fix(hatch): radial gradients and correct gradient stop colours

A gradient hatch was drawn linear from the entity colour to its second
stop, so a red->yellow spherical fill came out as a pale linear wash. Two
fixes:
- Colour: start from the gradient's first stop, not the entity colour.
  hatch_model_from_dxf already baked stop-0 in; stop synced_hatch_models
  from clobbering it with the entity's resolved colour for gradient fills.
- Shape: spherical / hemispherical / curved gradient names now render as a
  radial fill (new shader mode 3, centred on the boundary with radius to the
  farthest vertex) instead of linear. Native and web shaders both updated.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/modules/draw/draw/hatch.rs

@@ -395,6 +395,7 @@ impl GradientCommand {
             pattern: HatchPattern::Gradient {
                 angle_deg: 0.0,
                 color2: [0.18, 0.18, 0.18, 0.0],
+                radial: false,
             },
             name: "LINEAR".into(),
             color: [0.30, 0.60, 0.95, 0.80],

src/scene/entity.rs

@@ -626,7 +626,12 @@ impl Scene {
                 // emitted first so LessEqual layering keeps it underneath.
                 let mut backdrop: Option<HatchModel> = None;
                 if let Some(e) = entity {
-                    m.color = self.render_style(e).0;
+                    // A gradient's colour is its first stop (already baked into
+                    // the cached model); only solid / pattern fills take the
+                    // entity's resolved colour.
+                    if !matches!(m.pattern, model::hatch_model::HatchPattern::Gradient { .. }) {
+                        m.color = self.render_style(e).0;
+                    }
                     if let EntityType::Hatch(dxf) = e {
                         if let Some(bg) = crate::entities::hatch::background_color(dxf) {
                             let mut b = m.clone();
@@ -1421,16 +1426,27 @@ impl Scene {
             && !dxf.gradient_color.is_enabled()
             && !dxf.pattern.lines.is_empty();
 
+        // The gradient's first stop is the fill's start colour (not the
+        // entity colour); capture it so the HatchModel draws stop-0 → stop-1.
+        let mut gradient_color1: Option<[f32; 4]> = None;
         let mut pattern = if dxf.gradient_color.is_enabled() {
-            let color2 = dxf
-                .gradient_color
-                .colors
-                .get(1)
-                .and_then(|e| e.color.rgb())
-                .map(|(r, g, b)| [r as f32 / 255.0, g as f32 / 255.0, b as f32 / 255.0, 1.0])
-                .unwrap_or(color);
+            let stop = |i: usize| {
+                dxf.gradient_color.colors.get(i).and_then(|e| e.color.rgb()).map(
+                    |(r, g, b)| [r as f32 / 255.0, g as f32 / 255.0, b as f32 / 255.0, 1.0],
+                )
+            };
+            gradient_color1 = stop(0);
+            let color2 = stop(1).unwrap_or(color);
             let angle_deg = dxf.pattern_angle.to_degrees() as f32;
-            model::hatch_model::HatchPattern::Gradient { angle_deg, color2 }
+            // Spherical / hemispherical / curved names are radial fills; linear
+            // and cylinder names run along the angle.
+            let n = dxf.gradient_color.name.to_ascii_uppercase();
+            let radial = n.contains("SPHERICAL") || n.contains("CURVED");
+            model::hatch_model::HatchPattern::Gradient {
+                angle_deg,
+                color2,
+                radial,
+            }
         } else if dxf.is_solid {
             model::hatch_model::HatchPattern::Solid
         } else if prebaked {
@@ -1571,7 +1587,9 @@ impl Scene {
             boundary_wcs: None,
             pattern,
             name,
-            color,
+            // A gradient starts from its first stop; other fills use the
+            // entity colour.
+            color: gradient_color1.unwrap_or(color),
             angle_offset: if prebaked { 0.0 } else { dxf.pattern_angle as f32 },
             scale: if prebaked { 1.0 } else { dxf.pattern_scale as f32 },
             world_origin,

src/scene/model/hatch_model.rs

@@ -36,8 +36,14 @@ pub enum HatchPattern {
     Solid,
     /// One or more line families (PAT format).
     Pattern(Vec<PatFamily>),
-    /// Linear gradient from `color` to `color2` along `angle_deg`.
-    Gradient { angle_deg: f32, color2: [f32; 4] },
+    /// Two-stop gradient from `color` to `color2`. Linear along `angle_deg`
+    /// unless `radial`, in which case it runs from the boundary centre outward
+    /// (spherical / hemispherical / curved fills).
+    Gradient {
+        angle_deg: f32,
+        color2: [f32; 4],
+        radial: bool,
+    },
 }
 
 /// A hatched region defined by a closed polygon boundary.

