master 6da021fce8: Fix artifacting on PGTK when bits are copied with an alpha channel

[Po Lu]

branch: master
commit 6da021fce86a06a97b0bff76f69aa57759533dc9
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Fix artifacting on PGTK when bits are copied with an alpha channel
    
    * src/pgtkterm.c (x_draw_stretch_glyph_string): Draw background
    respecting `alpha-background'.
    (pgtk_copy_bits): Use CAIRO_OPERATOR_SOURCE to draw onto the
    destination surface.
---
 src/pgtkterm.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/pgtkterm.c b/src/pgtkterm.c
index 9bb611e4c5..c0b76b077c 100644
--- a/src/pgtkterm.c
+++ b/src/pgtkterm.c
@@ -2381,7 +2381,7 @@ x_draw_stretch_glyph_string (struct glyph_string *s)
          else
            {
              pgtk_fill_rectangle (s->f, color, x, y, w, h,
-                                  false);
+                                  true);
            }
 
          pgtk_end_cr_clip (s->f);
@@ -2966,17 +2966,20 @@ pgtk_draw_window_cursor (struct window *w, struct 
glyph_row *glyph_row, int x,
 }
 
 static void
-pgtk_copy_bits (struct frame *f, cairo_rectangle_t * src_rect,
-               cairo_rectangle_t * dst_rect)
+pgtk_copy_bits (struct frame *f, cairo_rectangle_t *src_rect,
+               cairo_rectangle_t *dst_rect)
 {
   cairo_t *cr;
+  GdkWindow *window;
   cairo_surface_t *surface;    /* temporary surface */
 
+  window = gtk_widget_get_window (FRAME_GTK_WIDGET (f));
+
   surface =
-    cairo_surface_create_similar (FRAME_CR_SURFACE (f),
-                                 CAIRO_CONTENT_COLOR_ALPHA,
-                                 (int) src_rect->width,
-                                 (int) src_rect->height);
+    gdk_window_create_similar_surface (window, CAIRO_CONTENT_COLOR_ALPHA,
+                                      FRAME_CR_SURFACE_DESIRED_WIDTH (f),
+                                      FRAME_CR_SURFACE_DESIRED_HEIGHT
+                                      (f));
 
   cr = cairo_create (surface);
   cairo_set_source_surface (cr, FRAME_CR_SURFACE (f), -src_rect->x,
@@ -2988,6 +2991,7 @@ pgtk_copy_bits (struct frame *f, cairo_rectangle_t * 
src_rect,
 
   cr = pgtk_begin_cr_clip (f);
   cairo_set_source_surface (cr, surface, dst_rect->x, dst_rect->y);
+  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
   cairo_rectangle (cr, dst_rect->x, dst_rect->y, dst_rect->width,
                   dst_rect->height);
   cairo_clip (cr);