Trade: support mesh level import in AbstractImporter.

Similar to image mip level import, but this is largely left to be
importer-specific. For example PLY defines per-face data and sometimes
one might want to import them as-is, without them being turned into a
per-vertex property.

src/Magnum/Trade/AbstractImporter.cpp

@@ -462,6 +462,16 @@ UnsignedInt AbstractImporter::meshCount() const {
 
 UnsignedInt AbstractImporter::doMeshCount() const { return 0; }
 
+UnsignedInt AbstractImporter::meshLevelCount(const UnsignedInt id) {
+    CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::meshLevelCount(): no file opened", {});
+    CORRADE_ASSERT(id < doMeshCount(), "Trade::AbstractImporter::meshLevelCount(): index" << id << "out of range for" << doMeshCount() << "entries", {});
+    const UnsignedInt out = doMeshLevelCount(id);
+    CORRADE_ASSERT(out, "Trade::AbstractImporter::meshLevelCount(): implementation reported zero levels", {});
+    return out;
+}
+
+UnsignedInt AbstractImporter::doMeshLevelCount(UnsignedInt) { return 1; }
+
 Int AbstractImporter::meshForName(const std::string& name) {
     CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::meshForName(): no file opened", {});
     return doMeshForName(name);
@@ -477,10 +487,21 @@ std::string AbstractImporter::meshName(const UnsignedInt id) {
 
 std::string AbstractImporter::doMeshName(UnsignedInt) { return {}; }
 
-Containers::Optional<MeshData> AbstractImporter::mesh(const UnsignedInt id) {
+Containers::Optional<MeshData> AbstractImporter::mesh(const UnsignedInt id, const UnsignedInt level) {
     CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::mesh(): no file opened", {});
     CORRADE_ASSERT(id < doMeshCount(), "Trade::AbstractImporter::mesh(): index" << id << "out of range for" << doMeshCount() << "entries", {});
-    Containers::Optional<MeshData> mesh = doMesh(id);
+    #ifndef CORRADE_NO_ASSERT
+    /* Check for the range only if requested level is nonzero, as
+       meshLevelCount() is expected to return >= 1. This is done to prevent
+       random assertions and messages from a doMeshLevelCount() to be printed
+       (which are unlikely, but let's be consistent with what image*D() does). */
+    if(level) {
+        const UnsignedInt levelCount = doMeshLevelCount(id);
+        CORRADE_ASSERT(levelCount, "Trade::AbstractImporter::mesh(): implementation reported zero levels", {});
+        CORRADE_ASSERT(level < levelCount, "Trade::AbstractImporter::mesh(): level" << level << "out of range for" << levelCount << "entries", {});
+    }
+    #endif
+    Containers::Optional<MeshData> mesh = doMesh(id, level);
     CORRADE_ASSERT(!mesh || (
         (!mesh->_indexData.deleter() || mesh->_indexData.deleter() == Implementation::nonOwnedArrayDeleter || mesh->_indexData.deleter() == ArrayAllocator<char>::deleter) &&
         (!mesh->_vertexData.deleter() || mesh->_vertexData.deleter() == Implementation::nonOwnedArrayDeleter || mesh->_vertexData.deleter() == ArrayAllocator<char>::deleter) &&
@@ -489,15 +510,15 @@ Containers::Optional<MeshData> AbstractImporter::mesh(const UnsignedInt id) {
     return mesh;
 }
 
-Containers::Optional<MeshData> AbstractImporter::doMesh(UnsignedInt) {
+Containers::Optional<MeshData> AbstractImporter::doMesh(UnsignedInt, UnsignedInt) {
     CORRADE_ASSERT(false, "Trade::AbstractImporter::mesh(): not implemented", {});
 }
 
-Containers::Optional<MeshData> AbstractImporter::mesh(const std::string& name) {
+Containers::Optional<MeshData> AbstractImporter::mesh(const std::string& name, const UnsignedInt level) {
     CORRADE_ASSERT(isOpened(), "Trade::AbstractImporter::mesh(): no file opened", {});
     const Int id = doMeshForName(name);
     if(id == -1) return {};
-    return mesh(id); /* not doMesh(), so we get the checks also */
+    return mesh(id, level); /* not doMesh(), so we get the checks also */
 }
 
 MeshAttribute AbstractImporter::meshAttributeForName(const std::string& name) {
@@ -602,7 +623,7 @@ Containers::Optional<MeshData3D> AbstractImporter::mesh3D(const UnsignedInt id)
 }
 
 Containers::Optional<MeshData3D> AbstractImporter::doMesh3D(const UnsignedInt id) {
-    Containers::Optional<MeshData> out = doMesh(id);
+    Containers::Optional<MeshData> out = doMesh(id, 0);
     if(out) return MeshData3D{*out};
     return Containers::NullOpt;
 }

src/Magnum/Trade/AbstractImporter.h

@@ -245,9 +245,9 @@ checked by the implementation:
     there is any file opened.
 -   All `do*()` implementations taking data ID as parameter are called only if
     the ID is from valid range.
--   For `doImage*()` and @p level parameter being nonzero, implementations are
-    called only if it is from valid range. Level zero is always expected to be
-    present and thus no check is done in that case.
+-   For @ref doMesh() and `doImage*()` and @p level parameter being nonzero,
+    implementations are called only if it is from valid range. Level zero is
+    always expected to be present and thus no check is done in that case.
 
