[gnome-shell/gbsneto/blur: 1/2] screenShield: Blur background



commit f73029ba1feabe42f15e2f9ef85d409d65ce3416
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Mon Oct 7 14:38:19 2019 -0300

    screenShield: Blur background
    
    This is a moderately fast two-pass gaussian blur implementation.
    It downscales the framebuffer by an eighth before applying the
    gaussian shader, which cuts down rendering time quite considerably.
    
    The blur shader takes 2 uniforms as input: the blur radius; and
    whether to blur vertically or horizontally.
    
    The blur radius is treated as an integer in C land to simplify
    calculations. The vertical parameter is treated as an integer by
    the shader simply due to Cogl not having proper boolean support
    in snippets.
    
    At last, brightness is also added to avoid needing to use an extra
    effect to achieve that. Brightness is applied in a different pipeline
    than blur, so we can control it more tightly.
    
    Related: https://gitlab.gnome.org/GNOME/gnome-shell/issues/1848
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/864

 js/ui/screenShield.js   |   9 +
 src/meson.build         |   2 +
 src/shell-blur-effect.c | 826 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/shell-blur-effect.h |  41 +++
 4 files changed, 878 insertions(+)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index dbeabedd06..8ca76c52a9 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -27,6 +27,10 @@ const LOCKDOWN_SCHEMA = 'org.gnome.desktop.lockdown';
 const DISABLE_LOCK_KEY = 'disable-lock-screen';
 
 const LOCKED_STATE_STR = 'screenShield.locked';
+
+const BLUR_BRIGHTNESS = 0.55;
+const BLUR_RADIUS = 200;
+
 // fraction of screen height the arrow must reach before completing
 // the slide up automatically
 var ARROW_DRAG_THRESHOLD = 0.1;
@@ -607,6 +611,11 @@ var ScreenShield = class {
         this._bgManagers.push(bgManager);
 
         this._backgroundGroup.add_child(widget);
+
+        widget.add_effect(new Shell.BlurEffect({
+            brightness: BLUR_BRIGHTNESS,
+            blur_radius: BLUR_RADIUS,
+        }));
     }
 
     _updateBackgrounds() {
diff --git a/src/meson.build b/src/meson.build
index 3523fb16cb..656be33893 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -95,6 +95,7 @@ libshell_public_headers = [
   'shell-app.h',
   'shell-app-system.h',
   'shell-app-usage.h',
+  'shell-blur-effect.h',
   'shell-embedded-window.h',
   'shell-glsl-effect.h',
   'shell-gtk-embed.h',
@@ -129,6 +130,7 @@ libshell_sources = [
   'shell-app.c',
   'shell-app-system.c',
   'shell-app-usage.c',
+  'shell-blur-effect.c',
   'shell-embedded-window.c',
   'shell-embedded-window-private.h',
   'shell-global.c',
diff --git a/src/shell-blur-effect.c b/src/shell-blur-effect.c
new file mode 100644
index 0000000000..d73e36db9d
--- /dev/null
+++ b/src/shell-blur-effect.c
@@ -0,0 +1,826 @@
+/* shell-blur-effect.c
+ *
+ * Copyright 2019 Georges Basile Stavracas Neto <georges stavracas gmail com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include "shell-blur-effect.h"
+
+/*
+ * ShellBlurEffect:
+ *
+ * Applies a gaussian blur to the actor. The gaussian blur is implemented in
+ * 2 passes: vertical and horizontal. Thus, it is a linear shader.
+ *
+ * The actor is drawn into a downscaled framebuffer; the blur passes are applied
+ * on the downscaled actor contents; and finally, the blurred contents are drawn
+ * upscaled again.
+ *
+ * At last, this blur implementation cuts down the number of sampling operations
+ * by exploiting the hardware interpolation that is performed when sampling between
+ * pixel boundaries. This technique is described at:
+ *
+ * http://rastergrid.com/blog/2010/09/efficient-gaussian-blur-with-linear-sampling/
+ *
+ * At last, ShellBlurEffect has an optional brighness value.
