static void
st_scroll_view_fade_dispose (GObject *gobject)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (gobject);

  if (self->program != COGL_INVALID_HANDLE)
    {
      cogl_handle_unref (self->program);

      self->program = COGL_INVALID_HANDLE;
      self->shader = COGL_INVALID_HANDLE;
    }

  if (self->vadjustment)
    {
      g_signal_handlers_disconnect_by_func (self->vadjustment,
                                            (gpointer)on_vadjustment_changed,
                                            self);
      self->vadjustment = NULL;
    }

  self->actor = NULL;

  G_OBJECT_CLASS (st_scroll_view_fade_parent_class)->dispose (gobject);
}
static void
st_scroll_view_fade_set_actor (ClutterActorMeta *meta,
                               ClutterActor *actor)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (meta);
  ClutterActorMetaClass *parent;

  g_return_if_fail (actor == NULL || ST_IS_SCROLL_VIEW (actor));

  if (self->shader == COGL_INVALID_HANDLE)
    {
      clutter_actor_meta_set_enabled (meta, FALSE);
      return;
    }

  if (self->vadjustment)
    {
      g_signal_handlers_disconnect_by_func (self->vadjustment,
                                            (gpointer)on_adjustment_changed,
                                            self);
      self->vadjustment = NULL;
    }

  if (self->hadjustment)
    {
      g_signal_handlers_disconnect_by_func (self->hadjustment,
                                            (gpointer)on_adjustment_changed,
                                            self);
      self->hadjustment = NULL;
    }


  if (actor)
    {
        StScrollView *scroll_view = ST_SCROLL_VIEW (actor);
        StScrollBar *vscroll = ST_SCROLL_BAR (st_scroll_view_get_vscroll_bar (scroll_view));
        StScrollBar *hscroll = ST_SCROLL_BAR (st_scroll_view_get_hscroll_bar (scroll_view));
        self->vadjustment = ST_ADJUSTMENT (st_scroll_bar_get_adjustment (vscroll));
        self->hadjustment = ST_ADJUSTMENT (st_scroll_bar_get_adjustment (hscroll));

        g_signal_connect (self->vadjustment, "changed",
                          G_CALLBACK (on_adjustment_changed),
                          self);

        g_signal_connect (self->hadjustment, "changed",
                          G_CALLBACK (on_adjustment_changed),
                          self);

        on_adjustment_changed (NULL, CLUTTER_EFFECT (self));
    }

  parent = CLUTTER_ACTOR_META_CLASS (st_scroll_view_fade_parent_class);
  parent->set_actor (meta, actor);

  /* we keep a back pointer here, to avoid going through the ActorMeta */
  self->actor = clutter_actor_meta_get_actor (meta);
}
static void
st_scroll_view_fade_paint_target (ClutterOffscreenEffect *effect)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (effect);
  ClutterOffscreenEffectClass *parent;
  CoglHandle material;

  gdouble value, lower, upper, page_size;
  ClutterActor *vscroll = st_scroll_view_get_vscroll_bar (ST_SCROLL_VIEW (self->actor));
  ClutterActor *hscroll = st_scroll_view_get_hscroll_bar (ST_SCROLL_VIEW (self->actor));
  gboolean h_scroll_visible, v_scroll_visible;

  g_object_get (ST_SCROLL_VIEW (self->actor),
                "hscrollbar-visible", &h_scroll_visible,
                "vscrollbar-visible", &v_scroll_visible,
                NULL);

  if (self->program == COGL_INVALID_HANDLE)
    goto out;

  st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);

  if (self->offset_top_uniform > -1) {
    if (value > lower + 0.1)
      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, self->fade_offset);
    else
      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, 0.0f);
  }

  if (self->offset_bottom_uniform > -1) {
    if (value < upper - page_size - 0.1)
      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, self->fade_offset);
    else
      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, 0.0f);
  }

  if (self->tex_uniform > -1)
    cogl_program_set_uniform_1i (self->program, self->tex_uniform, 0);
  if (self->height_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->height_uniform, clutter_actor_get_height (self->actor));
  if (self->width_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->width_uniform, clutter_actor_get_width (self->actor));
  if (self->scrollbar_width_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->scrollbar_width_uniform, v_scroll_visible ? clutter_actor_get_width (vscroll) : 0);
  if (self->scrollbar_height_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->scrollbar_height_uniform, h_scroll_visible ? clutter_actor_get_height (hscroll) : 0);
  if (self->rtl_uniform > -1)
    cogl_program_set_uniform_1i (self->program, self->rtl_uniform, (st_widget_get_direction (ST_WIDGET (self->actor)) == ST_TEXT_DIRECTION_RTL));

  material = clutter_offscreen_effect_get_target (effect);
  cogl_material_set_user_program (material, self->program);

out:
  parent = CLUTTER_OFFSCREEN_EFFECT_CLASS (st_scroll_view_fade_parent_class);
  parent->paint_target (effect);
}
static gboolean
st_scroll_view_fade_pre_paint (ClutterEffect *effect)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (effect);
  ClutterEffectClass *parent_class;

  if (self->shader == COGL_INVALID_HANDLE)
    return FALSE;

  if (!clutter_actor_meta_get_enabled (CLUTTER_ACTOR_META (effect)))
    return FALSE;

  if (self->actor == NULL)
    return FALSE;

  if (self->program == COGL_INVALID_HANDLE)
    self->program = cogl_create_program ();

  if (!self->is_attached)
    {
      g_assert (self->shader != COGL_INVALID_HANDLE);
      g_assert (self->program != COGL_INVALID_HANDLE);

      cogl_program_attach_shader (self->program, self->shader);
      cogl_program_link (self->program);

      cogl_handle_unref (self->shader);

      self->is_attached = TRUE;

