openquell/systems/grid_system.go

package systems

import (
	"image"
	"image/draw"
	"openquell/components"
	. "openquell/components"
	. "openquell/config"
	"openquell/grid"

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

type GridSystem struct {
	World                                   *ecs.World
	Selector                                *generic.Filter3[Renderable, Position, Solid]
	UseCache                                bool
	Cache                                   *ebiten.Image
	Count                                   int // register tile count, invalidates cache
	Background                              *ebiten.Image
	Width, Height, TilesX, TilesY, Tilesize int
	Grid                                    *grid.Grid
}

func NewGridSystem(world *ecs.World, width, height,
	tilesize int, background *ebiten.Image) *GridSystem {

	cache := ebiten.NewImage(width, height)

	system := &GridSystem{
		Selector:   generic.NewFilter3[Renderable, Position, Solid](),
		UseCache:   false,
		Cache:      cache,
		Width:      width,
		Height:     height,
		TilesX:     width / tilesize,
		TilesY:     height / tilesize,
		Tilesize:   tilesize,
		Background: background,
		World:      world,
	}

	return system
}

func (system *GridSystem) SetGrid(grid *grid.Grid) {
	system.Grid = grid
}

func (system *GridSystem) Update() {}

func (system *GridSystem) Draw(screen *ebiten.Image) {
	op := &ebiten.DrawImageOptions{}
	query := system.Selector.Query(system.World)

	if !system.UseCache || query.Count() != system.Count {
		// map not cached or cacheable, write it to the cache
		draw.Draw(system.Cache, system.Background.Bounds(), system.Background, image.ZP, draw.Src)

		system.Count = query.Count()

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

			draw.Draw(
				system.Cache,
				image.Rect(pos.X, pos.Y, pos.X+pos.Cellsize, pos.Y+pos.Cellsize),
				sprite.Image, image.ZP, draw.Over)
		}

		op.GeoM.Reset()
		screen.DrawImage(system.Cache, op)

		system.UseCache = true
	} else {
		// use the cached map
		op.GeoM.Reset()
		screen.DrawImage(system.Cache, op)
		query.Close()
	}
}

func (system *GridSystem) GetSolidNeighborPosition(
	position *components.Position,
	velocity *components.Velocity,
	solid bool) (bool, *components.Position) {

	if !solid {
		return false, nil
	}

	// set to true,  if we are already on the last  tile in the current
	// direction, i.e. on the edge of the grid
	edge := true
	neighborpos := position.Point()

	switch velocity.Direction {
	case East:
		if neighborpos.X < system.TilesX {
			neighborpos.X++
			edge = false
		}
	case West:
		if neighborpos.X > 0 {
			neighborpos.X--
			edge = false
		}
	case South:
		if neighborpos.Y < system.TilesY {
			neighborpos.Y++
			edge = false
		}
	case North:
		if neighborpos.Y > 0 {
			neighborpos.Y--
			edge = false
		}
	}

	newpos := components.NewPosition(neighborpos, system.Tilesize)

	if !edge && system.Grid.Map[neighborpos].Solid {
		return true, newpos
	}

	return false, nil
}

func (system *GridSystem) BumpEdge(
	pos *components.Position,
	velocity *components.Velocity) (bool, *components.Position) {

	x := pos.X + velocity.Data.X
	y := pos.Y + velocity.Data.Y

	if x < 0 || x > system.Width-system.Tilesize || y < 0 || y > system.Height-system.Tilesize {
		newpos := &components.Position{}
		X := pos.X
		Y := pos.Y

		switch velocity.Direction {
		case East:
			X = 0
		case West:
			X = system.Width - system.Tilesize
		case South:
			Y = 0
		case North:
			Y = system.Height - system.Tilesize
		}

		newpos.Update(X, Y, system.Tilesize)
		return true, newpos
	}

	return false, nil
}