ui: the HIGHLIGHT draw layer is the highlight state, and starts off

A texture an addon made with `CreateTexture(nil, "HIGHLIGHT")` drew all the
time. Only the region `SetHighlightTexture` installs was hover-gated, through
`ButtonState::region_visible`; anything else an addon left in layer 4 was an
ordinary region that nothing ever hid.

In the reference that layer is the highlight *state*, not a place to keep
highlight art, and four things move it:

  OnEnter  0x76b6a0  test [frame+0xf8]; push 4; call 0x76a710  EnableDrawLayer
  OnLeave  0x76b6f0  test [frame+0xf8]; push 4; call 0x76a730  DisableDrawLayer
  Lock     0x76c2e0  writes [frame+0xf8], then enables; on an unlock disables
                     only when this frame is not the mouse focus ([root+0x7c])
  Disable  0x7791bb  disables it outright

`0x77983c` settles what the layer means: a Button picks its label's font
instance by reading that layer's own enabled flag at [frame+0x1a8], which is
[frame+0x198] + 4*4, and takes the highlight font object at +0x3b8 when it is
set. So the layer starts off, and every path that can highlight a frame moves
it -- taking whatever the addon put there along.

What this was costing: hand-built column headers and list rows, which are
everywhere. The <Below Average> guild market's Browse page puts
UI-Character-Tab-Highlight in that layer on each of its nine sort headers, so
every header wore a permanent blue glow bar, and its Statistics page showed all
six filter buttons lit at once instead of the two that were selected.

The nameplate glow lives in layer 4 too, and its hover feed drove only the
region's shown flag. Its own OnEnter override chains back into the base notify
(0x7cb8a5 -> 0x76b6a0), so it now moves the layer with it; addons still read
mouseover from glow:IsShown().

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SgstFWtn1RxEJ5kVrpgYwn

crates/benilla-ui/src/script/button.rs

@@ -13,7 +13,7 @@ use crate::justify::Justify;
 use crate::order::DrawLayer;
 use crate::widget::{
     ButtonFont, ButtonState, ButtonVisualState, FrameHandle, FrameKind, KindState, RegionHandle,
-    RegionKind,
+    RegionKind, HIGHLIGHT_OFF,
 };
 
 pub(in crate::script) const REG_BUTTON_METHODS: &str = "__benilla_button_methods";
@@ -192,27 +192,70 @@ fn with_button<T>(
     }
 }
 
