MeshTools: use only the first set of vertex attribs in compile().

doc/changelog.dox

@@ -99,6 +99,9 @@ See also:
     destroyed could fail with an error saying "cannot make the previous context
     current" on certain system. This was due to EGL not destroying the context
     if it's still made current.
+-   For meshes with multiple sets of vertex attributes (such as texture
+    coordinates), @ref MeshTools::compile() should be using only the first set
+    but it wasn't.
 
 @subsection changelog-latest-compatibility Potential compatibility breakages, removed APIs
 

src/Magnum/MeshTools/Compile.cpp

@@ -66,6 +66,11 @@ GL::Mesh compileInternal(const Trade::MeshData& meshData, GL::Buffer&& indices,
 
     /* Vertex data */
     GL::Buffer verticesRef = GL::Buffer::wrap(vertices.id(), GL::Buffer::TargetHint::Array);
+
+    /* Ensure each known attribute gets bound only once. There's 16 generic
+       attribs at most. */
+    Math::BoolVector<16> boundAttributes;
+
     for(UnsignedInt i = 0; i != meshData.attributeCount(); ++i) {
         Containers::Optional<GL::DynamicAttribute> attribute;
 
@@ -131,6 +136,14 @@ GL::Mesh compileInternal(const Trade::MeshData& meshData, GL::Buffer&& indices,
             continue;
         }
 
+        /* Ensure each attribute gets bound only once -- so for example when
+           there are two texture coordinate sets, we don't bind them both to
+           the same slot, effectively ignoring the first one */
+        /** @todo revisit when there are secondary generic texture coordinates */
+        if(boundAttributes[attribute->location()])
+            continue;
+        boundAttributes.set(attribute->location(), true);
+
         /* For the first attribute move the buffer in, for all others use the
            reference */
         if(vertices.id()) mesh.addVertexBuffer(std::move(vertices),