Keep OBJ Texture Coordinates That Carry a W Component

The vt parser stopped reading the optional third component when texture
coordinates were cut down to u and v, but the check that nothing is left
on the line stayed. A legal "vt u v w" line was therefore rejected and
silently dropped, shifting every later texture index. The w component is
parsed again and discarded.

The texture coordinate stride is now a named constant, OBJ_TEXCOORD_LENGTH,
used by the parser and the importer, so the relative-index rebase cannot
drift from the storage layout again.

src/libslic3r/Format/DRC.cpp

@@ -48,24 +48,37 @@ bool load_drc(const char *path, TriangleMesh *meshptr)
         indexed_triangle_set its;
 
         const PointAttribute *const positions = dracoMesh.GetNamedAttribute(GeometryAttribute::POSITION);
+        if (positions == nullptr) {
+            BOOST_LOG_TRIVIAL(error) << "load_drc: the mesh has no POSITION attribute";
+            return false;
+        }
         size_t num_vertices = positions->size();
         its.vertices.reserve(num_vertices);
         for (AttributeValueIndex i(0); i < num_vertices; ++ i) {
             float pos[3];
-            positions->ConvertValue<float>(i, 3, pos);
+            if (!positions->ConvertValue<float>(i, 3, pos)) {
+                BOOST_LOG_TRIVIAL(error) << "load_drc: invalid vertex position";
+                return false;
+            }
             its.vertices.emplace_back(pos[0], pos[1], pos[2]);
         }
 
+        // The Draco decoder does not check face indices against the point count.
+        const uint32_t num_points = dracoMesh.num_points();
         size_t num_faces = dracoMesh.num_faces();
         its.indices.reserve(num_faces);
         for (FaceIndex i(0); i < num_faces; ++ i) {
-            Mesh::Face face = dracoMesh.face(i);
-
-            its.indices.emplace_back(
-                positions->mapped_index(face[0]).value(),
-                positions->mapped_index(face[1]).value(),
-                positions->mapped_index(face[2]).value()
-            );
+            const Mesh::Face &face = dracoMesh.face(i);
+            stl_triangle_vertex_indices facet;
+            for (int k = 0; k < 3; ++ k) {
+                const size_t vertex_idx = face[k].value() < num_points ? positions->mapped_index(face[k]).value() : num_vertices;
+                if (vertex_idx >= num_vertices) {
+                    BOOST_LOG_TRIVIAL(error) << "load_drc: invalid vertex index";
+                    return false;
+                }
+                facet[k] = static_cast<int>(vertex_idx);
+            }
+            its.indices.emplace_back(facet);
         }
 
         *meshptr = TriangleMesh(std::move(its));

src/libslic3r/Format/OBJ.cpp

@@ -166,10 +166,15 @@ bool load_obj(const char *path, TriangleMesh *meshptr, ObjInfo& obj_info, std::s
                             obj_info.uv_map_pngs[face_index] = png_name;
                         }
                         if (data.textureCoordinates.size() > 0) {
-                            Vec2f                uv0(data.textureCoordinates[uvs[0] * 2], data.textureCoordinates[uvs[0] * 2 + 1]);
-                            Vec2f                uv1(data.textureCoordinates[uvs[1] * 2], data.textureCoordinates[uvs[1] * 2 + 1]);
-                            Vec2f                uv2(data.textureCoordinates[uvs[2] * 2], data.textureCoordinates[uvs[2] * 2 + 1]);
-                            std::array<Vec2f, 3> uv_array{uv0, uv1, uv2};
+                            // A face vertex may omit vt or reference a missing one. Fall back to (0, 0) rather than
+                            // skipping the face, so obj_info.uvs stays aligned with the face indices.
+                            const int uv_count = static_cast<int>(data.textureCoordinates.size() / OBJ_TEXCOORD_LENGTH);
+                            auto      uv_at    = [&data, uv_count](int idx) -> Vec2f {
+                                if (idx < 0 || idx >= uv_count)
+                                    return Vec2f::Zero();
+                                return Vec2f(data.textureCoordinates[idx * OBJ_TEXCOORD_LENGTH], data.textureCoordinates[idx * OBJ_TEXCOORD_LENGTH + 1]);
+                            };
+                            std::array<Vec2f, 3> uv_array{uv_at(uvs[0]), uv_at(uvs[1]), uv_at(uvs[2])};
                             obj_info.uvs.emplace_back(uv_array);
                         }
                         obj_info.face_colors.emplace_back(face_color);

