Fix UV editor not showing polygon correctly

Fix polygon not showing correctly if UVs have been moved around. Show the actual contents of the polygon instead.

(cherry picked from commit a45db4d6168d9b7074b1ff322ce2d04129f8c761)

editor/plugins/polygon_2d_editor_plugin.cpp

@@ -456,6 +456,7 @@ void Polygon2DEditor::_uv_mode(int p_mode) {
 	for (int i = 0; i < UV_MODE_MAX; i++) {
 		uv_button[i]->set_pressed(p_mode == i);
 	}
+	uv_edit_draw->queue_redraw();
 }
 
 void Polygon2DEditor::_uv_input(const Ref<InputEvent> &p_input) {
@@ -980,12 +981,36 @@ void Polygon2DEditor::_uv_draw() {
 	mtx.columns[2] = -uv_draw_ofs;
 	mtx.scale_basis(Vector2(uv_draw_zoom, uv_draw_zoom));
 
-	Transform2D texture_transform = Transform2D(node->get_texture_rotation(), node->get_texture_offset());
-	texture_transform.scale(node->get_texture_scale());
-	texture_transform.affine_invert();
-	RS::get_singleton()->canvas_item_add_set_transform(uv_edit_draw->get_canvas_item(), mtx * texture_transform);
-	uv_edit_draw->draw_texture(base_tex, Point2());
-	RS::get_singleton()->canvas_item_add_set_transform(uv_edit_draw->get_canvas_item(), Transform2D());
+	// Draw texture as a background if editing uvs or no uv mapping exist.
+	if (uv_edit_mode[0]->is_pressed() || uv_mode == UV_MODE_CREATE || node->get_polygon().is_empty() || node->get_uv().size() != node->get_polygon().size()) {
+		Transform2D texture_transform = Transform2D(node->get_texture_rotation(), node->get_texture_offset());
+		texture_transform.scale(node->get_texture_scale());
+		texture_transform.affine_invert();
+		RS::get_singleton()->canvas_item_add_set_transform(uv_edit_draw->get_canvas_item(), mtx * texture_transform);
+		uv_edit_draw->draw_texture(base_tex, Point2());
+		RS::get_singleton()->canvas_item_add_set_transform(uv_edit_draw->get_canvas_item(), Transform2D());
+		preview_polygon->hide();
+	} else {
+		preview_polygon->set_transform(mtx);
+		// Keep in sync with newly added Polygon2D properties (when relevant).
+		preview_polygon->set_texture(node->get_texture());
+		preview_polygon->set_texture_offset(node->get_texture_offset());
+		preview_polygon->set_texture_rotation(node->get_texture_rotation());
+		preview_polygon->set_texture_scale(node->get_texture_scale());
+		preview_polygon->set_texture_filter(node->get_texture_filter_in_tree());
+		preview_polygon->set_texture_repeat(node->get_texture_repeat_in_tree());
+		preview_polygon->set_polygon(node->get_polygon());
+		preview_polygon->set_uv(node->get_uv());
+		preview_polygon->set_invert(node->get_invert());
+		preview_polygon->set_invert_border(node->get_invert_border());
+		preview_polygon->set_internal_vertex_count(node->get_internal_vertex_count());
+		if (uv_mode == UV_MODE_ADD_POLYGON) {
+			preview_polygon->set_polygons(Array());
+		} else {
+			preview_polygon->set_polygons(node->get_polygons());
+		}
+		preview_polygon->show();
+	}
 
 	if (snap_show_grid) {
 		Color grid_color = Color(1.0, 1.0, 1.0, 0.15);
@@ -1350,10 +1375,19 @@ Polygon2DEditor::Polygon2DEditor() {
 	HSplitContainer *uv_main_hsc = memnew(HSplitContainer);
 	uv_main_vb->add_child(uv_main_hsc);
 	uv_main_hsc->set_v_size_flags(SIZE_EXPAND_FILL);
-	uv_edit_draw = memnew(Panel);
-	uv_main_hsc->add_child(uv_edit_draw);
-	uv_edit_draw->set_h_size_flags(SIZE_EXPAND_FILL);
-	uv_edit_draw->set_custom_minimum_size(Size2(200, 200) * EDSCALE);
+
+	uv_edit_background = memnew(Panel);
+	uv_main_hsc->add_child(uv_edit_background);
+	uv_edit_background->set_h_size_flags(SIZE_EXPAND_FILL);
+	uv_edit_background->set_custom_minimum_size(Size2(200, 200) * EDSCALE);
+	uv_edit_background->set_clip_contents(true);
+
+	preview_polygon = memnew(Polygon2D);
+	uv_edit_background->add_child(preview_polygon);
+
+	uv_edit_draw = memnew(Control);
+	uv_edit_background->add_child(uv_edit_draw);
+	uv_edit_draw->set_anchors_and_offsets_preset(Control::PRESET_FULL_RECT);
 
 	Control *space = memnew(Control);
 	uv_mode_hb->add_child(space);
@@ -1494,8 +1528,6 @@ Polygon2DEditor::Polygon2DEditor() {
 
 	error = memnew(AcceptDialog);
 	add_child(error);
-
-	uv_edit_draw->set_clip_contents(true);
 }
 
 Polygon2DEditorPlugin::Polygon2DEditorPlugin() :

editor/plugins/polygon_2d_editor_plugin.h

@@ -82,7 +82,9 @@ class Polygon2DEditor : public AbstractPolygon2DEditor {
 	Button *uv_button[UV_MODE_MAX];
 	Button *b_snap_enable = nullptr;
 	Button *b_snap_grid = nullptr;
-	Panel *uv_edit_draw = nullptr;
+	Panel *uv_edit_background = nullptr;
+	Polygon2D *preview_polygon = nullptr;
+	Control *uv_edit_draw = nullptr;
 	HSlider *uv_zoom = nullptr;
 	SpinBox *uv_zoom_value = nullptr;
 	HScrollBar *uv_hscroll = nullptr;