GL: store Mesh index buffer by value.

This allows moving Buffer instances without fear of breaking stuff. I
thought this was in since a long time, but doesn't seem so. This
reintroduces a header dependency, but until I have Containers::Storage
or something that *can* store forward-declared type safely, it's
inevitable.

src/Magnum/GL/Mesh.cpp

@@ -228,7 +228,7 @@ Mesh::Mesh(Mesh&& other) noexcept: _id(other._id), _primitive(other._primitive),
     #ifndef MAGNUM_TARGET_GLES2
     _indexStart(other._indexStart), _indexEnd(other._indexEnd),
     #endif
-    _indexOffset(other._indexOffset), _indexType(other._indexType), _indexBuffer(other._indexBuffer)
+    _indexOffset(other._indexOffset), _indexType(other._indexType), _indexBuffer{std::move(other._indexBuffer)}
 {
     (this->*Context::current().state().mesh->moveConstructImplementation)(std::move(other));
     other._id = 0;
@@ -294,12 +294,12 @@ Mesh& Mesh::setLabelInternal(const Containers::ArrayView<const char> label) {
 #endif
 
 MeshIndexType Mesh::indexType() const {
-    CORRADE_ASSERT(_indexBuffer, "Mesh::indexType(): mesh is not indexed", {});
+    CORRADE_ASSERT(_indexBuffer.id(), "Mesh::indexType(): mesh is not indexed", {});
     return _indexType;
 }
 
 UnsignedInt Mesh::indexTypeSize() const {
-    CORRADE_ASSERT(_indexBuffer, "Mesh::indexTypeSize(): mesh is not indexed", {});
+    CORRADE_ASSERT(_indexBuffer.id(), "Mesh::indexTypeSize(): mesh is not indexed", {});
 
     switch(_indexType) {
         case MeshIndexType::UnsignedByte: return 1;
@@ -331,7 +331,7 @@ Mesh& Mesh::setIndexBuffer(Buffer& buffer, GLintptr offset, MeshIndexType type,
         "GL::Mesh::setIndexBuffer(): the buffer has unexpected target hint, expected" << Buffer::TargetHint::ElementArray << "but got" << buffer.targetHint(), *this);
     #endif
 
-    _indexBuffer = &buffer;
+    _indexBuffer = Buffer::wrap(buffer.id());
     _indexOffset = offset;
     _indexType = type;
     #ifndef MAGNUM_TARGET_GLES2
@@ -377,7 +377,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
     /* Non-instanced mesh */
     if(instanceCount == 1) {
         /* Non-indexed mesh */
-        if(!_indexBuffer) {
+        if(!_indexBuffer.id()) {
             glDrawArrays(GLenum(_primitive), baseVertex, count);
 
         /* Indexed mesh with base vertex */
@@ -415,7 +415,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
     /* Instanced mesh */
     } else {
         /* Non-indexed mesh */
-        if(!_indexBuffer) {
+        if(!_indexBuffer.id()) {
             #ifndef MAGNUM_TARGET_GLES
             /* Non-indexed mesh with base instance */
             if(baseInstance) {
@@ -698,7 +698,7 @@ void Mesh::bindImplementationDefault() {
         vertexAttribPointer(attribute);
 
     /* Bind index buffer, if the mesh is indexed */
-    if(_indexBuffer) _indexBuffer->bindInternal(Buffer::TargetHint::ElementArray);
+    if(_indexBuffer.id()) _indexBuffer.bindInternal(Buffer::TargetHint::ElementArray);
 }
 
 void Mesh::bindImplementationVAO() {

src/Magnum/GL/Mesh.h

@@ -35,6 +35,7 @@
 #include "Magnum/Tags.h"
 #include "Magnum/GL/AbstractObject.h"
 #include "Magnum/GL/Attribute.h"
+#include "Magnum/GL/Buffer.h"
 #include "Magnum/GL/GL.h"
 
 namespace Magnum { namespace GL {
@@ -489,7 +490,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          *
          * @see @ref setIndexBuffer(), @ref setCount()
          */
-        bool isIndexed() const { return _indexBuffer; }
+        bool isIndexed() const { return _indexBuffer.id(); }
 
         /**
          * @brief Index type
@@ -1052,7 +1053,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
         #endif
         GLintptr _indexOffset{};
         MeshIndexType _indexType{};
-        Buffer* _indexBuffer{};
+        Buffer _indexBuffer{NoCreate};
 
         /* Storage for std::vector with attribute layout / attribute buffer
            instances. 4 pointers should be one pointer more than enough. */

src/Magnum/GL/MeshView.cpp

@@ -82,7 +82,7 @@ void MeshView::multiDrawImplementationDefault(std::initializer_list<std::referen
             #ifndef MAGNUM_TARGET_GLES
             hasBaseVertex = true;
             #else
-            CORRADE_ASSERT(!original._indexBuffer, "GL::MeshView::draw(): desktop OpenGL is required for base vertex specification in indexed meshes", );
+            CORRADE_ASSERT(!original._indexBuffer.id(), "GL::MeshView::draw(): desktop OpenGL is required for base vertex specification in indexed meshes", );
             #endif
         }
 
@@ -92,7 +92,7 @@ void MeshView::multiDrawImplementationDefault(std::initializer_list<std::referen
     (original.*state.bindImplementation)();
 
     /* Non-indexed meshes */
-    if(!original._indexBuffer) {
+    if(!original._indexBuffer.id()) {
         #ifndef MAGNUM_TARGET_GLES
         glMultiDrawArrays(GLenum(original._primitive), baseVertex, count, meshes.size());
         #else
@@ -140,7 +140,7 @@ void MeshView::multiDrawImplementationFallback(std::initializer_list<std::refere
 #endif
 
 MeshView& MeshView::setIndexRange(Int first) {
-     CORRADE_ASSERT(_original.get()._indexBuffer, "MeshView::setIndexRange(): mesh is not indexed", *this);
+     CORRADE_ASSERT(_original.get()._indexBuffer.id(), "MeshView::setIndexRange(): mesh is not indexed", *this);
     _indexOffset = _original.get()._indexOffset + first*_original.get().indexTypeSize();
     return *this;
 }