View-dependent display refinement: finer curved faces and edges as you zoom in (#1320) (#1425)

* View-dependent display refinement: bodies seen up close are drawn from finer display plans (#1320)

Each frame the viewport works out every shown body's screen-space error (the display
quality's chord tolerance in pixels where the body is nearest the eye) and picks a
refinement step past the chosen display quality, each halving the chord, with hysteresis.
Steps are planned off the UI thread and swapped in when ready, within a triangle budget
and a cache size. Faces (GPU plan or CPU mesh), edges, silhouettes and highlights of a
refined body all come from the refined plan, so a highlight stays on the drawn triangles.
Planned bodies are chunked by content on the GPU, so a refinement re-evaluates only its
own chunk. Display only: the reference mesh, the B-rep and exports never change.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Display refinement: only collect finished plans while the view stands still, time the choice, keep the web planning one step a frame

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Format

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Keep the Display quality note as it was (the longer one pushed the Colour vision list off the Graphics page)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

---------

Co-authored-by: Claude Opus 5.5 <[email protected]>

crates/doc/src/eval.rs

@@ -126,6 +126,25 @@ impl ModelBody {
             .clone()
     }
 
+    /// The display plan and its mesh `k` steps finer than `q` (view-dependent refinement, #1320;
+    /// see [`crate::display_quality::refinement_for`]). Step 0 is the cached plan at `q`; finer
+    /// steps are made on each call and kept by the viewport, which evicts them when it runs over
+    /// its budget. `None` when the body has no plan at that step.
+    pub fn refined_display(&self, q: crate::display_quality::DisplayQuality, k: u8) -> Option<(Arc<TessPlan>, Arc<Mesh>)> {
+        if k == 0 {
+            return Some((self.display_plan_at(q)?, self.plan_mesh_at(q)?));
+        }
+        let plan = match self.body.display_plan_angular(q.refined_chord(self.body.size(), k), q.refined_angle(k)) {
+            Ok(plan) => plan,
+            Err(e) => {
+                log::debug!("{}: no display plan refined {k} steps ({e})", self.name);
+                return None;
+            }
+        };
+        let mesh = self.body.display_mesh_of(&plan).ok()?;
+        Some((Arc::new(plan), Arc::new(mesh)))
+    }
+
     /// The display mesh's chord tolerance: 1/1000 of the body's size.
     fn display_tol(&self) -> f64 {
         (self.body.size() * 1e-3).max(1e-3)