About glyph matrices

About glyph matrices

[Xue Fuqiao]

In (info "(elisp) Window Internals"):

  `current_matrix'
  `desired_matrix'
     Glyph matrices describing the current and desired display of this
     window.

I didn't know what is "the current and desired display" of window.  Then I went
to window.h:

    /* Glyph matrices.  */
    struct glyph_matrix *current_matrix;
    struct glyph_matrix *desired_matrix;

But they didn't help.  I didn't find it in the manual, either.  Can
anybody help?  Thanks.

-- 
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao

Re: About glyph matrices

[Eli Zaretskii]

> Date: Sat, 2 Mar 2013 08:36:22 +0800
> From: Xue Fuqiao <xfq.free@gmail.com>
> 
> In (info "(elisp) Window Internals"):
> 
>   `current_matrix'
>   `desired_matrix'
>      Glyph matrices describing the current and desired display of this
>      window.
> 
> I didn't know what is "the current and desired display" of window.

These are data structures manipulated by the Emacs display engine.
The current matrix describes the current state of the window display;
the desired matrix describes what _should_ be displayed.  The display
engine constructs the desired matrix, then compares it with the
current matrix, and invokes the display-specific back end to redraw
the parts that are different.