adjust the stand a bit

test/stand_surface_test.rb

@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class StandSurfaceTest < Minitest::Test
+  def test_fuller_blends_remove_port_creases_without_thinning_or_moving_feet
+    [[6.0,6.0,6.0], [6.0,4.56,4.56]].each do |widths|
+      mesh, surface, ports, ends = junction_fixture(widths)
+      before = Marshal.load(Marshal.dump(mesh))
+      before_angles = port_angles(before, ports)
+      before_volume = surface.signed_volume
+      surface.fair_junctions!
+      surface.validate!
+      after_angles = port_angles(mesh, ports)
+
+      assert_operator after_angles.max, :<, before_angles.max * 0.40
+      # A 48-sided profile has 7.5-degree facets; compare actual flat-shaded
+      # triangle normals, allowing that discretization but not the old crease.
+      assert_operator after_angles.max, :<, 10.0, "avoid sharp creases across the arm openings"
+      collars = ports.map { |port| { ring: port[:collar_rings].last } }
+      assert_operator port_angles(mesh, collars).max, :<, 1.0, "the blend must taper smoothly into the unchanged rail"
+      assert_operator surface.signed_volume, :>, before_volume
+      assert mesh.vertices.each_with_index.all? { |p,i| p.first(2) == before.vertices[i].first(2) }, "preserve the footprint and routes"
+      assert before.vertices.each_with_index.all? { |p,i| p[2] > 1e-7 || mesh.vertices[i] == p }, "hold every table-contact vertex fixed"
+      assert ends.flatten.all? { |id| mesh.vertices[id] == before.vertices[id] }, "outer collar boundaries must stay fixed"
+      sides = surface.instance_variable_get(:@sides)
+      assert mesh.vertices.each_with_index.all? { |p,i| (p[2]-before.vertices[i][2])*sides.fetch(i,0) >= -1e-9 }, "only add thickness"
+      assert_equal before.triangles, mesh.triangles, "retain the connected topology"
+    end
+  end
+
+  private
+
+  def junction_fixture(widths)
+    mesh = MoonModel::Mesh.new(name: "junction_fixture")
+    surface = MoonModel::StandSurface.new(mesh, 48, 48)
+    section = ->(_x,_y,q,z) { [z + (q < 0 ? 3.75 : 3.0)*q, 0.0].max }
+    junction = { center: [0.0,0.0,3.0], section: section, ports: [] }
+    ends = []
+    widths.each_with_index do |width,i|
+      angle = i*2*Math::PI/3
+      port = surface.port(junction, angle, 6.0, width)
+      junction[:ports] << port
+      finish = { center: [18*Math.cos(angle),18*Math.sin(angle),3.0], section: section }
+      terminal = surface.port(finish, angle+Math::PI, 0, width)
+      surface.rail(port, terminal, width, 128, section)
+      ends << terminal[:ring]
+      center = mesh.vertex(finish[:center])
+      48.times { |j| mesh.triangle(center, terminal[:ring][j], terminal[:ring][(j+1)%48]) }
+    end
+    surface.junction(junction)
+    surface.orient!
+    [mesh, surface, junction[:ports], ends]
+  end
+
+  def port_angles(mesh, ports)
+    geometry = MoonModel::StandSurface.new(mesh, 48, 24)
+    edges = geometry.edge_faces
+    ports.flat_map do |port|
+      # Exclude the silhouette and intentional flat-bottom edges.
+      (2...22).map do |index|
+        ids = [port[:ring][index],port[:ring][index+1]].minmax
+        normals = edges.fetch(ids).map do |face,_|
+          n = geometry.normal(mesh.triangles[face])
+          length = Math.sqrt(n.sum { |v| v*v })
+          n.map { |v| v/length }
+        end
+        cosine = normals[0].zip(normals[1]).sum { |a,b| a*b }
+        Math.acos([[cosine,-1.0].max,1.0].min)*180/Math::PI
+      end
+    end
+  end
+end