+/* pass 0 to just swap vmem_back/vmem_front with page flipping
+ * pass a pointer to a system-ram pixel buffer to copy it to vmem_front,
+ * instead of flipping.
+ */
+void swap_buffers(void *pixels);
+
+/* call each frame to get 3D viewing spherical coordinates */
+void mouse_orbit_update(float *theta, float *phi, float *dist);
+
+void draw_mouse_pointer(uint16_t *fb);
+