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The OffscreenEffect class is meant to be used to implement Effect
sub-classes that create an offscreen framebuffer and redirect the
actor's paint sequence there. The OffscreenEffect is useful for
effects using fragment shaders.
Any shader-based effect being applied to an actor through an offscreen
buffer should be used before painting the resulting target material and
not for every actor. This means that doing:
pre_paint: cogl_program_use(program)
set up offscreen buffer
paint: [ actors ] → offscreen buffer → target material
post_paint: paint target material
cogl_program_use(null)
Is not correct. Unfortunately, we cannot really do:
post_paint: cogl_program_use(program)
paint target material
cogl_program_use(null)
Because the OffscreenEffect::post_paint() implementation also pops the
offscreen buffer and re-instates the previous framebuffer:
post_paint: cogl_program_use(program)
change frame buffer ← ouch!
paint target material
cogl_program_use(null)
One way to fix it is to allow using the shader right before painting
the target material - which means adding a new virtual inside the
OffscreenEffect class vtable in additions to the ones defined by the
parent Effect class.
The newly-added paint_target() virtual allows the correct sequence of
actions by adding an entry point for sub-classes to wrap the "paint
target material" operation with custom code, in order to implement the
case above correctly as:
post_paint: change frame buffer
cogl_program_use(program)
paint target material
cogl_program_use(null)
The added upside is that sub-classes of OffscreenEffect involving
shaders really just need to override the prepare() and paint_target()
virtuals, since the pre_paint() and post_paint() do all that's needed.
97 lines
3.2 KiB
C
97 lines
3.2 KiB
C
/*
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* Clutter.
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*
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* An OpenGL based 'interactive canvas' library.
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*
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* Copyright (C) 2010 Intel Corporation.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library. If not, see <http://www.gnu.org/licenses/>.
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*
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* Author:
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* Emmanuele Bassi <ebassi@linux.intel.com>
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*/
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#if !defined(__CLUTTER_H_INSIDE__) && !defined(CLUTTER_COMPILATION)
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#error "Only <clutter/clutter.h> can be included directly."
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#endif
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#ifndef __CLUTTER_OFFSCREEN_EFFECT_H__
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#define __CLUTTER_OFFSCREEN_EFFECT_H__
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#include <clutter/clutter-effect.h>
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G_BEGIN_DECLS
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#define CLUTTER_TYPE_OFFSCREEN_EFFECT (clutter_offscreen_effect_get_type ())
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#define CLUTTER_OFFSCREEN_EFFECT(o) (G_TYPE_CHECK_INSTANCE_CAST ((o), CLUTTER_TYPE_OFFSCREEN_EFFECT, ClutterOffscreenEffect))
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#define CLUTTER_IS_OFFSCREEN_EFFECT(o) (G_TYPE_CHECK_INSTANCE_TYPE ((o), CLUTTER_TYPE_OFFSCREEN_EFFECT))
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#define CLUTTER_OFFSCREEN_EFFECT_CLASS(k) (G_TYPE_CHECK_CLASS_CAST ((k), CLUTTER_TYPE_OFFSCREEN_EFFECT, ClutterOffscreenEffectClass))
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#define CLUTTER_IS_OFFSCREEN_EFFECT_CLASS(k) (G_TYPE_CHECK_CLASS_TYPE ((k), CLUTTER_TYPE_OFFSCREEN_EFFECT))
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#define CLUTTER_OFFSCREEN_EFFECT_GET_CLASS(o) (G_TYPE_INSTANCE_GET_CLASS ((o), CLUTTER_TYPE_OFFSCREEN_EFFECT, ClutterOffscreenEffectClass))
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typedef struct _ClutterOffscreenEffect ClutterOffscreenEffect;
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typedef struct _ClutterOffscreenEffectPrivate ClutterOffscreenEffectPrivate;
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typedef struct _ClutterOffscreenEffectClass ClutterOffscreenEffectClass;
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/**
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* ClutterOffscreenEffect:
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*
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* The #ClutterOffscreenEffect structure contains only private data
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* and should be accessed using the provided API
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*
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* Since: 1.4
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*/
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struct _ClutterOffscreenEffect
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{
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/*< private >*/
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ClutterEffect parent_instance;
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ClutterOffscreenEffectPrivate *priv;
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};
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/**
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* ClutterOffscreenEffectClass:
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* @paint_target: virtual function
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*
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* The #ClutterOffscreenEffectClass structure contains only private data
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*
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* Since: 1.4
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*/
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struct _ClutterOffscreenEffectClass
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{
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/*< private >*/
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ClutterEffectClass parent_class;
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/*< public >*/
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void (* paint_target) (ClutterOffscreenEffect *effect);
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/*< private >*/
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void (* _clutter_offscreen1) (void);
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void (* _clutter_offscreen2) (void);
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void (* _clutter_offscreen3) (void);
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void (* _clutter_offscreen4) (void);
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void (* _clutter_offscreen5) (void);
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void (* _clutter_offscreen6) (void);
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void (* _clutter_offscreen7) (void);
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};
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GType clutter_offscreen_effect_get_type (void) G_GNUC_CONST;
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CoglHandle clutter_offscreen_effect_get_target (ClutterOffscreenEffect *effect);
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void clutter_offscreen_effect_paint_target (ClutterOffscreenEffect *effect);
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G_END_DECLS
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#endif /* __CLUTTER_OFFSCREEN_EFFECT_H__ */
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