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feat: implement OCS→WCS transform for Arc, Circle, and Line

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Entities carrying a non-standard extrusion normal (normal ≠ (0,0,1)) were
rendered flat in the XY plane. The DXF arbitrary-axis algorithm is now
implemented in scene::transform::{ocs_axes, ocs_point_to_wcs} and applied
during tessellation of Arc, Circle, and Line so they render correctly on
tilted planes in 3D DXF files.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Hakan Seven 2026-05-02 17:13:42 +03:00
commit 674a94f756
4 changed files with 117 additions and 33 deletions
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32
src/entities/arc.rs
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@ -18,8 +18,12 @@ fn to_truck(arc: &Arc) -> TruckEntity {
let r = arc.radius;
let sa = arc.start_angle;
let ea = arc.end_angle;
// normal.z < 0 means the arc sweeps clockwise in the XY plane;
// place the midpoint on the CW side so the curve goes the right way.
let normal = (arc.normal.x, arc.normal.y, arc.normal.z);
// Compute OCS basis vectors for this entity's normal.
let (ax, ay) = crate::scene::transform::ocs_axes(normal);
// When normal.z < 0 the arc sweeps clockwise; reverse the half-angle choice.
let mid_a = if arc.normal.z < 0.0 {
let cw_span = if sa >= ea { sa - ea } else { sa - ea + TAU };
sa - cw_span * 0.5
@ -27,18 +31,32 @@ fn to_truck(arc: &Arc) -> TruckEntity {
let ccw_end = if ea >= sa { ea } else { ea + TAU };
sa + (ccw_end - sa) * 0.5
};
let p_start = Point3::new(cx + r * sa.cos(), cy + r * sa.sin(), cz);
let p_end = Point3::new(cx + r * ea.cos(), cy + r * ea.sin(), cz);
let p_mid = Point3::new(cx + r * mid_a.cos(), cy + r * mid_a.sin(), cz);
// Arc centre in WCS.
let (cwx, cwy, cwz) = crate::scene::transform::ocs_point_to_wcs((cx, cy, cz), normal);
// Arc points in WCS: centre_wcs + r*cos(a)*Ax + r*sin(a)*Ay
let arc_pt = |a: f64| {
let (c, s) = (a.cos(), a.sin());
Point3::new(
cwx + r * c * ax.0 + r * s * ay.0,
cwy + r * c * ax.1 + r * s * ay.1,
cwz + r * c * ax.2 + r * s * ay.2,
)
};
let p_start = arc_pt(sa);
let p_end = arc_pt(ea);
let p_mid = arc_pt(mid_a);
let v_start = builder::vertex(p_start);
let v_end = builder::vertex(p_end);
let edge = builder::circle_arc(&v_start, &v_end, p_mid);
let cv = Vec3::new(cx as f32, cy as f32, cz as f32);
let cv = Vec3::new(cwx as f32, cwy as f32, cwz as f32);
TruckEntity {
object: TruckObject::Curve(edge),
snap_pts: vec![(cv, SnapHint::Center)],
tangent_geoms: vec![TangentGeom::Circle {
center: [cx as f32, cy as f32, cz as f32],
center: [cwx as f32, cwy as f32, cwz as f32],
radius: r as f32,
}],
key_vertices: vec![],