Re: Drawing UI elements behind text

[Cecilio Pardo <cpardo@imayhem.com>]

On 28/11/2024 10:57, Eli Zaretskii wrote:
>> The segments are drawn independently of redisplay, on top of its result,
>> without affecting it (so that the next redisplay finds it exactly as it
>> was). So no optimizations are disabled, and the time added by them is
>> independent of what redisplay had to do.
> 
> I'm probably missing something: if Emacs uses the scroll_run_hook,
> which bitblts a portion of the screen's pixels, doesn't that move also
> the pixels of the segments?  If not, does it mean those segments'
> pixels are not drawn on the screen, but somehow overlaid on it using
> some video driver trick?

This is working only if emacs is using a double buffered configuration. 
Redisplay works on the back buffer, where we don't draw anything. When 
the back buffer goes to the screen, we add the segments to the screen. 
scroll_run_hook works on the back buffer.