+ */
+
+static const gchar *gaussian_blur_glsl_declarations =
+"uniform float blur_radius;                                        \n"
+"uniform float pixel_step;                                         \n"
+"uniform int vertical;                                             \n"
+"                                                                  \n"
+"float gaussian (float sigma, float x) {                           \n"
+"  return exp ( - (x * x) / (2.0 * sigma * sigma));                \n"
+"}                                                                 \n"
+"                                                                  \n";
+
+static const gchar *gaussian_blur_glsl =
+"  float radius = blur_radius * 2.30348;                           \n"
+"  float total = 0.0;                                              \n"
+"  int horizontal = 1 - vertical;                                  \n"
+"                                                                  \n"
+"  vec4 ret = vec4 (0);                                            \n"
+"  vec2 uv = vec2(cogl_tex_coord.st);                              \n"
+"                                                                  \n"
+"  float half_radius = radius / 2.0;                               \n"
+"  int n_steps = max(int(ceil(half_radius)), 1);                   \n"
+"                                                                  \n"
+"  for (int i = 0; i < n_steps; i += 2) {                          \n"
+"    float weight0 = gaussian (half_radius, float(i));             \n"
+"    float weight1 = gaussian (half_radius, float(i) + 1);         \n"
+"    float weight = weight0 + weight1;                             \n"
+"                                                                  \n"
+"    float step0 = float(i) * pixel_step;                          \n"
+"    float step1 = float(i + 1) * pixel_step;                      \n"
+"                                                                  \n"
+"    float foffset = (step0 * weight0 + step1 * weight1) / weight; \n"
+"    vec2 offset = vec2(foffset * float(horizontal),               \n"
+"                       foffset * float(vertical));                \n"
+"                                                                  \n"
+"    vec4 c = texture2D(cogl_sampler, uv + offset);                \n"
+"    total += weight;                                              \n"
+"    ret += c * weight;                                            \n"
+"                                                                  \n"
+"    c = texture2D(cogl_sampler, uv - offset);                     \n"
+"    total += weight;                                              \n"
+"    ret += c * weight;                                            \n"
+"  }                                                               \n"
+"                                                                  \n"
+"  cogl_texel = vec4 (ret / total);                                \n";
+
+static const gchar *brightness_glsl_declarations =
+"uniform float brightness;                                         \n";
+
+static const gchar *brightness_glsl =
+"  cogl_color_out.rgb *= brightness;                               \n";
+
+#define MIN_DOWNSCALE_SIZE 256.f
+#define MAX_BLUR_RADIUS 10.f
+
+typedef enum
+{
+  VERTICAL,
+  HORIZONTAL,
+} BlurType;
+
+typedef struct
+{
+  CoglFramebuffer *framebuffer;
+  CoglTexture *texture;
+
+  BlurType type;
+
+  CoglPipeline *pipeline;
+  int blur_radius_uniform;
+  int pixel_step_uniform;
+  int vertical_uniform;
+} BlurData;
+
+struct _ShellBlurEffect
+{
+  ClutterEffect parent_instance;
+
+  ClutterActor *actor;
+  uint8_t old_opacity_override;
+
+  BlurData blur[2];
+
+  unsigned int tex_width;
+  unsigned int tex_height;
+
+  /* The cached contents */
+  CoglFramebuffer *framebuffer;
+  CoglTexture *texture;
+
+  CoglPipeline *pipeline;
+  int brightness_uniform;
+
+  float downscale_factor;
