Re: Stipples and scroll optimizations

[Po Lu <luangruo@yahoo.com>]

Eli Zaretskii <eliz@gnu.org> writes:

> Sorry, I don't understand: what is the "previous" glyph matrix, and
> how can you use it for this test?

I mean the glyph matrix representing what is currently on the glass, the
"current matrix".

> Really?  I see that 'struct face' has a 'stipple' member, which is set
> in realize_gui_face, and that happens when we realize the face, long
> before x_draw_glyph_string is called.  And each glyph in a glyph_row
> has a face_id member, which allows you to get at the corresponding
> face structure.  Why cannot you use this to detect glyph_row's that
> use stipples?  The only type of glyph whose stipple is ignored is the
> cursor glyph, and that hardly matters for your purposes here, no?

Whether or not a stipple is present usually depends on the `stippled_p'
flag, which is set in `x_set_glyph_string_gc'.  But for starters,
drawing an image glyph might change that flag, and an image might also
obscure the stipple entirely, in which case we don't want to inhibit the
scrolling optimization.