GL: accept Mesh index offset as a pointer-sized value.

Vertex buffer offsets are like this already (and I already had a use
case with a mesh of size larger than 4 GB), with index buffers so far I
thought it's not needed, but it makes sense to do that as well -- there
can be a giant index buffer for many meshes and even though the total
drawn element count won't reach 1 billion (or 1 million, even), it can
still go over. Since it was internally already stored as a pointer-sized
value and some (but not all) code was treating it as pointer-sized, this
change just makes sense.

This also fixes "warning C4244: 'return': conversion from 'const
GLintptr' to 'Magnum::Int', possible loss of data" on MSVC, although in
a very different way.

src/Magnum/GL/Mesh.cpp

@@ -438,7 +438,7 @@ UnsignedInt Mesh::indexTypeSize() const {
 }
 #endif
 
-Mesh& Mesh::setIndexOffset(Int offset) {
+Mesh& Mesh::setIndexOffset(GLintptr offset) {
     CORRADE_ASSERT(_indexBuffer.id(),
         "GL::Mesh::setIndexOffset(): mesh is not indexed", *this);
     _indexOffset = offset;
@@ -871,7 +871,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
 {
     const Implementation::MeshState& state = Context::current().state().mesh;
 
-    const UnsignedInt indexByteOffset = _indexBuffer.id() ?
+    const GLintptr indexByteOffset = _indexBuffer.id() ?
         _indexBufferOffset + indexOffset*meshIndexTypeSize(_indexType) :
         0;
 
@@ -900,7 +900,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawRangeElementsBaseVertexImplementation
                 #endif
-                    (GLenum(_primitive), indexStart, indexEnd, count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), baseVertex);
+                    (GLenum(_primitive), indexStart, indexEnd, count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), baseVertex);
 
             /* Indexed mesh */
             } else
@@ -911,7 +911,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawElementsBaseVertexImplementation
                 #endif
-                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), baseVertex);
+                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), baseVertex);
             }
             #else
             CORRADE_ASSERT_UNREACHABLE("GL::AbstractShaderProgram::draw(): indexed mesh draw with base vertex specification possible only since WebGL 2.0", );
@@ -922,7 +922,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
             #ifndef MAGNUM_TARGET_GLES2
             /* Indexed mesh with specified range */
             if(indexEnd) {
-                glDrawRangeElements(GLenum(_primitive), indexStart, indexEnd, count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)));
+                glDrawRangeElements(GLenum(_primitive), indexStart, indexEnd, count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset));
 
             /* Indexed mesh */
             } else
@@ -931,7 +931,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
             static_cast<void>(indexEnd);
             #endif
             {
-                glDrawElements(GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)));
+                glDrawElements(GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset));
             }
         }
 
@@ -971,7 +971,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawElementsInstancedBaseVertexBaseInstanceImplementation
                 #endif
-                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), instanceCount, baseVertex, baseInstance);
+                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), instanceCount, baseVertex, baseInstance);
 
             /* Indexed mesh with base vertex */
             } else {
@@ -980,7 +980,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawElementsInstancedBaseVertexImplementation
                 #endif
-                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), instanceCount, baseVertex);
+                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), instanceCount, baseVertex);
             }
             #else
             CORRADE_ASSERT_UNREACHABLE("GL::AbstractShaderProgram::draw(): instanced indexed mesh draw with base vertex specification possible only since OpenGL ES 3.0", );
@@ -996,7 +996,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawElementsInstancedBaseInstanceImplementation
                 #endif
-                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), instanceCount, baseInstance);
+                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), instanceCount, baseInstance);
 
             /* Instanced mesh */
             } else
@@ -1007,7 +1007,7 @@ void Mesh::drawInternal(Int count, Int baseVertex, Int instanceCount, GLintptr i
                 #else
                 state.drawElementsInstancedImplementation
                 #endif
-                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(std::size_t(indexByteOffset)), instanceCount);
+                    (GLenum(_primitive), count, GLenum(_indexType), reinterpret_cast<GLvoid*>(indexByteOffset), instanceCount);
             }
         }
     }

src/Magnum/GL/Mesh.h

@@ -753,7 +753,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          * @brief Index offset
          * @m_since_latest
          */
-        Int indexOffset() const { return _indexOffset; }
+        GLintptr indexOffset() const { return _indexOffset; }
 
         /**
          * @brief Set index offset
@@ -768,7 +768,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          * @p start and @p end parameters may help to improve memory access
          * performance, as only a portion of vertex buffer needs to be
          * acccessed. On OpenGL ES 2.0 this function behaves the same as
-         * @ref setIndexOffset(Int), as index range functionality is not
+         * @ref setIndexOffset(GLintptr), as index range functionality is not
          * available there. Ignored when calling
          * @ref AbstractShaderProgram::drawTransformFeedback().
          *
@@ -776,7 +776,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          * @see @ref setCount(), @ref isIndexed()
          */
         /* MinGW/MSVC needs inline also here to avoid linkage conflicts */
-        inline Mesh& setIndexOffset(Int offset, UnsignedInt start, UnsignedInt end);
+        inline Mesh& setIndexOffset(GLintptr offset, UnsignedInt start, UnsignedInt end);
 
         /**
          * @brief Set index offset
@@ -785,14 +785,14 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          *
          * The offset gets multiplied by index type size and added to the base
          * offset that was specified in @ref Mesh::setIndexBuffer(). Prefer to
-         * use @ref setIndexOffset(Int, UnsignedInt, UnsignedInt) for potential
-         * better performance on certain drivers. Ignored when calling
-         * @ref AbstractShaderProgram::drawTransformFeedback().
+         * use @ref setIndexOffset(GLintptr, UnsignedInt, UnsignedInt) for
+         * potential better performance on certain drivers. Ignored when
+         * calling @ref AbstractShaderProgram::drawTransformFeedback().
          *
          * Expects that the mesh is indexed.
          * @see @ref setCount(), @ref isIndexed()
          */
-        Mesh& setIndexOffset(Int offset);
+        Mesh& setIndexOffset(GLintptr offset);
 
         /** @brief Instance count */
         Int instanceCount() const { return _instanceCount; }
@@ -1443,7 +1443,7 @@ MAGNUM_GL_EXPORT Debug& operator<<(Debug& debug, MeshPrimitive value);
 /** @debugoperatorenum{MeshIndexType} */
 MAGNUM_GL_EXPORT Debug& operator<<(Debug& debug, MeshIndexType value);
 
-inline Mesh& Mesh::setIndexOffset(Int first, UnsignedInt start, UnsignedInt end) {
+inline Mesh& Mesh::setIndexOffset(GLintptr first, UnsignedInt start, UnsignedInt end) {
     setIndexOffset(first);
     #ifndef MAGNUM_TARGET_GLES2
     _indexStart = start;