Re: [AD] vsync and SVGAlib (was Problems: Grabber and windowing)

[Eric Botcazou <ebotcazou@xxxxxxxxxx>]

> However, if you noticed earlier when I first mentioned this problem, some
> people told me that show_video_bitmap does not guarantee vsync. That is
> because the docs do say "This function will wait for a vertical retrace
> **if the graphics card requires it**."  If in must wait for a vsync then
> how about saying "This function will wait for a vertical retrace." Instead
> of this 'if requires' confusion.

1. Historically (in the good old days of DOS), some gfx cards may not have 
required to wait for the vertical retrace in order to do scrolling.
2. You can probably disable the vsync() at the gfx driver level.

But you're right, some clarification certainly can't hurt. What about the 
following changes, borrowed from scroll_screen() ?


--- /home/eric/cvs/allegro/docs/src/allegro._tx	Mon Jan 20 16:06:21 2003
+++ allegro/docs/src/allegro._tx	Tue Jan 21 23:07:13 2003
@@ -2884,9 +2884,11 @@
    Attempts to page flip the hardware screen to display the specified video 
    bitmap object, which must be the same size as the physical screen, and 
    should have been obtained by calling the create_video_bitmap() function. 
-   Returns zero on success. This function will wait for a vertical retrace 
-   if the graphics card requires it, so you don't need to call vsync() 
-   yourself.
+   Returns zero on success and non-zero on failure.
+   
+   Allegro will handle any necessary vertical retrace synchronisation when 
+   page flipping, so you don't need to call vsync() before it. This means
+   that show_video_bitmap() has the same time delay effects as vsync().
 
 @@int @request_video_bitmap(BITMAP *bitmap);
 @xref poll_scroll, request_scroll, gfx_capabilities, timer_simulate_retrace


-- 
Eric Botcazou