perf: build hatch/image/mesh caches off the UI thread

Parsing + DerivedCaches construction now runs entirely in a dedicated
OS thread inside open_path(). FileOpened handler only assigns the
pre-built caches, keeping the UI thread free during file load.

- Add build_derived_caches(): parallel hatch + mesh tessellation via rayon
- Extend Message::FileOpened / open_path return type with DerivedCaches
- Drop populate_*_from_document() calls from FileOpened handler

src/app/mod.rs

@@ -212,7 +212,7 @@ pub enum DsField {
 pub enum Message {
     Tick(Instant),
     OpenFile,
-    FileOpened(Result<(String, PathBuf, CadDocument), String>),
+    FileOpened(Result<(String, PathBuf, CadDocument, crate::scene::DerivedCaches), String>),
     SaveFile,
     SaveAs,
     // ── Custom Save-As dialog ─────────────────────────────────────────────

src/app/update.rs

@@ -35,7 +35,7 @@ impl H7CAD {
 
             Message::OpenFile => Task::perform(crate::io::pick_and_open(), Message::FileOpened),
 
-            Message::FileOpened(Ok((name, path, doc))) => {
+            Message::FileOpened(Ok((name, path, doc, caches))) => {
                 let entity_count = doc.entities().count();
                 self.command_line
                     .push_output(&format!("Opened \"{name}\" — {entity_count} entities"));
@@ -87,10 +87,12 @@ impl H7CAD {
                     }
                 }
 
-                self.tabs[i].scene.compute_and_set_world_offset();
-                self.tabs[i].scene.populate_hatches_from_document();
-                self.tabs[i].scene.populate_images_from_document();
-                self.tabs[i].scene.populate_meshes_from_document();
+                // Caches were built on the background thread inside open_path().
+                self.tabs[i].scene.world_offset = caches.world_offset;
+                self.tabs[i].scene.local_extent_max = caches.local_extent_max;
+                self.tabs[i].scene.hatches = caches.hatches;
+                self.tabs[i].scene.images = caches.images;
+                self.tabs[i].scene.meshes = caches.meshes;
                 self.tabs[i].scene.selected = std::collections::HashSet::new();
                 self.tabs[i].scene.preview_wires = vec![];
                 self.tabs[i].scene.current_layout = "Model".to_string();

src/io/mod.rs

@@ -14,13 +14,14 @@ pub mod xref;
 use acadrust::entities::{Dimension, EntityType};
 use acadrust::io::dwg::DwgReader;
 use acadrust::{CadDocument, DwgWriter, DxfReader, DxfWriter};
+use crate::scene::DerivedCaches;
 use std::path::{Path, PathBuf};
 
 // ── Open ──────────────────────────────────────────────────────────────────
 
 /// Show a file-open dialog and load the selected DWG or DXF file.
-/// Returns `(filename, path, document)` or an error string.
-pub async fn pick_and_open() -> Result<(String, PathBuf, CadDocument), String> {
+/// Returns `(filename, path, document, caches)` or an error string.
+pub async fn pick_and_open() -> Result<(String, PathBuf, CadDocument, DerivedCaches), String> {
     let handle = rfd::AsyncFileDialog::new()
         .set_title("Open CAD file")
         .add_filter("CAD Files", &["dwg", "dxf", "DWG", "DXF"])
@@ -40,13 +41,22 @@ pub async fn pick_and_open() -> Result<(String, PathBuf, CadDocument), String> {
 }
 
 /// Load a CAD file from a known path (used by recent files).
-pub async fn open_path(path: PathBuf) -> Result<(String, PathBuf, CadDocument), String> {
+/// Parsing and cache building run on a dedicated OS thread so the async
+/// executor stays free for rendering during the load.
+pub async fn open_path(path: PathBuf) -> Result<(String, PathBuf, CadDocument, DerivedCaches), String> {
     let name = path
         .file_name()
         .map(|n| n.to_string_lossy().into_owned())
         .unwrap_or_else(|| "unknown".into());
-    let doc = load_file(&path)?;
-    Ok((name, path, doc))
+    let path2 = path.clone();
+    let (doc, caches) = std::thread::spawn(move || -> Result<_, String> {
+        let doc = load_file(&path2)?;
+        let caches = crate::scene::build_derived_caches(&doc);
+        Ok((doc, caches))
+    })
+    .join()
+    .map_err(|_| "parser thread panicked".to_string())??;
+    Ok((name, path, doc, caches))
 }
 
 /// Load a DWG or DXF file directly from a path (auto-detect by extension).

