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Re: Universal functions to manage multiple window caches.

From: Alex Gramiak
Subject: Re: Universal functions to manage multiple window caches.
Date: Thu, 18 Apr 2019 15:02:15 -0600
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)

Keith David Bershatsky <address@hidden> writes:

> I am working on feature requests 22873 (multiple fake cursors) and 17684 
> (crosshairs that track the cursor position).
> window.h defines four different caches of fake cursors, with the only 
> difference between them being their names:
>   struct multiple_cursors_cache *temp_elts;
>   ptrdiff_t temp_elts_allocated;
>   int temp_nelts;
>   struct multiple_cursors_cache *mc_elts;
>   ptrdiff_t mc_elts_allocated;
>   int mc_nelts;
>   struct multiple_cursors_cache *ch_elts;
>   ptrdiff_t ch_elts_allocated;
>   int ch_nelts;
>   struct multiple_cursors_cache *fc_elts;
>   ptrdiff_t fc_elts_allocated;
>   int fc_nelts;

Each of the four could just be structs themselves. Something like:

  struct multiple_cursor_cache
    ptrdiff_t allocated;
    ptrdiff_t used;
    struct items
      int x;
      int fx;
      int y;
      int fy;
      int hpos;
      int vpos;
      int wd;
      int h;
      int cursor_type;
      int cursor_width;
      struct RGB
        double red;
        double green;
        double blue;
      } foreground, background;
      bool active_p;
      int glyph_flavor;
      bool enabled_p;
    } *caches;

If you need to differentiate them in a helper procedure, you can add an
enum element to the outermost struct.

P.S. Why do you need to memset the used portion of the caches on every
window update? I would think that just setting the used/*_nelts count
would be sufficient as long as you make sure not to go past that and
access garbage data.

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