Resolves: tdf#101213 drop use of CAIRO_OPERATOR_DIFFERENCE

for tdf#99446 and rhbz#1283420 there is a hackaround which ended up in 5.1.5,
which is not in 5.1.4, for corrupt glyphs under X. I can still reproduce the
problem if I drop the CAIRO_OPERATOR_DIFFERENCE usage here with master and
gtk2.

This alternative hackaround to force a read of the underlying surface works
just as well (help->license information is the reproducer) but reportedly
solves the performance regression.

(cherry picked from commit 705d7597480b2307d7e4929ce9386d80ce2a0f16)

Change-Id: Ie3c5b07409537a1734226b4ce034620351297e25
Reviewed-on: https://gerrit.libreoffice.org/27984
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit d89abe0806947149eafbd9d7ce4b3095ec38b236)

1 files changed, 9 insertions, 14 deletions

diff --git a/vcl/unx/generic/gdi/x11cairotextrender.cxx b/vcl/unx/generic/gdi/x11cairotextrender.cxx
index 17cb4622b6cf..c2242b58d01f 100644
--- a/vcl/unx/generic/gdi/x11cairotextrender.cxx
+++ b/vcl/unx/generic/gdi/x11cairotextrender.cxx
@@ -42,10 +42,6 @@ struct _XRegion
     BOX extents;
 };
 
-#if CAIRO_VERSION < CAIRO_VERSION_ENCODE(1, 10, 0)
-#    define CAIRO_OPERATOR_DIFFERENCE (static_cast<cairo_operator_t>(23))
-#endif
-
 X11CairoTextRender::X11CairoTextRender(X11SalGraphics& rParent)
     : mrParent(rParent)
 {
@@ -83,17 +79,16 @@ cairo_t* X11CairoTextRender::getCairoContext()
     cairo_t *cr = cairo_create(surface);
     cairo_surface_destroy(surface);
 
-    //rhbz#1283420 bodge to draw and undraw something which has the side effect
-    //of making the mysterious xrender related problem go away
-    if (cairo_version() >= CAIRO_VERSION_ENCODE(1, 10, 0))
+    //rhbz#1283420 bodge to force a read from the underlying surface which has
+    //the side effect of making the mysterious xrender related problem go away
     {
-        cairo_save(cr);
-        cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
-        cairo_set_operator(cr, CAIRO_OPERATOR_DIFFERENCE);
-        cairo_rectangle(cr, 0, 0, 1, 1);
-        cairo_fill_preserve(cr);
-        cairo_fill(cr);
-        cairo_restore(cr);
+        cairo_surface_t *target = cairo_get_target(cr);
+        cairo_surface_t *throw_away = cairo_surface_create_similar(target, cairo_surface_get_content(target), 1, 1);
+        cairo_t *force_read_cr = cairo_create(throw_away);
+        cairo_set_source_surface(force_read_cr, target, 0, 0);
+        cairo_paint(force_read_cr);
+        cairo_destroy(force_read_cr);
+        cairo_surface_destroy(throw_away);
     }
 
     return cr;