mutter/clutter/clutter-offscreen-effect.c

/*
 * Clutter.
 *
 * An OpenGL based 'interactive canvas' library.
 *
 * Copyright (C) 2010  Intel Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 * Authors:
 *   Emmanuele Bassi <ebassi@linux.intel.com>
 *   Robert Bragg <robert@linux.intel.com>
 */

/**
 * SECTION:clutter-offscreen-effect
 * @short_description: Base class for effects using offscreen buffers
 * @see_also: #ClutterBlurEffect, #ClutterEffect
 *
 * #ClutterOffscreenEffect is an abstract class that can be used by
 * #ClutterEffect sub-classes requiring access to an offscreen buffer.
 *
 * Some effects, like the fragment shader based effects, can only use GL
 * textures, and in order to apply those effects to any kind of actor they
 * require that all drawing operations are applied to an offscreen framebuffer
 * that gets redirected to a texture.
 *
 * #ClutterOffscreenEffect provides all the heavy-lifting for creating the
 * offscreen framebuffer, the redirection and the final paint of the texture on
 * the desired stage.
 *
 * <refsect2 id="ClutterOffscreenEffect-implementing">
 *   <title>Implementing a ClutterOffscreenEffect</title>
 *   <para>Creating a sub-class of #ClutterOffscreenEffect requires, in case
 *   of overriding the #ClutterEffect virtual functions, to chain up to the
 *   #ClutterOffscreenEffect's implementation.</para>
 *   <para>On top of the #ClutterEffect's virtual functions,
 *   #ClutterOffscreenEffect also provides a <function>paint_target()</function>
 *   function, which encapsulates the effective painting of the texture that
 *   contains the result of the offscreen redirection.</para>
 *   <para>The size of the target material is defined to be as big as the
 *   transformed size of the #ClutterActor using the offscreen effect.
 *   Sub-classes of #ClutterOffscreenEffect can change the texture creation
 *   code to provide bigger textures by overriding the
 *   <function>create_texture()</function> virtual function; no chain up
 *   to the #ClutterOffscreenEffect implementation is required in this
 *   case.</para>
 * </refsect2>
 *
 * #ClutterOffscreenEffect is available since Clutter 1.4
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "clutter-offscreen-effect.h"

#include "cogl/cogl.h"

#include "clutter-actor-private.h"
#include "clutter-debug.h"
#include "clutter-private.h"
#include "clutter-stage-private.h"

struct _ClutterOffscreenEffectPrivate
{
  CoglHandle offscreen;
  CoglMaterial *target;

  ClutterActor *actor;
  ClutterActor *stage;

  gfloat x_offset;
  gfloat y_offset;

  gfloat target_width;
  gfloat target_height;
};

G_DEFINE_ABSTRACT_TYPE (ClutterOffscreenEffect,
                        clutter_offscreen_effect,
                        CLUTTER_TYPE_EFFECT);

static void
clutter_offscreen_effect_set_actor (ClutterActorMeta *meta,
                                    ClutterActor     *actor)
{
  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (meta);
  ClutterOffscreenEffectPrivate *priv = self->priv;
  ClutterActorMetaClass *meta_class;

  meta_class = CLUTTER_ACTOR_META_CLASS (clutter_offscreen_effect_parent_class);
  meta_class->set_actor (meta, actor);

  /* clear out the previous state */
  if (priv->offscreen != COGL_INVALID_HANDLE)
    {
      cogl_handle_unref (priv->offscreen);
      priv->offscreen = COGL_INVALID_HANDLE;
    }

