Add new `CanvasItem` snapping option

doc/classes/CanvasItem.xml

@@ -604,6 +604,9 @@
 		<member name="show_behind_parent" type="bool" setter="set_draw_behind_parent" getter="is_draw_behind_parent_enabled" default="false">
 			If [code]true[/code], the object draws behind its parent.
 		</member>
+		<member name="snap_to_pixel" type="int" setter="set_snap_to_pixel" getter="get_snap_to_pixel" enum="CanvasItem.SnapToPixel" default="0">
+			The snapping to pixel mode to use on this [CanvasItem].
+		</member>
 		<member name="texture_filter" type="int" setter="set_texture_filter" getter="get_texture_filter" enum="CanvasItem.TextureFilter" default="0">
 			The texture filtering mode to use on this [CanvasItem].
 		</member>
@@ -736,5 +739,17 @@
 		<constant name="CLIP_CHILDREN_MAX" value="3" enum="ClipChildrenMode">
 			Represents the size of the [enum ClipChildrenMode] enum.
 		</constant>
+		<constant name="SNAP_TO_PIXEL_PARENT_NODE" value="0" enum="SnapToPixel">
+			The [CanvasItem] will inherit the snapping mode from its parent.
+		</constant>
+		<constant name="SNAP_TO_PIXEL_DISABLED" value="1" enum="SnapToPixel">
+			The [CanvasItem] will not snap.
+		</constant>
+		<constant name="SNAP_TO_PIXEL_ENABLED" value="2" enum="SnapToPixel">
+			The [CanvasItem] will snap.
+		</constant>
+		<constant name="SNAP_TO_PIXEL_MAX" value="3" enum="SnapToPixel">
+			Represents the size of the [enum SnapToPixel] enum.
+		</constant>
 	</constants>
 </class>

scene/main/canvas_item.cpp

@@ -328,6 +328,7 @@ void CanvasItem::_notification(int p_what) {
 
 			_update_texture_filter_changed(false);
 			_update_texture_repeat_changed(false);
+			_update_snap_to_pixel_changed(false);
 
 			if (!block_transform_notify && !xform_change.in_list()) {
 				get_tree()->xform_change_list.add(&xform_change);
@@ -1270,6 +1271,9 @@ void CanvasItem::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_clip_children_mode", "mode"), &CanvasItem::set_clip_children_mode);
 	ClassDB::bind_method(D_METHOD("get_clip_children_mode"), &CanvasItem::get_clip_children_mode);
 
+	ClassDB::bind_method(D_METHOD("set_snap_to_pixel", "snap"), &CanvasItem::set_snap_to_pixel);
+	ClassDB::bind_method(D_METHOD("get_snap_to_pixel"), &CanvasItem::get_snap_to_pixel);
+
 	GDVIRTUAL_BIND(_draw);
 
 	ADD_GROUP("Visibility", "");
@@ -1294,6 +1298,10 @@ void CanvasItem::_bind_methods() {
 	ADD_GROUP("Material", "");
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "material", PROPERTY_HINT_RESOURCE_TYPE, "CanvasItemMaterial,ShaderMaterial"), "set_material", "get_material");
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "use_parent_material"), "set_use_parent_material", "get_use_parent_material");
+
+	ADD_GROUP("Snap", "");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "snap_to_pixel", PROPERTY_HINT_ENUM, "Inherit,Disabled,Enabled"), "set_snap_to_pixel", "get_snap_to_pixel");
+
 	// ADD_PROPERTY(PropertyInfo(Variant::BOOL,"transform/notify"),"set_transform_notify","is_transform_notify_enabled");
 
 	ADD_SIGNAL(MethodInfo("draw"));
@@ -1328,6 +1336,11 @@ void CanvasItem::_bind_methods() {
 	BIND_ENUM_CONSTANT(CLIP_CHILDREN_ONLY);
 	BIND_ENUM_CONSTANT(CLIP_CHILDREN_AND_DRAW);
 	BIND_ENUM_CONSTANT(CLIP_CHILDREN_MAX);
+
+	BIND_ENUM_CONSTANT(SNAP_TO_PIXEL_PARENT_NODE);
+	BIND_ENUM_CONSTANT(SNAP_TO_PIXEL_DISABLED);
+	BIND_ENUM_CONSTANT(SNAP_TO_PIXEL_ENABLED);
+	BIND_ENUM_CONSTANT(SNAP_TO_PIXEL_MAX);
 }
 
 Transform2D CanvasItem::get_canvas_transform() const {
@@ -1565,6 +1578,62 @@ CanvasItem::TextureRepeat CanvasItem::get_texture_repeat_in_tree() const {
 	return (TextureRepeat)texture_repeat_cache;
 }
 
