ObjImporter: support quads.

Now I'm able to measure -- with the Rungholt scene from McGuire
archives, it takes it a whooping 7.3 seconds, measured with

    magnum-sceneconverter --info-meshes --profile rungholt.obj

Compared to that, AssimpImporter in the default configuration takes 10.3
seconds, but with

    magnum-sceneconverter --info-meshes --profile -I AssimpImporter \
      -i postprocess/JoinIdenticalVertices=false,postprocess/SortByPType=false \
      rungholt.obj

it takes just 4.3 seconds. And has the same vertex data size in total,
so that should probably be the default. I got some work to do, then.

doc/changelog.dox

@@ -1097,7 +1097,7 @@ See also:
     consistent with @ref Trade::SceneData::findFieldId().
 -   Added @ref Trade::MeshData::attributeId() that returns ID of an attribute
     in a set of attributes of the same name
--   @relativeref{Trade,ObjImporter} now supports negative indices
+-   @relativeref{Trade,ObjImporter} now supports quads and negative indices
 -   Added @ref Trade::TextureType::Texture1DArray,
     @relativeref{Trade::TextureType,Texture2DArray} and
     @relativeref{Trade::TextureType,CubeMapArray} in order to be able to

src/MagnumPlugins/ObjImporter/ObjImporter.cpp

@@ -383,18 +383,19 @@ Containers::Optional<MeshData> ObjImporter::doMesh(const UnsignedInt id, Unsigne
 
         /* Indices */
         } else if(keyword == "p"_s || keyword == "l"_s || keyword == "f"_s) {
-            /* Decide on how many tuples we expect */
-            std::size_t indexTupleCount;
-            if(keyword == "p"_s) indexTupleCount = 1;
-            else if(keyword == "l"_s) indexTupleCount = 2;
-            else if(keyword == "f"_s) indexTupleCount = 3;
+            /* Decide on how many tuples we expect. Since we handle both
+               triangles and quads, it can't be an exact count. */
+            std::size_t maxIndexTupleCount;
+            if(keyword == "p"_s) maxIndexTupleCount = 1;
+            else if(keyword == "l"_s) maxIndexTupleCount = 2;
+            else if(keyword == "f"_s) maxIndexTupleCount = 4;
             else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */
 
             /* Parse them all. If there's less than expected, `i` would be too
                small; if there's more then `contents` would stay non-empty. */
-            Vector3ui data[3];
+            Vector3ui data[4];
             std::size_t i = 0;
-            for(; i != indexTupleCount && contents; ++i) {
+            for(; i != maxIndexTupleCount && contents; ++i) {
                 const Containers::StringView foundSpace = contents.findAnyOr(Whitespace, contents.end());
                 Containers::StringView indexTuple = contents.prefix(foundSpace.begin());
 
@@ -457,6 +458,9 @@ Containers::Optional<MeshData> ObjImporter::doMesh(const UnsignedInt id, Unsigne
 
                 primitive = MeshPrimitive::Points;
 
+                /** @todo fix arrayAppend() to not need the cast here */
+                arrayAppend(indices, Containers::ArrayView<const Vector3ui>{data}.prefix(1));
+
             /* Lines */
             } else if(keyword == "l") {
                 if(primitive && primitive != MeshPrimitive::Lines) {
@@ -470,6 +474,9 @@ Containers::Optional<MeshData> ObjImporter::doMesh(const UnsignedInt id, Unsigne
 
                 primitive = MeshPrimitive::Lines;
 
+                /** @todo fix arrayAppend() to not need the cast here */
+                arrayAppend(indices, Containers::ArrayView<const Vector3ui>{data}.prefix(2));
+
             /* Faces */
             } else if(keyword == "f") {
                 if(primitive && primitive != MeshPrimitive::Triangles) {
@@ -477,17 +484,45 @@ Containers::Optional<MeshData> ObjImporter::doMesh(const UnsignedInt id, Unsigne
                     return Containers::NullOpt;
                 }
                 if(i < 3 || contents) {
-                    Error() << "Trade::ObjImporter::mesh(): expected exactly 3 position index tuples for a triangle, got" << line.suffix(keywordEnd.end());
+                    Error() << "Trade::ObjImporter::mesh(): expected 3 or 4 position index tuples for a face, got" << line.suffix(keywordEnd.end());
                     return Containers::NullOpt;
                 }
 
