From b68dfd70e5d3bd0785aa0ce0528da857b3854e78 Mon Sep 17 00:00:00 2001
From: Kayshen-X <kayshen_xu@163.com>
Date: Thu, 14 May 2026 15:43:46 +0800
Subject: [PATCH] feat(shell-core/canvas): paint-time \$ref substitution active
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`paint_fill_then_stroke` now takes the resolved fill explicitly
rather than reading `node.fill` directly. Callers in `paint_node`
pre-resolve via `node_fill(node, var_table)` which checks
`var_table.fill_for(node.id)` first, falling through to `node.fill`
otherwise. Result: a Frame / Rect whose canonical loader registered
a `$ref` for its fill paints the current themed value at runtime;
flipping `active_theme` repaints with the new colour.

  - `paint_fill_then_stroke` signature: adds `fill: Option<Color>`
    as the last arg (after world_rect + zoom).
  - Both `NodeKind::Frame` + `NodeKind::Rect` branches in
    `paint_node` now compute `node_fill(node, var_table)` before
    calling the helper.

#5 Variables/Themes: types + storage + canonical loader +
fill_refs map + resolve + paint-time substitution all working.
Variables panel UI (active-theme picker + variable list with
edit) is the remaining piece — that's a widget, not a model
change.

Tests total: 236 shell-core (no new assertions in this commit;
the existing 8 variable tests cover the resolution chain that
paint now consumes). Wasm32 build clean.
---
 .../src/widgets/canvas_viewport.rs             |  4 ++--
 .../src/widgets/canvas_viewport_overlay.rs     | 18 +++++++++++-------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/crates/openpencil-shell-core/src/widgets/canvas_viewport.rs b/crates/openpencil-shell-core/src/widgets/canvas_viewport.rs
index 8bdae843f..0a1691948 100644
--- a/crates/openpencil-shell-core/src/widgets/canvas_viewport.rs
+++ b/crates/openpencil-shell-core/src/widgets/canvas_viewport.rs
@@ -412,7 +412,7 @@ fn paint_node(
 
     match &node.kind {
         NodeKind::Frame => {
-            paint_fill_then_stroke(cx, node, world_rect, zoom);
+            paint_fill_then_stroke(cx, node, world_rect, zoom, node_fill(node, var_table));
             for child in &node.children {
                 paint_node(cx, child, viewport_origin, zoom, selected, edit_caret, cull, var_table);
             }
@@ -426,7 +426,7 @@ fn paint_node(
             }
         }
         NodeKind::Rect => {
-            paint_fill_then_stroke(cx, node, world_rect, zoom);
+            paint_fill_then_stroke(cx, node, world_rect, zoom, node_fill(node, var_table));
         }
         NodeKind::Ellipse => {
             if let Some(fill) = node.fill {
diff --git a/crates/openpencil-shell-core/src/widgets/canvas_viewport_overlay.rs b/crates/openpencil-shell-core/src/widgets/canvas_viewport_overlay.rs
index 9dabb58db..83cf0b907 100644
--- a/crates/openpencil-shell-core/src/widgets/canvas_viewport_overlay.rs
+++ b/crates/openpencil-shell-core/src/widgets/canvas_viewport_overlay.rs
@@ -138,15 +138,19 @@ pub fn paint_selection_overlay(
 
 /// Paint a node's fill rect followed by its stroke rect. Stroke
 /// width is scaled by `zoom` so it stays visually constant under
-/// canvas zoom.
-pub fn paint_fill_then_stroke(cx: &mut PaintCx<'_>, node: &Node, world_rect: Rect, zoom: f32) {
-    // Scale doc-space radius into world-space alongside the rect.
-    // 0.5px is below the visible threshold for most renders; collapse
-    // to a square fill so the round-rect path doesn't accidentally
-    // soften 0-radius corners due to sub-pixel rounding.
+/// canvas zoom. Effective `fill` is passed explicitly so callers
+/// can substitute via `var_table.fill_for(node.id)` before
+/// rendering (paint-time `$ref` resolution — #5).
+pub fn paint_fill_then_stroke(
+    cx: &mut PaintCx<'_>,
+    node: &Node,
+    world_rect: Rect,
+    zoom: f32,
+    fill: Option<crate::Color>,
+) {
     let r = node.corner_radius * zoom;
     let use_round = r > 0.5;
-    if let Some(fill) = node.fill {
+    if let Some(fill) = fill {
         if use_round {
             cx.backend.fill_round_rect(world_rect, r, fill);
         } else {