+void CanvasItem::_refresh_snap_to_pixel_cache() const {
+	if (!is_inside_tree()) {
+		return;
+	}
+
+	if (snap_to_pixel == SNAP_TO_PIXEL_PARENT_NODE) {
+		CanvasItem *parent_item = get_parent_item();
+		if (parent_item) {
+			snap_to_pixel_cache = parent_item->snap_to_pixel_cache;
+		} else {
+			snap_to_pixel_cache = RS::CANVAS_ITEM_SNAP_TO_PIXEL_DEFAULT;
+		}
+	} else {
+		snap_to_pixel_cache = RS::CanvasItemSnapToPixel(snap_to_pixel);
+	}
+}
+
+void CanvasItem::_update_self_snap_to_pixel(RS::CanvasItemSnapToPixel p_snap) {
+	RS::get_singleton()->canvas_item_set_snap_to_pixel(get_canvas_item(), p_snap);
+	queue_redraw();
+}
+
+void CanvasItem::_update_snap_to_pixel_changed(bool p_propagate) {
+	if (!is_inside_tree()) {
+		return;
+	}
+	_refresh_snap_to_pixel_cache();
+	_update_self_snap_to_pixel(snap_to_pixel_cache);
+
+	if (p_propagate) {
+		for (CanvasItem *E : children_items) {
+			if (!E->top_level && E->snap_to_pixel == SNAP_TO_PIXEL_PARENT_NODE) {
+				E->_update_snap_to_pixel_changed(true);
+			}
+		}
+	}
+}
+
+void CanvasItem::set_snap_to_pixel(SnapToPixel p_snap_to_pixel) {
+	ERR_THREAD_GUARD;
+	ERR_FAIL_COND(p_snap_to_pixel >= SNAP_TO_PIXEL_MAX);
+
+	if (snap_to_pixel == p_snap_to_pixel) {
+		return;
+	}
+
+	snap_to_pixel = p_snap_to_pixel;
+	_update_snap_to_pixel_changed(true);
+	notify_property_list_changed();
+}
+
+CanvasItem::SnapToPixel CanvasItem::get_snap_to_pixel() const {
+	ERR_READ_THREAD_GUARD_V(SNAP_TO_PIXEL_DISABLED);
+	return snap_to_pixel;
+}
+
 CanvasItem::CanvasItem() :
 		xform_change(this) {
 	canvas_item = RenderingServer::get_singleton()->canvas_item_create();

scene/main/canvas_item.h

@@ -73,6 +73,13 @@ public:
 		CLIP_CHILDREN_MAX,
 	};
 
+	enum SnapToPixel {
+		SNAP_TO_PIXEL_PARENT_NODE,
+		SNAP_TO_PIXEL_DISABLED,
+		SNAP_TO_PIXEL_ENABLED,
+		SNAP_TO_PIXEL_MAX,
+	};
+
 private:
 	mutable SelfList<Node>
 			xform_change;
@@ -112,8 +119,10 @@ private:
 
 	mutable RS::CanvasItemTextureFilter texture_filter_cache = RS::CANVAS_ITEM_TEXTURE_FILTER_LINEAR;
 	mutable RS::CanvasItemTextureRepeat texture_repeat_cache = RS::CANVAS_ITEM_TEXTURE_REPEAT_DISABLED;
+	mutable RS::CanvasItemSnapToPixel snap_to_pixel_cache = RS::CANVAS_ITEM_SNAP_TO_PIXEL_DISABLED;
 	TextureFilter texture_filter = TEXTURE_FILTER_PARENT_NODE;
 	TextureRepeat texture_repeat = TEXTURE_REPEAT_PARENT_NODE;
+	SnapToPixel snap_to_pixel = SNAP_TO_PIXEL_PARENT_NODE;
 
 	Ref<Material> material;
 
@@ -148,12 +157,15 @@ private:
 	void _update_texture_repeat_changed(bool p_propagate);
 	void _refresh_texture_filter_cache() const;
 	void _update_texture_filter_changed(bool p_propagate);
+	void _refresh_snap_to_pixel_cache() const;
+	void _update_snap_to_pixel_changed(bool p_propagate);
 
 	void _notify_transform_deferred();
 
 protected:
 	virtual void _update_self_texture_repeat(RS::CanvasItemTextureRepeat p_texture_repeat);
 	virtual void _update_self_texture_filter(RS::CanvasItemTextureFilter p_texture_filter);
+	virtual void _update_self_snap_to_pixel(RS::CanvasItemSnapToPixel p_snap);
 
 	_FORCE_INLINE_ void _notify_transform() {
 		_notify_transform(this);
@@ -380,6 +392,9 @@ public:
 	int get_canvas_layer() const;
 	CanvasLayer *get_canvas_layer_node() const;
 
