add offset to tiles and make storage sparse

engine/tiles.go

@@ -18,8 +18,9 @@ type Tilemap struct {
 	Disabled bool
 	Hidden   bool
 	ID
-	Map      [][]Tile
+	Map      map[image.Point]Tile
 	Ersatz   bool        // "fake wall"
+	Offset   image.Point // world coordinates
 	Src      ImageRef
 	TileSize int
 	ZPos
@@ -34,13 +35,13 @@ func (t *Tilemap) CollidesWith(r image.Rectangle) bool {
 	// If we round down r.Min, and round up r.Max, to the nearest tile
 	// coordinates, that gives the full range of tiles to test.
 	sm1 := t.TileSize - 1
+	r = r.Sub(t.Offset)
 	min := r.Min.Div(t.TileSize)
 	max := r.Max.Add(image.Pt(sm1, sm1)).Div(t.TileSize)
 
-	for j := min.Y; j <= max.Y && j < len(t.Map); j++ {
+	for j := min.Y; j <= max.Y; j++ {
-		row := t.Map[j]
+		for i := min.X; i <= max.X; i++ {
-		for i := min.X; i <= max.X && i < len(row); i++ {
+			if t.Map[image.Pt(i, j)] == nil {
-			if row[i] == nil {
 				continue
 			}
 			if r.Overlaps(image.Rect(i*t.TileSize, j*t.TileSize, (i+1)*t.TileSize, (j+1)*t.TileSize)) {
@@ -60,13 +61,12 @@ func (t *Tilemap) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
 	w, _ := src.Size()
 	og := opts.GeoM
 	var geom ebiten.GeoM
-	for j, row := range t.Map {
+	for p, tile := range t.Map {
-		for i, tile := range row {
 		if tile == nil {
 			continue
 		}
 		geom.Reset()
-			geom.Translate(float64(i*t.TileSize), float64(j*t.TileSize))
+		geom.Translate(float64(p.X*t.TileSize+t.Offset.X), float64(p.Y*t.TileSize+t.Offset.Y))
 		geom.Concat(og)
 		opts.GeoM = geom
 
@@ -75,7 +75,6 @@ func (t *Tilemap) Draw(screen *ebiten.Image, opts ebiten.DrawImageOptions) {
 		src := src.SubImage(image.Rect(sx, sy, sx+t.TileSize, sy+t.TileSize)).(*ebiten.Image)
 		screen.DrawImage(src, &opts)
 	}
-	}
 }
 
 // Update calls Update on any tiles that are Updaters, e.g. AnimatedTile.
@@ -83,15 +82,13 @@ func (t *Tilemap) Update() error {
 	if t.Disabled {
 		return nil
 	}
-	for _, row := range t.Map {
+	for _, tile := range t.Map {
-		for _, tile := range row {
 		if u, ok := tile.(Updater); ok {
 			if err := u.Update(); err != nil {
 				return err
 			}
 		}
 	}
-	}
 	return nil
 }
 

main.go

@@ -23,7 +23,7 @@ func main() {
 	engine.AssetFS = assets
 	// engine.AnimDefs set in game/anims.go
 
-	tiles := [][]engine.Tile{
+	denseTiles := [][]engine.Tile{
 		{engine.StaticTile(9), nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, engine.StaticTile(9)},
 		{nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, &engine.AnimatedTile{AnimRef: engine.AnimRef{Key: "red_tiles"}}, nil, nil, nil, nil, nil, nil, nil, nil, nil},
 		{nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, &engine.AnimatedTile{AnimRef: engine.AnimRef{Key: "red_tiles"}}, nil, nil, nil},
@@ -40,6 +40,12 @@ func main() {
 		{engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), &engine.AnimatedTile{AnimRef: engine.AnimRef{Key: "red_tiles"}}, engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), &engine.AnimatedTile{AnimRef: engine.AnimRef{Key: "green_tiles"}}, engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7)},
 		{engine.StaticTile(9), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(7), engine.StaticTile(9)},
 	}
+	tiles := make(map[image.Point]engine.Tile)
+	for j, row := range denseTiles {
+		for i, tile := range row {
+			tiles[image.Pt(i, j)] = tile
+		}
+	}
 
 	level1 := &engine.Scene{
 		ID: "level_1",