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+# acadrust Integration Gaps
+
+Missing or incomplete integrations between acadrust entity definitions and H7CAD rendering/interaction systems. Ordered by priority within each category.
+
+---
+
+## Entity Field Gaps (acadrust fields ignored in tessellation)
+
+### High Impact
+
+| Entity | Ignored Field(s) | Effect |
+|---|---|---|
+| **INSERT** | `column_count`, `row_count`, `column_spacing`, `row_spacing` | MINSERT array inserts not expanded — only one copy rendered |
+| **LWPolyline** | `constant_width`, vertex `start_width` / `end_width` | Polylines always render at zero width; thick/tapered strokes lost |
+| **Polyline (legacy)** | `Vertex2D.start_width` / `end_width` | Same as above for old-format polylines |
+
+### Medium Impact
+
+| Entity | Ignored Field(s) | Effect |
+|---|---|---|
+| **Dimension** | `DIMSCALE`, `DIMASZ`, `DIMEXO`, `DIMEXE` (from dimstyle) | Arrow size hardcoded to `0.12`; extension line offsets fixed regardless of style |
+| **Spline** | `weights` (rational NURBS control point weights) | Circles/conics stored as NURBS lose curvature precision; treated as uniform B-spline |
+| **Spline** | `flags.closed` / `flags.periodic` | Closed splines may have a gap or C1 discontinuity at the join |
+| **Text / MText** | `normal` extrusion XY | Entities on tilted planes render flat in XY (rare in 2D drawings) |
+| **Hatch** | `BoundaryEdge::Spline` tessellation | Spline boundary edges plotted point-to-point instead of smooth B-spline curve — boundary appears angular |
+| **MultiLeader** | `MultiLeaderPathType::Spline` | Spline-type leader lines rendered as straight segments instead of smooth curves |
+| **RasterImage** | `clip_boundary` (polygonal/rectangular) | Clip boundary read but not applied — image renders full rectangle regardless of clip region |
+
+### Low Impact
+
+| Entity | Ignored Field(s) | Effect |
+|---|---|---|
+| **Arc / Circle / Line / Polyline** | `thickness` | No 3D extrusion along Z; invisible in pure 2D views |
+| **LWPolyline** | `plinegen` flag | Linetype pattern resets at each vertex instead of continuing |
+
+---
+
+## Entity Type Gaps (entire types with missing subsystems)
+
+### Renders Nothing / Placeholder Only
+
+| Entity | Status |
+|---|---|
+| **Face3D** | No tessellation — renders as small cross only; no snap, grip, or properties |
+| **OLE2Frame** | Bounding box + X mark only; no interactivity |
+
+### Wire Fallback Only (no full mesh)
+
+| Entity | Missing |
+|---|---|
+| **Solid3D / Region / Body** | Only ACIS wire fallback; no grip, no properties panel |
+
+### Partial Render
+
+| Entity | Missing |
+|---|---|
+| **Viewport** (paper space) | Only frame rendered; interior model-space view not composited |
+
+---
+
+## Systemic Gap — OCS→WCS Transform
+
+17 entity types carry a `normal` extrusion vector defining their Object Coordinate System but **none apply the arbitrary-axis OCS→WCS transform** during tessellation. When `normal ≠ (0, 0, 1)` the entity is incorrectly rendered flat in the XY plane.
+
+**Affected entities:** Arc, Circle, Ellipse, Point, Line, Spline, LwPolyline, Polyline, AttributeDefinition, AttributeEntity, Dimension, Hatch, MLine, Leader, Insert, Shape
+
+**Only mitigation today:** `Arc` checks `normal.z < 0` to reverse sweep direction — not a real OCS transform.
+
+**Impact:** Low for typical 2D plan files (nearly all normals are `(0,0,1)`); high for 3D DXF files with entities on non-horizontal planes.
+
+The DXF arbitrary-axis algorithm:
+```
+if |Wx| < 1/64 and |Wy| < 1/64:
+    Ax = (0,0,1) × N   (Y-world cross N)
+else:
+    Ax = (0,1,0) × N   (X-world cross N)
+Ax = normalize(Ax)
+Ay = N × Ax
+```
+Then transform each OCS point: `WCS = origin + x*Ax + y*Ay + z*N`
+
+---
+
+## Render Style Gaps (color, linetype, lineweight resolution)
+
+### High Impact
+
+| Gap | Effect | Location |
+|---|---|---|
+| **ByBlock color** not resolved through INSERT chain | ByBlock entities render white instead of inheriting INSERT's color | `render.rs::render_style_for()` |
+| **ByBlock linetype** not resolved through INSERT chain | ByBlock entities use default linetype instead of INSERT's linetype | `render.rs::render_style_for()` |
+
+### Medium Impact
+
+| Gap | Effect | Location |
+|---|---|---|
+| **ByBlock lineweight** resolved from layer instead of INSERT entity | Block children with ByBlock weight don't inherit INSERT's line weight | `render.rs` lines 213-228 |
+
+---
+
+## Text & Style Gaps
+
+### Medium Impact
+
+| Gap | Effect | Location |
+|---|---|---|
+| **TextStyle `is_backward`** flag ignored | Text with backward flag renders left-to-right instead of mirrored | `src/entities/text_support.rs::resolve_text_style()` |
+| **TextStyle `is_upside_down`** flag ignored | Text with upside-down flag renders normally instead of flipped vertically | `src/entities/text_support.rs::resolve_text_style()` |
+
+### Low-Medium Impact
+
+| Gap | Effect | Location |
+|---|---|---|
+| **Complex linetype text shapes** not rendered | Linetypes with embedded text elements (e.g. GAS_LINE with "GAS" text) show only geometry gaps | `src/scene/complex_lt.rs` |
+
+---
+
+## Polyline3D Vertex Type Gap
+
+acadrust `Vertex3D` carries `VertexFlags` (SPLINE_VERTEX, SPLINE_CONTROL) but `tessellate_polyline3d()` ignores them entirely — all vertices treated as plain points regardless of spline flag.