+/// Draw layer 4, HIGHLIGHT, as a whole -- not only the region `SetHighlightTexture` made.
+///
+/// The reference keeps the highlight *state* in that layer's own enabled flag
+/// (`[frame+0x198] + 4*4`), which is why `0x77983c` reads it to decide whether a Button's label
+/// takes the highlight font object. Everything that can highlight a frame therefore moves the
+/// layer, and anything an addon left in it moves with them. See [`HIGHLIGHT_OFF`].
+pub(super) fn set_highlight_layer(model: &mut Model, h: FrameHandle, on: bool) {
+    if let Some(frame) = model.arena.frame_mut(h) {
+        if on {
+            frame.disabled_layers &= !HIGHLIGHT_OFF;
+        } else {
+            frame.disabled_layers |= HIGHLIGHT_OFF;
+        }
+    }
+}
+
+/// Whether `LockHighlight()` is holding the layer on for `h`. Only a Button has the method, so
+/// anything else answers false.
+fn highlight_locked(model: &Model, h: FrameHandle) -> bool {
+    matches!(
+        model.arena.frame(h).map(|f| &f.kind_state),
+        Some(KindState::Button(bs)) if bs.locked_highlight
+    )
+}
+
+/// The highlight half of a hover edge: `OnEnter` (`0x76b6a0`) enables the layer and `OnLeave`
+/// (`0x76b6f0`) disables it, each after `test [frame+0xf8]` skips it while `LockHighlight` holds.
+/// A disabled Button reaches neither notify (`0x779490`/`0x7794e0` guard on `[+0x328]`), so the
+/// layer does not move there either -- and it is already off, from `Disable()`.
+pub(super) fn hover_highlight(model: &mut Model, h: Option<FrameHandle>, entering: bool) {
+    let Some(h) = h else { return };
+    if !hover_notify_runs(model, Some(h)) || highlight_locked(model, h) {
+        return;
+    }
+    set_highlight_layer(model, h, entering);
+}
+
 /// `Enable()`/`Disable()`. `Disable` (`0x77ffd0`) reaches `SetEnabled` (`0x779160`), which also
 /// turns draw layer 4, HIGHLIGHT, off (`0x7791bb`) in the array `DisableDrawLayer` writes, so every
-/// region in that layer goes dark, not only the HighlightTexture. `Enable()` here turns it back
-/// on; the reference restores it only on a hovered button, by re-running its `<OnEnter>`
-/// (`0x779183`), and never while `LockHighlight` holds (`[frame+0xf8]`).
+/// region in that layer goes dark, not only the HighlightTexture. `Enable()` restores it only on a
+/// hovered button, by re-running its `<OnEnter>` (`0x779183`), and never while `LockHighlight`
+/// holds (`[frame+0xf8]`) -- a button enabled under the cursor lights up, one enabled anywhere
+/// else does not.
 fn set_enabled(lua: &Lua, this: &Table, on: bool) -> mlua::Result<()> {
     let h = frame_handle_of(lua, this)?;
     let mut model = lua.app_data_mut::<Model>().expect("model app_data");
+    let hovered = model.mouseover == Some(h);
     let frame = model
         .arena
         .frame_mut(h)
         .ok_or_else(|| mlua::Error::runtime("stale frame handle"))?;
-    match &mut frame.kind_state {
-        KindState::Button(bs) => bs.set_enabled(on),
+    let locked = match &mut frame.kind_state {
+        KindState::Button(bs) => {
+            bs.set_enabled(on);
+            bs.locked_highlight
+        }
         _ => return Err(mlua::Error::runtime("not a Button")),
     };
-    let bit = 1u8 << DrawLayer::Highlight.index();
     if on {
-        frame.disabled_layers &= !bit;
+        if hovered || locked {
+            frame.disabled_layers &= !HIGHLIGHT_OFF;
+        }
     } else {
-        frame.disabled_layers |= bit;
+        frame.disabled_layers |= HIGHLIGHT_OFF;
     }
     Ok(())
 }
@@ -796,17 +839,30 @@ pub(super) fn install(lua: &Lua) -> mlua::Result<()> {
         )?,
     )?;
 
-    // LockHighlight (`0x782840`) and UnlockHighlight: the highlight shows regardless of hover.
+    // LockHighlight (`0x782840`) and UnlockHighlight (`0x782920`), both through `0x76c2e0`: the
+    // highlight shows regardless of hover. That function writes `[frame+0xf8]` and then moves draw
+    // layer 4 with it -- enabling it on a lock, and on an unlock disabling it *unless this frame is
+    // the mouse focus* (`cmp [root+0x7c], ecx`), so unlocking under the cursor leaves it lit.
     m.set(
         "LockHighlight",
         lua.create_function(|lua, this: Table| {
-            with_button(lua, &this, |bs| bs.locked_highlight = true)
+            let h = frame_handle_of(lua, &this)?;
+            with_button(lua, &this, |bs| bs.locked_highlight = true)?;
+            let mut model = lua.app_data_mut::<Model>().expect("model app_data");
+            set_highlight_layer(&mut model, h, true);
+            Ok(())
         })?,
     )?;
     m.set(
         "UnlockHighlight",
         lua.create_function(|lua, this: Table| {
-            with_button(lua, &this, |bs| bs.locked_highlight = false)
+            let h = frame_handle_of(lua, &this)?;
+            with_button(lua, &this, |bs| bs.locked_highlight = false)?;
+            let mut model = lua.app_data_mut::<Model>().expect("model app_data");
+            if model.mouseover != Some(h) {
+                set_highlight_layer(&mut model, h, false);
+            }
+            Ok(())
         })?,
     )?;
 

