Separate measured-answer dependencies from retained drawing validity

src/widget/position/pad.rs

@@ -13,7 +13,7 @@ impl Widget for Pad {
         // it; where the box is bigger -- a share of a row, a rule over this
         // widget -- the slack is the inner's to sit in, and forcing the near
         // edge pinned it to a corner it had not asked for.
-        let inside = DrawRegion::Extent(self.padding.region());
+        let inside = self.padding.region_of(painter.placement());
         let inner = painter.widget_within(&self.inner, inside).size();
         Size {
             x: LayoutLen {

src/widget/position/stack.rs

@@ -13,6 +13,7 @@ impl Widget for Stack {
             StackSize::Default => None,
             StackSize::Child(i) => Some(i),
         };
+        let placement = painter.placement();
         // Whichever child sizes the stack keeps the stack's whole region as
         // its own -- the stack is the length that child asked for, so taking
         // the fraction of the stack's box again would take it twice -- and is
@@ -23,7 +24,13 @@ impl Widget for Stack {
             // drawing belongs to the layer it was made on.
             Some((i, child)) => {
                 painter.child_layer_at(i);
-                painter.widget(child).size()
+                painter
+                    .widget_at(
+                        child,
+                        UiRegion::FULL,
+                        [Some(placement.x), Some(placement.y)],
+                    )
+                    .size()
             }
             None => Size::LEFTOVER,
         };
@@ -35,7 +42,7 @@ impl Widget for Stack {
             // Every other child has the stack's own box for its region, since
             // the stack is what contains it, and where it sits in one bigger
             // than itself is its own business.
-            painter.widget_within(child, DrawRegion::Extent(UiRegion::FULL));
+            painter.widget_within(child, placement);
         }
         size
     }