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Re: Drawing UI elements behind text


From: Cecilio Pardo
Subject: Re: Drawing UI elements behind text
Date: Thu, 28 Nov 2024 11:41:25 +0100
User-agent: Mozilla Thunderbird

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.



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