+  float brightness;
+  int blur_radius;
+};
+
+G_DEFINE_TYPE (ShellBlurEffect, shell_blur_effect, CLUTTER_TYPE_EFFECT)
+
+enum {
+  PROP_0,
+  PROP_BLUR_RADIUS,
+  PROP_BRIGHTNESS,
+  N_PROPS
+};
+
+static GParamSpec *properties [N_PROPS] = { NULL, };
+
+static CoglPipeline*
+create_blur_pipeline (void)
+{
+  static CoglPipeline *base_pipeline = NULL;
+
+  if (G_UNLIKELY (base_pipeline == NULL))
+    {
+      CoglSnippet *snippet;
+      CoglContext *ctx =
+        clutter_backend_get_cogl_context (clutter_get_default_backend ());
+
+      base_pipeline = cogl_pipeline_new (ctx);
+
+      snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_TEXTURE_LOOKUP,
+                                  gaussian_blur_glsl_declarations,
+                                  NULL);
+      cogl_snippet_set_replace (snippet, gaussian_blur_glsl);
+      cogl_pipeline_add_layer_snippet (base_pipeline, 0, snippet);
+      cogl_object_unref (snippet);
+
+      cogl_pipeline_set_layer_null_texture (base_pipeline, 0);
+      cogl_pipeline_set_layer_filters (base_pipeline,
+                                       0,
+                                       COGL_PIPELINE_FILTER_LINEAR,
+                                       COGL_PIPELINE_FILTER_LINEAR);
+      cogl_pipeline_set_layer_wrap_mode (base_pipeline,
+                                         0,
+                                         COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
+    }
+
+  return cogl_pipeline_copy (base_pipeline);
+}
+
+
+static CoglPipeline*
+create_brightness_pipeline (void)
+{
+  static CoglPipeline *base_pipeline = NULL;
+
+  if (G_UNLIKELY (base_pipeline == NULL))
+    {
+      CoglSnippet *snippet;
+      CoglContext *ctx =
+        clutter_backend_get_cogl_context (clutter_get_default_backend ());
+
+      base_pipeline = cogl_pipeline_new (ctx);
+
+      snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_FRAGMENT,
+                                  brightness_glsl_declarations,
+                                  brightness_glsl);
+      cogl_pipeline_add_snippet (base_pipeline, snippet);
+      cogl_object_unref (snippet);
+
+      cogl_pipeline_set_layer_null_texture (base_pipeline, 0);
+      cogl_pipeline_set_layer_filters (base_pipeline,
+                                       0,
+                                       COGL_PIPELINE_FILTER_LINEAR,
+                                       COGL_PIPELINE_FILTER_LINEAR);
+    }
+
+  return cogl_pipeline_copy (base_pipeline);
+}
+
+static void
+setup_blur (BlurData *blur,
+            BlurType  type)
+{
+  blur->type = type;
+  blur->pipeline = create_blur_pipeline ();
+
+  blur->blur_radius_uniform =
+    cogl_pipeline_get_uniform_location (blur->pipeline, "blur_radius");
+  blur->pixel_step_uniform =
+    cogl_pipeline_get_uniform_location (blur->pipeline, "pixel_step");
+  blur->vertical_uniform =
+    cogl_pipeline_get_uniform_location (blur->pipeline, "vertical");
+}
+
+static void
+update_blur_uniforms (ShellBlurEffect *self,
+                      BlurData        *blur)
+{
+  gboolean is_vertical = blur->type == VERTICAL;
+
+  if (blur->pixel_step_uniform > -1)
+    {
+      float pixel_step;
+
+      if (is_vertical)
+        pixel_step = 1.f / cogl_texture_get_height (blur->texture);
+      else
+        pixel_step = 1.f / cogl_texture_get_width (blur->texture);
+
+      cogl_pipeline_set_uniform_1f (blur->pipeline,
+                                    blur->pixel_step_uniform,
+                                    pixel_step);
+    }
+
+  if (blur->blur_radius_uniform > -1)
+    {
+      cogl_pipeline_set_uniform_1f (blur->pipeline,
+                                    blur->blur_radius_uniform,
+                                    self->blur_radius / self->downscale_factor);
+    }
+
+  if (blur->vertical_uniform > -1)
+    {
+      cogl_pipeline_set_uniform_1i (blur->pipeline,
+                                    blur->vertical_uniform,
