mesh-tool: mesht - create/inspect/edit OBJ+STL with ASCII multi-view rendering

- OBJ read/write (multi-object, ngon fan-triangulation, negative indices),
  STL binary+ascii with auto-detect and vertex welding
- info: bbox/size/area/volume + watertightness via edge manifold stats
- view: z-buffered orthographic ASCII renders (front/side/top/iso/back)
- transform: center/mirror/scale/rotate/translate/fit, per-object filter,
  winding auto-flip on negative determinant
- create: box/sphere/cylinder/cone/plane/torus; merge; convert
- go tests: primitive volumes vs analytic values, roundtrips, topology

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

mesh-tool/mesh/mesh_test.go

@@ -0,0 +1,184 @@
+package mesh
+
+import (
+	"bytes"
+	"math"
+	"strings"
+	"testing"
+)
+
+func almost(t *testing.T, name string, got, want, tol float64) {
+	t.Helper()
+	if math.Abs(got-want) > tol {
+		t.Errorf("%s = %g, want %g (±%g)", name, got, want, tol)
+	}
+}
+
+func TestPrimitiveVolumes(t *testing.T) {
+	box := Box(Vec3{1, 2, 3})
+	almost(t, "box volume", box.SignedVolume(), 6, 1e-9)
+	almost(t, "box area", box.SurfaceArea(), 22, 1e-9)
+	if !box.Closed() {
+		t.Error("box should be watertight")
+	}
+
+	sph := Sphere(1, 64, 32)
+	almost(t, "sphere volume", sph.SignedVolume(), 4*math.Pi/3, 0.07)
+	almost(t, "sphere area", sph.SurfaceArea(), 4*math.Pi, 0.15)
+	if !sph.Closed() {
+		t.Error("sphere should be watertight")
+	}
+
+	cyl := Cylinder(0.5, 2, 64)
+	almost(t, "cylinder volume", cyl.SignedVolume(), math.Pi*0.25*2, 0.01)
+	if !cyl.Closed() {
+		t.Error("cylinder should be watertight")
+	}
+
+	cone := Cone(1, 3, 64)
+	almost(t, "cone volume", cone.SignedVolume(), math.Pi/3*3, 0.02)
+	if !cone.Closed() {
+		t.Error("cone should be watertight")
+	}
+
+	tor := Torus(2, 0.5, 64, 32)
+	almost(t, "torus volume", tor.SignedVolume(), 2*math.Pi*math.Pi*2*0.25, 0.25)
+	if !tor.Closed() {
+		t.Error("torus should be watertight")
+	}
+}
+
+func TestBBoxAndMeasure(t *testing.T) {
+	box := Box(Vec3{2, 4, 6})
+	mn, mx := box.BBox()
+	if mn != (Vec3{-1, -2, -3}) || mx != (Vec3{1, 2, 3}) {
+		t.Errorf("bbox = %v..%v", mn, mx)
+	}
+}
+
+func TestTransformMirrorKeepsVolumePositive(t *testing.T) {
+	box := Box(Vec3{1, 1, 1})
+	box.Apply(ScaleXYZ(Vec3{-1, 1, 1}))
+	almost(t, "mirrored box volume", box.SignedVolume(), 1, 1e-9)
+	box.Apply(RotateY(45).Mul(RotateX(30)))
+	almost(t, "rotated box volume", box.SignedVolume(), 1, 1e-9)
+	box.Apply(Translate(Vec3{10, -5, 3}))
+	almost(t, "translated box volume", box.SignedVolume(), 1, 1e-6)
+}
+
+func TestOBJRoundTrip(t *testing.T) {
+	scene := &Scene{Meshes: []*Mesh{Box(Vec3{1, 2, 3}), Sphere(1, 8, 4)}}
+	scene.Meshes[0].Name = "crate"
+	scene.Meshes[1].Name = "ball"
+	var buf bytes.Buffer
+	if err := WriteOBJ(&buf, scene); err != nil {
+		t.Fatal(err)
+	}
