[patch] Refresh previews on branch toggle?

[Scott Kostyshak]

On Sun, Dec 08, 2019 at 11:03:20PM -0500, Richard Kimberly Heck wrote:
> On 12/8/19 9:20 PM, Scott Kostyshak wrote:
> > Attached is a patch that refreshes previews whenever the user activates
> > or deactivates a branch. The motivation for this patch is that if a
> > child document is previewed in the master document, and if the child
> > document has the branch inside it as well, the preview will be incorrect
> > when the branch is toggled (without this patch).
> >
> > However, this patch will cause all previews to refresh. I'm concerned
> > that the inefficiency is not worth the benefit. Any thoughts on this
> > patch and any thoughts on an ideal solution? For example, would
> > removePreviews() and updatePreviews() ideally have arguments that allow
> > to specify which type of previews to update?
> 
> It makes sense to me.
> 
> Do we have to remove previews first?

Good question. It doesn't work if I don't include that line, and it's
consistent with Buffer::reload(). The following contains a clue for why
I think it's needed (copied from RenderPreview.h):

  /** Remove a snippet from the cache of previews.
   *  Useful if previewing the contents of a file that has changed.
   */
  void removePreview(Buffer const &);

From the perspective of the master document, the LaTeX export
corresponding to the child document has not changed (it is just
\input{child.tex}). So if we only "update" the previews, I think that
would only regenerate previews for insets where the LaTeX as viewed by
the master document has changed.

The patch does not actually call the function I reference above. It uses
removePreviews() (note the extra 's'), which creates an entirely new
previewLoader. Perhaps it would be more efficient to loop through the
insets and call removePreview() on them (or only the ones that depend on
a file?).

Scott
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