gohan/examples/twinstick/system/movement.go

//go:build example
// +build example

package system

import (
	"code.rocketnine.space/tslocum/gohan"
	"code.rocketnine.space/tslocum/gohan/_examples/twinstick/component"
	"github.com/hajimehoshi/ebiten/v2"
)

type MovementSystem struct {
	ScreenW, ScreenH float64
}

func (_ *MovementSystem) Matches(entity gohan.EntityID) bool {
	position := entity.Component(component.PositionComponentID)
	velocity := entity.Component(component.VelocityComponentID)

	return position != nil && velocity != nil
}

func (s *MovementSystem) Update(entity gohan.EntityID) error {
	position := entity.Component(component.PositionComponentID).(*component.PositionComponent)
	velocity := entity.Component(component.VelocityComponentID).(*component.VelocityComponent)

	bullet := entity.Component(component.BulletComponentID)

	// Check for collision.
	if bullet == nil {
		if position.X+velocity.X < 16 {
			position.X = 16
			velocity.X = 0
		} else if position.X+velocity.X > s.ScreenW-16 {
			position.X = s.ScreenW - 16
			velocity.X = 0
		}
		if position.Y+velocity.Y < 16 {
			position.Y = 16
			velocity.Y = 0
		} else if position.Y+velocity.Y > s.ScreenH-16 {
			position.Y = s.ScreenH - 16
			velocity.Y = 0
		}
	}

	position.X, position.Y = position.X+velocity.X, position.Y+velocity.Y

	if bullet == nil {
		velocity.X *= 0.95
		velocity.Y *= 0.95
	}

	return nil
}

func (_ *MovementSystem) Draw(entity gohan.EntityID, screen *ebiten.Image) error {
	return gohan.ErrSystemWithoutDraw
}