 @m_class{m-block m-warning}
 
@@ -760,16 +760,27 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
          * @m_since_latest
          *
          * Expects that a file is opened.
+         * @see @ref meshLevelCount()
          */
         UnsignedInt meshCount() const;
 
+        /**
+         * @brief Mesh level count
+         * @param id        Mesh ID, from range [0, @ref meshCount()).
+         * @m_since_latest
+         *
+         * Always returns at least one level, import failures are deferred to
+         * @ref mesh(). Expects that a file is opened.
+         */
+        UnsignedInt meshLevelCount(UnsignedInt id);
+
         /**
          * @brief Mesh ID for given name
          * @m_since_latest
          *
          * If no mesh for given name exists, returns @cpp -1 @ce. Expects that
          * a file is opened.
-         * @see @ref meshName(), @ref mesh(const std::string&)
+         * @see @ref meshName(), @ref mesh(const std::string&, UnsignedInt)
          */
         Int meshForName(const std::string& name);
 
@@ -786,24 +797,30 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
         /**
          * @brief Mesh
          * @param id        Mesh ID, from range [0, @ref meshCount()).
+         * @param level     Mesh level, from range [0, @ref meshLevelCount())
          * @m_since_latest
          *
          * Returns given mesh or @ref Containers::NullOpt if importing failed.
-         * Expects that a file is opened.
-         * @see @ref mesh(const std::string&)
+         * The @p level parameter allows access to additional data and is
+         * largely left as importer-specific --- for example allowing access to
+         * per-instance, per-face or per-edge data. Expects that a file is
+         * opened.
+         * @see @ref mesh(const std::string&, UnsignedInt),
+         *      @ref MeshPrimitive::Instances, @ref MeshPrimitive::Faces,
+         *      @ref MeshPrimitive::Edges
          */
-        Containers::Optional<MeshData> mesh(UnsignedInt id);
+        Containers::Optional<MeshData> mesh(UnsignedInt id, UnsignedInt level = 0);
 
         /**
          * @brief Mesh for given name
          * @m_since_latest
          *
          * A convenience API combining @ref meshForName() and
-         * @ref mesh(UnsignedInt). Returns @ref Containers::NullOpt either if
-         * @ref meshForName() returns @cpp -1 @ce or if importing fails.
-         * Expects that a file is opened.
+         * @ref mesh(UnsignedInt, UnsignedInt). Returns
+         * @ref Containers::NullOpt either if @ref meshForName() returns
+         * @cpp -1 @ce or if importing fails. Expects that a file is opened.
          */
-        Containers::Optional<MeshData> mesh(const std::string& name);
+        Containers::Optional<MeshData> mesh(const std::string& name, UnsignedInt level = 0);
 
         /**
          * @brief Mesh attribute for given name
@@ -1403,6 +1420,20 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
          */
         virtual UnsignedInt doMeshCount() const;
 
+        /**
+         * @brief Implementation for @ref meshLevelCount()
+         * @m_since_latest
+         *
+         * Default implementation returns @cpp 1 @ce. Similarly to all other
+         * `*Count()` functions, this function isn't expected to fail --- if an
+         * import error occus, this function should return @cpp 1 @ce and the
+         * error state should be returned from @ref mesh() instead.
+         *
+         * Deliberately not @cpp const @ce to allow plugins cache decoded
+         * data.
+         */
+        virtual UnsignedInt doMeshLevelCount(UnsignedInt id);
+
         /**
          * @brief Implementation for @ref meshForName()
          * @m_since_latest
@@ -1423,7 +1454,7 @@ class MAGNUM_TRADE_EXPORT AbstractImporter: public PluginManager::AbstractManagi
          * @brief Implementation for @ref mesh()
          * @m_since_latest
          */
-        virtual Containers::Optional<MeshData> doMesh(UnsignedInt id);
+        virtual Containers::Optional<MeshData> doMesh(UnsignedInt id, UnsignedInt level);
 