crates/benilla-ui/src/script/event.rs

@@ -138,6 +138,9 @@ pub(super) fn fire_visibility_changes(lua: &Lua, changed: Vec<FrameHandle>) {
         let notified = super::button::hover_notify_runs(&model, hidden_hover);
         if let Some(m) = hidden_hover {
             model.mouseover = None;
+            // The leave carries its half of the highlight with it: the layer must not stay enabled
+            // on a frame that is no longer under the cursor, or it comes back lit on the next show.
+            super::button::hover_highlight(&mut model, Some(m), false);
             if model.drag.as_ref().is_some_and(|d| d.source == m) {
                 model.drag = None;
             }

crates/benilla-ui/src/script/nameplate.rs

@@ -893,6 +893,11 @@ impl Plate {
             model.region_data.entry(name).or_default().vertex_color = Some(c);
             // The glow really shows, as addons read mouseover from it; it only paints nothing.
             model.region_data.entry(glow).or_default().hidden = !state.hovered;
+            // The glow lives in draw layer 4, HIGHLIGHT, which is off until something highlights
+            // the frame. The plate's own `OnEnter` override chains back into the base notify
+            // (`0x7cb8a5` -> `0x76b6a0`), so the hover that shows the region enables the layer
+            // under it; the region's shown flag alone would leave it dark.
+            super::button::set_highlight_layer(model, frame, state.hovered);
         }
 
         if last.as_ref().is_none_or(|l| {

crates/benilla-ui/src/script/pointer.rs

@@ -237,6 +237,10 @@ impl UiScript {
                 // is still the hover: the reference moves `[root+0x7c]` before either notify.
                 let old_id = old_id.filter(|_| button::hover_notify_runs(&model, old_handle));
                 let enter_id = new_id.filter(|_| button::hover_notify_runs(&model, new_handle));
+                // Both notifies move draw layer 4, HIGHLIGHT, before the Lua handler runs, so an
+                // `<OnEnter>` that reads the frame already sees the highlighted state.
+                button::hover_highlight(&mut model, old_handle, false);
+                button::hover_highlight(&mut model, new_handle, true);
                 (old_id, drag_start, enter_id, slider_change, color_change)
             }
         };

crates/benilla-ui/src/script/tests/button.rs

@@ -223,6 +223,164 @@ fn disabling_a_button_takes_its_whole_highlight_layer() {
     assert!(s.errors().is_empty(), "{:?}", s.errors());
 }
 