+
+**Effect:** Polyline3D entities with spline fitting render as straight segments instead of smooth curves.  
+**Location:** `src/entities/polyline.rs::tessellate_polyline3d()`  
+**Impact:** Medium.
+
+---
+
+## Snap Point Gaps
+
+### Critical / High
+
+| Entity | Missing Snap | Effect | Location |
+|---|---|---|---|
+| **INSERT** | `Insertion` snap point entirely absent | Cannot snap to block reference insertion point with OSNAP Insertion | `src/entities/insert.rs` — no `snap_pts` in TruckEntity |
+| **INSERT** | Nested entity snap points not traversed | Cannot snap to geometry inside a block without exploding it | `src/snap/mod.rs` — only top-level wire snap_pts checked |
+| **Hatch** | All snap points empty | Cannot snap to hatch boundary vertices/arcs with Endpoint or Midpoint | `src/scene/tessellate.rs:558` — returns `snap_pts: vec![]` |
+
+### Medium
+
+| Entity | Missing Snap | Effect | Location |
+|---|---|---|---|
+| **Dimension** | No snap hints on geometry | Cannot snap to dimension defpoints, line endpoints | `src/scene/tessellate.rs:247` — `snap_pts: vec![]` |
+| **Spline** | Fit/control points not in snap_pts | Cannot snap to spline construction points | `src/entities/spline.rs:42` |
+| **MultiLeader** | Vertices not in snap_pts | Cannot snap to leader line endpoints | `src/entities/multileader.rs:116` |
+| **MLine** | Vertices not in snap_pts | Cannot snap to multiline segment endpoints | `src/entities/mline.rs:97` |
+
+### Low
+
+| Entity | Missing Snap | Effect | Location |
+|---|---|---|---|
+| **Ellipse** (partial arc) | Endpoints not in pre-baked snap_pts | Arc endpoints emitted only as `Center`; functional via wire tessellation but semantically wrong | `src/entities/ellipse.rs:108` |
+| **Hatch** | Elevation Z ignored | Snap Z is always 0 instead of `hatch.elevation` | `src/scene/tessellate.rs:564` — hardcoded `0.0` |
+
+---
+
+## Grip Gaps
+
+| Entity | Missing Grip | Effect | Location |
+|---|---|---|---|
+| **LWPolyline** | Midpoint grips between vertices (arc segment handles) | Cannot drag a segment midpoint to adjust arc bulge | `src/entities/lwpolyline.rs` |
+
+---
+
+## Text Rendering Gaps
+
+| Gap | Effect | Location |
+|---|---|---|
+| **TextStyle `is_backward`** flag not applied | Text with backward flag renders left-to-right | `src/entities/text_support.rs::resolve_text_style()` |
+| **TextStyle `is_upside_down`** flag not applied | Text with upside-down flag renders normally | `src/entities/text_support.rs::resolve_text_style()` |
+| **Unicode characters** not in CXF fonts silently dropped | Non-ASCII characters render as blank gaps with no warning | `src/scene/cxf.rs:174` |
+
+---
+
+## DXF Reader Unit Gaps (acadrust bugs we work around)
+
+These are fixed in our post-load `fix_dxf_dimension_rotations()` in `src/io/mod.rs`, documented here for reference.
+
+| Entity | Field | DXF Code | Bug | Fix Location |
+|---|---|---|---|---|
+| **Dimension (Linear)** | `rotation` | 50 | Stored in degrees, used as radians | `io/mod.rs::fix_dxf_dimension_rotations()` |
+| **Dimension (all)** | `text_rotation` | 53 | Code 53 never parsed; always 0 | `tessellate.rs::dimension_text_natural_rotation()` |
+| **AttributeEntity** | `rotation` | 50 | No `.to_radians()` in reader | Needs fixup (not yet applied) |
+| **AttributeDefinition** | `rotation` | 50 | No `.to_radians()` in reader | Needs fixup (not yet applied) |
+| **Shape** | `rotation` | 50 | No `.to_radians()` in reader | Shape not currently rendered — low priority |
+
+---
+
+## Coverage Summary
+
+| Subsystem | Coverage |
+|---|---|
+| Tessellation | 34/41 entity types fully, 4 legacy fallback, 3 missing |
+| Snap points | 36/41 (Face3D, Solid3D, Region, Body, OLE2Frame missing) |
+| Grip points | 36/41 (same 5 missing) |
+| Properties panel | 36/41 (same 5 missing) |
+| Hit testing | 41/41 (all via fallback) |