+	virtual void set_snap_to_pixel(SnapToPixel p_snap_to_pixel);
+	SnapToPixel get_snap_to_pixel() const;
+
 	CanvasItem();
 	~CanvasItem();
 };
@@ -387,6 +402,7 @@ public:
 VARIANT_ENUM_CAST(CanvasItem::TextureFilter)
 VARIANT_ENUM_CAST(CanvasItem::TextureRepeat)
 VARIANT_ENUM_CAST(CanvasItem::ClipChildrenMode)
+VARIANT_ENUM_CAST(CanvasItem::SnapToPixel)
 
 class CanvasTexture : public Texture2D {
 	GDCLASS(CanvasTexture, Texture2D);

servers/rendering/renderer_canvas_cull.cpp

@@ -283,7 +283,7 @@ void RendererCanvasCull::_cull_canvas_item(Item *p_canvas_item, const Transform2
 		rect.position -= repeat_size / scale * (repeat_times / 2);
 	}
 
-	if (snapping_2d_transforms_to_pixel) {
+	if ((p_canvas_item->snap_to_pixel == RS::CANVAS_ITEM_SNAP_TO_PIXEL_DEFAULT && snapping_2d_transforms_to_pixel) || (p_canvas_item->snap_to_pixel == RS::CANVAS_ITEM_SNAP_TO_PIXEL_ENABLED)) {
 		final_xform.columns[2] = (final_xform.columns[2] + Point2(0.5, 0.5)).floor();
 		parent_xform.columns[2] = (parent_xform.columns[2] + Point2(0.5, 0.5)).floor();
 	}
@@ -2311,6 +2311,12 @@ void RendererCanvasCull::canvas_item_set_default_texture_repeat(RID p_item, RS::
 	ci->texture_repeat = p_repeat;
 }
 
+void RendererCanvasCull::canvas_item_set_snap_to_pixel(RID p_item, RS::CanvasItemSnapToPixel p_snap) {
+	Item *ci = canvas_item_owner.get_or_null(p_item);
+	ERR_FAIL_NULL(ci);
+	ci->snap_to_pixel = p_snap;
+}
+
 void RendererCanvasCull::update_visibility_notifiers() {
 	SelfList<Item::VisibilityNotifierData> *E = visibility_notifier_list.first();
 	while (E) {

servers/rendering/renderer_canvas_cull.h

@@ -339,6 +339,7 @@ public:
 
 	void canvas_item_set_default_texture_filter(RID p_item, RS::CanvasItemTextureFilter p_filter);
 	void canvas_item_set_default_texture_repeat(RID p_item, RS::CanvasItemTextureRepeat p_repeat);
+	void canvas_item_set_snap_to_pixel(RID p_item, RS::CanvasItemSnapToPixel p_snap);
 
 	void update_visibility_notifiers();
 

servers/rendering/renderer_canvas_render.h

@@ -458,6 +458,7 @@ public:
 
 		RS::CanvasItemTextureFilter texture_filter;
 		RS::CanvasItemTextureRepeat texture_repeat;
+		RS::CanvasItemSnapToPixel snap_to_pixel;
 
 		Item() {
 			commands = nullptr;

servers/rendering/rendering_server_default.h

@@ -883,6 +883,8 @@ public:
 
 	FUNC2(canvas_item_set_draw_behind_parent, RID, bool)
 
+	FUNC2(canvas_item_set_snap_to_pixel, RID, CanvasItemSnapToPixel)
+
 	FUNC6(canvas_item_add_line, RID, const Point2 &, const Point2 &, const Color &, float, bool)
 	FUNC5(canvas_item_add_polyline, RID, const Vector<Point2> &, const Vector<Color> &, float, bool)
 	FUNC5(canvas_item_add_multiline, RID, const Vector<Point2> &, const Vector<Color> &, float, bool)

servers/rendering_server.h

@@ -860,6 +860,13 @@ public:
 		CANVAS_ITEM_TEXTURE_REPEAT_MAX,
 	};
 
+	enum CanvasItemSnapToPixel {
+		CANVAS_ITEM_SNAP_TO_PIXEL_DEFAULT,
+		CANVAS_ITEM_SNAP_TO_PIXEL_DISABLED,
+		CANVAS_ITEM_SNAP_TO_PIXEL_ENABLED,
+		CANVAS_ITEM_SNAP_TO_PIXEL_MAX,
+	};
+
 	virtual RID viewport_create() = 0;
 
 	enum ViewportScaling3DMode {
@@ -1451,6 +1458,8 @@ public:
 
 	virtual void canvas_item_set_draw_behind_parent(RID p_item, bool p_enable) = 0;
 
+	virtual void canvas_item_set_snap_to_pixel(RID p_item, CanvasItemSnapToPixel p_snap) = 0;
+
 	enum NinePatchAxisMode {
 		NINE_PATCH_STRETCH,
 		NINE_PATCH_TILE,