+/// Draw layer 4, HIGHLIGHT, is the highlight *state*, not a place for art that is always on: the
+/// base hover notifies toggle the whole layer (`0x76b6a0` enables, `0x76b6f0` disables), which is
+/// why a Button picks its highlight font by reading the layer's own flag (`0x77983c` tests
+/// `[frame+0x1a8]`). So it starts off, and a region an addon creates in it stays dark until the
+/// cursor arrives. Hand-built column headers and list rows all over the addon world depend on it:
+/// EGM's guild market puts `UI-Character-Tab-Highlight` there and never hides it itself.
+#[test]
+fn a_highlight_layer_region_is_dark_until_the_cursor_is_on_the_frame() {
+    let mut s = script();
+    s.set_screen_size(800.0, 600.0);
+    s.run(
+        r#"
+        local f = CreateFrame("Frame", "HiLayer")
+        f:SetPoint("BOTTOMLEFT", 0, 0); f:SetWidth(100); f:SetHeight(100)
+        f:EnableMouse(true)
+        local base = f:CreateTexture(nil, "ARTWORK")
+        base:SetAllPoints(f); base:SetTexture("Interface\\Base.blp")
+        local hi = f:CreateTexture(nil, "HIGHLIGHT")
+        hi:SetAllPoints(f); hi:SetTexture("Interface\\Hi.blp")
+    "#,
+    )
+    .unwrap();
+    s.resolve();
+
+    let art = |s: &UiScript| -> Vec<String> {
+        s.extract()
+            .iter()
+            .filter(|q| s.quad_owner_name(q.target).as_deref() == Some("HiLayer"))
+            .filter_map(|q| match &q.content {
+                QuadContent::Texture { path: Some(p), .. } => Some(p.clone()),
+                _ => None,
+            })
+            .collect()
+    };
+
+    s.mouse_move(400.0, 400.0);
+    assert_eq!(
+        art(&s),
+        vec!["Interface\\Base.blp".to_string()],
+        "the layer is off at rest, so only the ARTWORK region draws"
+    );
+    assert_eq!(
+        s.eval::<i64>(r#"return HiLayer:IsShown()"#).unwrap(),
+        1,
+        "the frame itself is shown; it is the layer that is off"
+    );
+
+    s.mouse_move(50.0, 50.0);
+    let v = art(&s);
+    assert!(
+        v.contains(&"Interface\\Hi.blp".to_string()),
+        "the cursor on the frame enables the layer: {v:?}"
+    );
+
+    s.mouse_move(400.0, 400.0);
+    assert_eq!(
+        art(&s),
+        vec!["Interface\\Base.blp".to_string()],
+        "and leaving disables it again"
+    );
+    assert!(s.errors().is_empty(), "{:?}", s.errors());
+}
+
+/// `LockHighlight`/`UnlockHighlight` (`0x782840`/`0x782920`) both reach `0x76c2e0`, which writes
+/// `[frame+0xf8]` and then moves layer 4 with it -- enabling it on a lock, and on an unlock
+/// disabling it *unless this frame is the mouse focus* (`cmp [root+0x7c], ecx`). That last branch
+/// is what keeps a selected trade-skill row lit when the cursor happens to be on it.
+#[test]
+fn lock_highlight_drives_the_layer_and_unlocking_under_the_cursor_leaves_it_lit() {
+    let mut s = script();
+    s.set_screen_size(800.0, 600.0);
+    s.run(
+        r#"
+        local b = CreateFrame("Button", "LockBtn")
+        b:SetPoint("BOTTOMLEFT", 0, 0); b:SetWidth(100); b:SetHeight(100)
+        local hi = b:CreateTexture(nil, "HIGHLIGHT")
+        hi:SetAllPoints(b); hi:SetTexture("Interface\\Hi.blp")
+    "#,
+    )
+    .unwrap();
+    s.resolve();
+
+    let lit = |s: &UiScript| -> bool {
+        s.extract()
+            .iter()
+            .filter(|q| s.quad_owner_name(q.target).as_deref() == Some("LockBtn"))
+            .any(|q| {
+                matches!(&q.content, QuadContent::Texture { path: Some(p), .. }
+                    if p == "Interface\\Hi.blp")
+            })
+    };
+
+    s.mouse_move(400.0, 400.0);
+    assert!(!lit(&s), "off at rest");
+
+    s.run("LockBtn:LockHighlight()").unwrap();
+    assert!(lit(&s), "a lock lights it with the cursor elsewhere");
+
+    s.mouse_move(50.0, 50.0);
+    s.run("LockBtn:UnlockHighlight()").unwrap();
+    assert!(
+        lit(&s),
+        "unlocking under the cursor leaves it lit: the hover owns it now"
+    );
+
+    s.mouse_move(400.0, 400.0);
+    assert!(!lit(&s), "and leaving finally takes it");
+
+    s.run("LockBtn:LockHighlight() LockBtn:UnlockHighlight()")
+        .unwrap();
+    assert!(!lit(&s), "unlocking away from the cursor disables it");
+    assert!(s.errors().is_empty(), "{:?}", s.errors());
+}
+
+/// `Enable()` does not light a button on its own: the reference restores the layer only by
+/// re-running `<OnEnter>` on a hovered button (`0x779183`), so a form that enables its Submit
+/// button when the fields are filled does not leave it glowing from across the screen.
+#[test]
+fn enable_lights_the_highlight_only_under_the_cursor() {
+    let mut s = script();
+    s.set_screen_size(800.0, 600.0);
+    s.run(
+        r#"
+        local b = CreateFrame("Button", "EnBtn")
+        b:SetPoint("BOTTOMLEFT", 0, 0); b:SetWidth(100); b:SetHeight(100)
+        local hi = b:CreateTexture(nil, "HIGHLIGHT")
+        hi:SetAllPoints(b); hi:SetTexture("Interface\\Hi.blp")
+        b:Disable()
+    "#,
+    )
+    .unwrap();
+    s.resolve();
+
+    let lit = |s: &UiScript| -> bool {
+        s.extract()
+            .iter()
+            .filter(|q| s.quad_owner_name(q.target).as_deref() == Some("EnBtn"))
+            .any(|q| {
+                matches!(&q.content, QuadContent::Texture { path: Some(p), .. }
+                    if p == "Interface\\Hi.blp")
+            })
+    };
+
+    s.mouse_move(400.0, 400.0);
+    s.run("EnBtn:Enable()").unwrap();
+    assert!(!lit(&s), "enabled away from the cursor stays dark");
+
+    s.mouse_move(50.0, 50.0);
+    assert!(lit(&s), "and the cursor arriving lights it");
+
+    s.run("EnBtn:Disable() EnBtn:Enable()").unwrap();
+    assert!(
+        lit(&s),
+        "enabled under the cursor comes back lit, as the re-run OnEnter would"
+    );
+    assert!(s.errors().is_empty(), "{:?}", s.errors());
+}
+
 /// `CButton::OnMouseDown` shows the pushed texture when the button is registered for that mouse
 /// button, up or down (`0x77924b`: `[this+0x330] & (m | m << 8)`), whether or not a click fires.
 #[test]

