[gtk+] gtkcssshadowvalue: Don't double-apply the alpha to shadows

[Jasper St. Pierre <jstpierre src gnome org>]

commit 9f2e0902f63f6af6c8d2b96dd4efcb52b70b451e
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Thu Jul 31 18:27:46 2014 +0200

    gtkcssshadowvalue: Don't double-apply the alpha to shadows
    
    It turns out that when we were painting the shadows, we painted the them
    with the base color once, which contained the alpha, and then blurred it
    and used it as a mask for the fill, which has the fill again.
    
    To fix this, always paint the base surface with full alpha. The existing
    code applies the blur conditionally sometimes in weird ways, so the code
    shuffling fix may not look correct, but be assured it is. If the blur
    happens, the new cr we return has the *default* color applied, which is
    fully opaque black, which works perfectly against the A8 surface.
    
    The fallback spinner code needs some modification, since it is
    intentionally using the alpha to paint the lobes which are "in the past".
    Since we shouldn't be hitting this fallback path very often, we use a
    temporary group and paint it with paint_with_alpha, even though it is
    slow.

 gtk/gtkcssshadowvalue.c       |   12 +++++-------
 gtk/gtkthemingengine.c        |   18 +++++++-----------
 gtk/gtkthemingengineprivate.h |    3 +--
 3 files changed, 13 insertions(+), 20 deletions(-)
---
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 7970626..0648352 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -391,9 +391,9 @@ _gtk_css_shadow_value_paint_layout (const GtkCssValue *shadow,
                      _gtk_css_number_value_get (shadow->hoffset, 0),
                      _gtk_css_number_value_get (shadow->voffset, 0));
 
+  gdk_cairo_set_source_rgba (cr, _gtk_css_rgba_value_get_rgba (shadow->color));
   cr = gtk_css_shadow_value_start_drawing (shadow, cr);
 
-  gdk_cairo_set_source_rgba (cr, _gtk_css_rgba_value_get_rgba (shadow->color));
   _gtk_pango_fill_layout (cr, layout);
 
   cr = gtk_css_shadow_value_finish_drawing (shadow, cr);
@@ -415,9 +415,8 @@ _gtk_css_shadow_value_paint_icon (const GtkCssValue *shadow,
   cairo_save (cr);
   pattern = cairo_pattern_reference (cairo_get_source (cr));
 
-  cr = gtk_css_shadow_value_start_drawing (shadow, cr);
-
   gdk_cairo_set_source_rgba (cr, _gtk_css_rgba_value_get_rgba (shadow->color));
+  cr = gtk_css_shadow_value_start_drawing (shadow, cr);
 
   cairo_translate (cr,
                    _gtk_css_number_value_get (shadow->hoffset, 0),
@@ -440,14 +439,13 @@ _gtk_css_shadow_value_paint_spinner (const GtkCssValue *shadow,
 
   cairo_save (cr);
 
+  gdk_cairo_set_source_rgba (cr, _gtk_css_rgba_value_get_rgba (shadow->color));
   cr = gtk_css_shadow_value_start_drawing (shadow, cr);
 
   cairo_translate (cr,
                    _gtk_css_number_value_get (shadow->hoffset, 0),
                    _gtk_css_number_value_get (shadow->voffset, 0));
-  _gtk_theming_engine_paint_spinner (cr,
-                                     radius, progress,
-                                     _gtk_css_rgba_value_get_rgba (shadow->color));
+  _gtk_theming_engine_paint_spinner (cr, radius, progress);
 
   cr = gtk_css_shadow_value_finish_drawing (shadow, cr);
 
@@ -503,6 +501,7 @@ draw_shadow (const GtkCssValue   *shadow,
   if (has_empty_clip (cr))
     return;
 
+  gdk_cairo_set_source_rgba (cr, _gtk_css_rgba_value_get_rgba (shadow->color));
   if (blur)
     shadow_cr = gtk_css_shadow_value_start_drawing (shadow, cr);
   else
@@ -513,7 +512,6 @@ draw_shadow (const GtkCssValue   *shadow,
   if (shadow->inset)
     _gtk_rounded_box_clip_path (clip_box, shadow_cr);
 
-  gdk_cairo_set_source_rgba (shadow_cr, _gtk_css_rgba_value_get_rgba (shadow->color));
   cairo_fill (shadow_cr);
 
   if (blur)
diff --git a/gtk/gtkthemingengine.c b/gtk/gtkthemingengine.c
index ac4009e..70a8de2 100644
--- a/gtk/gtkthemingengine.c
+++ b/gtk/gtkthemingengine.c
@@ -2546,8 +2546,7 @@ gtk_theming_engine_render_handle (GtkThemingEngine *engine,
 void
 _gtk_theming_engine_paint_spinner (cairo_t       *cr,
                                    gdouble        radius,
-                                   gdouble        progress,
-                                   const GdkRGBA *color)
+                                   gdouble        progress)
 {
   guint num_steps, step;
   gdouble half;
@@ -2576,11 +2575,7 @@ _gtk_theming_engine_paint_spinner (cairo_t       *cr,
       gdouble xscale = - sin (i * G_PI / half);
       gdouble yscale = - cos (i * G_PI / half);
 
-      cairo_set_source_rgba (cr,
-                             color->red,
-                             color->green,
-                             color->blue,
-                             color->alpha * t);
+      cairo_push_group (cr);
 
       cairo_move_to (cr,
                      (radius - inset) * xscale,
@@ -2590,6 +2585,9 @@ _gtk_theming_engine_paint_spinner (cairo_t       *cr,
                      radius * yscale);
 
       cairo_stroke (cr);
+
+      cairo_pop_group_to_source (cr);
+      cairo_paint_with_alpha (cr, t);
     }
 
   cairo_restore (cr);
@@ -2620,10 +2618,8 @@ render_spinner (GtkThemingEngine *engine,
                                         radius,
                                         -1);
 
-  _gtk_theming_engine_paint_spinner (cr,
-                                     radius,
-                                     -1,
-                                     &color);
+  gdk_cairo_set_source_rgba (cr, &color);
+  _gtk_theming_engine_paint_spinner (cr, radius, -1);
 
   cairo_restore (cr);
 }
diff --git a/gtk/gtkthemingengineprivate.h b/gtk/gtkthemingengineprivate.h
index 1b61eb4..3f7b884 100644
--- a/gtk/gtkthemingengineprivate.h
+++ b/gtk/gtkthemingengineprivate.h
@@ -26,8 +26,7 @@ G_BEGIN_DECLS
 
 void _gtk_theming_engine_paint_spinner (cairo_t       *cr,
                                         gdouble        radius,
-                                        gdouble        progress,
-                                        const GdkRGBA *color);
+                                        gdouble        progress);
 
 GtkCssValue  *_gtk_theming_engine_peek_property (GtkThemingEngine *engine,
                                                  guint             property_id);