  /* we keep a back pointer here, to avoid going through the ActorMeta */
  priv->actor = clutter_actor_meta_get_actor (meta);
}

static CoglHandle
clutter_offscreen_effect_real_create_texture (ClutterOffscreenEffect *effect,
                                              gfloat                  width,
                                              gfloat                  height)
{
  return cogl_texture_new_with_size (MAX (width, 1), MAX (height, 1),
                                     COGL_TEXTURE_NO_SLICING,
                                     COGL_PIXEL_FORMAT_RGBA_8888_PRE);
}

static gboolean
update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
{
  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
  ClutterOffscreenEffectPrivate *priv = self->priv;
  CoglHandle texture;

  priv->stage = clutter_actor_get_stage (priv->actor);
  if (priv->stage == NULL)
    {
      CLUTTER_NOTE (MISC, "The actor '%s' is not part of a stage",
                    clutter_actor_get_name (priv->actor) == NULL
                      ? G_OBJECT_TYPE_NAME (priv->actor)
                      : clutter_actor_get_name (priv->actor));
      return FALSE;
    }

  if (priv->target_width == fbo_width &&
      priv->target_height == fbo_height &&
      priv->offscreen != COGL_INVALID_HANDLE)
    return TRUE;

  if (priv->target == COGL_INVALID_HANDLE)
    priv->target = cogl_material_new ();

  texture =
    clutter_offscreen_effect_create_texture (self, fbo_width, fbo_height);
  if (texture == COGL_INVALID_HANDLE)
     return FALSE;

  cogl_material_set_layer (priv->target, 0, texture);
  cogl_handle_unref (texture);

  /* we need to use the size of the texture target and not the minimum
   * size we passed to the create_texture() vfunc, as any sub-class might
   * give use a bigger texture
   */
  priv->target_width = cogl_texture_get_width (texture);
  priv->target_height = cogl_texture_get_height (texture);

  if (priv->offscreen != COGL_INVALID_HANDLE)
    cogl_handle_unref (priv->offscreen);

  priv->offscreen = cogl_offscreen_new_to_texture (texture);
  if (priv->offscreen == COGL_INVALID_HANDLE)
    {
      g_warning ("%s: Unable to create an Offscreen buffer", G_STRLOC);

      cogl_handle_unref (priv->target);
      priv->target = COGL_INVALID_HANDLE;

      priv->target_width = 0;
      priv->target_height = 0;

      return FALSE;
    }

  return TRUE;
}

static gboolean
clutter_offscreen_effect_pre_paint (ClutterEffect *effect)
{
  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
  ClutterOffscreenEffectPrivate *priv = self->priv;
  ClutterActorBox box;
  CoglMatrix projection;
  CoglColor transparent;
  CoglMatrix modelview;
  gfloat fbo_width, fbo_height;
  gfloat width, height;
  gfloat xexpand, yexpand;

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

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

  /* The paint box is the bounding box of the actor's paint volume in
   * stage coordinates. This will give us the size for the framebuffer
   * we need to redirect its rendering offscreen and its position will
   * be used to setup an offset viewport */
  if (clutter_actor_get_paint_box (priv->actor, &box))
    clutter_actor_box_get_size (&box, &fbo_width, &fbo_height);
  else
    {
      /* If we can't get a valid paint box then we fallback to
       * creating a full stage size fbo. */
      ClutterActor *stage = _clutter_actor_get_stage_internal (priv->actor);
      clutter_actor_get_size (stage, &fbo_width, &fbo_height);
    }

  /* First assert that the framebuffer is the right size... */
  if (!update_fbo (effect, fbo_width, fbo_height))
    return FALSE;

  /* get the current modelview matrix so that we can copy it
   * to the framebuffer
   */
  cogl_get_modelview_matrix (&modelview);

  /* let's draw offscreen */
  cogl_push_framebuffer (priv->offscreen);

  /* Set up the viewport so that it has the same size as the stage,
   * but offset it so that the actor of interest lands on our
   * framebuffer. */
  clutter_actor_get_size (priv->stage, &width, &height);
  clutter_actor_box_get_origin (&box, &priv->x_offset, &priv->y_offset);

