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,
     )

src/scene/entity.rs

@@ -136,6 +136,8 @@ impl Scene {
         };
         let image_seed = self.image_seed_for(&entity);
         let facet_res = self.document.header.facet_resolution;
+        let chordal_deflection =
+            crate::entities::solid3d::display_deflection(&self.document.header, facet_res);
         let isolines = self.document.header.isolines.max(0) as usize;
         let mesh_seed = if matches!(
             &entity,
@@ -148,8 +150,14 @@ impl Scene {
                 | EntityType::PolyfaceMesh(_)
         ) {
             let color = self.render_style(&entity).0;
-            crate::entities::solid3d::tessellate_volume(&entity, color, facet_res, isolines)
-                .map(|m| offset_mesh_lod_set(m))
+            crate::entities::solid3d::tessellate_volume(
+                &entity,
+                color,
+                facet_res,
+                chordal_deflection,
+                isolines,
+            )
+            .map(offset_mesh_lod_set)
         } else {
             None
         };
@@ -357,6 +365,8 @@ impl Scene {
         };
         let image_seed = self.image_seed_for(&entity);
         let facet_res = self.document.header.facet_resolution;
+        let chordal_deflection =
+            crate::entities::solid3d::display_deflection(&self.document.header, facet_res);
         let isolines = self.document.header.isolines.max(0) as usize;
         let mesh_seed = if matches!(
             &entity,
@@ -369,8 +379,14 @@ impl Scene {
                 | EntityType::PolyfaceMesh(_)
         ) {
             let color = self.render_style(&entity).0;
-            crate::entities::solid3d::tessellate_volume(&entity, color, facet_res, isolines)
-                .map(|m| offset_mesh_lod_set(m))
+            crate::entities::solid3d::tessellate_volume(
+                &entity,
+                color,
+                facet_res,
+                chordal_deflection,
+                isolines,
+            )
+            .map(offset_mesh_lod_set)
         } else {
             None
         };
@@ -538,6 +554,8 @@ impl Scene {
                 })
                 .collect();
         let facet_res = self.document.header.facet_resolution;
+        let chordal_deflection =
+            crate::entities::solid3d::display_deflection(&self.document.header, facet_res);
         let isolines = self.document.header.isolines.max(0) as usize;
         use crate::par::prelude::*;
         let built: Vec<(Handle, MeshLodSet, bool)> = entries
@@ -547,6 +565,7 @@ impl Scene {
                     entity.as_ref(),
                     color,
                     facet_res,
+                    chordal_deflection,
                     isolines,
                 )
                 .map(|mut mesh| {
@@ -1892,6 +1911,8 @@ impl Scene {
 
         use crate::par::prelude::*;
         let facet_res = self.document.header.facet_resolution;
+        let chordal_deflection =
+            crate::entities::solid3d::display_deflection(&self.document.header, facet_res);
         let isolines = self.document.header.isolines.max(0) as usize;
         // Top-level solids: offset into the render frame, drawn flat.
         // Block-definition solids: keep block-local coords for per-INSERT
@@ -1899,7 +1920,14 @@ impl Scene {
         let built: Vec<(Handle, MeshLodSet, bool)> = entries
             .into_par_iter()
             .filter_map(|(handle, entity, color, top_level)| {
-                crate::entities::solid3d::tessellate_volume(&entity, color, facet_res, isolines).map(|mut mesh| {
+                crate::entities::solid3d::tessellate_volume(
+                    &entity,
+                    color,
+                    facet_res,
+                    chordal_deflection,
+                    isolines,
+                )
+                .map(|mut mesh| {
                     let material = crate::scene::model::material_model::resolve_material_with_base(
                         &self.document,
                         &entity,

src/scene/mod.rs

@@ -763,12 +763,12 @@ fn build_derived_caches_impl(
         })
         .collect();
 
-    // meshes (parallel tessellation). FACETRES (header.facet_resolution)
-    // scales the per-LOD segment counts so users with finer drawings get
-    // smoother solids; clamped to AutoCAD's [0.01, 10.0] range inside.
+    // FACETRES biases one shared chordal tolerance for all solids.
     // Top-level (layout-owned) solids are offset into the render frame; block
     // definition solids keep block-local coords for per-INSERT instancing. (#123)
     let facet_res = doc.header.facet_resolution;
+    let chordal_deflection =
+        crate::entities::solid3d::display_deflection(&doc.header, facet_res);
     let isolines = doc.header.isolines.max(0) as usize;
     // Real layout blocks come from the Layout objects' block_record handles —
     // `BlockRecord::is_layout()` is unreliable here (it flags ordinary blocks).
@@ -796,8 +796,14 @@ fn build_derived_caches_impl(
                 material_base_dir,
             );
             let top_level = layout_blocks.contains(&e.common().owner_handle);
-            let result = crate::entities::solid3d::tessellate_volume(e, color, facet_res, isolines)
-                .map(|mut mesh| {
+            let result = crate::entities::solid3d::tessellate_volume(
+                e,
+                color,
+                facet_res,
+                chordal_deflection,
+                isolines,
+            )
+            .map(|mut mesh| {
                 material.apply_to_with_face_overrides(
                     &mut mesh,
                     doc,
@@ -810,7 +816,7 @@ fn build_derived_caches_impl(
                 );
                 let mesh = if top_level { offset_mesh_lod_set(mesh) } else { mesh };
                 (handle, mesh, top_level)
-                });
+            });
             let done = detail_done.fetch_add(1, Ordering::Relaxed) + 1;
             if done & 0xff == 0 || done == detail_total {
                 report_detail(done);