[librsvg/rustification] Do not inherit gradient stop color and opacity from the gradient's parent object

[Federico Mena Quintero <federico src gnome org>]

commit e28afe422968f8a5bdc57ce29b46b196e0a7ead7
Author: Federico Mena Quintero <federico gnome org>
Date:   Fri Nov 11 17:02:37 2016 -0600

    Do not inherit gradient stop color and opacity from the gradient's parent object
    
    Per the spec, stop-color and stop-opacity don't inherit from the
    parent object of a gradient, unless explicitly requested.
    
    This makes the test pservers-grad-18-b.svg pass.

 rsvg-paint-server.c                                |   35 +++++++++++++++++---
 .../reftests/svg1.1/pservers-grad-18-b-ref.png     |  Bin 5654 -> 4783 bytes
 2 files changed, 30 insertions(+), 5 deletions(-)
---
diff --git a/rsvg-paint-server.c b/rsvg-paint-server.c
index e03040f..fe070c6 100644
--- a/rsvg-paint-server.c
+++ b/rsvg-paint-server.c
@@ -149,10 +149,14 @@ rsvg_paint_server_unref (RsvgPaintServer * ps)
 static void
 rsvg_stop_set_atts (RsvgNode * self, RsvgHandle * ctx, RsvgPropertyBag * atts)
 {
+    gboolean has_stop_color = FALSE;
+    gboolean has_stop_opacity = FALSE;
     gboolean is_current_color = FALSE;
     const char *value;
     RsvgGradientStop *stop;
     RsvgState *state;
+    int opacity;
+    guint32 color;
 
     stop = (RsvgGradientStop *) self;
 
@@ -181,9 +185,16 @@ rsvg_stop_set_atts (RsvgNode * self, RsvgHandle * ctx, RsvgPropertyBag * atts)
         if ((value = rsvg_property_bag_lookup (atts, "style")))
             rsvg_parse_style (ctx, self->state, value);
 
-        if ((value = rsvg_property_bag_lookup (atts, "stop-color")))
+        if ((value = rsvg_property_bag_lookup (atts, "stop-color"))) {
+            has_stop_color = TRUE;
+
             if (!strcmp (value, "currentColor"))
                 is_current_color = TRUE;
+        }
+
+        if ((value = rsvg_property_bag_lookup (atts, "stop-opacity"))) {
+            has_stop_opacity = TRUE;
+        }
 
         rsvg_parse_style_pairs (ctx, self->state, atts);
     }
@@ -192,9 +203,23 @@ rsvg_stop_set_atts (RsvgNode * self, RsvgHandle * ctx, RsvgPropertyBag * atts)
     state = rsvg_state_new ();
     rsvg_state_reconstruct (state, self);
 
-    if (is_current_color)
-        state->stop_color = state->current_color;
-    stop->rgba = (state->stop_color << 8) | state->stop_opacity;
+    if (has_stop_color) {
+        if (is_current_color)
+            color = state->current_color;
+        else {
+            color = state->stop_color & 0x00ffffff;
+        }
+    } else {
+        color = 0x0;
+    }
+
+    if (has_stop_opacity) {
+        opacity = state->stop_opacity;
+    } else {
+        opacity = 0xff;
+    }
+
+    stop->rgba = (color << 8) | opacity;
 
     rsvg_state_free (state);
 }
@@ -206,7 +231,7 @@ rsvg_new_stop (void)
     _rsvg_node_init (&stop->super, RSVG_NODE_TYPE_STOP);
     stop->super.set_atts = rsvg_stop_set_atts;
     stop->offset = 0;
-    stop->rgba = 0;
+    stop->rgba = 0xff000000;
     stop->is_valid = FALSE;
     return &stop->super;
 }
diff --git a/tests/fixtures/reftests/svg1.1/pservers-grad-18-b-ref.png 
b/tests/fixtures/reftests/svg1.1/pservers-grad-18-b-ref.png
index b288dc7..704ae63 100644
Binary files a/tests/fixtures/reftests/svg1.1/pservers-grad-18-b-ref.png and 
b/tests/fixtures/reftests/svg1.1/pservers-grad-18-b-ref.png differ