feat(render): double-single vertices for the mesh pipeline

3D solid / surface meshes were the last single-f32 path. truck's mesh
tessellation now returns a paired verts_low residual (TruckTessResult::Mesh,
polygon_to_result), MeshModel/MeshLodSet carry it, the model-space offset
and block-instance transforms reconstruct the f64 position and re-split it
after subtracting world_offset, MeshVertex gains position_low (location 3),
and mesh.wgsl reconstructs the eye-relative position. Native SAT / ACIS /
OBJ mesh paths default to a zero residual (no regression — they were never
sub-f32 precise).

With this every world-space pipeline (wire, hatch, image, face3d, mesh)
is full double-single relative-to-eye; large-coordinate jitter is gone.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/cmd_result.rs

@@ -1274,11 +1274,13 @@ impl OpenCADStudio {
                                 match truck_tess::tessellate_solid(&solid, woff) {
                                     truck_tess::TruckTessResult::Mesh {
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                     } => Some(crate::scene::model::mesh_model::MeshModel {
                                         name: String::new(),
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                         color,
@@ -1352,11 +1354,13 @@ impl OpenCADStudio {
                         match truck_tess::tessellate_shell(&shell, woff) {
                             truck_tess::TruckTessResult::Mesh {
                                 verts,
+                                verts_low,
                                 normals,
                                 indices,
                             } => Some(crate::scene::model::mesh_model::MeshModel {
                                 name: String::new(),
                                 verts,
+                                verts_low,
                                 normals,
                                 indices,
                                 color,
@@ -1437,11 +1441,13 @@ impl OpenCADStudio {
                                 match truck_tess::tessellate_solid(&solid, woff) {
                                     truck_tess::TruckTessResult::Mesh {
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                     } => Some(crate::scene::model::mesh_model::MeshModel {
                                         name: String::new(),
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                         color,
@@ -1454,11 +1460,13 @@ impl OpenCADStudio {
                                 match truck_tess::tessellate_shell(&shell, woff) {
                                     truck_tess::TruckTessResult::Mesh {
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                     } => Some(crate::scene::model::mesh_model::MeshModel {
                                         name: String::new(),
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                         color,
@@ -1486,11 +1494,13 @@ impl OpenCADStudio {
                                 match truck_tess::tessellate_solid(&solid, woff) {
                                     truck_tess::TruckTessResult::Mesh {
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                     } => Some(crate::scene::model::mesh_model::MeshModel {
                                         name: String::new(),
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                         color,
@@ -1503,11 +1513,13 @@ impl OpenCADStudio {
                                 match truck_tess::tessellate_shell(&shell, woff) {
                                     truck_tess::TruckTessResult::Mesh {
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                     } => Some(crate::scene::model::mesh_model::MeshModel {
                                         name: String::new(),
                                         verts,
+                                        verts_low,
                                         normals,
                                         indices,
                                         color,
@@ -1593,11 +1605,13 @@ impl OpenCADStudio {
                     match truck_tess::tessellate_shell(&shell, woff) {
                         truck_tess::TruckTessResult::Mesh {
                             verts,
+                            verts_low,
                             normals,
                             indices,
                         } => Some(crate::scene::model::mesh_model::MeshModel {
                             name: String::new(),
                             verts,
+                            verts_low,
                             normals,
                             indices,
                             color,

src/io/obj.rs

@@ -103,6 +103,7 @@ pub fn parse_obj(src: &str, color: [f32; 4]) -> Option<MeshModel> {
     Some(MeshModel {
         name: String::new(),
         verts,
+        verts_low: Vec::new(),
         normals: norms,
         indices,
         color,

src/scene/convert/acis_to_truck.rs

@@ -110,6 +110,7 @@ pub fn tessellate_sat_truck(
     let mut mesh = MeshModel {
         name: name.clone(),
         verts: Vec::new(),
+        verts_low: Vec::new(),
         normals: Vec::new(),
         indices: Vec::new(),
         color,