+                /* If it's a quad, convert it to two triangles */
+                if(i == 4) {
+                    /** @todo use MeshTools::generateQuadIndices() once it
+                        can take extra index data into account */
+                    /* 0 0---3
+                       |\ \  |
+                       | \ \ |
+                       |  \ \|
+                       1---2 2 */
+                    arrayAppend(indices, {
+                        data[0],
+                        data[1],
+                        data[2],
+                        data[0],
+                        data[2],
+                        data[3]
+                    });
+
+                    /* If we have texture coordinate / normal indices, add two
+                       more to the counters as well. If they matched the index
+                       array size before, they'll continue to match; if they
+                       didn't, they'll continue to not match. */
+                    if(textureCoordinateIndexCount)
+                        textureCoordinateIndexCount += 2;
+                    if(normalIndexCount)
+                        normalIndexCount += 2;
+                } else {
+                    /** @todo fix arrayAppend() to not need the cast here */
+                    arrayAppend(indices, Containers::ArrayView<const Vector3ui>{data}.prefix(3));
+                }
+
                 primitive = MeshPrimitive::Triangles;
 
             } else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */
 
-            /** @todo fix arrayAppend() to not need the cast here */
-            arrayAppend(indices, Containers::ArrayView<const Vector3ui>{data}.prefix(i));
-
         /* Unknown keyword */
         } else {
             Error{} << "Trade::ObjImporter::mesh(): unknown keyword" << keyword;

src/MagnumPlugins/ObjImporter/ObjImporter.h

@@ -108,9 +108,10 @@ positions with optional @ref VertexFormat::Vector3 normals and
 Negative indices (where @cpp -1 @ce is the last position / texture coordinate
 / normal known at given point in the file, @cpp -2 @ce is the second-to-last,
 etc.), produced for example by 3ds Max or [Mineways](http://mineways.com), are
+supported. Quads are converted to two triangles, higher-order polygons are not
 supported.
 
-Polygons (quads etc.) and material properties are currently not supported.
+Material properties are currently not supported.
 */
 class MAGNUM_OBJIMPORTER_EXPORT ObjImporter: public AbstractImporter {
     public:

src/MagnumPlugins/ObjImporter/Test/CMakeLists.txt

@@ -66,6 +66,7 @@ corrade_add_test(ObjImporterTest ObjImporterTest.cpp
         mesh-primitive-lines.obj
         mesh-primitive-points.obj
         mesh-primitive-triangles.obj
+        mesh-quads.obj
         mesh-texture-coordinates.obj
         mesh-texture-coordinates-normals.obj
         mesh-texture-coordinates-optional-coordinate.obj)

src/MagnumPlugins/ObjImporter/Test/ObjImporterTest.cpp

@@ -57,6 +57,7 @@ struct ObjImporterTest: TestSuite::Tester {
     void meshTextureCoordinatesNormals();
 
     void meshNegativeIndices();
+    void meshQuads();
 
     void meshIgnoredKeyword();
 
@@ -153,8 +154,8 @@ const struct {
     {"four-component index tuple", "invalid integer literal 1/1"},
     {"point with two indices", "expected exactly 1 position index tuple for a point, got 9 9"},
     {"line with one index", "expected exactly 2 position index tuples for a line, got 10"},
-    {"triangle with two indices", "expected exactly 3 position index tuples for a triangle, got 11 11"},
-    {"quad", "expected exactly 3 position index tuples for a triangle, got 12 12 12 12"}
+    {"triangle with two indices", "expected 3 or 4 position index tuples for a face, got 11 11"},
+    {"five-vertex face", "expected 3 or 4 position index tuples for a face, got 12 12 12 12 12"}
 };
 
 const struct {
@@ -199,6 +200,7 @@ ObjImporterTest::ObjImporterTest() {
               &ObjImporterTest::meshTextureCoordinatesNormals,
 
               &ObjImporterTest::meshNegativeIndices,
+              &ObjImporterTest::meshQuads,
 
               &ObjImporterTest::meshIgnoredKeyword,
 
@@ -509,6 +511,63 @@ void ObjImporterTest::meshNegativeIndices() {
         }), TestSuite::Compare::Container);
 }
 
