Sprite: Implement Y based Z draw ordering (RGSS2)

If two sprites have the same Z, their order is decided based
on their Y coordinate first, and only then (if equal) by creation
time.

src/scene.cpp

@@ -105,12 +105,14 @@ void Scene::composite()
 }
 
 
-SceneElement::SceneElement(Scene &scene, int z)
+SceneElement::SceneElement(Scene &scene, int z, bool isSprite)
     : link(this),
       creationStamp(shState->genTimeStamp()),
       z(z),
       visible(true),
-      scene(&scene)
+      scene(&scene),
+      spriteY(0),
+      isSprite(isSprite)
 {
 	scene.insert(*this);
 }
@@ -120,7 +122,9 @@ SceneElement::SceneElement(Scene &scene, int z, unsigned int cStamp)
       creationStamp(cStamp),
       z(z),
       visible(true),
-      scene(&scene)
+      scene(&scene),
+      spriteY(0),
+      isSprite(false)
 {
 	scene.insert(*this);
 }
@@ -167,11 +171,23 @@ void SceneElement::setVisible(bool value)
 
 bool SceneElement::operator<(const SceneElement &o) const
 {
+	/* Element draw order is decided by their Z value.
+	 * If two Z values are equal, the later created object
+	 * has priority */
+
 	if (z <= o.z)
 	{
 		if (z == o.z)
-			if (creationStamp > o.creationStamp)
-				return false;
+		{
+#ifdef RGSS2
+			/* RGSS2: If two sprites' Z values collide,
+			 * their Y coordinates decide draw order. Only
+			 * on equal Y does the creation time take effect */
+			if (isSprite && o.isSprite && spriteY != o.spriteY)
+				return (spriteY < o.spriteY);
+#endif
+			return (creationStamp <= o.creationStamp);
+		}
 
 		return true;
 	}
@@ -179,6 +195,12 @@ bool SceneElement::operator<(const SceneElement &o) const
 	return false;
 }
 
+void SceneElement::setSpriteY(int value)
+{
+	spriteY = value;
+	scene->reinsert(*this);
+}
+
 void SceneElement::unlink()
 {
 	if (scene)

src/scene.h

@@ -71,7 +71,7 @@ protected:
 class SceneElement
 {
 public:
-	SceneElement(Scene &scene, int z = 0);
+	SceneElement(Scene &scene, int z = 0, bool isSprite = false);
 	SceneElement(Scene &scene, int z, unsigned int cStamp);
 	virtual ~SceneElement();
 
@@ -108,6 +108,7 @@ protected:
 	 * elements with lower priority are drawn earlier */
 	bool operator<(const SceneElement &o) const;
 
+	void setSpriteY(int value);
 	void unlink();
 
 	IntruListLink<SceneElement> link;
@@ -119,6 +120,10 @@ protected:
 	friend class Scene;
 	friend class Viewport;
 	friend struct TilemapPrivate;
+
+private:
+	int spriteY;
+	const bool isSprite;
 };
 
 #endif // SCENE_H

src/sprite.cpp

@@ -302,7 +302,7 @@ struct SpritePrivate
 };
 
 Sprite::Sprite(Viewport *viewport)
-	: ViewportElement(viewport)
+	: ViewportElement(viewport, 0, true)
 {
 	p = new SpritePrivate;
 	onGeometryChange(scene->getGeometry());
@@ -393,6 +393,8 @@ void Sprite::setY(int value)
 
 #ifdef RGSS2
 	p->wave.dirty = true;
+
+	setSpriteY(value);
 #endif
 }
 

src/viewport.cpp

@@ -218,8 +218,8 @@ void Viewport::onGeometryChange(const Geometry &geo)
 }
 
 
-ViewportElement::ViewportElement(Viewport *viewport, int z)
-    : SceneElement(viewport ? *viewport : *shState->screen(), z),
+ViewportElement::ViewportElement(Viewport *viewport, int z, bool isSprite)
+    : SceneElement(viewport ? *viewport : *shState->screen(), z, isSprite),
       m_viewport(viewport)
 {}
 

src/viewport.h

@@ -65,7 +65,7 @@ private:
 class ViewportElement : public SceneElement
 {
 public:
-	ViewportElement(Viewport *viewport = 0, int z = 0);
+	ViewportElement(Viewport *viewport = 0, int z = 0, bool isSprite = false);
 	ViewportElement(Viewport *viewport, int z, unsigned int cStamp);
 
 	Viewport *getViewport() const;