Premultiply background color by alpha for images

* src/xterm.c (x_query_frame_background_color): Premultiply
colors as X wants them when built without Cairo.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 9cde6c9a683..cff4b07c6ea 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -3146,13 +3146,35 @@ static void
 x_query_frame_background_color (struct frame *f, XColor *bgcolor)
 {
   unsigned long background = FRAME_BACKGROUND_PIXEL (f);
+#ifndef USE_CAIRO
+  XColor bg;
+#endif
 
   if (FRAME_DISPLAY_INFO (f)->alpha_bits)
     {
+#ifdef USE_CAIRO
       background = (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);
+#else
+      if (FRAME_DISPLAY_INFO (f)->alpha_bits
+          && f->alpha_background < 1.0)
+        {
+          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);
+        }
+#endif
     }
 
   bgcolor->pixel = background;