Introduce ShellBlurEffect

This is a moderately fast two-pass gaussian blur implementation.
It downscales the framebuffer dynamically 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.

ShellBlurEffect also implements a "background" mode, where the contents
beneath the actor are blurred, but not the actor itself. This mode is
performance-heavy.

Related: https://gitlab.gnome.org/GNOME/gnome-shell/issues/1848

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/864

src/meson.build

@@ -91,6 +91,7 @@ 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',
@@ -125,6 +126,7 @@ 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',

src/shell-blur-effect.h

@@ -0,0 +1,57 @@
+/* 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
+
+/**
+ * ShellBlurMode:
+ * @SHELL_BLUR_MODE_ACTOR: blur the actor contents, and its children
+ * @SHELL_BLUR_MODE_BACKGROUND: blur what's beneath the actor
+ *
+ * The mode of blurring of the effect.
+ */
+typedef enum
+{
+  SHELL_BLUR_MODE_ACTOR,
+  SHELL_BLUR_MODE_BACKGROUND,
+} ShellBlurMode;
+
+#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);
+
+ShellBlurMode shell_blur_effect_get_mode (ShellBlurEffect *self);
+void shell_blur_effect_set_mode (ShellBlurEffect *self,
+                                 ShellBlurMode    mode);
+
+G_END_DECLS