Compile error in my ubuntu 14 enviroment. 

lib/shader.c: In function ‘shader_init’:
lib/shader.c:23:27: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
# define BUFFER_OFFSET(f) ((int)&(((struct vertex *)NULL)->f))

^
lib/shader.c:102:38: note: in expansion of macro ‘BUFFER_OFFSET’
{ "position", 0, 2, sizeof(float), BUFFER_OFFSET(vp.vx) },

My gcc verion is gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1)
