master d49c8cea43: Correctly premultiply background color of fringe bitmaps

[Po Lu]

branch: master
commit d49c8cea4377066e8fd8035d941bf671e51722eb
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Correctly premultiply background color of fringe bitmaps
    
    * src/xterm.c (x_draw_fringe_bitmap): Premultiply alphas by
    alpha_background.
---
 src/xterm.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index bd0fdde01e..469077c897 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -2111,6 +2111,7 @@ x_draw_fringe_bitmap (struct window *w, struct glyph_row 
*row, struct draw_fring
       int depth = FRAME_DISPLAY_INFO (f)->n_planes;
       XGCValues gcv;
       unsigned long background = face->background;
+      XColor bg;
 #ifdef HAVE_XRENDER
       Picture picture = None;
       XRenderPictureAttributes attrs;
@@ -2123,9 +2124,18 @@ x_draw_fringe_bitmap (struct window *w, struct glyph_row 
*row, struct draw_fring
       else
        bits = (char *) p->bits + p->dh;
 
-      if (FRAME_DISPLAY_INFO (f)->alpha_bits)
+      if (FRAME_DISPLAY_INFO (f)->alpha_bits
+         && f->alpha_background < 1.0)
        {
-         background = (background & ~FRAME_DISPLAY_INFO (f)->alpha_mask);
+         bg.pixel = background;
+         x_query_colors (f, &bg, 1);
+         bg.red *= f->alpha_background;
+         bg.green *= f->alpha_background;
+         bg.blue *= f->alpha_background;
+
+         background = x_make_truecolor_pixel (FRAME_DISPLAY_INFO (f),
+                                              bg.red, bg.green, bg.blue);
+         background &= ~FRAME_DISPLAY_INFO (f)->alpha_mask;
          background |= (((unsigned long) (f->alpha_background * 0xffff)
                          >> (16 - FRAME_DISPLAY_INFO (f)->alpha_bits))
                         << FRAME_DISPLAY_INFO (f)->alpha_offset);