review(#1630): one table rebuild loop that also refreshes formulas; one cell layout

- main already rebuilt an edited table's block; the PR added a second
  loop after it that could never fire. Formula refresh and the block
  cache bump now live in the one loop.
- Formula refresh copies the drawing only for a table that has a field.
- A field cell lays its text out once and boxes it from those cells.
- A zero text height at one level falls through to the next instead of
  ending the lookup.
- Field box constants and BACKGROUND keep their own doc comments.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/entities/field.rs

@@ -137,7 +137,17 @@ pub fn update_fields(
 /// Recompute a table's cell formulas into its block after the table changed;
 /// returns the cell texts that changed.
 pub fn refresh_table_formulas(document: &mut CadDocument, table: Handle) -> Vec<Handle> {
-    if document.fields.is_empty() {
+    // Copying the drawing is only worth it for a table with a field.
+    let has_field = matches!(
+        document.get_entity(table),
+        Some(codec::EntityType::Table(t)) if t
+            .rows
+            .iter()
+            .flat_map(|row| &row.cells)
+            .flat_map(|cell| &cell.contents)
+            .any(|content| content.field_handle.is_some())
+    );
+    if !has_field {
         return Vec::new();
     }
     let snapshot = document.clone();
@@ -332,13 +342,13 @@ pub fn set_display(on: bool) {
     FIELD_DISPLAY.store(on, std::sync::atomic::Ordering::Relaxed);
 }
 
-/// The gray the reference draws behind a field.
 /// FIELDDISPLAY box extent around a line of field text, in text heights:
 /// from a third of the height below the baseline to 1.19 heights above it
 /// (the reference's box, measured at 2.5 and 10 unit text).
 pub const BOX_BELOW: f64 = 0.345;
 pub const BOX_ABOVE: f64 = 1.19;
 
+/// The gray the reference draws behind a field.
 pub const BACKGROUND: [f32; 4] = [203.0 / 255.0, 203.0 / 255.0, 203.0 / 255.0, 1.0];
 
 /// Whether `entity` hosts a field: its extension dictionary has ACAD_FIELD.

src/entities/table.rs

@@ -135,11 +135,14 @@ fn cell_text_height(
     content: &codec::entities::table::CellContent,
 ) -> Option<f64> {
     use codec::entities::table::CellStylePropertyFlags as P;
+    let set = |h: f64| (h > 1e-6).then_some(h);
     let own = content.sets(P::TEXT_HEIGHT);
-    own.then_some(content.text_height)
-        .or_else(|| style_for_property(table, row, column, cell, P::TEXT_HEIGHT).map(|s| s.text_height))
-        .or(Some(content.text_height))
-        .filter(|h| *h > 1e-6)
+    own.then(|| set(content.text_height))
+        .flatten()
+        .or_else(|| {
+            style_for_property(table, row, column, cell, P::TEXT_HEIGHT).and_then(|s| set(s.text_height))
+        })
+        .or_else(|| set(content.text_height))
 }
 
 /// A cell's text style: the content's own, else the cell, row, column or
@@ -1960,6 +1963,8 @@ pub fn tessellate_table(
                     .map(|style| style.rotation as f32)
                     .unwrap_or(cell.rotation as f32)
                 };
+                // FIELDDISPLAY boxes come from this same layout's cells.
+                let field_boxes = content.field_handle.is_some() && crate::entities::field::display();
                 let layout = layout_mtext(&MTextRenderOpts {
                     columns: Default::default(),
                     value: text,
@@ -1974,31 +1979,15 @@ pub fn tessellate_table(
                     exact_line_spacing: false,
                     rectangle_height: 0.0,
                     vertical_text: false,
-                    want_glyph_boxes: false,
+                    want_glyph_boxes: field_boxes,
                 });
                 // FIELDDISPLAY: a field cell's text on a gray box, one per line,
                 // from the same layout's character cells (screen only).
-                if content.field_handle.is_some() && crate::entities::field::display() {
-                    let cells = layout_mtext(&MTextRenderOpts {
-                        columns: Default::default(),
-                        value: text,
-                        insertion: [to.x as f64, to.y as f64, to.z as f64],
-                        height: cell_h,
-                        rect_w: (col_width - margin_left - margin_right).max(0.0),
-                        rotation: rot,
-                        style: &resolved,
-                        attach_h_anchor,
-                        v_anchor,
-                        line_spacing_factor: 1.0,
-                        exact_line_spacing: false,
-                        rectangle_height: 0.0,
-                        vertical_text: false,
-                        want_glyph_boxes: true,
-                    })
-                        .glyph_boxes;
+                if field_boxes {
+                    let cells = &layout.glyph_boxes;
                     let (sin_r, cos_r) = (rot as f64).sin_cos();
                     let mut lines: Vec<[f64; 4]> = Vec::new();
-                    for b in &cells {
+                    for b in cells {
                         let [l, base, r, top] = b.local.map(|v| v as f64);
                         match lines.last_mut() {
                             Some(c) if (c[1] - base).abs() <= 1e-3 * (top - base).max(c[3]) => {

src/scene/mod.rs

@@ -3617,7 +3617,9 @@ impl Scene {
         // (the *T block) redrawn from the cells. Tables keeping their picture
         // (moved, restyled, opened from a file) are never redrawn: the block
         // may hold authored content the redraw does not reproduce.
+        // Its cell formulas are worked out again into that block.
         if !appearance_only {
+            let mut rebuilt = false;
             for (handle, kind) in &changes {
                 if !matches!(kind, ChangeKind::Removed)
                     && matches!(
@@ -3625,9 +3627,15 @@ impl Scene {
                         Some(EntityType::Table(t)) if t.block_record_handle.is_none()
                     )
                 {
-                    self.document.refresh_table_block(*handle);
+                    rebuilt |= self.document.refresh_table_block(*handle);
+                    rebuilt |= !crate::entities::field::refresh_table_formulas(&mut self.document, *handle)
+                        .is_empty();
                 }
             }
+            // The block's cached drawing is stale once its texts change.
+            if rebuilt {
+                self.block_epoch = GEOMETRY_EPOCH.fetch_add(1, Ordering::Relaxed);
+            }
         }
         // A restyle (layer on/off, colour, text or dimension style) moves no
         // geometry, so nothing measured from it is re-resolved: an
@@ -3695,20 +3703,6 @@ impl Scene {
                 }
             }
         }
-        // An edited table lets go of its block; rebuild it from the cells so
-        // the drawing shows and saves the cell texts and grid it now holds.
-        let mut rebuilt_table_block = false;
-        for (handle, kind) in &changes {
-            if !matches!(kind, ChangeKind::Removed)
-                && matches!(self.document.get_entity(*handle), Some(EntityType::Table(t)) if t.block_record_handle.is_none())
-            {
-                rebuilt_table_block |= self.document.refresh_table_block(*handle);
-                rebuilt_table_block |= !crate::entities::field::refresh_table_formulas(&mut self.document, *handle).is_empty();
-            }
-        }
-        if rebuilt_table_block {
-            self.block_epoch = GEOMETRY_EPOCH.fetch_add(1, Ordering::Relaxed);
-        }
         if !changes.is_empty() {
             self.refresh_dependency_index_for_changes(&changes);
         }