Underlays are rasterised for the view's scale; DGN V7 strokes one pixel wide

A page shown small was drawn from its full-size raster and thin lines broke
up into dots. Once a zoom settles on another quarter-octave step, PDF, DWF
and DGN underlays are rasterised again near their size on screen (never
above the full-size raster), frames are requested until that happens, and
the adjusted-pixel memo is kept per raster size. V7 element weights no longer
widen strokes, matching V8 models.

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

src/app/update/viewport.rs

@@ -850,6 +850,8 @@ impl OpenCADStudio {
         self.tabs[i].scene.update(t - self.start);
         // Dynamic dimensions keep their screen size across zoom bands.
         self.tabs[i].scene.refresh_dynamic_dimension_scales(false);
+        // Underlays are rasterised again for the zoom once it settles.
+        self.tabs[i].scene.refresh_underlay_resolution(t);
 
         // If the camera moved since we last synced, write it back to
         // the document and mark the file dirty.

src/app/view/mod.rs

@@ -2544,7 +2544,10 @@ impl OpenCADStudio {
         // driven by input events, but once the cursor stops no event would fire
         // the one full-quality frame that re-renders hatches — this tick does,
         // then the scene-render cache holds it and the subscription auto-stops.
-        let nav_settle = if self.tabs[self.active_tab].scene.is_settling() {
+        // Underlay rasters follow the zoom once it settles; tick until then.
+        let nav_settle = if self.tabs[self.active_tab].scene.is_settling()
+            || self.tabs[self.active_tab].scene.underlay_resolution_stale()
+        {
             window::frames().map(Message::Tick)
         } else {
             Subscription::none()