[mutter] compositor: fix background vignette for non-stretched styles

[Ray Strode <halfline src gnome org>]

commit 6e831c88a6f2f795cda41a25a82bb15f8e313579
Author: Ray Strode <rstrode redhat com>
Date:   Sun Feb 24 21:24:54 2013 -0500

    compositor: fix background vignette for non-stretched styles
    
    The background vignette currently fits itself to the painted
    texture, instead of the monitor.  This causes some very
    wrong looking drawing for backgrounds that don't fill the screen.
    
    This commit reworks the vignette shader code to be clearer, more
    correct, and parameterized so that it knows how to scale and
    position the vignette.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=694393

 src/compositor/meta-background.c |   50 ++++++++++++++++++++++++++++++++++---
 1 files changed, 46 insertions(+), 4 deletions(-)
---
diff --git a/src/compositor/meta-background.c b/src/compositor/meta-background.c
index a43d68c..880b53d 100644
--- a/src/compositor/meta-background.c
+++ b/src/compositor/meta-background.c
@@ -64,14 +64,16 @@
 "cogl_texel = apply_blur(cogl_sampler, cogl_tex_coord.st);\n"
 
 #define FRAGMENT_SHADER_DECLARATIONS                                           \
+"uniform vec2 texture_scale;\n"                                                \
+"uniform vec2 actor_size;\n"                                                   \
+"uniform vec2 offset;\n"                                                       \
 "uniform float brightness;\n"                                                  \
 "uniform float vignette_sharpness;\n"                                          \
 
 #define VIGNETTE_CODE                                                          \
-"float unit_length = 0.5;\n"                                                   \
-"vec2 center = vec2(unit_length, unit_length);\n"                              \
-"vec2 position = cogl_tex_coord_in[0].xy - center;\n"                          \
-"float t = min(length(position), unit_length) / unit_length;\n"                \
+"vec2 position = cogl_tex_coord_in[0].xy * texture_scale - offset;\n"          \
+"float t = length(2.0 * (position / actor_size));\n"                           \
+"t = clamp(t, 0.0, 1.0);\n"                                                    \
 "float pixel_brightness = mix(1.0, 1.0 - vignette_sharpness, t);\n"            \
 "cogl_color_out.rgb = cogl_color_out.rgb * pixel_brightness * brightness;\n"
 
@@ -374,6 +376,44 @@ set_blur_parameters (MetaBackground  *self,
 }
 
 static void
+set_vignette_parameters (MetaBackground        *self,
+                         ClutterActorBox       *actor_box,
+                         cairo_rectangle_int_t *texture_area,
+                         float                  texture_x_scale,
+                         float                  texture_y_scale)
+{
+  MetaBackgroundPrivate *priv = self->priv;
+  float                  texture_scale[2];
+  float                  actor_size[2];
+  float                  offset[2];
+
+  if (!(priv->effects & META_BACKGROUND_EFFECTS_VIGNETTE))
+    return;
+
+  texture_scale[0] = 1.0 / texture_x_scale;
+  texture_scale[1] = 1.0 / texture_y_scale;
+  actor_size[0] = actor_box->x2 - actor_box->x1;
+  actor_size[1] = actor_box->y2 - actor_box->y1;
+  offset[0] = -texture_area->x + (actor_size[0] / 2.0);
+  offset[1] = -texture_area->y + (actor_size[1] / 2.0);
+
+  cogl_pipeline_set_uniform_float (priv->pipeline,
+                                   cogl_pipeline_get_uniform_location (priv->pipeline,
+                                                                       "texture_scale"),
+                                   2, 1, texture_scale);
+
+  cogl_pipeline_set_uniform_float (priv->pipeline,
+                                   cogl_pipeline_get_uniform_location (priv->pipeline,
+                                                                       "actor_size"),
+                                   2, 1, actor_size);
+
+  cogl_pipeline_set_uniform_float (priv->pipeline,
+                                   cogl_pipeline_get_uniform_location (priv->pipeline,
+                                                                       "offset"),
+                                   2, 1, offset);
+}
+
+static void
 meta_background_paint_content (ClutterContent   *content,
                                ClutterActor     *actor,
                                ClutterPaintNode *root)
@@ -408,6 +448,8 @@ meta_background_paint_content (ClutterContent   *content,
                               &texture_x_scale,
                               &texture_y_scale);
 
+  set_vignette_parameters (self, &actor_box, &texture_area, texture_x_scale, texture_y_scale);
+
   /* Now figure out what to actually paint. We start by clipping the texture area to
    * the actor's bounds.
    */