Re: Text shadows

[Po Lu]

Kai Ma <justksqsf@gmail.com> writes:

>  On Mar 12, 2023, at 16:46, Po Lu <luangruo@yahoo.com> wrote:
>
>  Theoretically, nothing.  I targeted Cairo because (I think) it is the most 
> popular option on GNU/Linux.
>
>  Speaking of this specific implementation, gaussian_blur() relies on a 
> specific Cairo image format ARGB32, (this assumption could be
>  easily removed), and then it is used by ftcrfont_draw() to generate shadows.
>
>  I don’t know whether non-Cairo builds (non-cairo X, win32) can/should use 
> gaussian_blur() though, since I’m not familiar with them.
>
>  Non-Cairo builds and Cairo builds alike should use the X Rendering
>  Extension, where an arbitrary blur kernel is a standard picture filter.
>  Cairo builds on X should as well.
>
> I agree XRender should be used for non-Cairo X builds (when XRender is 
> available).

You can create a scratch Cairo surface backed by the drawable and
suitable picture format.

Temporary drawable and GC allocation is usually very fast in X servers
descending from the MIT sample server because they internally use many
different kinds of ``scratch pixmaps'' and ``scratch GCs'', but if you
worry about this kind of thing you can reuse the surface if you want
too.

Then, place a filter on that surface's picture and composite its
contents to FRAME_X_PICTURE (f).

Any code which involves Emacs writing to memory is unacceptable under X.
The reason is that the shared memory extension is not always available,
and is slower.