+                                    is_vertical);
+    }
+}
+
+static void
+update_brightness_uniform (ShellBlurEffect *self)
+{
+  if (self->brightness_uniform > -1)
+    {
+      cogl_pipeline_set_uniform_1f (self->pipeline,
+                                    self->brightness_uniform,
+                                    self->brightness);
+    }
+}
+
+static gboolean
+update_fbo (CoglFramebuffer **framebuffer,
+            CoglTexture     **texture,
+            CoglPipeline     *pipeline,
+            unsigned int      width,
+            unsigned int      height,
+            float             downscale_factor)
+{
+  CoglContext *ctx =
+    clutter_backend_get_cogl_context (clutter_get_default_backend ());
+
+  g_clear_pointer (texture, cogl_object_unref);
+  g_clear_pointer (framebuffer, cogl_object_unref);
+
+  *texture =
+    cogl_texture_2d_new_with_size (ctx,
+                                   width / downscale_factor,
+                                   height / downscale_factor);
+  if (!*texture)
+    return FALSE;
+
+  cogl_pipeline_set_layer_texture (pipeline, 0, *texture);
+
+  *framebuffer = cogl_offscreen_new_with_texture (*texture);
+  if (!*framebuffer)
+    {
+      g_warning ("%s: Unable to create an Offscreen buffer", G_STRLOC);
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static gboolean
+update_cache_fbo (ClutterEffect *effect,
+                  unsigned int   width,
+                  unsigned int   height,
+                  float          downscale_factor)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+
+  if (self->tex_width == width &&
+      self->tex_height == height &&
+      self->framebuffer)
+    {
+      return TRUE;
+    }
+
+  return update_fbo (&self->framebuffer,
+                     &self->texture,
+                     self->pipeline,
+                     width, height,
+                     downscale_factor);
+}
+
+static gboolean
+update_blur_fbo (ClutterEffect *effect,
+                 BlurData      *blur,
+                 unsigned int   width,
+                 unsigned int   height,
+                 float          downscale_factor)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+
+  if (self->tex_width == width &&
+      self->tex_height == height &&
+      blur->framebuffer)
+    {
+      return TRUE;
+    }
+
+  return update_fbo (&blur->framebuffer,
+                     &blur->texture,
+                     blur->pipeline,
+                     width, height,
+                     downscale_factor);
+}
+
+static void
+clear_blur (BlurData *blur)
+{
+  g_clear_pointer (&blur->texture, cogl_object_unref);
+  g_clear_pointer (&blur->framebuffer, cogl_object_unref);
+}
+
+static void
+setup_projection_matrix (CoglFramebuffer *framebuffer,
+                         float            width,
+                         float            height,
+                         float            downscale_factor)
+{
+  CoglMatrix projection;
+  float downscaled_width = width / downscale_factor;
+  float downscaled_height = height / downscale_factor;
+
+  cogl_matrix_init_identity (&projection);
+  cogl_matrix_scale (&projection,
+                     2.0 / downscaled_width,
+                     -2.0 / downscaled_height,
+                     1.f);
+  cogl_matrix_translate (&projection,
+                         -downscaled_width / 2.0,
+                         -downscaled_height / 2.0,
+                         0);
+
+  cogl_framebuffer_set_projection_matrix (framebuffer, &projection);
+}
+
+static float
+calculate_downscale_factor (float width,
+                            float height,
+                            float blur_radius)
+{
+  float downscale_factor = 1.0;
+  float scaled_width = width;
+  float scaled_height = height;
+  float scaled_radius = blur_radius;
+
+  /* This is the algorithm used by Firefox; keep downscaling until either the
+   * blur radius is lower than the threshold, or the downscaled texture is too
+   * small.