src/scene/convert/solid3d_tess.rs

@@ -125,6 +125,7 @@ fn tessellate_sat(
     Some(MeshModel {
         name,
         verts,
+        verts_low: Vec::new(),
         normals,
         indices,
         color,

src/scene/convert/truck_tess.rs

@@ -78,9 +78,11 @@ pub enum TruckTessResult {
     /// returned as parallel double-single (high, low) f32 buffers so the GPU
     /// keeps sub-unit precision at UTM-scale coordinates.
     Lines(Vec<[f32; 3]>, Vec<[f32; 3]>),
-    /// A triangle mesh (from Face, Shell, or Solid).
+    /// A triangle mesh (from Face, Shell, or Solid). `verts` is the high half
+    /// of the double-single position; `verts_low` the paired residual.
     Mesh {
         verts: Vec<[f32; 3]>,
+        verts_low: Vec<[f32; 3]>,
         normals: Vec<[f32; 3]>,
         indices: Vec<u32>,
     },
@@ -177,6 +179,7 @@ pub fn tessellate_shell(s: &Shell, offset: [f64; 3]) -> TruckTessResult {
 pub fn tessellate_shell(_s: &Shell, _offset: [f64; 3]) -> TruckTessResult {
     TruckTessResult::Mesh {
         verts: Vec::new(),
+        verts_low: Vec::new(),
         normals: Vec::new(),
         indices: Vec::new(),
     }
@@ -197,6 +200,7 @@ pub fn tessellate_solid(s: &Solid, offset: [f64; 3]) -> TruckTessResult {
 pub fn tessellate_solid(_s: &Solid, _offset: [f64; 3]) -> TruckTessResult {
     TruckTessResult::Mesh {
         verts: Vec::new(),
+        verts_low: Vec::new(),
         normals: Vec::new(),
         indices: Vec::new(),
     }
@@ -206,11 +210,14 @@ pub fn tessellate_solid(_s: &Solid, _offset: [f64; 3]) -> TruckTessResult {
 
 #[cfg(feature = "solid3d")]
 fn polygon_to_result(mesh: PolygonMesh, offset: [f64; 3]) -> TruckTessResult {
-    let verts: Vec<[f32; 3]> = mesh
-        .positions()
-        .iter()
-        .map(|p| to_local(p.x, p.y, p.z, offset))
-        .collect();
+    let positions = mesh.positions();
+    let mut verts: Vec<[f32; 3]> = Vec::with_capacity(positions.len());
+    let mut verts_low: Vec<[f32; 3]> = Vec::with_capacity(positions.len());
+    for p in positions.iter() {
+        let hi = to_local(p.x, p.y, p.z, offset);
+        verts_low.push(to_local_low(p.x, p.y, p.z, offset, hi));
+        verts.push(hi);
+    }
 
     // Per-vertex normals: if the mesh has normals, map each triangle vertex's
     // normal index back to the normals array.  Fall back to empty if absent.
@@ -262,6 +269,7 @@ fn polygon_to_result(mesh: PolygonMesh, offset: [f64; 3]) -> TruckTessResult {
 
     TruckTessResult::Mesh {
         verts,
+        verts_low,
         normals,
         indices,
     }

