fix(core/ui/rust): painting of overlapping Maybe<T> components

[no changelog]

core/embed/rust/src/ui/component/base.rs

@@ -4,7 +4,11 @@ use heapless::Vec;
 
 use crate::{
     time::Duration,
-    ui::{component::Map, geometry::Rect},
+    ui::{
+        component::{maybe::PaintOverlapping, Map},
+        display::Color,
+        geometry::Rect,
+    },
 };
 
 #[cfg(feature = "buttons")]
@@ -136,6 +140,22 @@ where
     }
 }
 
+impl<T> PaintOverlapping for Child<T>
+where
+    T: PaintOverlapping,
+{
+    fn cleared_area(&self) -> Option<(Rect, Color)> {
+        self.component.cleared_area()
+    }
+
+    fn paint_overlapping(&mut self) {
+        if self.marked_for_paint {
+            self.marked_for_paint = false;
+            self.component.paint_overlapping()
+        }
+    }
+}
+
 #[cfg(feature = "ui_debug")]
 impl<T> crate::trace::Trace for Child<T>
 where
@@ -167,6 +187,11 @@ where
         self.0.paint();
         self.1.paint();
     }
+
+    fn bounds(&self, sink: &mut dyn FnMut(Rect)) {
+        self.0.bounds(sink);
+        self.1.bounds(sink);
+    }
 }
 
 #[cfg(feature = "ui_debug")]

core/embed/rust/src/ui/component/maybe.rs

@@ -1,6 +1,6 @@
 use crate::ui::{
     component::{Component, ComponentExt, Event, EventCtx, Pad},
-    display::Color,
+    display::{self, Color},
     geometry::Rect,
 };
 
@@ -98,3 +98,48 @@ where
         self.inner.bounds(sink);
     }
 }
+
+pub trait PaintOverlapping {
+    /// Return area that would be cleared during regular paint, along with
+    /// background color, or None if clearing isn't requested.
+    fn cleared_area(&self) -> Option<(Rect, Color)>;
+
+    /// Paint the component but do not clear background beforehand.
+    fn paint_overlapping(&mut self);
+}
+
+impl<T> PaintOverlapping for Maybe<T>
+where
+    T: Component,
+{
+    fn cleared_area(&self) -> Option<(Rect, Color)> {
+        self.pad.will_paint()
+    }
+
+    fn paint_overlapping(&mut self) {
+        self.pad.cancel_clear();
+        self.paint()
+    }
+}
+
+/// Paint multiple Maybe<T> components, correctly handling clearing of
+/// background in the case the areas overlap, i.e. clear the combined area first
+/// and then paint over it.
+pub fn paint_overlapping(components: &mut [&mut dyn PaintOverlapping]) {
+    let mut area = Rect::zero();
+    let mut color = Color::rgb(0, 0, 0);
+    for component in components.iter() {
+        if let Some((clear_area, clear_color)) = component.cleared_area() {
+            area = area.union(clear_area);
+            color = clear_color;
+        }
+    }
+
+    if area != Rect::zero() {
+        display::rect_fill(area, color)
+    }
+
+    for component in components.iter_mut() {
+        component.paint_overlapping()
+    }
+}

core/embed/rust/src/ui/component/pad.rs

@@ -26,6 +26,18 @@ impl Pad {
         self.clear = true;
     }
 
+    pub fn cancel_clear(&mut self) {
+        self.clear = false;
+    }
+
+    pub fn will_paint(&self) -> Option<(Rect, Color)> {
+        if self.clear {
+            Some((self.area, self.color))
+        } else {
+            None
+        }
+    }
+
     pub fn paint(&mut self) {
         if self.clear {
             self.clear = false;

core/embed/rust/src/ui/model_tt/component/keyboard/mnemonic.rs

@@ -1,7 +1,7 @@
 use core::ops::Deref;
 
 use crate::ui::{
-    component::{Child, Component, Event, EventCtx, Label, Maybe},
+    component::{maybe::paint_overlapping, Child, Component, Event, EventCtx, Label, Maybe},
     geometry::{Alignment, Grid, Rect},
     model_tt::{
         component::{Button, ButtonMsg},
@@ -139,9 +139,7 @@ where
     }
 
     fn paint(&mut self) {
-        self.prompt.paint();
+        paint_overlapping(&mut [&mut self.prompt, &mut self.input, &mut self.back]);
-        self.input.paint();
-        self.back.paint();
         for btn in &mut self.keys {
             btn.paint();
         }