         /**
          * @brief Implementation for @ref meshAttributeForName()

src/Magnum/Trade/Test/AbstractImporterTest.cpp

@@ -171,6 +171,10 @@ struct AbstractImporterTest: TestSuite::Tester {
     #endif
     void meshCountNotImplemented();
     void meshCountNoFile();
+    void meshLevelCountNotImplemented();
+    void meshLevelCountNoFile();
+    void meshLevelCountOutOfRange();
+    void meshLevelCountZero();
     void meshForNameNotImplemented();
     void meshForNameNoFile();
     void meshNameNotImplemented();
@@ -179,6 +183,7 @@ struct AbstractImporterTest: TestSuite::Tester {
     void meshNotImplemented();
     void meshNoFile();
     void meshOutOfRange();
+    void meshLevelOutOfRange();
     void meshNonOwningDeleters();
     void meshGrowableDeleters();
     void meshCustomIndexDataDeleter();
@@ -420,6 +425,10 @@ AbstractImporterTest::AbstractImporterTest() {
               #endif
               &AbstractImporterTest::meshCountNotImplemented,
               &AbstractImporterTest::meshCountNoFile,
+              &AbstractImporterTest::meshLevelCountNotImplemented,
+              &AbstractImporterTest::meshLevelCountNoFile,
+              &AbstractImporterTest::meshLevelCountOutOfRange,
+              &AbstractImporterTest::meshLevelCountZero,
               &AbstractImporterTest::meshForNameNotImplemented,
               &AbstractImporterTest::meshForNameNoFile,
               &AbstractImporterTest::meshNameNotImplemented,
@@ -428,6 +437,7 @@ AbstractImporterTest::AbstractImporterTest() {
               &AbstractImporterTest::meshNotImplemented,
               &AbstractImporterTest::meshNoFile,
               &AbstractImporterTest::meshOutOfRange,
+              &AbstractImporterTest::meshLevelOutOfRange,
               &AbstractImporterTest::meshNonOwningDeleters,
               &AbstractImporterTest::meshGrowableDeleters,
               &AbstractImporterTest::meshCustomIndexDataDeleter,
@@ -2239,6 +2249,10 @@ void AbstractImporterTest::mesh() {
         void doClose() override {}
 
         UnsignedInt doMeshCount() const override { return 8; }
+        UnsignedInt doMeshLevelCount(UnsignedInt id) override {
+            if(id == 7) return 3;
+            else return {};
+        }
         Int doMeshForName(const std::string& name) override {
             if(name == "eighth") return 7;
             else return -1;
@@ -2247,10 +2261,10 @@ void AbstractImporterTest::mesh() {
             if(id == 7) return "eighth";
             else return {};
         }
-        Containers::Optional<MeshData> doMesh(UnsignedInt id) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt id, UnsignedInt level) override {
             /* Verify that initializer list is converted to an array with
                the default deleter and not something disallowed */
-            if(id == 7) return MeshData{MeshPrimitive::Points, nullptr, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}, &state};
+            if(id == 7 && level == 2) return MeshData{MeshPrimitive::Points, nullptr, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}, &state};
             else return {};
         }
     } importer;
@@ -2260,11 +2274,11 @@ void AbstractImporterTest::mesh() {
     CORRADE_COMPARE(importer.meshName(7), "eighth");
 
     {
-        auto data = importer.mesh(7);
+        auto data = importer.mesh(7, 2);
         CORRADE_VERIFY(data);
         CORRADE_COMPARE(data->importerState(), &state);
     } {
-        auto data = importer.mesh("eighth");
+        auto data = importer.mesh("eighth", 2);
         CORRADE_VERIFY(data);
         CORRADE_COMPARE(data->importerState(), &state);
     } {
@@ -2289,8 +2303,8 @@ void AbstractImporterTest::meshDeprecatedFallback() {
             if(id == 7) return "eighth";
             else return {};
         }
-        Containers::Optional<MeshData> doMesh(UnsignedInt id) override {
-            if(id == 7) return MeshData{MeshPrimitive::Points, nullptr, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}, &state};
+        Containers::Optional<MeshData> doMesh(UnsignedInt id, UnsignedInt level) override {
+            if(id == 7 && level == 0) return MeshData{MeshPrimitive::Points, nullptr, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}, &state};
             else return {};
         }
     } importer;
@@ -2336,6 +2350,70 @@ void AbstractImporterTest::meshCountNoFile() {
     CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshCount(): no file opened\n");
 }
 