src/libslic3r/Format/objparser.cpp

@@ -51,19 +51,18 @@ static bool obj_parseline(const char *line, ObjData &data)
 				line = endptr;
 				EATWS();
 			}
-			/*double w = 0;
+			// The optional w is accepted but not stored: only u and v are used.
 			if (*line != 0) {
-				w = strtod(line, &endptr);
+				strtod(line, &endptr);
 				if (endptr == 0 || (*endptr != ' ' && *endptr != '\t' && *endptr != 0))
 					return false;
 				line = endptr;
 				EATWS();
-			}*/
+			}
 			if (*line != 0)
 				return false;
 			data.textureCoordinates.push_back((float)u);
 			data.textureCoordinates.push_back((float)v);
-			//data.textureCoordinates.push_back((float)w);
 			break;
 		}
 		case 'n':
@@ -245,7 +244,7 @@ static bool obj_parseline(const char *line, ObjData &data)
             else
 				-- vertex.normalIdx;
 			if (vertex.textureCoordIdx < 0)
-                vertex.textureCoordIdx += (int)data.textureCoordinates.size() / 3;
+                vertex.textureCoordIdx += (int)data.textureCoordinates.size() / OBJ_TEXCOORD_LENGTH;
             else
 				-- vertex.textureCoordIdx;
 			data.vertices.push_back(vertex);

src/libslic3r/Format/objparser.hpp

@@ -92,6 +92,7 @@ inline bool operator==(const ObjSmoothingGroup &v1, const ObjSmoothingGroup &v2)
 }
 #define OBJ_VERTEX_COLOR_ALPHA 6
 #define OBJ_VERTEX_LENGTH   7  // x, y, z, color_x,color_y,color_z,color_w
+#define OBJ_TEXCOORD_LENGTH 2  // u, v
 #define ONE_FACE_SIZE 4//ONE_FACE format: f 8/4/6 7/3/6 6/2/6 -1/-1/-1
 struct ObjData {
 	// Version of the data structure for load / store in the private binary format.
@@ -100,7 +101,7 @@ struct ObjData {
 	// x, y, z, color_x,color_y,color_z,color_w
 	std::vector<float>				coordinates;
     bool                            has_vertex_color{false};
-	// u, v, w
+	// u, v
 	std::vector<float>				textureCoordinates;
 	// x, y, z
 	std::vector<float>				normals;

tests/libslic3r/CMakeLists.txt

@@ -14,6 +14,7 @@ add_executable(${_TEST_NAME}_tests
     test_clipper_utils.cpp
     test_config.cpp
     test_config_variant_expansion.cpp
+    test_drc.cpp
     test_toolordering_nozzle_group.cpp
     test_preset_bundle_loading.cpp
     test_preset_setting_id.cpp
@@ -32,6 +33,7 @@ add_executable(${_TEST_NAME}_tests
     test_mutable_priority_queue.cpp
     test_minimum_spanning_tree.cpp
     test_nozzle_volume_type.cpp
+    test_obj.cpp
     test_step.cpp
     test_stl.cpp
     test_triangle_selector.cpp
@@ -67,7 +69,9 @@ if (TARGET OpenVDB::openvdb)
     target_sources(${_TEST_NAME}_tests PRIVATE test_hollowing.cpp)
 endif()
 
-target_link_libraries(${_TEST_NAME}_tests test_common libslic3r Catch2::Catch2WithMain)
+# libslic3r links Draco privately; test_drc.cpp encodes its own fixtures.
+find_package(Draco REQUIRED)
+target_link_libraries(${_TEST_NAME}_tests test_common libslic3r draco::draco Catch2::Catch2WithMain)
 target_include_directories(${_TEST_NAME}_tests PRIVATE ${CMAKE_SOURCE_DIR}/src)
 set_property(TARGET ${_TEST_NAME}_tests PROPERTY FOLDER "tests")
 