crates/benilla-ui/src/widget/mod.rs

@@ -136,6 +136,20 @@ pub use kinds::{
 
 // ── Frame and Region nodes ───────────────────────────────────────────────────────────────────
 
+/// [`Frame::disabled_layers`] with layer 4, HIGHLIGHT, off: a frame's resting state.
+///
+/// In the reference that layer is the highlight state itself, not merely where highlight art
+/// lives. The base hover notifies toggle the whole layer -- `OnEnter` (`0x76b6a0`) enables it
+/// (`0x76a710`), `OnLeave` (`0x76b6f0`) disables it (`0x76a730`), both skipped while
+/// `LockHighlight` holds (`[frame+0xf8]`) -- `LockHighlight` drives it directly (`0x76c2e0`), and
+/// `SetEnabled(false)` turns it off outright (`0x7791bb`). A Button even picks its label's font
+/// instance by reading the layer's own flag: `0x77983c` tests `[frame+0x1a8]`, which is
+/// `[frame+0x198] + 4*4`, and takes the highlight font object at `+0x3b8` when it is set.
+///
+/// So it has to start off. An addon writing `CreateTexture(nil, "HIGHLIGHT")` is relying on that
+/// -- a hand-built column header or list row puts its hover art there and never hides it itself.
+pub const HIGHLIGHT_OFF: u8 = 1 << DrawLayer::Highlight.index();
+
 /// A frame node, the modelled subset of `CSimpleFrame`. The `effective_*` fields and the tree
 /// links belong to the [`WidgetArena`] mutators: change state through them so it propagates.
 #[derive(Clone, Debug, PartialEq)]
@@ -144,6 +158,9 @@ pub struct Frame {
     /// Layers switched off by `DisableDrawLayer` (`0x775680`) and back on by `EnableDrawLayer`
     /// (`0x7755b0`), bit `n` for [`DrawLayer::index`] `n`: a frame-level mask, so each region
     /// keeps its own shown state underneath.
+    ///
+    /// Layer 4, HIGHLIGHT, starts here set -- that layer is the client's highlight *state*, not a
+    /// place to put art that is always on. See [`HIGHLIGHT_OFF`].
     pub disabled_layers: u8,
     /// The global name, which a later duplicate carries without owning ([`WidgetArena::lookup`]).
     pub name: Option<String>,
@@ -468,7 +485,7 @@ impl WidgetArena {
         let effective_alpha = alpha;
 
         let frame = Frame {
-            disabled_layers: 0,
+            disabled_layers: HIGHLIGHT_OFF,
             kind,
             name: name.clone(),
             parent,