partial_renderer: Fix visible:true-expr item being always dirty

The issue is that an element with visibility creates a `Clip` item as a
parent with a size of 0x0, and the clip property.
When the visible property becomes true, the tracker for this Clip item
will be dirty and will force everything inside to be re-drawn.
But since the `Clip` itself is no longer clipping and its size is 0, the
special code in `iterm_rendering::render_item_children` that handle the
clip specially will not kick in, and the `Clip` itself will not go
through the partial renderer, so its tracker will stay dirty forever

Author: ogoffart

api/rs/slint/tests/partial_renderer.rs

@@ -244,6 +244,7 @@ fn visibility() {
     slint::slint! {
         export component Ui inherits Window {
             in property <bool> c : true;
+            in property <bool> another: false;
             background: black;
             Rectangle {
                 x: 10phx;
@@ -255,6 +256,13 @@ fn visibility() {
                     height: 13phx;
                     background: red;
                     visible: c;
+                    Rectangle {
+                        x: 3phx;
+                        y: 3phx;
+                        width: 3phx;
+                        height: 3phx;
+                        background: another ? blue: green;
+                    }
                 }
                 Rectangle {
                     x: 50phx;
@@ -263,6 +271,13 @@ fn visibility() {
                     height: 17phx;
                     background: gray;
                     visible: !c;
+                    Rectangle {
+                        x: 3phx;
+                        y: 3phx;
+                        width: 3phx;
+                        height: 3phx;
+                        background: another ? blue: green;
+                    }
                 }
             }
         }
@@ -277,16 +292,28 @@ fn visibility() {
         do_test_render_region(renderer, 0, 0, 180, 260);
     }));
     assert!(!window.draw_if_needed(|_| { unreachable!() }));
+
     ui.set_c(false);
     assert!(window.draw_if_needed(|renderer| {
         do_test_render_region(renderer, 10 + 5, 19 + 8, 10 + 50 + 15, 19 + 80 + 13);
     }));
     assert!(!window.draw_if_needed(|_| { unreachable!() }));
+    ui.set_another(true);
+    assert!(window.draw_if_needed(|renderer| {
+        do_test_render_region(renderer, 10 + 50 + 3, 19 + 8 + 3, 10 + 50 + 6, 19 + 8 + 6);
+    }));
+    assert!(!window.draw_if_needed(|_| { unreachable!() }));
+
     ui.set_c(true);
     assert!(window.draw_if_needed(|renderer| {
         do_test_render_region(renderer, 10 + 5, 19 + 8, 10 + 50 + 15, 19 + 80 + 13);
     }));
     assert!(!window.draw_if_needed(|_| { unreachable!() }));
+    ui.set_another(false);
+    assert!(window.draw_if_needed(|renderer| {
+        do_test_render_region(renderer, 10 + 5 + 3, 19 + 80 + 3, 10 + 5 + 6, 19 + 80 + 6);
+    }));
+    assert!(!window.draw_if_needed(|_| { unreachable!() }));
 }
 
 #[test]

internal/core/partial_renderer.rs

@@ -432,6 +432,11 @@ impl<'a, T: ItemRenderer + ItemRendererFeatures> PartialRenderer<'a, T> {
                             // When the opacity or the clip change, this will impact all the children, including
                             // the ones outside the element, regardless if they are themselves dirty or not.
                             new_state.must_refresh_children |= rendering_dirty || geometry_changed;
+
+                            if rendering_dirty {
+                                // Destroy the tracker as we we might not re-render this clipped item but it would stay dirty
+                                *tracker = None;
+                            }
                         }
 
                         if geometry_changed {