+void AbstractImporterTest::meshLevelCountNotImplemented() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    CORRADE_COMPARE(importer.meshLevelCount(7), 1);
+}
+
+void AbstractImporterTest::meshLevelCountNoFile() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return false; }
+        void doClose() override {}
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    importer.meshLevelCount(7);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshLevelCount(): no file opened\n");
+}
+
+void AbstractImporterTest::meshLevelCountOutOfRange() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    importer.meshLevelCount(8);
+    CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::meshLevelCount(): index 8 out of range for 8 entries\n");
+}
+
+void AbstractImporterTest::meshLevelCountZero() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+        Int doMeshForName(const std::string&) override { return 0; }
+        UnsignedInt doMeshLevelCount(UnsignedInt) override { return 0; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    importer.meshLevelCount(7);
+    /* This should print a similar message instead of a confusing
+       "level 1 out of range for 0 entries" */
+    importer.mesh(7, 1);
+    importer.mesh("", 1);
+    CORRADE_COMPARE(out.str(),
+        "Trade::AbstractImporter::meshLevelCount(): implementation reported zero levels\n"
+        "Trade::AbstractImporter::mesh(): implementation reported zero levels\n"
+        "Trade::AbstractImporter::mesh(): implementation reported zero levels\n");
+}
+
 void AbstractImporterTest::meshForNameNotImplemented() {
     struct: AbstractImporter {
         ImporterFeatures doFeatures() const override { return {}; }
@@ -2451,6 +2529,26 @@ void AbstractImporterTest::meshOutOfRange() {
     CORRADE_COMPARE(out.str(), "Trade::AbstractImporter::mesh(): index 8 out of range for 8 entries\n");
 }
 
+void AbstractImporterTest::meshLevelOutOfRange() {
+    struct: AbstractImporter {
+        ImporterFeatures doFeatures() const override { return {}; }
+        bool doIsOpened() const override { return true; }
+        void doClose() override {}
+
+        UnsignedInt doMeshCount() const override { return 8; }
+        Int doMeshForName(const std::string&) override { return 0; }
+        UnsignedInt doMeshLevelCount(UnsignedInt) override { return 3; }
+    } importer;
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    importer.mesh(7, 3);
+    importer.mesh("", 3);
+    CORRADE_COMPARE(out.str(),
+        "Trade::AbstractImporter::mesh(): level 3 out of range for 3 entries\n"
+        "Trade::AbstractImporter::mesh(): level 3 out of range for 3 entries\n");
+}
+
 void AbstractImporterTest::meshNonOwningDeleters() {
     struct: AbstractImporter {
         ImporterFeatures doFeatures() const override { return {}; }
@@ -2458,7 +2556,7 @@ void AbstractImporterTest::meshNonOwningDeleters() {
         void doClose() override {}
 
         UnsignedInt doMeshCount() const override { return 1; }
-        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt, UnsignedInt) override {
             return MeshData{MeshPrimitive::Triangles,
                 Containers::Array<char>{indexData, 1, Implementation::nonOwnedArrayDeleter}, MeshIndexData{MeshIndexType::UnsignedByte, indexData},
                 Containers::Array<char>{nullptr, 0, Implementation::nonOwnedArrayDeleter},
@@ -2483,7 +2581,7 @@ void AbstractImporterTest::meshGrowableDeleters() {
         void doClose() override {}
 
         UnsignedInt doMeshCount() const override { return 1; }
-        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt, UnsignedInt) override {
             Containers::Array<char> indexData;
             Containers::arrayAppend<ArrayAllocator>(indexData, '\xab');
             Containers::Array<Vector3> vertexData;
@@ -2511,7 +2609,7 @@ void AbstractImporterTest::meshCustomIndexDataDeleter() {
 
         UnsignedInt doMeshCount() const override { return 1; }
         Int doMeshForName(const std::string&) override { return 0; }
-        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt, UnsignedInt) override {
             return MeshData{MeshPrimitive::Triangles, Containers::Array<char>{data, 1, [](char*, std::size_t) {}}, MeshIndexData{MeshIndexType::UnsignedByte, data}};
         }
 
@@ -2536,7 +2634,7 @@ void AbstractImporterTest::meshCustomVertexDataDeleter() {
 
         UnsignedInt doMeshCount() const override { return 1; }
         Int doMeshForName(const std::string&) override { return 0; }
-        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt, UnsignedInt) override {
             return MeshData{MeshPrimitive::Triangles, Containers::Array<char>{nullptr, 0, [](char*, std::size_t) {}}, {MeshAttributeData{MeshAttribute::Position, VertexFormat::Vector3, nullptr}}};
         }
     } importer;
@@ -2559,7 +2657,7 @@ void AbstractImporterTest::meshCustomAttributesDeleter() {
 
         UnsignedInt doMeshCount() const override { return 1; }
         Int doMeshForName(const std::string&) override { return 0; }
-        Containers::Optional<MeshData> doMesh(UnsignedInt) override {
+        Containers::Optional<MeshData> doMesh(UnsignedInt, UnsignedInt) override {
             return MeshData{MeshPrimitive::Triangles, nullptr, Containers::Array<MeshAttributeData>{&positions, 1, [](MeshAttributeData*, std::size_t) {}}};
         }