From 6527ec35c2c2ac76cedc0c75efb32420787f9f7f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Mon, 17 Jan 2022 17:44:33 +0100
Subject: [PATCH] MeshTools: assert in compile() if non-contiguous index
 buffers are used.

---
 src/Magnum/MeshTools/Compile.cpp            |  3 +++
 src/Magnum/MeshTools/Compile.h              |  3 +++
 src/Magnum/MeshTools/Test/CompileGLTest.cpp | 21 +++++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/src/Magnum/MeshTools/Compile.cpp b/src/Magnum/MeshTools/Compile.cpp
index 9ceee82f0..2603c4200 100644
--- a/src/Magnum/MeshTools/Compile.cpp
+++ b/src/Magnum/MeshTools/Compile.cpp
@@ -160,6 +160,9 @@ GL::Mesh compileInternal(const Trade::MeshData& meshData, GL::Buffer&& indices,
     }
 
     if(meshData.isIndexed()) {
+        CORRADE_ASSERT(Short(meshIndexTypeSize(meshData.indexType())) == meshData.indexStride(),
+            "MeshTools::compile():" << meshData.indexType() << "with stride of" << meshData.indexStride() << "bytes isn't supported by OpenGL", GL::Mesh{});
+
         mesh.setIndexBuffer(std::move(indices), meshData.indexOffset(), meshData.indexType())
             .setCount(meshData.indexCount());
     } else mesh.setCount(meshData.vertexCount());
diff --git a/src/Magnum/MeshTools/Compile.h b/src/Magnum/MeshTools/Compile.h
index fac98b79f..0b694c23f 100644
--- a/src/Magnum/MeshTools/Compile.h
+++ b/src/Magnum/MeshTools/Compile.h
@@ -120,6 +120,9 @@ 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.
+-   The index buffer is expected to be contiguous (size of the index type equal
+    to @ref Trade::MeshData::indexStride()). OpenGL doesn't support interleaved
+    index buffers.
 -   Stride of all attributes is expected to be positive. OpenGL doesn't support
     zero and negative strides.
 
diff --git a/src/Magnum/MeshTools/Test/CompileGLTest.cpp b/src/Magnum/MeshTools/Test/CompileGLTest.cpp
index 554283253..0ede0d7a7 100644
--- a/src/Magnum/MeshTools/Test/CompileGLTest.cpp
+++ b/src/Magnum/MeshTools/Test/CompileGLTest.cpp
@@ -104,6 +104,8 @@ struct CompileGLTest: GL::OpenGLTester {
         void multipleAttributes();
         void packedAttributes();
 
+        void unsupportedIndexStride();
+
         void customAttribute();
         void unsupportedAttribute();
         void unsupportedAttributeStride();
@@ -256,6 +258,8 @@ CompileGLTest::CompileGLTest() {
         &CompileGLTest::renderSetup,
         &CompileGLTest::renderTeardown);
 
+    addTests({&CompileGLTest::unsupportedIndexStride});
+
     addInstancedTests({&CompileGLTest::customAttribute,
                        &CompileGLTest::unsupportedAttribute},
         Containers::arraySize(CustomAttributeWarningData));
@@ -1153,6 +1157,23 @@ void CompileGLTest::packedAttributes() {
     #endif
 }
 
+void CompileGLTest::unsupportedIndexStride() {
+    #ifdef CORRADE_NO_ASSERT
+    CORRADE_SKIP("CORRADE_NO_ASSERT defined, can't test assertions");
+    #endif
+
+    UnsignedShort indices[2]{};
+    Trade::MeshData data{MeshPrimitive::Points,
+        {}, indices, Trade::MeshIndexData{Containers::stridedArrayView(indices).every(2)},
+        1};
+
+    std::ostringstream out;
+    Error redirectError{&out};
+    compile(data);
+    CORRADE_COMPARE(out.str(),
+        "MeshTools::compile(): MeshIndexType::UnsignedShort with stride of 4 bytes isn't supported by OpenGL\n");
+}
+
 void CompileGLTest::customAttribute() {
     auto&& instanceData = CustomAttributeWarningData[testCaseInstanceId()];
     setTestCaseDescription(instanceData.name);