Fix ParallaxLayer / make mirroring use repeating

doc/classes/RenderingServer.xml

@@ -944,7 +944,8 @@
 			<param index="1" name="item" type="RID" />
 			<param index="2" name="mirroring" type="Vector2" />
 			<description>
-				A copy of the canvas item will be drawn with a local offset of the mirroring [Vector2].
+				A copy of the canvas item will be drawn with a local offset of the [param mirroring].
+				[b]Note:[/b] It is equivalent to calling [method canvas_set_item_repeat] like [code]canvas_set_item_repeat(item, mirroring, 1)[/code], with an additional check ensuring [param canvas] is a parent of [param item].
 			</description>
 		</method>
 		<method name="canvas_set_item_repeat">

servers/rendering/renderer_canvas_cull.cpp

@@ -51,7 +51,7 @@ void RendererCanvasCull::_render_canvas_item_tree(RID p_to_render_target, Canvas
 	memset(z_last_list, 0, z_range * sizeof(RendererCanvasRender::Item *));
 
 	for (int i = 0; i < p_child_item_count; i++) {
-		_cull_canvas_item(p_child_items[i].item, p_transform, p_clip_rect, Color(1, 1, 1, 1), 0, z_list, z_last_list, nullptr, nullptr, true, p_canvas_cull_mask, p_child_items[i].mirror, 1, nullptr);
+		_cull_canvas_item(p_child_items[i].item, p_transform, p_clip_rect, Color(1, 1, 1, 1), 0, z_list, z_last_list, nullptr, nullptr, true, p_canvas_cull_mask, Point2(), 1, nullptr);
 	}
 
 	RendererCanvasRender::Item *list = nullptr;
@@ -453,7 +453,12 @@ void RendererCanvasCull::canvas_set_item_mirroring(RID p_canvas, RID p_item, con
 
 	int idx = canvas->find_item(canvas_item);
 	ERR_FAIL_COND(idx == -1);
-	canvas->child_items.write[idx].mirror = p_mirroring;
+
+	bool is_repeat_source = (p_mirroring.x || p_mirroring.y);
+	canvas_item->repeat_source = is_repeat_source;
+	canvas_item->repeat_source_item = is_repeat_source ? canvas_item : nullptr;
+	canvas_item->repeat_size = p_mirroring;
+	canvas_item->repeat_times = 1;
 }
 
 void RendererCanvasCull::canvas_set_item_repeat(RID p_item, const Point2 &p_repeat_size, int p_repeat_times) {

servers/rendering/renderer_canvas_cull.h

@@ -126,7 +126,6 @@ class RendererCanvasCull {
 	struct Canvas : public RendererViewport::CanvasBase {
 		HashSet<RID> viewports;
 		struct ChildItem {
-			Point2 mirror;
 			Item *item = nullptr;
 			bool operator<(const ChildItem &p_item) const {
 				return item->index < p_item.item->index;