      self->tex_uniform =
        cogl_program_get_uniform_location (self->program, "tex");
      self->height_uniform =
        cogl_program_get_uniform_location (self->program, "height");
      self->width_uniform =
        cogl_program_get_uniform_location (self->program, "width");
      self->scrollbar_width_uniform =
        cogl_program_get_uniform_location (self->program, "scrollbar_width");
      self->scrollbar_height_uniform =
        cogl_program_get_uniform_location (self->program, "scrollbar_height");
      self->rtl_uniform =
        cogl_program_get_uniform_location (self->program, "rtl");
      self->offset_top_uniform =
        cogl_program_get_uniform_location (self->program, "offset_top");
      self->offset_bottom_uniform =
        cogl_program_get_uniform_location (self->program, "offset_bottom");
    }

  parent_class = CLUTTER_EFFECT_CLASS (st_scroll_view_fade_parent_class);
  return parent_class->pre_paint (effect);
}
static void
st_scroll_view_fade_get_property (GObject *object,
                                  guint prop_id,
                                  GValue *value,
                                  GParamSpec *pspec)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (object);

  switch (prop_id)
    {
    case PROP_FADE_OFFSET:
      g_value_set_float (value, self->fade_offset);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
    }
}
static void
on_adjustment_changed (StAdjustment *adjustment,
                       ClutterEffect *effect)
{
  gdouble value, lower, upper, page_size;
  gboolean needs_fade;
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (effect);

  st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
  needs_fade = (value > lower + 0.1) || (value < upper - page_size - 0.1);

  if (!needs_fade)
    {
      st_adjustment_get_values (self->hadjustment, &value, &lower, &upper, NULL, NULL, &page_size);
      needs_fade = (value > lower + 0.1) || (value < upper - page_size - 0.1);
    }

  clutter_actor_meta_set_enabled (CLUTTER_ACTOR_META (effect), needs_fade);
}
static void
st_scroll_view_fade_paint_target (ClutterOffscreenEffect *effect)
{
  StScrollViewFade *self = ST_SCROLL_VIEW_FADE (effect);
  ClutterOffscreenEffectClass *parent;
  CoglHandle material;

  gdouble value, lower, upper, page_size;
  ClutterActor *vscroll = st_scroll_view_get_vscroll_bar (ST_SCROLL_VIEW (self->actor));
  ClutterActor *hscroll = st_scroll_view_get_hscroll_bar (ST_SCROLL_VIEW (self->actor));
  gboolean h_scroll_visible, v_scroll_visible;

  ClutterActorBox allocation, content_box, paint_box;

  /*
   * Used to pass the fade area to the shader
   *
   * [0][0] = x1
   * [0][1] = y1
   * [1][0] = x2
   * [1][1] = y2
   *
   */
  float fade_area[2][2];
  ClutterVertex verts[4];

  if (self->program == COGL_INVALID_HANDLE)
    goto out;

  clutter_actor_get_paint_box (self->actor, &paint_box);
  clutter_actor_get_abs_allocation_vertices (self->actor, verts);

  clutter_actor_get_allocation_box (self->actor, &allocation);
  st_theme_node_get_content_box (st_widget_get_theme_node (ST_WIDGET (self->actor)),
                                (const ClutterActorBox *)&allocation, &content_box);

  /*
   * The FBO is based on the paint_volume's size which can be larger then the actual
   * allocation, so we have to account for that when passing the positions
   */
  fade_area[0][0] = content_box.x1 + (verts[0].x - paint_box.x1);
  fade_area[0][1] = content_box.y1 + (verts[0].y - paint_box.y1);
  fade_area[1][0] = content_box.x2 + (verts[3].x - paint_box.x2);
  fade_area[1][1] = content_box.y2 + (verts[3].y - paint_box.y2);

  g_object_get (ST_SCROLL_VIEW (self->actor),
                "hscrollbar-visible", &h_scroll_visible,
                "vscrollbar-visible", &v_scroll_visible,
                NULL);

  if (v_scroll_visible)
    {
      if (st_widget_get_direction (ST_WIDGET (self->actor)) == ST_TEXT_DIRECTION_RTL)
          fade_area[0][0] += clutter_actor_get_width (vscroll);

      fade_area[1][0] -= clutter_actor_get_width (vscroll);
    }

  if (h_scroll_visible)
      fade_area[1][1] -= clutter_actor_get_height (hscroll);

  st_adjustment_get_values (self->vadjustment, &value, &lower, &upper, NULL, NULL, &page_size);

  if (self->offset_top_uniform > -1) {
    if (value > lower + 0.1)
      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, self->fade_offset);
    else
      cogl_program_set_uniform_1f (self->program, self->offset_top_uniform, 0.0f);
  }

  if (self->offset_bottom_uniform > -1) {
    if (value < upper - page_size - 0.1)
      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, self->fade_offset);
    else
      cogl_program_set_uniform_1f (self->program, self->offset_bottom_uniform, 0.0f);
  }

  if (self->tex_uniform > -1)
    cogl_program_set_uniform_1i (self->program, self->tex_uniform, 0);
  if (self->height_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->height_uniform, clutter_actor_get_height (self->actor));
  if (self->width_uniform > -1)
    cogl_program_set_uniform_1f (self->program, self->width_uniform, clutter_actor_get_width (self->actor));
  if (self->fade_area_uniform > -1)
    cogl_program_set_uniform_matrix (self->program, self->fade_area_uniform, 2, 1, FALSE, (const float *)fade_area);

  material = clutter_offscreen_effect_get_target (effect);
  cogl_material_set_user_program (material, self->program);

out:
  parent = CLUTTER_OFFSCREEN_EFFECT_CLASS (st_scroll_view_fade_parent_class);
  parent->paint_target (effect);
}