+	back, err := ReadOBJ(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(back.Meshes) != 2 {
+		t.Fatalf("got %d meshes, want 2", len(back.Meshes))
+	}
+	if back.Meshes[0].Name != "crate" || back.Meshes[1].Name != "ball" {
+		t.Errorf("names = %q, %q", back.Meshes[0].Name, back.Meshes[1].Name)
+	}
+	almost(t, "roundtrip crate volume", back.Meshes[0].SignedVolume(), 6, 1e-9)
+	if !back.Meshes[1].Closed() {
+		t.Error("roundtripped sphere should stay watertight")
+	}
+}
+
+func TestOBJQuadsAndNegativeIndices(t *testing.T) {
+	src := `
+v 0 0 0
+v 1 0 0
+v 1 1 0
+v 0 1 0
+f 1 2 3 4
+f -4 -3 -2
+`
+	s, err := ReadOBJ(strings.NewReader(src))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := s.TotalTris(); got != 3 {
+		t.Errorf("tris = %d, want 3 (quad fan + one negative-index tri)", got)
+	}
+}
+
+func TestSTLRoundTrips(t *testing.T) {
+	box := Box(Vec3{1, 2, 3})
+	scene := &Scene{Meshes: []*Mesh{box}}
+
+	var bin bytes.Buffer
+	if err := WriteSTLBinary(&bin, scene); err != nil {
+		t.Fatal(err)
+	}
+	back, err := ReadSTL(bytes.NewReader(bin.Bytes()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	m := back.Meshes[0]
+	if len(m.Verts) != 8 {
+		t.Errorf("binary stl weld: %d verts, want 8", len(m.Verts))
+	}
+	almost(t, "binary stl volume", m.SignedVolume(), 6, 1e-6)
+
+	var asc bytes.Buffer
+	if err := WriteSTLAscii(&asc, scene); err != nil {
+		t.Fatal(err)
+	}
+	back2, err := ReadSTL(bytes.NewReader(asc.Bytes()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	almost(t, "ascii stl volume", back2.Meshes[0].SignedVolume(), 6, 1e-6)
+	if !back2.Meshes[0].Closed() {
+		t.Error("ascii stl roundtrip should stay watertight")
+	}
+}
+
+func TestSceneAppendRenames(t *testing.T) {
+	a := &Scene{Meshes: []*Mesh{Box(Vec3{1, 1, 1})}}
+	b := &Scene{Meshes: []*Mesh{Box(Vec3{2, 2, 2})}}
+	a.Append(b)
+	if a.Meshes[0].Name == a.Meshes[1].Name {
+		t.Errorf("duplicate names after append: %q", a.Meshes[0].Name)
+	}
+}
+
+func TestRenderASCII(t *testing.T) {
+	sph := Sphere(1, 32, 16)
+	out := RenderASCII(sph, Views["front"], 40)
+	if !strings.Contains(out, "front view") {
+		t.Errorf("missing header:\n%s", out)
+	}
+	ink := 0
+	for _, r := range out {
+		if strings.ContainsRune(shadeRamp[1:], r) {
+			ink++
+		}
+	}
+	if ink < 100 {
+		t.Errorf("sphere render suspiciously empty (%d shaded cells):\n%s", ink, out)
+	}
+	// a sphere should be roughly as tall as wide after aspect correction
+	lines := strings.Split(strings.TrimRight(out, "\n"), "\n")
+	rows := len(lines) - 2 // minus the two header lines
+	if rows < 15 || rows > 25 {
+		t.Errorf("40-wide sphere should be ~20 rows, got %d", rows)
+	}
+}
+
+func TestEdgeStatsOpenMesh(t *testing.T) {
+	p := Plane(1, 1)
+	if p.Closed() {
+		t.Error("plane must not be watertight")
+	}
+	b, nm := p.EdgeStats()
+	if b != 4 || nm != 0 {
+		t.Errorf("plane edge stats = %d boundary, %d non-manifold; want 4, 0", b, nm)
+	}
+}