+   */
+  while (scaled_radius > MAX_BLUR_RADIUS &&
+         scaled_width > MIN_DOWNSCALE_SIZE &&
+         scaled_height > MIN_DOWNSCALE_SIZE)
+    {
+      downscale_factor *= 2.f;
+
+      scaled_width = width / downscale_factor;
+      scaled_height = height / downscale_factor;
+      scaled_radius = blur_radius / downscale_factor;
+    }
+
+  return downscale_factor;
+}
+
+static void
+shell_blur_effect_set_actor (ClutterActorMeta *meta,
+                             ClutterActor     *actor)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (meta);
+  ClutterActorMetaClass *meta_class;
+
+  meta_class = CLUTTER_ACTOR_META_CLASS (shell_blur_effect_parent_class);
+  meta_class->set_actor (meta, actor);
+
+  /* clear out the previous state */
+  clear_blur (&self->blur[VERTICAL]);
+  clear_blur (&self->blur[HORIZONTAL]);
+
+  g_clear_pointer (&self->texture, cogl_object_unref);
+  g_clear_pointer (&self->framebuffer, cogl_object_unref);
+
+  /* we keep a back pointer here, to avoid going through the ActorMeta */
+  self->actor = clutter_actor_meta_get_actor (meta);
+}
+
+static gboolean
+shell_blur_effect_pre_paint (ClutterEffect *effect)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+  ClutterActorBox box;
+  CoglColor transparent;
+  BlurData *vblur;
+  BlurData *hblur;
+  float width = -1;
+  float height = -1;
+  float resource_scale;
+  float ceiled_resource_scale;
+  float downscale_factor;
+
+  if (!clutter_actor_meta_get_enabled (CLUTTER_ACTOR_META (effect)))
+    return FALSE;
+
+  if (!self->actor)
+    return FALSE;
+
+  if (clutter_actor_get_resource_scale (self->actor, &resource_scale))
+    ceiled_resource_scale = ceilf (resource_scale);
+  else
+    g_assert_not_reached ();
+
+  clutter_actor_get_allocation_box (self->actor, &box);
+  clutter_actor_box_scale (&box, ceiled_resource_scale);
+  clutter_actor_box_get_size (&box, &width, &height);
+
+  width = ceilf (width);
+  height = ceilf (height);
+  downscale_factor = calculate_downscale_factor (width, height, self->blur_radius);
+
+  if (!update_blur_fbo (effect, &self->blur[VERTICAL], width, height, downscale_factor) ||
+      !update_blur_fbo (effect, &self->blur[HORIZONTAL], width, height, downscale_factor) ||
+      !update_cache_fbo (effect, width, height, downscale_factor))
+    {
+      return FALSE;
+    }
+
+  self->tex_width = width;
+  self->tex_height = height;
+  self->downscale_factor = downscale_factor;
+
+  self->old_opacity_override = clutter_actor_get_opacity_override (self->actor);
+  clutter_actor_set_opacity_override (self->actor, 0xff);
+
+  /* Draw the actor contents at the vertical blur framebuffer */
+  vblur = &self->blur[VERTICAL];
+  hblur = &self->blur[HORIZONTAL];
+
+  G_GNUC_BEGIN_IGNORE_DEPRECATIONS;
+  cogl_push_framebuffer (vblur->framebuffer);
+  G_GNUC_END_IGNORE_DEPRECATIONS;
+
+  setup_projection_matrix (vblur->framebuffer, width, height, downscale_factor);
+  setup_projection_matrix (hblur->framebuffer, width, height, downscale_factor);
+  setup_projection_matrix (self->framebuffer, width, height, downscale_factor);
+
+  cogl_color_init_from_4ub (&transparent, 0, 0, 0, 0);
+  cogl_framebuffer_clear (vblur->framebuffer,
+                          COGL_BUFFER_BIT_COLOR |
+                          COGL_BUFFER_BIT_DEPTH,
+                          &transparent);
+  cogl_framebuffer_clear (hblur->framebuffer,
+                          COGL_BUFFER_BIT_COLOR |
+                          COGL_BUFFER_BIT_DEPTH,
+                          &transparent);
+  cogl_framebuffer_clear (self->framebuffer,
+                          COGL_BUFFER_BIT_COLOR |
+                          COGL_BUFFER_BIT_DEPTH,
+                          &transparent);
+
+  cogl_framebuffer_push_matrix (vblur->framebuffer);
+
+  cogl_framebuffer_scale (vblur->framebuffer,
+                          1.f / downscale_factor,
+                          1.f / downscale_factor,
+                          1.f);
+
+  return TRUE;
+}
+
+static void
+paint_texture (ShellBlurEffect *self)
+{
+  CoglFramebuffer *framebuffer = cogl_get_draw_framebuffer ();
+  ClutterActor *actor;
+  CoglMatrix modelview;
+  BlurData *vblur;
+  BlurData *hblur;
+  guint8 paint_opacity;
+  float resource_scale;
+
+  vblur = &self->blur[VERTICAL];
+  hblur = &self->blur[HORIZONTAL];
+
+  actor = clutter_actor_meta_get_actor (CLUTTER_ACTOR_META (self));
+  paint_opacity = clutter_actor_get_paint_opacity (actor);
+
+  /* Pass 1:
+   *
+   * Draw the actor contents (which is in the vblur framebuffer
+   * at this point) into the hblur framebuffer. This will run the
+   * vertical blur fragment shader, and will output a vertically
+   * blurred image.