+void ObjImporterTest::meshQuads() {
+    Containers::Pointer<AbstractImporter> importer = _manager.instantiate("ObjImporter");
+    CORRADE_VERIFY(importer->openFile(Utility::Path::join(OBJIMPORTER_TEST_DIR, "mesh-quads.obj")));
+    CORRADE_COMPARE(importer->meshCount(), 1);
+
+    /*    1            1
+         / \          / \
+        /   \        /   \
+       2 --- 5      2 --- 3
+       |     |  ->  4 --- 7
+       |     |      |     |
+       3 --- 4      5 --- 6 */
+    const Containers::Optional<MeshData> data = importer->mesh(0);
+    CORRADE_VERIFY(data);
+    CORRADE_COMPARE(data->primitive(), MeshPrimitive::Triangles);
+    CORRADE_COMPARE(data->attributeCount(), 3);
+    CORRADE_COMPARE_AS(data->attribute<Vector3>(MeshAttribute::Position),
+        Containers::arrayView<Vector3>({
+            {0.0f, 3.0f, 0.0f},
+            {-1.0f, 1.0f, 0.0f},
+            {1.0f, 1.0f, 0.0f},
+
+            {-1.0f, 1.0f, 0.0f},
+            {-1.0f, -1.0f, 0.0f},
+            {1.0f, -1.0f, 0.0f},
+            {1.0f, 1.0f, 0.0f},
+        }), TestSuite::Compare::Container);
+    CORRADE_COMPARE_AS(data->attribute<Vector2>(MeshAttribute::TextureCoordinates),
+        Containers::arrayView<Vector2>({
+            {0.5f, 1.0f},
+            {0.0f, 0.5f},
+            {1.0f, 0.5f},
+
+            {0.0f, 0.5f},
+            {0.0f, 0.0f},
+            {1.0f, 0.0f},
+            {1.0f, 0.5f},
+        }), TestSuite::Compare::Container);
+    CORRADE_COMPARE_AS(data->attribute<Vector3>(MeshAttribute::Normal),
+        Containers::arrayView<Vector3>({
+            {0.0f, 1.0f, 0.0f},
+            {-1.0f, 0.0f, 0.0f},
+            {1.0f, 0.0f, 0.0f},
+
+            {0.0f, -1.0f, 0.0f},
+            {0.0f, -1.0f, 0.0f},
+            {0.0f, -1.0f, 0.0f},
+            {0.0f, -1.0f, 0.0f},
+        }), TestSuite::Compare::Container);
+    CORRADE_VERIFY(data->isIndexed());
+    CORRADE_COMPARE(data->indexType(), MeshIndexType::UnsignedInt);
+    CORRADE_COMPARE_AS(data->indices<UnsignedInt>(),
+        Containers::arrayView<UnsignedInt>({
+            0, 1, 2, 3, 4, 5, 3, 5, 6
+        }), TestSuite::Compare::Container);
+}
+
 void ObjImporterTest::meshIgnoredKeyword() {
     Containers::Pointer<AbstractImporter> importer = _manager.instantiate("ObjImporter");
     CORRADE_VERIFY(importer->openFile(Utility::Path::join(OBJIMPORTER_TEST_DIR, "mesh-ignored-keyword.obj")));

src/MagnumPlugins/ObjImporter/Test/invalid-number-count.obj

@@ -57,6 +57,6 @@ o triangle with two indices
 v 1 2 3
 f 11 11
 
-o quad
+o five-vertex face
 v 1 2 3
-f 12 12 12 12
+f 12 12 12 12 12

src/MagnumPlugins/ObjImporter/Test/mesh-quads.obj

@@ -0,0 +1,31 @@
+# A house.
+#
+#    1
+#   / \
+#  /   \
+# 2 --- 5
+# |     |
+# |     |
+# 3 --- 4
+
+v 0 3 0
+v -1 1 0
+v -1 -1 0
+v 1 -1 0
+v 1 1 0
+
+vt 0.5 1
+vt 0 0.5
+vt 0 0
+vt 1 0
+vt 1 0.5
+
+# Normals of the roof are pointing up, to the left and to the right
+vn 0 1 0
+vn -1 0 0
+vn 1 0 0
+f 1/1/1 2/2/2 5/5/3
+
+# Normals of the walls are all pointing down
+vn 0 -1 0
+f 2/2/4 3/3/4 4/4/4 5/5/4