Track retained layout validity explicitly

core/src/ui/active.rs

@@ -1,23 +1,27 @@
 use crate::{
-    LayerId, Len, MaskIdx, MoveIdx, PrimitiveHandle, Size, TextureHandle, UiRegion, WidgetId,
-    util::Vec2,
+    Holds, LayerId, Len, MaskIdx, MoveIdx, PrimitiveHandle, Size, TextureHandle, UiRegion, WidgetId,
 };
 
-/// important non rendering data for retained drawing
+/// What is kept of a widget its parent has asked about. `drawn` says whether
+/// it currently draws; one that does not is kept so that a change to it, or
+/// under it, still reaches whoever asked.
 #[derive(Debug)]
 pub struct ActiveData {
     pub id: WidgetId,
     pub region: UiRegion,
-    /// What the widget said it used of `region`, the last time it drew.
+    /// The box its parent first asked about it in, as a part of the box the
+    /// parent was itself asked in. Any later box it was given was decided
+    /// knowing its answer, so this is where a question about it is asked
+    /// again -- and it is kept relative so that it follows the parent's.
+    pub offer: UiRegion,
+    /// What it answered there: the size and what that held for.
+    pub answer: (Size, [Holds; 2]),
+    /// What the widget said it used of its box, the last time it drew.
     pub size: Size,
-    /// The pixel size of the box it drew against. `region` alone cannot say:
-    /// it is a fraction of a slot's box, and the same fraction of a box that
-    /// has since changed is a different number of pixels.
-    pub px: Vec2,
-    /// The pixel size of the box its parent first asked about it in, before
-    /// knowing what it came to. `px` may be a box derived from that answer,
-    /// and a size measured there is only the same answer asked again.
-    pub offered_px: Vec2,
+    /// The pixel lengths of its box, per axis, that its drawing and `size`
+    /// hold for.
+    pub holds: [Holds; 2],
+    pub drawn: bool,
     pub parent: Option<WidgetId>,
     /// How far down the tree it was drawn, the root being 1. Carried down a
     /// draw rather than worked out by walking up, so it is right for every
@@ -28,14 +32,6 @@ pub struct ActiveData {
     pub children: Vec<WidgetId>,
     /// The children whose size this widget read while drawing.
     pub size_deps: Vec<WidgetId>,
-    /// Offered pixel axes which flowed into this widget's reported size,
-    /// directly or through a child size it read.
-    pub size_box_inputs: [bool; 2],
-    /// Output axes read while producing `size`, distinct from the widget's
-    /// own box when that box has a fixed pixel length.
-    pub size_output_inputs: [bool; 2],
-    /// The output dimensions against which those dependencies were observed.
-    pub output_px: Vec2,
     /// The slot its primitives are positioned through: its own if its parent
     /// placed it, otherwise the nearest ancestor that has one.
     pub move_idx: MoveIdx,
@@ -48,3 +44,10 @@ pub struct ActiveData {
     pub mask: MaskIdx,
     pub layer: LayerId,
 }
+
+impl ActiveData {
+    /// Whether its drawing and size hold for a box of these pixel lengths.
+    pub fn holds_at(&self, px: crate::util::Vec2) -> bool {
+        self.holds[0].contains(px.x) && self.holds[1].contains(px.y)
+    }
+}