+/* returns the number of swapchain images */
+int vk_num_swap_images(void);
+VkImageView vk_swap_image(int idx);
+/* returns the image index, or -1 on failure. Pass optional semaphore to signal */
+int vk_next_swap_image(VkSemaphore sem);
+
+int vk_submit(VkQueue q, VkCommandBuffer cmdbuf, VkSemaphore semwait, VkSemaphore semsig);
+int vk_present(VkQueue q, int imgid, VkSemaphore semwait);
+