openquell/systems/particle_system.go

package systems

import (
	. "openquell/components"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/mlange-42/arche/ecs"
	"github.com/mlange-42/arche/generic"
)

type ParticleSystem struct {
	World    *ecs.World
	Selector *generic.Filter2[Position, Particle]
	Cellsize int
}

func NewParticleSystem(world *ecs.World, cellsize int) *ParticleSystem {
	system := &ParticleSystem{
		Selector: generic.NewFilter2[Position, Particle](),
		World:    world,
		Cellsize: cellsize,
	}

	return system
}

func (system *ParticleSystem) Update() {
	// display debris after collecting
	EntitiesToRemove := []ecs.Entity{}

	query := system.Selector.Query(system.World)

	for query.Next() {
		// we loop, but it's only one anyway
		_, particle := query.Get()

		switch {
		// particle shows from earlier tick, animate
		case particle.Index > -1 && particle.Index < len(particle.Particles)-1:
			particle.Index++
		default:
			// last sprite reached, remove it
			EntitiesToRemove = append(EntitiesToRemove, query.Entity())
		}
	}

	for _, entity := range EntitiesToRemove {
		system.World.RemoveEntity(entity)
	}
}

func (system *ParticleSystem) Draw(screen *ebiten.Image) {
	// write particles (these are no tiles!)
	op := &ebiten.DrawImageOptions{}
	query := system.Selector.Query(system.World)

	for query.Next() {
		pos, particle := query.Get()

		op.GeoM.Reset()
		op.GeoM.Translate(float64(pos.X), float64(pos.Y))
		screen.DrawImage(particle.Particles[particle.Index], op)
	}
}