+   */
+  update_blur_uniforms (self, vblur);
+  cogl_pipeline_set_color4ub (vblur->pipeline,
+                              paint_opacity,
+                              paint_opacity,
+                              paint_opacity,
+                              paint_opacity);
+
+  cogl_framebuffer_draw_textured_rectangle (hblur->framebuffer,
+                                            vblur->pipeline,
+                                            0, 0,
+                                            cogl_texture_get_width (vblur->texture),
+                                            cogl_texture_get_height (vblur->texture),
+                                            0.f, 0.f,
+                                            1.f, 1.f);
+
+  /* Pass 2:
+   *
+   * Now the opposite; draw the vertically blurred image using the
+   * horizontal blur pipeline into the cache framebuffer.
+   */
+  update_blur_uniforms (self, hblur);
+  cogl_pipeline_set_color4ub (hblur->pipeline,
+                              paint_opacity,
+                              paint_opacity,
+                              paint_opacity,
+                              paint_opacity);
+
+  cogl_framebuffer_draw_textured_rectangle (self->framebuffer,
+                                            hblur->pipeline,
+                                            0, 0,
+                                            cogl_texture_get_width (hblur->texture),
+                                            cogl_texture_get_height (hblur->texture),
+                                            0.f, 0.f,
+                                            1.f, 1.f);
+
+  /* Now self->texture contains the vertically AND horizontally blurred
+   * texture. Paint that texture into the onscreen framebuffer, this time
+   * without any blur shader applied.
+   */
+  cogl_framebuffer_push_matrix (framebuffer);
+  cogl_framebuffer_get_modelview_matrix (framebuffer, &modelview);
+
+  if (clutter_actor_get_resource_scale (self->actor, &resource_scale) &&
+      resource_scale != 1.0f)
+    {
+      float paint_scale = 1.0f / resource_scale;
+      cogl_matrix_scale (&modelview, paint_scale, paint_scale, 1);
+    }
+
+  cogl_framebuffer_set_modelview_matrix (framebuffer, &modelview);
+
+  update_brightness_uniform (self);
+  cogl_framebuffer_draw_textured_rectangle (framebuffer,
+                                            self->pipeline,
+                                            0, 0,
+                                            self->tex_width,
+                                            self->tex_height,
+                                            0.f, 0.f,
+                                            1.f, 1.f);
+
+  cogl_framebuffer_pop_matrix (framebuffer);
+}
+
+static void
+shell_blur_effect_paint (ClutterEffect           *effect,
+                         ClutterEffectPaintFlags  flags)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+
+  if (!self->framebuffer || (flags & CLUTTER_EFFECT_PAINT_ACTOR_DIRTY))
+    {
+      /* Chain up to the parent paint method which will call the pre and
+         post paint functions to update the image */
+      CLUTTER_EFFECT_CLASS (shell_blur_effect_parent_class)->paint (effect, flags);
+    }
+  else
+    {
+      /* If we've already got a cached image and the actor hasn't been redrawn
+       * then we can just use the cached image in the FBO.