  /* Expand the viewport if the actor is partially off-stage,
   * otherwise the actor will end up clipped to the stage viewport
   */
  xexpand = 0.f;
  if (priv->x_offset < 0.f)
    xexpand = -priv->x_offset;
  if (priv->x_offset + fbo_width > width)
    xexpand = MAX (xexpand, (priv->x_offset + fbo_width) - width);

  yexpand = 0.f;
  if (priv->y_offset < 0.f)
    yexpand = -priv->y_offset;
  if (priv->y_offset + fbo_height > height)
    yexpand = MAX (yexpand, (priv->y_offset + fbo_height) - height);

  /* Set the viewport */
  cogl_set_viewport (-(priv->x_offset + xexpand), -(priv->y_offset + yexpand),
                     width + (2 * xexpand), height + (2 * yexpand));

  /* Copy the stage's projection matrix across to the framebuffer */
  _clutter_stage_get_projection_matrix (CLUTTER_STAGE (priv->stage),
                                        &projection);
  cogl_set_projection_matrix (&projection);

  /* If we've expanded the viewport, make sure to scale the modelview
   * matrix accordingly (as it's been initialised to work with the
   * original viewport and not our expanded one).
   */
  if (xexpand > 0.f || yexpand > 0.f)
    {
      CoglMatrix correction;
      gfloat new_width, new_height;

      new_width = width + (2 * xexpand);
      new_height = height + (2 * yexpand);

      cogl_matrix_init_identity (&correction);
      cogl_matrix_scale (&correction,
                         width / new_width,
                         height / new_height,
                         1);

      cogl_matrix_multiply (&correction, &correction, &modelview);
      modelview = correction;
    }

  /* Copy the modelview that would have been used if rendering onscreen */
  cogl_set_modelview_matrix (&modelview);

  cogl_color_init_from_4ub (&transparent, 0, 0, 0, 0);
  cogl_clear (&transparent,
              COGL_BUFFER_BIT_COLOR |
              COGL_BUFFER_BIT_DEPTH);

  cogl_push_matrix ();

  /* Override the actor's opacity to fully opaque - we paint the offscreen
   * texture with the actor's paint opacity, so we need to do this to avoid
   * multiplying the opacity twice.
   */
  _clutter_actor_set_opacity_override (priv->actor, 0xff);

  return TRUE;
}

static void
clutter_offscreen_effect_real_paint_target (ClutterOffscreenEffect *effect)
{
  ClutterOffscreenEffectPrivate *priv = effect->priv;
  guint8 paint_opacity;

  paint_opacity = clutter_actor_get_paint_opacity (priv->actor);

  cogl_material_set_color4ub (priv->target,
                              paint_opacity,
                              paint_opacity,
                              paint_opacity,
                              paint_opacity);
  cogl_set_source (priv->target);

  /* At this point we are in stage coordinates translated so if
   * we draw our texture using a textured quad the size of the paint
   * box then we will overlay where the actor would have drawn if it
   * hadn't been redirected offscreen.
   */
  cogl_rectangle_with_texture_coords (0, 0,
                                      priv->target_width,
                                      priv->target_height,
                                      0.0, 0.0,
                                      1.0, 1.0);
}

static void
clutter_offscreen_effect_post_paint (ClutterEffect *effect)
{
  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
  ClutterOffscreenEffectPrivate *priv = self->priv;
  CoglMatrix modelview;

  if (priv->offscreen == COGL_INVALID_HANDLE ||
      priv->target == COGL_INVALID_HANDLE ||
      priv->actor == NULL)
    return;

  cogl_pop_matrix ();
  cogl_pop_framebuffer ();

  cogl_push_matrix ();

  /* Now reset the modelview to put us in stage coordinates so
   * we can drawn the result of our offscreen render as a textured
   * quad... */

  cogl_matrix_init_identity (&modelview);
  _clutter_actor_apply_modelview_transform (priv->stage, &modelview);
  cogl_matrix_translate (&modelview, priv->x_offset, priv->y_offset, 0.0f);
  cogl_set_modelview_matrix (&modelview);

  /* Remove the opacity override */
  _clutter_actor_set_opacity_override (priv->actor, -1);

