBox2dSystem.Conv.ToBox2d2Vec(leftWall.SpaceComponent.Center())
	leftWallBodyDef.Angle = engoBox2dSystem.Conv.DegToRad(leftWall.SpaceComponent.Rotation)
	leftWall.Box2dComponent.Body = engoBox2dSystem.World.CreateBody(leftWallBodyDef)
	var leftWallBodyShape box2d.B2PolygonShape
	leftWallBodyShape.SetAsBox(engoBox2dSystem.Conv.PxToMeters(leftWall.SpaceComponent.Width/2),
		engoBox2dSystem.Conv.PxToMeters(leftWall.SpaceComponent.Height/2))
	leftWallFixtureDef := box2d.B2FixtureDef{Shape: &leftWallBodyShape}
	leftWall.Box2dComponent.Body.CreateFixtureFromDef(&leftWallFixtureDef)

	// Add it to appropriate systems
	for _, system := range w.Systems() {
		switch sys := system.(type) {
		case *engoBox2dSystem.PhysicsSystem:
			sys.Add(&leftWall.BasicEntity, &leftWall.SpaceComponent, &leftWall.Box2dComponent)
		}
	}

Adding stars with a pentagon shaped hitbox

star := guy{BasicEntity: ecs.NewBasic()}
// Initialize the components, set scale to 8x
star.RenderComponent = common.RenderComponent{
	Drawable: starTexture,
}
star.SpaceComponent = common.SpaceComponent{
	Position: engo.Point{
		X: 0 + float32(150*i),
		Y: 0,
	},
	Width:  starTexture.Width(),
	Height: starTexture.Height(),
}

//box2d component setup
starBodyDef := box2d.NewB2BodyDef()
starBodyDef.Position = engoBox2dSystem.Conv.ToBox2d2Vec(star.SpaceComponent.Center())
starBodyDef.Angle = engoBox2dSystem.Conv.DegToRad(star.SpaceComponent.Rotation)
starBodyDef.Type = box2d.B2BodyType.B2_dynamicBody
star.Box2dComponent.Body = engoBox2dSystem.World.CreateBody(starBodyDef)
var starBodyShape box2d.B2PolygonShape
var vertices []box2d.B2Vec2
vertices = append(vertices, box2d.B2Vec2{X: engoBox2dSystem.Conv.PxToMeters(0), Y: engoBox2dSystem.Conv.PxToMeters(-50)})
vertices = append(vertices, box2d.B2Vec2{X: engoBox2dSystem.Conv.PxToMeters(49), Y: engoBox2dSystem.Conv.PxToMeters(-15)})
vertices = append(vertices, box2d.B2Vec2{X: engoBox2dSystem.Conv.PxToMeters(30), Y: engoBox2dSystem.Conv.PxToMeters(41)})
vertices = append(vertices, box2d.B2Vec2{X: engoBox2dSystem.Conv.PxToMeters(-31), Y: engoBox2dSystem.Conv.PxToMeters(41)})
vertices = append(vertices, box2d.B2Vec2{X: engoBox2dSystem.Conv.PxToMeters(-50), Y: engoBox2dSystem.Conv.PxToMeters(-15)})
starBodyShape.Set(vertices, 5)
starFixtureDef := box2d.B2FixtureDef{Shape: &starBodyShape}
star.Box2dComponent.Body.CreateFixtureFromDef(&starFixtureDef)

// Add it to appropriate systems
for _, system := range w.Systems() {
	switch sys := system.(type) {
	case *common.RenderSystem:
		sys.Add(&star.BasicEntity, &star.RenderComponent, &star.SpaceComponent)
	case *engoBox2dSystem.PhysicsSystem:
		sys.Add(&star.BasicEntity, &star.SpaceComponent, &star.Box2dComponent)
	case *engoBox2dSystem.CollisionSystem:
		sys.Add(&star.BasicEntity, &star.SpaceComponent, &star.Box2dComponent)
	case *starCollectionSystem:
		sys.Add(star.BasicEntity, &star.Box2dComponent, false)
	}
}

Movement via Box2d

In the controlSystem, we have the Guy move by applying impulses in the Box2d world instead of updating the space component directily

func (c *controlSystem) Update(dt float32) {
	for _, e := range c.entities {
		if engo.Input.Button("up").JustPressed() {
			e.Body.ApplyLinearImpulseToCenter(box2d.B2Vec2{X: 0, Y: -500}, true)
		} else if engo.Input.Button("left").JustPressed() {
			e.Body.SetLinearVelocity(box2d.B2Vec2{X: -10, Y: e.Body.GetLinearVelocity().Y})
		} else if engo.Input.Button("right").JustPressed() {
			e.Body.SetLinearVelocity(box2d.B2Vec2{X: 10, Y: e.Body.GetLinearVelocity().Y})
		}
	}
}

Collision Detection via Box2d

In the starCollectionSystem, we listen for the CollisionStartMessage and destroy the star and add to our score if they're touching

engo.Mailbox.Listen("CollisionStartMessage", func(message engo.Message) {
	c, isCollision := message.(engoBox2dSystem.CollisionStartMessage)
	if isCollision {
		if c.Contact.IsTouching() {
			a := c.Contact.GetFixtureA().GetBody().GetUserData()
			b := c.Contact.GetFixtureB().GetBody().GetUserData()
			for i1, e1 := range s.entities {
				if !e1.isGuy {
					continue
				}
				if e1.BasicEntity.ID() == a || e1.BasicEntity.ID() == b {
					for i2, e2 := range s.entities {
						if i1 == i2 {
							continue
						}
						if e2.BasicEntity.ID() == a || e2.BasicEntity.ID() == b {
							// Remove it from all the appropriate systems
							for _, system := range w.Systems() {
								switch sys := system.(type) {
								case *common.RenderSystem:
									sys.Remove(e2.BasicEntity)
								case *engoBox2dSystem.PhysicsSystem:
									sys.Remove(e2.BasicEntity)
								case *engoBox2dSystem.CollisionSystem:
									sys.Remove(e2.BasicEntity)
								case *starCollectionSystem:
									sys.Remove(e2.BasicEntity)
								}
							}
							e2.Box2dComponent.DestroyBody()
							engo.Mailbox.Dispatch(scoreMessage{})
						}
					}
				}
			}
		}
	}
})