[gtk+] cssimage: Fix angle computation for gradients to corners

[Benjamin Otte <otte src gnome org>]

commit 9474215a43b116cf6098b11ef967a10afc495923
Author: Benjamin Otte <otte redhat com>
Date:   Thu Jan 8 19:30:19 2015 +0100

    cssimage: Fix angle computation for gradients to corners

 gtk/gtkcssimagelinear.c |   43 +++++++++++++++++++++++++++----------------
 1 files changed, 27 insertions(+), 16 deletions(-)
---
diff --git a/gtk/gtkcssimagelinear.c b/gtk/gtkcssimagelinear.c
index a5b0955..f8ee0b2 100644
--- a/gtk/gtkcssimagelinear.c
+++ b/gtk/gtkcssimagelinear.c
@@ -135,6 +135,7 @@ gtk_css_image_linear_draw (GtkCssImage        *image,
 {
   GtkCssImageLinear *linear = GTK_CSS_IMAGE_LINEAR (image);
   cairo_pattern_t *pattern;
+  double angle; /* actual angle of the gradiant line in degrees */
   double x, y; /* coordinates of start point */
   double length; /* distance in pixels for 100% */
   double start, end; /* position of first/last point on gradient line - with gradient line being [0, 1] */
@@ -145,27 +146,37 @@ gtk_css_image_linear_draw (GtkCssImage        *image,
     {
       guint side = _gtk_css_number_value_get (linear->angle, 100);
 
-      if (side & (1 << GTK_CSS_RIGHT))
-        x = width;
-      else if (side & (1 << GTK_CSS_LEFT))
-        x = -width;
-      else
-        x = 0;
-
-      if (side & (1 << GTK_CSS_TOP))
-        y = -height;
-      else if (side & (1 << GTK_CSS_BOTTOM))
-        y = height;
-      else
-        y = 0;
+      /* special casing the regular cases here so we don't get rounding errors */
+      switch (side)
+      {
+        case 1 << GTK_CSS_RIGHT:
+          angle = 90;
+          break;
+        case 1 << GTK_CSS_LEFT:
+          angle = 270;
+          break;
+        case 1 << GTK_CSS_TOP:
+          angle = 0;
+          break;
+        case 1 << GTK_CSS_BOTTOM:
+          angle = 180;
+          break;
+        default:
+          angle = atan2 (side & 1 << GTK_CSS_TOP ? -width : width,
+                         side & 1 << GTK_CSS_LEFT ? -height : height);
+          angle = 180 * angle / G_PI + 90;
+          break;
+      }
     }
   else
     {
-      gtk_css_image_linear_compute_start_point (_gtk_css_number_value_get (linear->angle, 100),
-                                                width, height,
-                                                &x, &y);
+      angle = _gtk_css_number_value_get (linear->angle, 100);
     }
 
+  gtk_css_image_linear_compute_start_point (angle,
+                                            width, height,
+                                            &x, &y);
+
   length = sqrt (x * x + y * y);
   gtk_css_image_linear_get_start_end (linear, length, &start, &end);
   pattern = cairo_pattern_create_linear (x * (start - 0.5), y * (start - 0.5),