openquell/systems/collision_system.go

package systems

import (
	"openquell/components"
	. "openquell/components"
	"openquell/grid"
	"openquell/observers"

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

type CollisionSystem struct {
	World         *ecs.World
	Selector      *generic.Filter4[Position, Velocity, Renderable, Collider]
	GridContainer *grid.GridContainer
}

func NewCollisionSystem(world *ecs.World, gridcontainer *grid.GridContainer) System {
	system := &CollisionSystem{
		Selector:      generic.NewFilter4[Position, Velocity, Renderable, Collider](),
		GridContainer: gridcontainer,
		World:         world,
	}

	return system
}

func (system CollisionSystem) Update() error {
	entityobserver := observers.GetEntityObserver(system.World)

	posID := ecs.ComponentID[components.Position](system.World)
	EntitiesToRemove := []ecs.Entity{}
	query := system.Selector.Query(system.World)

	for query.Next() {
		position, velocity, _, handler := query.Get()
		if velocity.Moving() {
			// check if we bump agains the screen edge
			ok, newpos := system.GridContainer.Grid.BumpEdge(position, velocity)
			if ok {
				if handler.EdgeHandler != nil {
					if !handler.EdgeHandler(system.World, position, newpos, velocity, query.Entity()) {
						EntitiesToRemove = append(EntitiesToRemove, query.Entity())
					}
				}
			} else {
				// check if we collide with some solid entity
				ok, tilepos := system.GridContainer.Grid.GetSolidNeighborPosition(position, velocity, true)
				if ok {
					intersects, newpos := tilepos.Intersects(position, velocity)
					if intersects {
						if handler.CollisionHandler != nil {
							if !handler.CollisionHandler(system.World, position, newpos, velocity, query.Entity()) {
								EntitiesToRemove = append(EntitiesToRemove, query.Entity())
							}
						}
					}
				}
			}

			// check if current entity bumps into another entity
			for foreign_entity := range entityobserver.Entities {
				if foreign_entity == query.Entity() {
					// don't check entity against itself
					continue
				}

				foreign_position := (*Position)(system.World.Get(foreign_entity, posID))

				ok, newpos := foreign_position.Intersects(position, velocity)
				if ok {
					if handler.CollisionHandler != nil {
						if !handler.CollisionHandler(system.World, position, newpos, velocity, foreign_entity) {
							EntitiesToRemove = append(EntitiesToRemove, query.Entity())
						}
					}
				}
			}

		}
	}

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

	return nil
}

func (system *CollisionSystem) Draw(screen *ebiten.Image) {}