+       */
+      paint_texture (self);
+    }
+}
+
+static void
+shell_blur_effect_post_paint (ClutterEffect *effect)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+
+  cogl_framebuffer_pop_matrix (self->blur[VERTICAL].framebuffer);
+
+  G_GNUC_BEGIN_IGNORE_DEPRECATIONS;
+  cogl_pop_framebuffer ();
+  G_GNUC_END_IGNORE_DEPRECATIONS;
+
+  clutter_actor_set_opacity_override (self->actor, self->old_opacity_override);
+
+  paint_texture (self);
+}
+
+static gboolean
+shell_blur_effect_modify_paint_volume (ClutterEffect      *effect,
+                                       ClutterPaintVolume *volume)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (effect);
+  graphene_point3d_t origin;
+  float width;
+  float height;
+
+  clutter_paint_volume_get_origin (volume, &origin);
+  width = clutter_paint_volume_get_width (volume);
+  height = clutter_paint_volume_get_height (volume);
+
+  origin.y -= self->blur_radius;
+  origin.x -= self->blur_radius;
+
+  height += 2 * self->blur_radius;
+  width += 2 * self->blur_radius;
+
+  clutter_paint_volume_set_origin (volume, &origin);
+  clutter_paint_volume_set_width (volume, width);
+  clutter_paint_volume_set_height (volume, height);
+
+  return TRUE;
+}
+
+static void
+shell_blur_effect_finalize (GObject *object)
+{
+  ShellBlurEffect *self = (ShellBlurEffect *)object;
+
+  clear_blur (&self->blur[VERTICAL]);
+  clear_blur (&self->blur[HORIZONTAL]);
+
+  g_clear_pointer (&self->blur[VERTICAL].pipeline, cogl_object_unref);
+  g_clear_pointer (&self->blur[HORIZONTAL].pipeline, cogl_object_unref);
+
+  g_clear_pointer (&self->texture, cogl_object_unref);
+  g_clear_pointer (&self->pipeline, cogl_object_unref);
+  g_clear_pointer (&self->framebuffer, cogl_object_unref);
+
+  G_OBJECT_CLASS (shell_blur_effect_parent_class)->finalize (object);
+}
+
+static void
+shell_blur_effect_get_property (GObject    *object,
+                                guint       prop_id,
+                                GValue     *value,
+                                GParamSpec *pspec)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (object);
+
+  switch (prop_id)
+    {
+    case PROP_BLUR_RADIUS:
+      g_value_set_int (value, self->blur_radius);
+      break;
+
+    case PROP_BRIGHTNESS:
+      g_value_set_int (value, self->brightness);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+    }
+}
+
+static void
+shell_blur_effect_set_property (GObject      *object,
+                                guint         prop_id,
+                                const GValue *value,
+                                GParamSpec   *pspec)
+{
+  ShellBlurEffect *self = SHELL_BLUR_EFFECT (object);
+
+  switch (prop_id)
+    {
+    case PROP_BLUR_RADIUS:
+      shell_blur_effect_set_blur_radius (self, g_value_get_int (value));
+      break;
+
+    case PROP_BRIGHTNESS:
+      shell_blur_effect_set_brightness (self, g_value_get_float (value));
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+    }
+}
+
+static void
+shell_blur_effect_class_init (ShellBlurEffectClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+  ClutterActorMetaClass *meta_class = CLUTTER_ACTOR_META_CLASS (klass);
+  ClutterEffectClass *effect_class = CLUTTER_EFFECT_CLASS (klass);
+
+  object_class->finalize = shell_blur_effect_finalize;
+  object_class->get_property = shell_blur_effect_get_property;
+  object_class->set_property = shell_blur_effect_set_property;
+
+  meta_class->set_actor = shell_blur_effect_set_actor;
+