src/scene/pipeline/hatch_gpu.rs

@@ -225,13 +225,21 @@ impl HatchGpu {
 
             let (mode, color2, grad_cos, grad_sin, grad_min, grad_range) = match &h.pattern {
                 HatchPattern::Solid => (1u32, [0.0; 4], 0.0, 0.0, 0.0, 1.0),
-                HatchPattern::Gradient { angle_deg, color2 } => {
-                    let r = angle_deg.to_radians();
-                    // Gradient projection range (proj_min / proj_range) —
-                    // computed at upload time, identical to per-hatch path.
-                    let (gmin, gmax) = boundary_projection_range(&h.boundary, r);
-                    let grange = (gmax - gmin).max(1.0);
-                    (2u32, *color2, r.cos(), r.sin(), gmin, grange)
+                HatchPattern::Gradient { angle_deg, color2, radial } => {
+                    if *radial {
+                        // Radial fill: the boundary is stored relative to its
+                        // centre (`world_origin`), so the centre is the local
+                        // origin; radius = the farthest boundary vertex. mode 3.
+                        let radius = radial_radius(&h.boundary);
+                        (3u32, *color2, 0.0, 0.0, 0.0, radius)
+                    } else {
+                        let r = angle_deg.to_radians();
+                        // Gradient projection range (proj_min / proj_range) —
+                        // computed at upload time, identical to per-hatch path.
+                        let (gmin, gmax) = boundary_projection_range(&h.boundary, r);
+                        let grange = (gmax - gmin).max(1.0);
+                        (2u32, *color2, r.cos(), r.sin(), gmin, grange)
+                    }
                 }
                 HatchPattern::Pattern(fams) => {
                     for fam in fams {
@@ -559,6 +567,18 @@ fn boundary_projection_range(boundary: &[[f32; 2]], theta: f32) -> (f32, f32) {
     (lo, hi)
 }
 
+/// Radius of a radial gradient — the distance from the boundary centre (the
+/// local origin, since vertices are stored relative to it) to the farthest
+/// vertex, so `t = 1` (the end colour) reaches the corners.
+fn radial_radius(boundary: &[[f32; 2]]) -> f32 {
+    boundary
+        .iter()
+        .filter(|p| p[0].is_finite() && p[1].is_finite())
+        .map(|p| (p[0] * p[0] + p[1] * p[1]).sqrt())
+        .fold(0.0_f32, f32::max)
+        .max(1.0)
+}
+
 // PatFamily is re-exported by hatch_model so we don't need to import
 // it explicitly anywhere else — but rust needs the type referenced to
 // confirm the layout assumption above.

src/scene/pipeline/hatch_web_gpu.rs

@@ -110,9 +110,14 @@ impl HatchWebGpu {
         let (mode, color2, grad_cos, grad_sin) = match &model.pattern {
             HatchPattern::Solid => (1u32, [0.0f32; 4], 0.0f32, 0.0f32),
             HatchPattern::Pattern(_) => (0u32, [0.0f32; 4], 0.0f32, 0.0f32),
-            HatchPattern::Gradient { angle_deg, color2 } => {
-                let r = angle_deg.to_radians();
-                (2u32, *color2, r.cos(), r.sin())
+            HatchPattern::Gradient { angle_deg, color2, radial } => {
+                if *radial {
+                    // Radial: centre is the local origin; grad_cos/sin unused.
+                    (3u32, *color2, 0.0, 0.0)
+                } else {
+                    let r = angle_deg.to_radians();
+                    (2u32, *color2, r.cos(), r.sin())
+                }
             }
         };
 
@@ -181,6 +186,16 @@ impl HatchWebGpu {
                 // Floor matches the desktop hatch renderer (hatch_gpu.rs).
                 (proj_min, (proj_max - proj_min).max(1.0))
             }
+        } else if mode == 3 {
+            // Radial: range = the farthest boundary vertex from the centre.
+            let radius = model
+                .boundary
+                .iter()
+                .filter(|v| v[0].is_finite() && v[1].is_finite())
+                .map(|&[x, y]| (x * x + y * y).sqrt())
+                .fold(0.0_f32, f32::max)
+                .max(1.0);
+            (0.0, radius)
         } else {
             (0.0, 1.0)
         };

src/scene/pipeline/wipeout_gpu.rs

@@ -138,7 +138,7 @@ impl WipeoutGpu {
         let (mode, color2, grad_cos, grad_sin) = match &model.pattern {
             HatchPattern::Solid => (1u32, [0.0f32; 4], 0.0f32, 0.0f32),
             HatchPattern::Pattern(_) => (0u32, [0.0f32; 4], 0.0f32, 0.0f32),
-            HatchPattern::Gradient { angle_deg, color2 } => {
+            HatchPattern::Gradient { angle_deg, color2, .. } => {
                 let r = angle_deg.to_radians();
                 (2u32, *color2, r.cos(), r.sin())
             }

src/shaders/hatch.wgsl

@@ -274,6 +274,11 @@ fn check_family(
         let proj = v.xz.x * inst.grad_cos + v.xz.y * inst.grad_sin;
         let t = clamp((proj - inst.grad_min) / inst.grad_range, 0.0, 1.0);
         return mix(inst.color, inst.color2, t);
+    } else if inst.mode == 3u {
+        // Radial gradient: centre is (grad_cos, grad_sin), radius is grad_range.
+        let d = length(v.xz - vec2<f32>(inst.grad_cos, inst.grad_sin));
+        let t = clamp(d / inst.grad_range, 0.0, 1.0);
+        return mix(inst.color, inst.color2, t);
     }
 
     // 3. Pattern LOD: when the densest family's spacing projects below

src/shaders/hatch_web.wgsl

@@ -228,6 +228,11 @@ fn check_family(
         let proj = v.xz.x * h.grad_cos + v.xz.y * h.grad_sin;
         let t    = clamp((proj - h.grad_min) / h.grad_range, 0.0, 1.0);
         return mix(h.color, h.color2, t);
+    } else if h.mode == 3u {
+        // Radial gradient: centre is (grad_cos, grad_sin), radius is grad_range.
+        let d = length(v.xz - vec2<f32>(h.grad_cos, h.grad_sin));
+        let t = clamp(d / h.grad_range, 0.0, 1.0);
+        return mix(h.color, h.color2, t);
     }
 
     // Pattern LOD: when the densest family projects below 2 px, lines blur into