tests/libslic3r/test_drc.cpp

@@ -0,0 +1,71 @@
+#include <catch2/catch_all.hpp>
+
+#include "libslic3r/Format/DRC.hpp"
+#include "libslic3r/TriangleMesh.hpp"
+
+#include <boost/nowide/fstream.hpp>
+
+#include <draco/compression/encode.h>
+#include <draco/mesh/mesh.h>
+
+#include "test_utils.hpp"
+
+using namespace Slic3r;
+
+namespace {
+
+// Encodes one triangle whose vertices carry a single attribute of the given type.
+// The decoder accepts both a mesh without POSITION and a face index past the point count.
+void write_drc_triangle(const std::string &path, draco::GeometryAttribute::Type attribute_type, uint32_t second_point)
+{
+    draco::Mesh mesh;
+    mesh.set_num_points(3);
+    draco::GeometryAttribute attribute;
+    attribute.Init(attribute_type, nullptr, 3, draco::DT_FLOAT32, false, sizeof(float) * 3, 0);
+    const int attribute_id = mesh.AddAttribute(attribute, true, 3);
+    const float points[3][3] = {{0, 0, 0}, {1, 0, 0}, {0, 1, 0}};
+    for (int i = 0; i < 3; ++i)
+        mesh.attribute(attribute_id)->SetAttributeValue(draco::AttributeValueIndex(i), points[i]);
+    draco::Mesh::Face face;
+    face[0] = draco::PointIndex(0);
+    face[1] = draco::PointIndex(second_point);
+    face[2] = draco::PointIndex(2);
+    mesh.AddFace(face);
+
+    draco::Encoder encoder;
+    encoder.SetEncodingMethod(draco::MESH_SEQUENTIAL_ENCODING);
+    draco::EncoderBuffer buffer;
+    REQUIRE(encoder.EncodeMeshToBuffer(mesh, &buffer).ok());
+    boost::nowide::ofstream out(path, std::ios::binary);
+    out.write(buffer.data(), static_cast<std::streamsize>(buffer.size()));
+}
+
+} // namespace
+
+TEST_CASE("A Draco triangle with positions loads", "[DRC]")
+{
+    ScopedTemporaryFile drc(".drc");
+    write_drc_triangle(drc.string(), draco::GeometryAttribute::POSITION, 1);
+
+    TriangleMesh mesh;
+    REQUIRE(load_drc(drc.string().c_str(), &mesh));
+    CHECK(mesh.facets_count() == 1);
+}
+
+TEST_CASE("A Draco mesh without a POSITION attribute fails to load", "[DRC][Regression]")
+{
+    ScopedTemporaryFile drc(".drc");
+    write_drc_triangle(drc.string(), draco::GeometryAttribute::GENERIC, 1);
+
+    TriangleMesh mesh;
+    CHECK_FALSE(load_drc(drc.string().c_str(), &mesh));
+}
+
+TEST_CASE("A Draco face referencing a missing point fails to load", "[DRC][Regression]")
+{
+    ScopedTemporaryFile drc(".drc");
+    write_drc_triangle(drc.string(), draco::GeometryAttribute::POSITION, 200);
+
+    TriangleMesh mesh;
+    CHECK_FALSE(load_drc(drc.string().c_str(), &mesh));
+}