src/scene/mod.rs

@@ -557,20 +557,31 @@ fn overlap_len(a: (f32, f32), b: (f32, f32)) -> f32 {
 /// uses the same space.
 fn offset_mesh_lod_set(mut set: MeshLodSet, world_offset: [f64; 3]) -> MeshLodSet {
     let [ox, oy, oz] = world_offset;
-    let (fx, fy, fz) = (ox as f32, oy as f32, oz as f32);
     let mut min_x = f32::INFINITY;
     let mut min_y = f32::INFINITY;
     let mut max_x = f32::NEG_INFINITY;
     let mut max_y = f32::NEG_INFINITY;
     for lod in &mut set.lods {
-        for v in &mut lod.verts {
-            v[0] -= fx;
-            v[1] -= fy;
-            v[2] -= fz;
-            if v[0] < min_x { min_x = v[0]; }
-            if v[1] < min_y { min_y = v[1]; }
-            if v[0] > max_x { max_x = v[0]; }
-            if v[1] > max_y { max_y = v[1]; }
+        // Reconstruct the f64 absolute position from the double-single pair,
+        // subtract world_offset in f64, then re-split into (high, low) so the
+        // relative-to-eye shader keeps sub-unit precision at UTM scale.
+        let has_low = lod.verts_low.len() == lod.verts.len();
+        if !has_low {
+            lod.verts_low = vec![[0.0; 3]; lod.verts.len()];
+        }
+        for (v, vl) in lod.verts.iter_mut().zip(lod.verts_low.iter_mut()) {
+            let ax = v[0] as f64 + vl[0] as f64 - ox;
+            let ay = v[1] as f64 + vl[1] as f64 - oy;
+            let az = v[2] as f64 + vl[2] as f64 - oz;
+            let hx = ax as f32;
+            let hy = ay as f32;
+            let hz = az as f32;
+            *v = [hx, hy, hz];
+            *vl = [(ax - hx as f64) as f32, (ay - hy as f64) as f32, (az - hz as f64) as f32];
+            if hx < min_x { min_x = hx; }
+            if hy < min_y { min_y = hy; }
+            if hx > max_x { max_x = hx; }
+            if hy > max_y { max_y = hy; }
         }
     }
     if min_x.is_finite() {
@@ -596,15 +607,30 @@ fn transform_block_mesh_lod_set(
     let mut max_x = f32::NEG_INFINITY;
     let mut max_y = f32::NEG_INFINITY;
     for lod in &mut out.lods {
-        for v in &mut lod.verts {
-            let w = xform.apply(Vector3::new(v[0] as f64, v[1] as f64, v[2] as f64));
-            v[0] = (w.x - ox) as f32;
-            v[1] = (w.y - oy) as f32;
-            v[2] = (w.z - oz) as f32;
-            if v[0] < min_x { min_x = v[0]; }
-            if v[1] < min_y { min_y = v[1]; }
-            if v[0] > max_x { max_x = v[0]; }
-            if v[1] > max_y { max_y = v[1]; }
+        let has_low = lod.verts_low.len() == lod.verts.len();
+        if !has_low {
+            lod.verts_low = vec![[0.0; 3]; lod.verts.len()];
+        }
+        for (v, vl) in lod.verts.iter_mut().zip(lod.verts_low.iter_mut()) {
+            // Reconstruct the block-local f64, apply the INSERT transform and
+            // subtract world_offset in f64, then re-split into (high, low).
+            let w = xform.apply(Vector3::new(
+                v[0] as f64 + vl[0] as f64,
+                v[1] as f64 + vl[1] as f64,
+                v[2] as f64 + vl[2] as f64,
+            ));
+            let ax = w.x - ox;
+            let ay = w.y - oy;
+            let az = w.z - oz;
+            let hx = ax as f32;
+            let hy = ay as f32;
+            let hz = az as f32;
+            *v = [hx, hy, hz];
+            *vl = [(ax - hx as f64) as f32, (ay - hy as f64) as f32, (az - hz as f64) as f32];
+            if hx < min_x { min_x = hx; }
+            if hy < min_y { min_y = hy; }
+            if hx > max_x { max_x = hx; }
+            if hy > max_y { max_y = hy; }
         }
         for n in &mut lod.normals {
             let d = xform.apply_rotation(Vector3::new(n[0] as f64, n[1] as f64, n[2] as f64));

src/scene/model/mesh_model.rs

@@ -9,8 +9,11 @@
 pub struct MeshModel {
     /// Unique identifier (entity handle value as decimal string).
     pub name: String,
-    /// World-space vertex positions.
+    /// World-space vertex positions (high half of the double-single pair).
     pub verts: Vec<[f32; 3]>,
+    /// Low residual paired with `verts` so meshes stay precise at UTM scale.
+    /// Empty = all-zero (legacy / interactive meshes near the origin).
+    pub verts_low: Vec<[f32; 3]>,
     /// Per-vertex normals (may be empty if not available).
     pub normals: Vec<[f32; 3]>,
     /// Triangle indices into `verts` (every 3 values = one triangle).

