Add a radial background shade for modal dialogs

Use a new ShellGLSLQuad actor class to build a RadialEffect that can be
enabled on Lightboxes to achieve a radial effect similar to the overview
one. Then enable it for modal dialogs.

https://bugzilla.gnome.org/show_bug.cgi?id=669798

src/shell-glsl-quad.c

@@ -0,0 +1,166 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/**
+ * SECTION:shell-glsl-quad
+ * @short_description: Draw a rectangle using GLSL
+ *
+ * A #ShellGLSLQuad draws one single rectangle, sized to the allocation
+ * box, but allows running custom GLSL to the vertex and fragment
+ * stages of the graphic pipeline.
+ *
+ * To ease writing the shader, a single texture layer is also used.
+ */
+
+#include "config.h"
+
+#define CLUTTER_ENABLE_EXPERIMENTAL_API
+#define COGL_ENABLE_EXPERIMENTAL_API
+
+#include <cogl/cogl.h>
+#include "shell-glsl-quad.h"
+
+G_DEFINE_TYPE (ShellGLSLQuad, shell_glsl_quad, CLUTTER_TYPE_ACTOR);
+
+struct _ShellGLSLQuadPrivate
+{
+  CoglPipeline  *pipeline;
+  CoglTexture2D *texture;
+};
+
+static void
+shell_glsl_quad_paint (ClutterActor *actor)
+{
+  ShellGLSLQuad *self = SHELL_GLSL_QUAD (actor);
+  ShellGLSLQuadPrivate *priv;
+  guint8 paint_opacity;
+  ClutterActorBox box;
+
+  priv = self->priv;
+
+  paint_opacity = clutter_actor_get_paint_opacity (actor);
+  clutter_actor_get_allocation_box (actor, &box);
+
+  /* semi-transparent black */
+  cogl_pipeline_set_color4ub (priv->pipeline,
+                              0, 0, 0,
+                              paint_opacity);
+  cogl_framebuffer_draw_rectangle (cogl_get_draw_framebuffer (),
+                                   priv->pipeline,
+                                   box.x1, box.y1,
+                                   box.x2, box.y2);
+}
+
+
+/**
+ * shell_glsl_quad_add_glsl_snippet:
+ * @quad: a #ShellGLSLQuad
+ * @hook: where to insert the code
+ * @declarations: GLSL declarations
+ * @code: GLSL code
+ * @is_replace: wheter Cogl code should be replaced by the custom shader
+ *
+ * Adds a GLSL snippet to the pipeline used for drawing the actor texture.
+ * See #CoglSnippet for details.
+ *
+ * This is only valid inside the a call to the build_pipeline() virtual
+ * function.
+ */
+void
+shell_glsl_quad_add_glsl_snippet (ShellGLSLQuad    *quad,
+                                  ShellSnippetHook  hook,
+                                  const char       *declarations,
+                                  const char       *code,
+                                  gboolean          is_replace)
+{
+  ShellGLSLQuadClass *klass = SHELL_GLSL_QUAD_GET_CLASS (quad);
+  CoglSnippet *snippet;
+
+  g_return_if_fail (klass->base_pipeline != NULL);
+
+  if (is_replace)
+    {
+      snippet = cogl_snippet_new (hook, declarations, NULL);
+      cogl_snippet_set_replace (snippet, code);
+    }
+  else
+    {
+      snippet = cogl_snippet_new (hook, declarations, code);
+    }
+
+  if (hook == SHELL_SNIPPET_HOOK_VERTEX ||
+      hook == SHELL_SNIPPET_HOOK_FRAGMENT)
+    cogl_pipeline_add_snippet (klass->base_pipeline, snippet);
+  else
+    cogl_pipeline_add_layer_snippet (klass->base_pipeline, 0, snippet);
+
+  cogl_object_unref (snippet);
+}
+
+static void
+shell_glsl_quad_dispose (GObject *gobject)
+{
+  ShellGLSLQuad *self = SHELL_GLSL_QUAD (gobject);
+  ShellGLSLQuadPrivate *priv;
+
+  priv = self->priv;
+
+  g_clear_pointer (&priv->pipeline, cogl_object_unref);
+  g_clear_pointer (&priv->texture, cogl_object_unref);
+
+  G_OBJECT_CLASS (shell_glsl_quad_parent_class)->dispose (gobject);
+}
+
+static void
+shell_glsl_quad_init (ShellGLSLQuad *quad)
+{
+  quad->priv = G_TYPE_INSTANCE_GET_PRIVATE (quad, SHELL_TYPE_GLSL_QUAD, ShellGLSLQuadPrivate);
+}
+
+static void
+shell_glsl_quad_constructed (GObject *object)
+{
+  ShellGLSLQuad *self;
+  ShellGLSLQuadClass *klass;
+  CoglContext *ctx =
+    clutter_backend_get_cogl_context (clutter_get_default_backend ());
+  static const uint8_t tex_data[] = { 0, 0, 0, 0 };
+
+  G_OBJECT_CLASS (shell_glsl_quad_parent_class)->constructed (object);
+
+  /* Note that, differently from ClutterBlurEffect, we are calling
+     this inside constructed, not init, so klass points to the most-derived
+     GTypeClass, not ShellGLSLQuadClass.
+  */
+  klass = SHELL_GLSL_QUAD_GET_CLASS (object);
+  self = SHELL_GLSL_QUAD (object);
+
+  if (G_UNLIKELY (klass->base_pipeline == NULL))
+    {
+      klass->base_pipeline = cogl_pipeline_new (ctx);
+
+      if (klass->build_pipeline != NULL)
+        klass->build_pipeline (self);
+    }
+
+  self->priv->pipeline = cogl_pipeline_copy (klass->base_pipeline);
+
+  self->priv->texture = cogl_texture_2d_new_from_data (ctx, 1, 1,
+                                                       COGL_PIXEL_FORMAT_RGBA_8888,
+                                                       0, tex_data, NULL);
+  cogl_pipeline_set_layer_texture (self->priv->pipeline, 0,
+                                   COGL_TEXTURE (self->priv->texture));
+}
+
+static void
+shell_glsl_quad_class_init (ShellGLSLQuadClass *klass)
+{
+  ClutterActorClass *actor_class = CLUTTER_ACTOR_CLASS (klass);
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+
+  gobject_class->constructed = shell_glsl_quad_constructed;
+  gobject_class->dispose = shell_glsl_quad_dispose;
+
+  actor_class->paint = shell_glsl_quad_paint;
+
+  g_type_class_add_private (klass, sizeof (ShellGLSLQuadPrivate));
+}