added transient entities: when crossed, turns into wall tile

game/game.go

@@ -33,6 +33,7 @@ func NewGame(width, height, cellsize, startlevel int, startscene SceneName) *Gam
 
 	observers.NewPlayerObserver(&world)
 	observers.NewParticleObserver(&world)
+	observers.NewObstacleObserver(&world)
 	game.Observer = observers.NewGameObserver(&world, startlevel, width, height, cellsize)
 
 	game.Scenes[Welcome] = NewWelcomeScene(game)

game/level_scene.go

@@ -70,7 +70,8 @@ func (scene *LevelScene) Update() error {
 
 func (scene *LevelScene) Draw(screen *ebiten.Image) {
 	if scene.CurrentLevel != scene.Game.Observer.CurrentLevel {
-		slog.Debug("level", "current", scene.CurrentLevel, "next", scene.Game.Observer.CurrentLevel)
+		slog.Debug("level", "current", scene.CurrentLevel,
+			"next", scene.Game.Observer.CurrentLevel)
 		scene.CurrentLevel = scene.Game.Observer.CurrentLevel
 		scene.Levels[scene.CurrentLevel].SetupGrid(scene.Game)
 	}

game/levels.go

@@ -8,6 +8,7 @@ import (
 	"openquell/grid"
 	"openquell/observers"
 	"openquell/systems"
+	"openquell/util"
 	"strings"
 
 	"github.com/hajimehoshi/ebiten/v2"
@@ -79,9 +80,11 @@ func (level *Level) SetupGrid(game *Game) {
 	playerobserver.RemoveEntities()
 
 	// setup world
-	level.GridSystem.SetGrid(grid.NewGrid(game.World, level.Cellsize, level.Width, level.Height, level.Mapslice))
+	level.GridSystem.SetGrid(
+		grid.NewGrid(game.World, level.Cellsize, level.Width, level.Height, level.Mapslice))
 }
 
+// parses a RawLevel and generates a mapslice from it, which is being used as grid
 func LevelToSlice(game *Game, level *assets.RawLevel, tilesize int) map[image.Point]*assets.Tile {
 	size := game.ScreenWidth * game.ScreenHeight
 	mapslice := make(map[image.Point]*assets.Tile, size)
@@ -93,6 +96,10 @@ func LevelToSlice(game *Game, level *assets.RawLevel, tilesize int) map[image.Po
 		}
 
 		for x, char := range line {
+			if !util.Exists(assets.Tiles, byte(char)) {
+				log.Fatalf("unregistered tile type %c encountered", char)
+			}
+
 			mapslice[image.Point{x, y}] = assets.Tiles[byte(char)]
 		}
 	}