Uniform mm-spacing spiral toolpath (Issue #22)

ARCHITECTURE.md

@@ -267,7 +267,7 @@ classDiagram
     class HelixParameters {
         double LayerHeight
         bool DirectionCCW
-        int FramesPerLayer
+        double FrameSpacingMm
         bool SpiralSlice
         bool OuterWallBracing
         int BracingContactPoints

CCL_Clay3DP/Core/BaseBuilder.cs

@@ -99,8 +99,10 @@ public static class BaseBuilder
         /// pitch as the part body.</param>
         /// <param name="beadDiameter">Material bead diameter in mm.
         /// Drives infill line spacing.</param>
-        /// <param name="framesPerLayer">Frame count per closed loop
-        /// (skirt and per-layer contour). Mirrors HelixParameters.FramesPerLayer.</param>
+        /// <param name="frameSpacingMm">Target arc-length spacing between
+        /// frames on the skirt and on each base layer contour, in mm.
+        /// Mirrors HelixParameters.FrameSpacingMm so the base prints at
+        /// the same bead density as the part body (Issue #22).</param>
         /// <returns>BaseResult with frames and bake geometry. Returns
         /// an empty result (LayerCount=0, empty lists) if the input
         /// contour is unusable — caller treats that as "no base".</returns>
@@ -109,7 +111,7 @@ public static BaseResult Build(
             BaseSettings settings,
             double layerHeight,
             double beadDiameter,
-            int framesPerLayer)
+            double frameSpacingMm)
         {
             var result = new BaseResult { LayerHeight = layerHeight };
 
@@ -142,7 +144,7 @@ public static BaseResult Build(
             if (result.SkirtCurve != null)
             {
                 result.SkirtFrames = SkirtBuilder.SampleSkirtFrames(
-                    result.SkirtCurve, framesPerLayer);
+                    result.SkirtCurve, frameSpacingMm);
             }
 
             for (int i = 0; i < n; i++)
@@ -153,7 +155,7 @@ public static BaseResult Build(
                 var contour = footprint.DuplicateCurve();
                 contour.Translate(0.0, 0.0, z);
                 result.ContourCurves.Add(contour);
-                result.Frames.AddRange(SampleContourFrames(contour, framesPerLayer));
+                result.Frames.AddRange(SampleContourFrames(contour, frameSpacingMm));
 
                 // Infill: alternating ±45 per layer. Even layers (i=0,2,…)
                 // at +45°; odd layers at -45°. Stacked, this gives a
@@ -181,14 +183,20 @@ public static BaseResult Build(
         /// <summary>
         /// Sample a closed planar contour into frames suitable for the
         /// robot. Mirrors SkirtBuilder.SampleSkirtFrames: uniform arc
-        /// length, last sample coincides with first to close the loop,
-        /// frame YAxis = +Z so the build plate stays flat regardless
+        /// length at frameSpacingMm (sample count derived from perimeter
+        /// per Issue #22), last sample coincides with first to close the
+        /// loop, frame YAxis = +Z so the build plate stays flat regardless
         /// of the SpiralFollowsCurveNormal setting.
         /// </summary>
-        private static List<Plane> SampleContourFrames(Curve contour, int sampleCount)
+        private static List<Plane> SampleContourFrames(Curve contour, double frameSpacingMm)
         {
             var frames = new List<Plane>();
-            if (contour == null || sampleCount < 4) return frames;
+            if (contour == null || frameSpacingMm <= 0.0) return frames;
+
+            double perimeter = contour.GetLength();
+            if (perimeter <= 0.0) return frames;
+
+            int sampleCount = Math.Max(4, (int)Math.Ceiling(perimeter / frameSpacingMm));
 
             double[] ts = contour.DivideByCount(sampleCount, true);
             if (ts == null || ts.Length == 0) return frames;

CCL_Clay3DP/Core/SkirtBuilder.cs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Rhino.Geometry;
@@ -92,19 +93,27 @@ private static Curve SafeOffset(Curve curve, Plane plane,
 
         /// <summary>
         /// Sample the skirt curve into a list of frames the robot can
-        /// follow. Sampling is by uniform arc-length so the per-frame
-        /// spacing is consistent regardless of where the curve's
-        /// internal seam lies. The last frame duplicates the first so
-        /// the loop closes back on itself when RoboDK traces the curve.
+        /// follow. Sampling is by uniform arc-length at frameSpacingMm
+        /// (Issue #22): the sample count is derived from the skirt's
+        /// perimeter, so the bead density matches the spiral toolpath
+        /// regardless of part size. The last frame duplicates the first
+        /// so the loop closes back on itself when RoboDK traces the curve.
         ///
         /// Frame normals are ALWAYS +Z world (build plate up). The
         /// SpiralFollowsCurveNormal toggle does not apply to the skirt
         /// — it sits flat on the plate by construction.
         /// </summary>
-        public static List<Plane> SampleSkirtFrames(Curve skirt, int sampleCount)
+        public static List<Plane> SampleSkirtFrames(Curve skirt, double frameSpacingMm)
         {
             var frames = new List<Plane>();
-            if (skirt == null || sampleCount < 4) return frames;
+            if (skirt == null || frameSpacingMm <= 0.0) return frames;
+
+            double perimeter = skirt.GetLength();
+            if (perimeter <= 0.0) return frames;
+
+            // Sample count = perimeter / spacing, but never below 4 — a
+            // closed loop needs at least four corners to be meaningful.
+            int sampleCount = Math.Max(4, (int)Math.Ceiling(perimeter / frameSpacingMm));
 
             // DivideByCount(N, true) returns N+1 parameters, with the last
             // one at curve.Domain.T1 — for a closed curve that coincides