MeshTools: added interleavedMutableData().

Needed a mutable variant of interleavedData() without having to do a
const_cast.

src/Magnum/MeshTools/Interleave.cpp

@@ -72,6 +72,16 @@ Containers::StridedArrayView2D<const char> interleavedData(const Trade::MeshData
     return *out;
 }
 
+Containers::StridedArrayView2D<char> interleavedMutableData(Trade::MeshData& data) {
+    Containers::StridedArrayView2D<const char> out = interleavedData(data);
+    CORRADE_ASSERT(data.vertexDataFlags() & Trade::DataFlag::Mutable,
+        "MeshTools::interleavedMutableData(): vertex data is not mutable", {});
+    return Containers::StridedArrayView2D<char>{
+        {nullptr, ~std::size_t{}}, /* to sidestep the range assertions */
+        const_cast<char*>(reinterpret_cast<const char*>(out.data())),
+        out.size(), out.stride()};
+}
+
 namespace Implementation {
 
 Containers::Array<Trade::MeshAttributeData> interleavedLayout(Trade::MeshData&& data, const Containers::ArrayView<const Trade::MeshAttributeData> extra) {

src/Magnum/MeshTools/Interleave.h

@@ -215,6 +215,16 @@ that the mesh is interleaved.
 */
 MAGNUM_MESHTOOLS_EXPORT Containers::StridedArrayView2D<const char> interleavedData(const Trade::MeshData& data);
 
+/**
+@brief Mutable type-erased view on interleaved mesh data
+@m_since_latest
+
+Same as @ref interleavedData(), but returns a mutable view. Expects that the
+mesh is interleaved and vertex data is mutable.
+@see @ref isInterleaved(), @ref Trade::MeshData::vertexDataFlags()
+*/
+MAGNUM_MESHTOOLS_EXPORT Containers::StridedArrayView2D<char> interleavedMutableData(Trade::MeshData& data);
+
 /**
 @brief Create an interleaved mesh layout
 @m_since_latest

src/Magnum/MeshTools/Test/InterleaveTest.cpp

@@ -66,6 +66,7 @@ struct InterleaveTest: Corrade::TestSuite::Tester {
     void interleavedDataNoVertices();
     void interleavedDataNotInterleaved();
     void interleavedDataVertexDataWholeMemory();
+    void interleavedMutableDataNotMutable();
 
     void interleavedLayout();
     void interleavedLayoutExtra();
@@ -116,6 +117,7 @@ InterleaveTest::InterleaveTest() {
               &InterleaveTest::interleavedDataNoVertices,
               &InterleaveTest::interleavedDataNotInterleaved,
               &InterleaveTest::interleavedDataVertexDataWholeMemory,
+              &InterleaveTest::interleavedMutableDataNotMutable,
 
               &InterleaveTest::interleavedLayout,
               &InterleaveTest::interleavedLayoutExtra,
@@ -398,6 +400,13 @@ void InterleaveTest::interleavedData() {
     CORRADE_COMPARE(interleaved.size()[1], 31);
     CORRADE_COMPARE(interleaved.stride()[0], 40);
     CORRADE_COMPARE(interleaved.stride()[1], 1);
+
+    Containers::StridedArrayView2D<char> interleavedMutable = MeshTools::interleavedMutableData(data);
+    CORRADE_COMPARE(interleavedMutable.data(), positions.data());
+    CORRADE_COMPARE(interleavedMutable.size()[0], 3);
+    CORRADE_COMPARE(interleavedMutable.size()[1], 31);
+    CORRADE_COMPARE(interleavedMutable.stride()[0], 40);
+    CORRADE_COMPARE(interleavedMutable.stride()[1], 1);
 }
 
 void InterleaveTest::interleavedDataNoAttributes() {
@@ -484,6 +493,21 @@ void InterleaveTest::interleavedDataVertexDataWholeMemory() {
     CORRADE_COMPARE(interleaved.stride()[1], 1);
 }
 
+void InterleaveTest::interleavedMutableDataNotMutable() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    char a[1];
+    Trade::MeshData data{MeshPrimitive::Lines, {}, a, {}, 15};
+    CORRADE_VERIFY(MeshTools::isInterleaved(data));
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    MeshTools::interleavedMutableData(data);
+    CORRADE_COMPARE(out.str(), "MeshTools::interleavedMutableData(): vertex data is not mutable\n");
+}
+
 void InterleaveTest::interleavedLayout() {
     Containers::Array<char> indexData{6};
     Containers::Array<char> vertexData{3*20};