[gimp] plug-ins: Apply the context-background color on exporting to pdf

[João Sebastião de Oliveira Bueno Calligaris <jsbueno src gnome org>]

commit 7829177e3c322cc5b63ebcbf67354836e47d1c02
Author: João S. O. Bueno <gwidion gmail com>
Date:   Sat Jul 25 03:19:47 2015 -0300

    plug-ins: Apply the context-background color on exporting to pdf
    
    PDF files have no transparency, still, transparent areas of
    exported images would always display white, regardless of the
    current background color.
    (The misbehavior was found while checking BUG #752819,
     but that is a cairo issue and is not fixed by this)

 plug-ins/common/file-pdf-save.c |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletions(-)
---
diff --git a/plug-ins/common/file-pdf-save.c b/plug-ins/common/file-pdf-save.c
index 1d7bddf..e4a80a9 100644
--- a/plug-ins/common/file-pdf-save.c
+++ b/plug-ins/common/file-pdf-save.c
@@ -508,9 +508,38 @@ run (const gchar      *name,
        */
       cairo_scale (cr, x_scale, y_scale);
 
-      /* Now, we should loop over the layers of each image */
       layers = gimp_image_get_layers (image_ID, &n_layers);
 
+      /* Fill image with background color -
+       * otherwise the output PDF will always show white for background,
+       * and may display artifacts at transparency boundaries
+       */
+      if (gimp_drawable_has_alpha(layers[n_layers - 1]))
+        {
+          GimpRGB color;
+          gint width=0, height=0;
+          for (j = 0; j < n_layers; j++)
+            {
+              gint32 layer_ID   = layers [n_layers - j - 1];
+
+              if (gimp_item_get_visible (layer_ID) &&
+                 (! optimize.ignore_hidden ||
+                  (optimize.ignore_hidden && gimp_layer_get_opacity (layer_ID) > 0.0)))
+                {
+                  width = MAX (width, gimp_drawable_width (layer_ID));
+                  height = MAX (height, gimp_drawable_height (layer_ID));
+                }
+            }
+          cairo_rectangle (cr, 0, 0, width, height);
+          gimp_context_get_background (&color);
+          cairo_set_source_rgb (cr,
+                                color.r,
+                                color.g,
+                                color.b);
+          cairo_fill (cr);
+        }
+
+      /* Now, we should loop over the layers of each image */
       for (j = 0; j < n_layers; j++)
         {
           gint32           layer_ID   = layers [n_layers - j - 1];