update orderin

engine/drawdag.go

@@ -19,7 +19,7 @@ type DrawDAG struct {
 	Hides
 
 	*dag
-	boxCache  map[DrawBoxer]geom.Box
+	boxCache  map[DrawBoxer]geom.Box        // used to find components that moved
 	chunks    map[image.Point]drawerSet     // chunk coord -> drawers with bounding rects intersecting chunk
 	chunksRev map[DrawBoxer]image.Rectangle // comopnent -> rectangle of chunk coords
 	game      *Game
@@ -45,6 +45,7 @@ func (d *DrawDAG) DrawAll(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 		},
 	}
 	// Draw everything in d.dag, where not hidden (itself or any parent)
+	// TODO: handle descendant DrawLayers
 	d.dag.topIterate(func(x Drawer) {
 		// Is d hidden itself?
 		if h, ok := x.(Hider); ok && h.Hidden() {
@@ -88,6 +89,7 @@ func (d *DrawDAG) DrawAll(screen *ebiten.Image, opts *ebiten.DrawImageOptions) {
 	})
 }
 
+// Prepare adds all subcomponents to the DAG.
 func (d *DrawDAG) Prepare(game *Game) error {
 	d.dag = newDAG()
 	d.boxCache = make(map[DrawBoxer]geom.Box)
@@ -109,7 +111,8 @@ func (d *DrawDAG) Scan() []interface{} { return d.Components }
 func (d *DrawDAG) Update() error {
 	// Re-evaluate bounding boxes for all descendants. If a box has changed,
 	// fix up the edges by removing and re-adding the vertex.
-	// TODO: ensure this happens after updates for the descendants.
+	// Thanks once again to postorder traversal, this happens after all
+	// descendant updates.
 	var readd []DrawBoxer
 	for db, bb := range d.boxCache {
 		nbb := db.BoundingBox()

engine/game.go

@@ -81,17 +81,20 @@ func (g *Game) Update() error {
 	}
 
 	// Update everything that is not disabled.
-	// TODO: do it in a fixed order? map essentially randomises iteration order
-	for u := range g.Query(g, UpdaterType) {
+	return PostorderWalk(g, func(c, _ interface{}) error {
 		// Skip g (note g satisfies Updater, so this would infinitely recurse)
-		if u == g {
-			continue
+		if c == g {
+			return nil
+		}
+		u, ok := c.(Updater)
+		if !ok {
+			return nil
 		}
 
 		// Is u disabled itself?
 		if d, ok := u.(Disabler); ok && d.Disabled() {
 			cache[u] = true
-			continue
+			return nil
 		}
 
 		// Walk up g.par to find the nearest state in accum.
@@ -117,19 +120,14 @@ func (g *Game) Update() error {
 
 		// Skip updating if disabled.
 		if st {
-			continue
-		}
-
-		if err := u.(Updater).Update(); err != nil {
-			return err
-		}
-	}
-
-	// Sort the draw list (on every frame - this isn't as bad as it sounds)
-	//g.drawList.topsort(g.Projection)
 			return nil
 		}
 
+		// Update
+		return u.Update()
+	})
+}
+
 // Ident returns "__GAME__".
 func (g *Game) Ident() string { return "__GAME__" }