src/scene/mod.rs

@@ -60,6 +60,109 @@ use std::sync::Arc;
 /// GPU Pipeline to skip re-uploading geometry when switching tabs.
 static GEOMETRY_EPOCH: AtomicU64 = AtomicU64::new(1);
 
+/// Pre-built entity caches returned by [`build_derived_caches`].
+/// Produced in the file-load background task so the UI thread only assigns.
+#[derive(Debug, Clone)]
+pub struct DerivedCaches {
+    pub world_offset: [f64; 3],
+    pub local_extent_max: f32,
+    pub hatches: HashMap<Handle, HatchModel>,
+    pub images: HashMap<Handle, ImageModel>,
+    pub meshes: HashMap<Handle, MeshModel>,
+}
+
+/// Build hatch / image / mesh caches from a document without needing `&mut Scene`.
+/// Intended to run on a background thread during file load.
+pub fn build_derived_caches(doc: &CadDocument) -> DerivedCaches {
+    // world_offset
+    let h = &doc.header;
+    let (min, max) = (h.model_space_extents_min, h.model_space_extents_max);
+    let valid = min.x < max.x && min.y < max.y;
+    let (world_offset, local_extent_max) = if valid {
+        let offset = [(min.x + max.x) * 0.5, (min.y + max.y) * 0.5, (min.z + max.z) * 0.5];
+        let hw = ((max.x - min.x) * 0.5) as f32;
+        let hh = ((max.y - min.y) * 0.5) as f32;
+        let hz = ((max.z - min.z) * 0.5).max(1.0) as f32;
+        (offset, hw.max(hh).max(hz) * 10.0)
+    } else {
+        ([0.0; 3], 1e9_f32)
+    };
+
+    // model-space block handle (same logic as Scene::model_space_block_handle)
+    let model_block = doc.objects.values().find_map(|obj| {
+        if let acadrust::objects::ObjectType::Layout(l) = obj {
+            if l.name == "Model" && !l.block_record.is_null() { Some(l.block_record) } else { None }
+        } else { None }
+    }).unwrap_or_else(|| {
+        doc.block_records.get("*Model_Space").map(|br| br.handle).unwrap_or(Handle::NULL)
+    });
+
+    use rayon::prelude::*;
+
+    // hatches
+    let hatch_entries: Vec<(Handle, EntityType)> = doc.entities()
+        .filter_map(|e| match e {
+            EntityType::Hatch(h2) => Some((h2.common.handle, e.clone())),
+            EntityType::Solid(s)  => Some((s.common.handle, e.clone())),
+            _ => None,
+        })
+        .collect();
+    let hatches: HashMap<Handle, HatchModel> = hatch_entries
+        .into_par_iter()
+        .filter_map(|(handle, kind)| {
+            let owner = kind.common().owner_handle;
+            let offset = if owner == model_block { world_offset } else { [0.0; 3] };
+            let model = match &kind {
+                EntityType::Hatch(dxf) => {
+                    let color = tessellate::aci_to_rgba(&dxf.common.color);
+                    Scene::hatch_model_from_dxf(dxf, color, offset)
+                }
+                EntityType::Solid(solid) => {
+                    let color = tessellate::aci_to_rgba(&solid.common.color);
+                    Some(Scene::solid_hatch_model(solid, color, offset))
+                }
+                _ => None,
+            };
+            model.map(|m| (handle, m))
+        })
+        .collect();
+
+    // images
+    let images: HashMap<Handle, ImageModel> = doc.entities()
+        .filter_map(|e| {
+            if let EntityType::RasterImage(img) = e {
+                ImageModel::from_raster_image(img).map(|m| (img.common.handle, m))
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    // meshes (parallel tessellation)
+    let mesh_entries: Vec<(Handle, EntityType)> = doc.entities()
+        .filter_map(|e| match e {
+            EntityType::Solid3D(_) | EntityType::Region(_) | EntityType::Body(_) =>
+                Some((e.common().handle, e.clone())),
+            _ => None,
+        })
+        .collect();
+    let meshes: HashMap<Handle, MeshModel> = mesh_entries
+        .into_par_iter()
+        .filter_map(|(handle, entity)| {
+            let color = tessellate::aci_to_rgba(&entity.common().color);
+            let model = match &entity {
+                EntityType::Solid3D(s) => solid3d_tess::tessellate_solid3d(s, color),
+                EntityType::Region(r)  => solid3d_tess::tessellate_region(r, color),
+                EntityType::Body(b)    => solid3d_tess::tessellate_body(b, color),
+                _ => None,
+            };
+            model.map(|m| (handle, m))
+        })
+        .collect();
+
+    DerivedCaches { world_offset, local_extent_max, hatches, images, meshes }
+}
+
 pub struct Scene {
     pub camera: Rc<RefCell<Camera>>,
     pub selection: Rc<RefCell<SelectionState>>,
@@ -2043,6 +2146,7 @@ impl Scene {
         self.hatches.clear();
 
         let model_block = self.model_space_block_handle();
+        let world_offset = self.world_offset;
 
         let entries: Vec<(Handle, EntityType)> = self
             .document
@@ -2054,26 +2158,29 @@ impl Scene {
             })
             .collect();
 
