MeshTools: assert in compile() if zero or negative strides are used.

doc/changelog.dox

@@ -453,8 +453,8 @@ See also:
     common texture coordinate set as a complement to a per-texture property
     added in 2020.06
 -   @ref Trade::MeshData now allows zero and negative strides for better
-    data layout flexibility. This is however not commonly supported in GPU
-    APIs.
+    data layout flexibility. This is however not commonly supported by GPU APIs
+    and tools like @ref MeshTools::compile() assert in that case.
 -   Added @ref Trade::MeshData::findAttributeId() for an ability to check that
     an attribute exists and retrieve its ID in a single step, avoiding a double
     lookup compared to @relativeref{Trade::MeshData,hasAttribute()} +

src/Magnum/MeshTools/Compile.cpp

@@ -144,13 +144,19 @@ GL::Mesh compileInternal(const Trade::MeshData& meshData, GL::Buffer&& indices,
             continue;
         boundAttributes.set(attribute->location(), true);
 
+        /* Negative strides are not supported by GL, zero strides are
+           understood as tightly packed instead of all attributes having the
+           same value */
+        const Int stride = meshData.attributeStride(i);
+        CORRADE_ASSERT(stride > 0,
+            "MeshTools::compile():" << meshData.attributeName(i) << "stride of" << stride << "bytes isn't supported by OpenGL", GL::Mesh{});
+
         /* For the first attribute move the buffer in, for all others use the
            reference */
         if(vertices.id()) mesh.addVertexBuffer(std::move(vertices),
-            meshData.attributeOffset(i), meshData.attributeStride(i),
-            *attribute);
+            meshData.attributeOffset(i), stride, *attribute);
         else mesh.addVertexBuffer(verticesRef, meshData.attributeOffset(i),
-            meshData.attributeStride(i), *attribute);
+            stride, *attribute);
     }
 
     if(meshData.isIndexed()) {

src/Magnum/MeshTools/Compile.h

@@ -120,6 +120,8 @@ possibly also an index buffer, if the mesh is indexed.
 -   Implementation-specific @ref Magnum::MeshPrimitive values are passed
     as-is with @ref meshPrimitiveUnwrap(). It's the user responsibility to
     ensure an implementation-specific value is valid in this context.
+-   Stride of all attributes is expected to be positive. OpenGL doesn't support
+    zero and negative strides.
 
 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

@@ -106,6 +106,7 @@ struct CompileGLTest: GL::OpenGLTester {
 
         void customAttribute();
         void unsupportedAttribute();
+        void unsupportedAttributeStride();
         void implementationSpecificAttributeFormat();
 
         void generateNormalsNoPosition();
@@ -256,8 +257,12 @@ CompileGLTest::CompileGLTest() {
         &CompileGLTest::renderTeardown);
 
     addInstancedTests({&CompileGLTest::customAttribute,
-                       &CompileGLTest::unsupportedAttribute,
-                       &CompileGLTest::implementationSpecificAttributeFormat},
+                       &CompileGLTest::unsupportedAttribute},
+        Containers::arraySize(CustomAttributeWarningData));
+
+    addTests({&CompileGLTest::unsupportedAttributeStride});
+
+    addInstancedTests({&CompileGLTest::implementationSpecificAttributeFormat},
         Containers::arraySize(CustomAttributeWarningData));
 
     addTests({&CompileGLTest::generateNormalsNoPosition,
@@ -1188,6 +1193,28 @@ void CompileGLTest::unsupportedAttribute() {
     #endif
 }
 
+void CompileGLTest::unsupportedAttributeStride() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    Vector3 data[2]{};
+    Trade::MeshData zero{MeshPrimitive::Points, {}, data, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Position, Containers::stridedArrayView(data, 1).broadcasted<0>(2)}
+    }};
+    Trade::MeshData negative{MeshPrimitive::Points, {}, data, {
+        Trade::MeshAttributeData{Trade::MeshAttribute::Normal, Containers::stridedArrayView(data).flipped<0>()}
+    }};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    compile(zero);
+    compile(negative);
+    CORRADE_COMPARE(out.str(),
+        "MeshTools::compile(): Trade::MeshAttribute::Position stride of 0 bytes isn't supported by OpenGL\n"
+        "MeshTools::compile(): Trade::MeshAttribute::Normal stride of -12 bytes isn't supported by OpenGL\n");
+}
+
 void CompileGLTest::implementationSpecificAttributeFormat() {
     auto&& instanceData = CustomAttributeWarningData[testCaseInstanceId()];
     setTestCaseDescription(instanceData.name);