  /* paint the target material; this is virtualized for
   * sub-classes that require special hand-holding
   */
  clutter_offscreen_effect_paint_target (self);

  cogl_pop_matrix ();
}

static void
clutter_offscreen_effect_finalize (GObject *gobject)
{
  ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (gobject);
  ClutterOffscreenEffectPrivate *priv = self->priv;

  if (priv->offscreen)
    cogl_handle_unref (priv->offscreen);

  if (priv->target)
    cogl_handle_unref (priv->target);

  G_OBJECT_CLASS (clutter_offscreen_effect_parent_class)->finalize (gobject);
}

static void
clutter_offscreen_effect_class_init (ClutterOffscreenEffectClass *klass)
{
  ClutterActorMetaClass *meta_class = CLUTTER_ACTOR_META_CLASS (klass);
  ClutterEffectClass *effect_class = CLUTTER_EFFECT_CLASS (klass);
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

  g_type_class_add_private (klass, sizeof (ClutterOffscreenEffectPrivate));

  klass->create_texture = clutter_offscreen_effect_real_create_texture;
  klass->paint_target = clutter_offscreen_effect_real_paint_target;

  meta_class->set_actor = clutter_offscreen_effect_set_actor;

  effect_class->pre_paint = clutter_offscreen_effect_pre_paint;
  effect_class->post_paint = clutter_offscreen_effect_post_paint;

  gobject_class->finalize = clutter_offscreen_effect_finalize;
}

static void
clutter_offscreen_effect_init (ClutterOffscreenEffect *self)
{
  self->priv = G_TYPE_INSTANCE_GET_PRIVATE (self,
                                            CLUTTER_TYPE_OFFSCREEN_EFFECT,
                                            ClutterOffscreenEffectPrivate);
}

/**
 * clutter_offscreen_effect_get_target:
 * @effect: a #ClutterOffscreenEffect
 *
 * Retrieves the material used as a render target for the offscreen
 * buffer created by @effect
 *
 * You should only use the returned #CoglMaterial when painting. The
 * returned material might change between different frames.
 *
 * Return value: (transfer none): a #CoglMaterial or %NULL. The
 *   returned material is owned by Clutter and it should not be
 *   modified or freed
 *
 * Since: 1.4
 */
CoglMaterial *
clutter_offscreen_effect_get_target (ClutterOffscreenEffect *effect)
{
  g_return_val_if_fail (CLUTTER_IS_OFFSCREEN_EFFECT (effect),
                        COGL_INVALID_HANDLE);

  return effect->priv->target;
}

/**
 * clutter_offscreen_effect_paint_target:
 * @effect: a #ClutterOffscreenEffect
 *
 * Calls the paint_target() virtual function of the @effect
 *
 * Since: 1.4
 */
void
clutter_offscreen_effect_paint_target (ClutterOffscreenEffect *effect)
{
  g_return_if_fail (CLUTTER_IS_OFFSCREEN_EFFECT (effect));

  CLUTTER_OFFSCREEN_EFFECT_GET_CLASS (effect)->paint_target (effect);
}

/**
 * clutter_offscreen_effect_create_texture:
 * @effect: a #ClutterOffscreenEffect
 * @width: the minimum width of the target texture
 * @height: the minimum height of the target texture
 *
 * Calls the create_texture() virtual function of the @effect
 *
 * Return value: (transfer full): a handle to a Cogl texture, or
 *   %COGL_INVALID_HANDLE. The returned handle has its reference
 *   count increased.
 *
 * Since: 1.4
 */
CoglHandle
clutter_offscreen_effect_create_texture (ClutterOffscreenEffect *effect,
                                         gfloat                  width,
                                         gfloat                  height)
{
  g_return_val_if_fail (CLUTTER_IS_OFFSCREEN_EFFECT (effect),
                        COGL_INVALID_HANDLE);

  return CLUTTER_OFFSCREEN_EFFECT_GET_CLASS (effect)->create_texture (effect,
                                                                      width,
                                                                      height);
}