-        for (handle, kind) in entries {
-            // Paper-space entities live in sheet coordinates — world_offset must not
-            // be applied to them.  Only model-space entities need the shift.
-            let owner = kind.common().owner_handle;
-            let offset = if owner == model_block { self.world_offset } else { [0.0; 3] };
-            let model = match &kind {
-                EntityType::Hatch(dxf) => {
-                    let color = tessellate::aci_to_rgba(&dxf.common.color);
-                    Self::hatch_model_from_dxf(dxf, color, offset)
-                }
-                EntityType::Solid(solid) => {
-                    let color = tessellate::aci_to_rgba(&solid.common.color);
-                    Some(Self::solid_hatch_model(solid, color, offset))
-                }
-                _ => None,
-            };
-            if let Some(m) = model {
-                self.hatches.insert(handle, m);
-            }
-        }
+        use rayon::prelude::*;
+        self.hatches = entries
+            .into_par_iter()
+            .filter_map(|(handle, kind)| {
+                // Paper-space entities live in sheet coordinates — world_offset must not
+                // be applied to them.  Only model-space entities need the shift.
+                let owner = kind.common().owner_handle;
+                let offset = if owner == model_block { world_offset } else { [0.0; 3] };
+                let model = match &kind {
+                    EntityType::Hatch(dxf) => {
+                        let color = tessellate::aci_to_rgba(&dxf.common.color);
+                        Self::hatch_model_from_dxf(dxf, color, offset)
+                    }
+                    EntityType::Solid(solid) => {
+                        let color = tessellate::aci_to_rgba(&solid.common.color);
+                        Some(Self::solid_hatch_model(solid, color, offset))
+                    }
+                    _ => None,
+                };
+                model.map(|m| (handle, m))
+            })
+            .collect();
+
         self.bump_geometry();
     }
 
@@ -2084,32 +2191,34 @@ impl Scene {
     /// `Solid3D` entity is represented in the mesh cache.
     pub fn populate_meshes_from_document(&mut self) {
         self.meshes.clear();
-        // Collect all ACIS-bearing entities: Solid3D, Region, Body.
-        let entries: Vec<(Handle, EntityType)> = self
+        // Collect all ACIS-bearing entities with their color resolved now,
+        // so the parallel phase only sees owned data.
+        let entries: Vec<(Handle, EntityType, [f32; 4])> = self
             .document
             .entities()
             .filter_map(|e| match e {
-                EntityType::Solid3D(_) | EntityType::Region(_) | EntityType::Body(_) =>
-                    Some((e.common().handle, e.clone())),
+                EntityType::Solid3D(_) | EntityType::Region(_) | EntityType::Body(_) => {
+                    let color = tessellate::aci_to_rgba(&e.common().color);
+                    Some((e.common().handle, e.clone(), color))
+                }
                 _ => None,
             })
             .collect();
-        for (handle, entity) in entries {
-            let color = if let Some(e) = self.document.get_entity(handle) {
-                tessellate::aci_to_rgba(&e.common().color)
-            } else {
-                [0.7, 0.7, 0.7, 1.0]
-            };
-            let model = match &entity {
-                EntityType::Solid3D(s) => solid3d_tess::tessellate_solid3d(s, color),
-                EntityType::Region(r)  => solid3d_tess::tessellate_region(r, color),
-                EntityType::Body(b)    => solid3d_tess::tessellate_body(b, color),
-                _ => None,
-            };
-            if let Some(m) = model {
-                self.meshes.insert(handle, m);
-            }
-        }
+
+        use rayon::prelude::*;
+        self.meshes = entries
+            .into_par_iter()
+            .filter_map(|(handle, entity, color)| {
+                let model = match &entity {
+                    EntityType::Solid3D(s) => solid3d_tess::tessellate_solid3d(s, color),
+                    EntityType::Region(r)  => solid3d_tess::tessellate_region(r, color),
+                    EntityType::Body(b)    => solid3d_tess::tessellate_body(b, color),
+                    _ => None,
+                };
+                model.map(|m| (handle, m))
+            })
+            .collect();
+
         self.bump_geometry();
     }