Added SpriteBatch:attachAttribute(attributename, mesh), which lets SpriteBatches use per-vertex information from a vertex attribute in a Mesh when drawing.

Each sprite in a SpriteBatch has 4 vertices in the following order: top-left, bottom-left, top-right, bottom-right. The index returned by SpriteBatch:add (and used by SpriteBatch:set) can be multiplied by 4 to determine the first vertex in a specific sprite.

src/modules/graphics/opengl/GLBuffer.cpp

@@ -90,6 +90,9 @@ void *GLBuffer::map()
 
 void GLBuffer::unmapStatic(size_t offset, size_t size)
 {
+	if (size == 0)
+		return;
+
 	// Upload the mapped data to the buffer.
 	glBufferSubData(getTarget(), (GLintptr) offset, (GLsizeiptr) size, memory_map + offset);
 }