til_fb: return queue delay from til_fb_page_get()

til_fb is triple buffered, but when rendering lags behind the
queue is empty making present-to-delay intervals smaller than
when rendering is keeping up and the queue is kept full.

This returns the duration of the returned pages last
submit-to-present delay, effectively measuring how long a page
can expect to wait to be flipped to/presented currently.

A subsequent commit will apply this delay value to the ticks
supplied to rendering.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/til_fb.h b/src/til_fb.h
index 5ad210f..7c6464e 100644
--- a/src/til_fb.h
+++ b/src/til_fb.h
@@ -47,7 +47,7 @@ typedef struct til_fb_ops_t {
 	int	(*page_flip)(til_fb_t *fb, void *context, void *page);
 } til_fb_ops_t;
 
-til_fb_fragment_t * til_fb_page_get(til_fb_t *fb);
+til_fb_fragment_t * til_fb_page_get(til_fb_t *fb, unsigned *res_delay_ticks);
 void til_fb_fragment_submit(til_fb_fragment_t *fragment);
 til_fb_fragment_t * til_fb_fragment_snapshot(til_fb_fragment_t **fragment_ptr, int preserve_original);
 til_fb_fragment_t * til_fb_fragment_reclaim(til_fb_fragment_t *fragment);