xcb surfaces and expose events

[Steven J Abner]

Having a strobe/flashing issue that hoping in cairo's design you 
figured a way to overcome. This issue occurs on x server, with or 
without a window manager, and configure notify events are involved.

This occurs on resizing. Two cases to hopefully qualify conditions. One 
I have a condition where resizing occurs internal to a window, cairo 
surfaces resized and redrawn with internal configuring and invalidate 
areas to cause an expose event. The other, resizing a window, configure 
notify events sent approx 1/60 sec, causing it to run through same 
internal configure as first, but no invalidate areas causing expose 
knowing that the x server sends one after configure notify. The 
strobe/flashing issue only occurs when I have to involve xorg with 
configure notify. Both resizing speeds are at same lightening pace.

This is a single thread operation, so only one possibility I haven't 
tried is lock the display server during 'blit' to video buffer or 
surface. Here is the expose event code:

bool
_event_expose(xcb_generic_event_t *nvt) {

  xcb_expose_event_t *expose = (xcb_expose_event_t*)nvt;
  PhxInterface *iface = ui_interface_for(expose->window);
  cairo_t *cr;

  DEBUG_ASSERT( ( ((int16_t)expose->x < 0) || ((int16_t)expose->y < 0) 
),
                   "probable failure: _event_expose().");

  _interface_draw(iface, expose);

  cr = cairo_create(iface->vid_buffer);
  cairo_rectangle(cr, expose->x, expose->y,
                      expose->width, expose->height);
  cairo_clip(cr);
  cairo_set_source_surface(cr, iface->surface, 0, 0);
  cairo_paint(cr);
  DEBUG_ASSERT((cairo_status(cr) != CAIRO_STATUS_SUCCESS),
                                "failure: _event_expose().");
  cairo_destroy(cr);
  cairo_surface_flush(iface->vid_buffer);
  return true;
}

I have also reduced configure timer to have expose events occur very 
close to 1/60 sec
which didn't appear to help. I also have not found a IN/OUT register 
type of call to receive start of blanking from either xorg or linux. I 
had assumed that xorg knows when it returned from it's expose, it draws 
surface at correct time. Assuming xorg does know, then can you tell, 
advise, on what I'm doing wrong? Do I need to lock the server, guessing 
that strobe/flashing occurs on my painting of vid buffer as xorg is 
drawing?
Vid buffer uses 'cairo_xcb_surface_set_size()' and drawing surfaces are 
only created anew when a surface is altered past it's max width/height 
used in any sizing attempt. Uses clip to draw valid surface areas. Draw 
surfaces drawn/painted to 'iface->surface'.

Here are the 2 case's pngs in hopes that it may help visualize what the 
heck this guy's talking 'bout. xxhbr blue button resizes window. xxgtx 
frame around text/label objects used as drag grip area to resize a 
'pane' area. Again, this is with/without a window manager. If thinking 
SYNC, that's for WM case only, afaict and remember, and produces odd 
results on which one choose.

I'm 99.99% certain this is not due to cairo. But being it's drawing, 
hopes are that you have encountered and worked this out before.
Fingers crossed,
Steve





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