fix(render): scale solid tessellation

Derive one drawing-space chordal tolerance so large curves stay smooth while small solids avoid excessive detail.

src/scene/convert/acis_kernel.rs

@@ -23,6 +23,7 @@ pub fn tessellate_sat(
     name: String,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
     let (bodies, loss) = lift(document);
@@ -53,7 +54,10 @@ pub fn tessellate_sat(
     } else {
         1.0
     };
-    let max_angle = cadkernel::tessellation::angle_for_resolution(resolution);
+    let max_angle = chordal_deflection.map_or_else(
+        || cadkernel::tessellation::angle_for_resolution(resolution),
+        |_| cadkernel::tessellation::display_angle_for_resolution(resolution),
+    );
 
     // Positions stay f64 until `finalize_mesh` splits them into the coarse
     // and fine pair, so a solid at survey coordinates keeps its millimetres.
@@ -106,11 +110,14 @@ pub fn tessellate_sat(
         DEFAULT_FIT_TOLERANCE
     };
     for (body, placement_scale) in &bodies {
-        let tolerance = brep::mesh::TessellationTolerance::new(
+        let mut tolerance = brep::mesh::TessellationTolerance::new(
             max_angle,
             source_fit * placement_scale,
         )
         .with_isolines(isolines);
+        if let Some(deflection) = chordal_deflection {
+            tolerance = tolerance.with_chordal_deflection(deflection);
+        }
         let tessellation = brep::mesh::tessellate(body, tolerance);
         undrawn += tessellation.missing_faces.len();
         for face in &tessellation.triangle_faces {
@@ -244,15 +251,4 @@ mod tests {
         assert_eq!(moved, [10.0, 20.0, 30.0]);
     }
 
-    fn sides(max_angle: f64) -> f64 {
-        std::f64::consts::TAU / max_angle
-    }
-
-    #[test]
-    fn a_round_surface_gets_the_same_sides_whatever_its_size() {
-        let angle = cadkernel::tessellation::DEFAULT_ANGLE;
-        assert!(sides(angle) > 24.0, "{}", sides(angle));
-        assert!(sides(angle) < 96.0, "{}", sides(angle));
-    }
-
 }

src/scene/convert/solid3d_tess.rs

@@ -8,9 +8,17 @@ fn tessellate_acis(
     name: String,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
-    crate::scene::convert::acis_kernel::tessellate_sat(sat, name, color, facet_res, isolines)
+    crate::scene::convert::acis_kernel::tessellate_sat(
+        sat,
+        name,
+        color,
+        facet_res,
+        chordal_deflection,
+        isolines,
+    )
 }
 
 pub(crate) fn body_transform(
@@ -167,10 +175,18 @@ fn finish(
     name: String,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
     acis: &acadrust::entities::AcisData,
 ) -> Option<MeshLodSet> {
-    let mut set = tessellate_acis(&sat, name, color, facet_res, isolines)?;
+    let mut set = tessellate_acis(
+        &sat,
+        name,
+        color,
+        facet_res,
+        chordal_deflection,
+        isolines,
+    )?;
     remap_acis_material_bindings(&mut set, acis);
     Some(set)
 }
@@ -179,6 +195,7 @@ pub fn tessellate_region(
     region: &Region,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
     let sat = parse_acis(
@@ -191,6 +208,7 @@ pub fn tessellate_region(
         region.common.handle.value().to_string(),
         color,
         facet_res,
+        chordal_deflection,
         isolines,
         &region.acis_data,
     )
@@ -200,6 +218,7 @@ pub fn tessellate_body(
     body: &Body,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
     let sat = parse_acis(
@@ -212,6 +231,7 @@ pub fn tessellate_body(
         body.common.handle.value().to_string(),
         color,
         facet_res,
+        chordal_deflection,
         isolines,
         &body.acis_data,
     )
@@ -221,6 +241,7 @@ pub fn tessellate_surface(
     surface: &acadrust::entities::Surface,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
     let sat = parse_acis(
@@ -233,6 +254,7 @@ pub fn tessellate_surface(
         surface.common.handle.value().to_string(),
         color,
         facet_res,
+        chordal_deflection,
         isolines,
         &surface.acis_data,
     )
@@ -242,6 +264,7 @@ pub fn tessellate_solid3d(
     solid: &Solid3D,
     color: [f32; 4],
     facet_res: f64,
+    chordal_deflection: Option<f64>,
     isolines: usize,
 ) -> Option<MeshLodSet> {
     let sat = parse_acis(
@@ -254,6 +277,7 @@ pub fn tessellate_solid3d(
         solid.common.handle.value().to_string(),
         color,
         facet_res,
+        chordal_deflection,
         isolines,
         &solid.acis_data,
     )