+  effect_class->pre_paint = shell_blur_effect_pre_paint;
+  effect_class->paint = shell_blur_effect_paint;
+  effect_class->post_paint = shell_blur_effect_post_paint;
+  effect_class->modify_paint_volume = shell_blur_effect_modify_paint_volume;
+
+  properties[PROP_BLUR_RADIUS] =
+    g_param_spec_int ("blur-radius",
+                      "Blur radius",
+                      "Blur radius",
+                      0, G_MAXINT, 0,
+                      G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
+
+  properties[PROP_BRIGHTNESS] =
+    g_param_spec_float ("brightness",
+                        "Brightness",
+                        "Brightness",
+                        0.f, 1.f, 1.f,
+                        G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
+
+  g_object_class_install_properties (object_class, N_PROPS, properties);
+}
+
+static void
+shell_blur_effect_init (ShellBlurEffect *self)
+{
+  self->blur_radius = 0;
+  self->brightness = 1.f;
+
+  self->pipeline = create_brightness_pipeline ();
+  self->brightness_uniform =
+    cogl_pipeline_get_uniform_location (self->pipeline, "brightness");
+
+  setup_blur (&self->blur[VERTICAL], VERTICAL);
+  setup_blur (&self->blur[HORIZONTAL], HORIZONTAL);
+}
+
+ShellBlurEffect *
+shell_blur_effect_new (void)
+{
+  return g_object_new (SHELL_TYPE_BLUR_EFFECT, NULL);
+}
+
+int
+shell_blur_effect_get_blur_radius (ShellBlurEffect *self)
+{
+  g_return_val_if_fail (SHELL_IS_BLUR_EFFECT (self), -1);
+
+  return self->blur_radius;
+}
+
+void
+shell_blur_effect_set_blur_radius (ShellBlurEffect *self,
+                                   int              radius)
+{
+  g_return_if_fail (SHELL_IS_BLUR_EFFECT (self));
+
+  if (self->blur_radius == radius)
+    return;
+
+  self->blur_radius = radius;
+  clutter_effect_queue_repaint (CLUTTER_EFFECT (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_BLUR_RADIUS]);
+}
+
+float
+shell_blur_effect_get_brightness (ShellBlurEffect *self)
+{
+  g_return_val_if_fail (SHELL_IS_BLUR_EFFECT (self), FALSE);
+
+  return self->brightness;
+}
+
+void
+shell_blur_effect_set_brightness (ShellBlurEffect *self,
+                                  float            brightness)
+{
+  g_return_if_fail (SHELL_IS_BLUR_EFFECT (self));
+
+  if (self->brightness == brightness)
+    return;
+
+  self->brightness = brightness;
+  clutter_effect_queue_repaint (CLUTTER_EFFECT (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_BRIGHTNESS]);
+}
diff --git a/src/shell-blur-effect.h b/src/shell-blur-effect.h
new file mode 100644
index 0000000000..0ce144af2d
--- /dev/null
+++ b/src/shell-blur-effect.h
@@ -0,0 +1,41 @@
+/* shell-blur-effect.h
+ *
+ * Copyright 2019 Georges Basile Stavracas Neto <georges stavracas gmail com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <clutter/clutter.h>
+
+G_BEGIN_DECLS
+
+#define SHELL_TYPE_BLUR_EFFECT (shell_blur_effect_get_type())
+
+G_DECLARE_FINAL_TYPE (ShellBlurEffect, shell_blur_effect, SHELL, BLUR_EFFECT, ClutterEffect)
+
+ShellBlurEffect *shell_blur_effect_new (void);
+
+int shell_blur_effect_get_blur_radius (ShellBlurEffect *self);
+void shell_blur_effect_set_blur_radius (ShellBlurEffect *self,
+                                        int              radius);
+
+float shell_blur_effect_get_brightness (ShellBlurEffect *self);
+void shell_blur_effect_set_brightness (ShellBlurEffect *self,
+                                       float            brightness);
+
+G_END_DECLS


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