tests/libslic3r/test_obj.cpp

@@ -0,0 +1,122 @@
+#include <catch2/catch_all.hpp>
+
+#include "libslic3r/TriangleMesh.hpp"
+#include "libslic3r/Format/OBJ.hpp"
+
+#include <boost/nowide/fstream.hpp>
+
+#include "test_utils.hpp"
+
+using namespace Slic3r;
+using Catch::Matchers::WithinAbs;
+
+namespace {
+
+struct LoadedObj
+{
+    bool         ok{false};
+    TriangleMesh mesh;
+    ObjInfo      info;
+};
+
+// A tetrahedron with a material and two texture coordinates, (0.25, 0.5) and (0.75, 1).
+// Only the first face and the vt lines are varied; the other three faces reference vt 1.
+LoadedObj load_textured_tetrahedron(const std::string &first_face, const std::string &vts = "vt 0.25 0.5\nvt 0.75 1\n")
+{
+    ScopedTemporaryFile obj(".obj");
+    ScopedTemporaryFile mtl(".mtl");
+    {
+        boost::nowide::ofstream out(mtl.string());
+        out << "newmtl a\nKd 1 0 0\n";
+    }
+    {
+        boost::nowide::ofstream out(obj.string());
+        out << "mtllib " << mtl.path().filename().string() << "\n"
+            << "v 0 0 0\nv 10 0 0\nv 0 10 0\nv 0 0 10\n"
+            << vts
+            << "usemtl a\n"
+            << first_face << "\n"
+            << "f 1/1 2/1 4/1\nf 1/1 4/1 3/1\nf 2/1 3/1 4/1\n";
+    }
+    LoadedObj   loaded;
+    std::string message;
+    loaded.ok = load_obj(obj.string().c_str(), &loaded.mesh, loaded.info, message);
+    return loaded;
+}
+
+} // namespace
+
+TEST_CASE("An out-of-range texture index falls back to a zero UV and keeps the geometry", "[OBJ][Regression]")
+{
+    const LoadedObj loaded = load_textured_tetrahedron("f 1/1000000000 3/1 2/1");
+
+    REQUIRE(loaded.ok);
+    CHECK(loaded.mesh.facets_count() == 4);
+    REQUIRE(loaded.info.uvs.size() == 4);
+    const std::array<Vec2f, 3> &uv = loaded.info.uvs.front();
+    CHECK_THAT(uv[0].x(), WithinAbs(0., 1e-6));
+    CHECK_THAT(uv[0].y(), WithinAbs(0., 1e-6));
+    CHECK_THAT(uv[1].x(), WithinAbs(0.25, 1e-6));
+    CHECK_THAT(uv[1].y(), WithinAbs(0.5, 1e-6));
+}
+
+TEST_CASE("A face without texture indices loads among faces that have them", "[OBJ][Regression]")
+{
+    const LoadedObj loaded = load_textured_tetrahedron("f 1 3 2");
+
+    REQUIRE(loaded.ok);
+    CHECK(loaded.mesh.facets_count() == 4);
+    // One UV entry per face, so later faces keep their own coordinates.
+    REQUIRE(loaded.info.uvs.size() == 4);
+    for (const Vec2f &uv : loaded.info.uvs.front()) {
+        CHECK_THAT(uv.x(), WithinAbs(0., 1e-6));
+        CHECK_THAT(uv.y(), WithinAbs(0., 1e-6));
+    }
+    CHECK_THAT(loaded.info.uvs[1][0].x(), WithinAbs(0.25, 1e-6));
+    CHECK_THAT(loaded.info.uvs[1][0].y(), WithinAbs(0.5, 1e-6));
+}
+
+TEST_CASE("A negative texture index counts back from the last texture coordinate", "[OBJ]")
+{
+    // -1 is the most recent vt (0.75, 1), -2 the one before it (0.25, 0.5).
+    const LoadedObj loaded = load_textured_tetrahedron("f 1/-2 3/-1 2/-1");
+
+    REQUIRE(loaded.ok);
+    CHECK(loaded.mesh.facets_count() == 4);
+    REQUIRE(loaded.info.uvs.size() == 4);
+    const std::array<Vec2f, 3> &uv = loaded.info.uvs.front();
+    CHECK_THAT(uv[0].x(), WithinAbs(0.25, 1e-6));
+    CHECK_THAT(uv[0].y(), WithinAbs(0.5, 1e-6));
+    CHECK_THAT(uv[1].x(), WithinAbs(0.75, 1e-6));
+    CHECK_THAT(uv[1].y(), WithinAbs(1., 1e-6));
+}
+
+TEST_CASE("Texture coordinates with a w component are kept", "[OBJ][Regression]")
+{
+    const LoadedObj loaded = load_textured_tetrahedron("f 1/1 3/2 2/2", "vt 0.25 0.5 0\nvt 0.75 1 0\n");
+
+    REQUIRE(loaded.ok);
+    CHECK(loaded.mesh.facets_count() == 4);
+    REQUIRE(loaded.info.uvs.size() == 4);
+    const std::array<Vec2f, 3> &uv = loaded.info.uvs.front();
+    CHECK_THAT(uv[0].x(), WithinAbs(0.25, 1e-6));
+    CHECK_THAT(uv[0].y(), WithinAbs(0.5, 1e-6));
+    CHECK_THAT(uv[1].x(), WithinAbs(0.75, 1e-6));
+    CHECK_THAT(uv[1].y(), WithinAbs(1., 1e-6));
+}
+
+TEST_CASE("A texture coordinate with w does not shift the indices of the ones after it", "[OBJ][Regression]")
+{
+    // The w on the first vt used to drop that line, so vt 2 resolved to the third coordinate.
+    const LoadedObj loaded = load_textured_tetrahedron("f 1/2 3/3 2/-1", "vt 0.1 0.2 0\nvt 0.25 0.5\nvt 0.75 1\n");
+
+    REQUIRE(loaded.ok);
+    REQUIRE(loaded.info.uvs.size() == 4);
+    const std::array<Vec2f, 3> &uv = loaded.info.uvs.front();
+    CHECK_THAT(uv[0].x(), WithinAbs(0.25, 1e-6));
+    CHECK_THAT(uv[0].y(), WithinAbs(0.5, 1e-6));
+    CHECK_THAT(uv[1].x(), WithinAbs(0.75, 1e-6));
+    CHECK_THAT(uv[1].y(), WithinAbs(1., 1e-6));
+    CHECK_THAT(uv[2].x(), WithinAbs(0.75, 1e-6));
+    CHECK_THAT(uv[2].y(), WithinAbs(1., 1e-6));
+}