Tilemap: Optimize scanrow z ordering

src/scene.cpp

@@ -59,6 +59,24 @@ void Scene::insert(SceneElement &element)
 	elements.append(element.link);
 }
 
+void Scene::insertAfter(SceneElement &element, SceneElement &after)
+{
+	IntruListLink<SceneElement> *iter;
+
+	for (iter = &after.link; iter != elements.end(); iter = iter->next)
+	{
+		SceneElement *e = iter->data;
+
+		if (element < *e)
+		{
+			elements.insertBefore(element.link, *iter);
+			return;
+		}
+	}
+
+	elements.append(element.link);
+}
+
 void Scene::reinsert(SceneElement &element)
 {
 	elements.remove(element.link);

src/scene.h

@@ -51,6 +51,7 @@ public:
 
 protected:
 	void insert(SceneElement &element);
+	void insertAfter(SceneElement &element, SceneElement &after);
 	void reinsert(SceneElement &element);
 
 	/* Notify all elements that geometry has changed */

src/tilemap.cpp

@@ -230,7 +230,7 @@ struct ScanRow : public ViewportElement
 	void drawInt();
 
 	void initUpdateZ();
-	void finiUpdateZ();
+	void finiUpdateZ(ScanRow *prev);
 };
 
 struct TilemapPrivate
@@ -1005,11 +1005,21 @@ struct TilemapPrivate
 
 	void updateZOrder()
 	{
+		if (elem.scanrows.isEmpty())
+			return;
+
 		for (int i = 0; i < elem.scanrows.count(); ++i)
 			elem.scanrows[i]->initUpdateZ();
 
-		for (int i = 0; i < elem.scanrows.count(); ++i)
+		ScanRow *prev = elem.scanrows.first();
-			elem.scanrows[i]->finiUpdateZ();
+		prev->finiUpdateZ(0);
+
+		for (int i = 1; i < elem.scanrows.count(); ++i)
+		{
+			ScanRow *row = elem.scanrows[i];
+			row->finiUpdateZ(prev);
+			prev = row;
+		}
 	}
 
 	void prepare()
@@ -1186,10 +1196,13 @@ void ScanRow::initUpdateZ()
 	unlink();
 }
 
-void ScanRow::finiUpdateZ()
+void ScanRow::finiUpdateZ(ScanRow *prev)
 {
 	z = 32 * (index+1) - p->offset.y;
 
+	if (prev)
+		scene->insertAfter(*this, *prev);
+	else
 		scene->insert(*this);
 }