MeshTools: explicitly handle unavailable attribute types in compile().

src/Magnum/MeshTools/Compile.cpp

@@ -140,7 +140,16 @@ GL::Mesh compile(const Trade::MeshData& meshData, GL::Buffer&& indices, GL::Buff
     GL::Buffer verticesRef = GL::Buffer::wrap(vertices.id(), GL::Buffer::TargetHint::Array);
     for(UnsignedInt i = 0; i != meshData.attributeCount(); ++i) {
         Containers::Optional<GL::DynamicAttribute> attribute;
+
+        /* Ignore implementation-specific formats because GL needs three
+           separate values to describe them so there's no way to put them in a
+           single 32-bit value :( */
         const VertexFormat format = meshData.attributeFormat(i);
+        if(isVertexFormatImplementationSpecific(format)) {
+            Warning{} << "MeshTools::compile(): ignoring attribute" << meshData.attributeName(i) << "with an implementation-specific format" << reinterpret_cast<void*>(vertexFormatUnwrap(format));
+            continue;
+        }
+
         switch(meshData.attributeName(i)) {
             case Trade::MeshAttribute::Position:
                 /* Pick 3D position always, the type will properly reduce it to

src/Magnum/MeshTools/Compile.h

@@ -103,6 +103,9 @@ possibly also an index buffer, if the mesh is indexed.
 -   If the mesh contains colors, these are bound to
     @ref Shaders::Generic::Color3 / @ref Shaders::Generic::Color4 based on
     their type.
+-   Custom attributes and known attributes of implementation-specific types
+    are ignored with a warning. See the @ref compile(const Trade::MeshData&, GL::Buffer&, GL::Buffer&)
+    for an example showing how to bind them manually.
 
 If normal generation is not requested, @ref Trade::MeshData::indexData() and
 @ref Trade::MeshData::vertexData() are uploaded as-is without any further

src/Magnum/MeshTools/Test/CompileGLTest.cpp

@@ -94,6 +94,7 @@ struct CompileGLTest: GL::OpenGLTester {
         void packedAttributes();
 
         void unknownAttribute();
+        void implementationSpecificAttributeFormat();
         void generateNormalsNoPosition();
         void generateNormals2DPosition();
         void generateNormalsNoFloats();
@@ -205,6 +206,7 @@ CompileGLTest::CompileGLTest() {
     addTests({&CompileGLTest::packedAttributes,
 
               &CompileGLTest::unknownAttribute,
+              &CompileGLTest::implementationSpecificAttributeFormat,
               &CompileGLTest::generateNormalsNoPosition,
               &CompileGLTest::generateNormals2DPosition,
               &CompileGLTest::generateNormalsNoFloats});
@@ -724,6 +726,18 @@ void CompileGLTest::unknownAttribute() {
         "MeshTools::compile(): ignoring unknown attribute Trade::MeshAttribute::Custom(115)\n");
 }
 
+void CompileGLTest::implementationSpecificAttributeFormat() {
+    Trade::MeshData data{MeshPrimitive::Triangles,
+        nullptr, {Trade::MeshAttributeData{Trade::MeshAttribute::Position,
+            vertexFormatWrap(0xdead), nullptr}}};
+
+    std::ostringstream out;
+    Warning redirectError{&out};
+    MeshTools::compile(data);
+    CORRADE_COMPARE(out.str(),
+        "MeshTools::compile(): ignoring attribute Trade::MeshAttribute::Position with an implementation-specific format 0xdead\n");
+}
+
 void CompileGLTest::generateNormalsNoPosition() {
     Trade::MeshData data{MeshPrimitive::Triangles, 1};