src/scene/model/solid_model.rs

@@ -172,12 +172,14 @@ pub fn mesh_from_solid(solid: &Solid, color: [f32; 4]) -> Option<MeshLodSet> {
     match tessellate_solid(solid, [0.0; 3]) {
         TruckTessResult::Mesh {
             verts,
+            verts_low,
             normals,
             indices,
         } if !indices.is_empty() => {
             let mesh = MeshModel {
                 name: String::new(),
                 verts,
+                verts_low,
                 normals,
                 indices,
                 color,

src/scene/pipeline/mesh_gpu.rs

@@ -19,30 +19,37 @@ pub struct MeshVertex {
     pub position: [f32; 3],
     pub normal: [f32; 3],
     pub color: [f32; 4],
+    pub position_low: [f32; 3],
 }
 
 impl MeshVertex {
     pub fn layout<'a>() -> wgpu::VertexBufferLayout<'a> {
+        const ATTRS: &[wgpu::VertexAttribute] = &[
+            wgpu::VertexAttribute {
+                offset: std::mem::offset_of!(MeshVertex, position) as u64,
+                shader_location: 0,
+                format: wgpu::VertexFormat::Float32x3,
+            },
+            wgpu::VertexAttribute {
+                offset: std::mem::offset_of!(MeshVertex, normal) as u64,
+                shader_location: 1,
+                format: wgpu::VertexFormat::Float32x3,
+            },
+            wgpu::VertexAttribute {
+                offset: std::mem::offset_of!(MeshVertex, color) as u64,
+                shader_location: 2,
+                format: wgpu::VertexFormat::Float32x4,
+            },
+            wgpu::VertexAttribute {
+                offset: std::mem::offset_of!(MeshVertex, position_low) as u64,
+                shader_location: 3,
+                format: wgpu::VertexFormat::Float32x3,
+            },
+        ];
         wgpu::VertexBufferLayout {
             array_stride: std::mem::size_of::<MeshVertex>() as u64,
             step_mode: wgpu::VertexStepMode::Vertex,
-            attributes: &[
-                wgpu::VertexAttribute {
-                    offset: 0,
-                    shader_location: 0,
-                    format: wgpu::VertexFormat::Float32x3,
-                },
-                wgpu::VertexAttribute {
-                    offset: 12,
-                    shader_location: 1,
-                    format: wgpu::VertexFormat::Float32x3,
-                },
-                wgpu::VertexAttribute {
-                    offset: 24,
-                    shader_location: 2,
-                    format: wgpu::VertexFormat::Float32x4,
-                },
-            ],
+            attributes: ATTRS,
         }
     }
 }
@@ -133,6 +140,7 @@ impl MeshGpu {
                     position: pos,
                     normal,
                     color,
+                    position_low: mesh.verts_low.get(i).copied().unwrap_or([0.0; 3]),
                 }
             })
             .collect();

src/shaders/mesh.wgsl

@@ -30,9 +30,10 @@ struct Uniforms {
 var<uniform> u: Uniforms;
 
 struct VertexIn {
-    @location(0) position: vec3<f32>,
-    @location(1) normal:   vec3<f32>,
-    @location(2) color:    vec4<f32>,
+    @location(0) position:     vec3<f32>,
+    @location(1) normal:       vec3<f32>,
+    @location(2) color:        vec4<f32>,
+    @location(3) position_low: vec3<f32>,
 };
 
 struct VertexOut {
@@ -45,7 +46,8 @@ struct VertexOut {
 @vertex
 fn vs_main(v: VertexIn) -> VertexOut {
     var out: VertexOut;
-    out.clip_pos  = u.view_rot * vec4<f32>((v.position - u.eye_high) - u.eye_low, 1.0);
+    let rel = (v.position - u.eye_high) + (v.position_low - u.eye_low);
+    out.clip_pos  = u.view_rot * vec4<f32>(rel, 1.0);
     out.color     = v.color;
     out.normal    = v.normal;
     out.world_pos = v.position;