docs: Add effects chapter, with introduction and first recipe
Add an effects chapter which gives a broad overview of the abstract classes in the effects API, plus a short example of how to apply one of the stock Clutter effects (ClutterColorizeEffect). The recipe explains how to create a custom ClutterDeformEffect to produce a page fold (code based on ClutterPageTurnEffect). The example code includes the effect class plus a small application to apply it to a texture.
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Elliot Smith
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doc/cookbook/examples/cb-page-fold-effect.c
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250
doc/cookbook/examples/cb-page-fold-effect.c
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#include <math.h>
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#include "cb-page-fold-effect.h"
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G_DEFINE_TYPE (CbPageFoldEffect, cb_page_fold_effect, CLUTTER_TYPE_DEFORM_EFFECT);
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#define CB_PAGE_FOLD_EFFECT_GET_PRIVATE(obj) (G_TYPE_INSTANCE_GET_PRIVATE ((obj), \
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CB_TYPE_PAGE_FOLD_EFFECT, \
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CbPageFoldEffectPrivate))
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struct _CbPageFoldEffectPrivate
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{
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gdouble angle;
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gdouble period;
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};
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enum {
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PROP_0,
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PROP_PERIOD,
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PROP_ANGLE,
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PROP_LAST
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};
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static GParamSpec *obj_props[PROP_LAST];
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/* ClutterDeformEffect implementation */
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static void
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cb_page_fold_effect_deform_vertex (ClutterDeformEffect *effect,
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gfloat width,
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gfloat height,
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CoglTextureVertex *vertex)
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{
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CbPageFoldEffectPrivate *priv = CB_PAGE_FOLD_EFFECT (effect)->priv;
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gfloat radians = (priv->angle * priv->period) / (180.0f / G_PI);
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/* rotate from the center of the actor on the y axis */
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gfloat adjusted_x = vertex->x - (width / 2);
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/* only rotate vertices to the right of the middle of the actor */
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if (adjusted_x >= 0.0)
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{
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vertex->x = (vertex->z * sin (radians))
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+ (adjusted_x * cos (radians))
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+ width / 2;
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/* NB add 1 to z to prevent "z fighting"; otherwise, when fully-folded
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* the image has "stripes" where vertices from the folded part
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* of the actor interfere with vertices from the unfolded part
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*/
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vertex->z = (vertex->z * cos (radians))
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+ (adjusted_x * sin (radians))
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+ 1;
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}
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/* adjust depth of all vertices so they fit inside the actor while folding;
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* this has the effect of making the image smaller within the texture,
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* but does produce a cleaner fold animation
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*/
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vertex->z -= width / 2;
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}
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/* GObject implementation */
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static void
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cb_page_fold_effect_set_property (GObject *gobject,
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guint prop_id,
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const GValue *value,
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GParamSpec *pspec)
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{
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CbPageFoldEffect *effect = CB_PAGE_FOLD_EFFECT (gobject);
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switch (prop_id)
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{
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case PROP_PERIOD:
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cb_page_fold_effect_set_period (effect, g_value_get_double (value));
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break;
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case PROP_ANGLE:
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cb_page_fold_effect_set_angle (effect, g_value_get_double (value));
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break;
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default:
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G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
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break;
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}
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}
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static void
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cb_page_fold_effect_get_property (GObject *gobject,
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guint prop_id,
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GValue *value,
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GParamSpec *pspec)
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{
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CbPageFoldEffectPrivate *priv = CB_PAGE_FOLD_EFFECT (gobject)->priv;
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switch (prop_id)
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{
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case PROP_PERIOD:
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g_value_set_double (value, priv->period);
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break;
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case PROP_ANGLE:
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g_value_set_double (value, priv->angle);
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break;
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default:
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G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
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break;
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}
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}
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/* GObject class and instance init */
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static void
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cb_page_fold_effect_class_init (CbPageFoldEffectClass *klass)
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{
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GParamSpec *pspec;
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ClutterDeformEffectClass *effect_class = CLUTTER_DEFORM_EFFECT_CLASS (klass);
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GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
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effect_class->deform_vertex = cb_page_fold_effect_deform_vertex;
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gobject_class->set_property = cb_page_fold_effect_set_property;
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gobject_class->get_property = cb_page_fold_effect_get_property;
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g_type_class_add_private (klass, sizeof (CbPageFoldEffectPrivate));
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/**
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* CbPageFoldEffect:period:
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*
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* The period of the page fold, between 0.0 (no fold) and
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* 1.0 (fully folded)
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*/
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pspec = g_param_spec_double ("period",
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"Period",
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"The period of the page fold",
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0.0, 1.0,
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0.0,
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G_PARAM_READWRITE);
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obj_props[PROP_PERIOD] = pspec;
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g_object_class_install_property (gobject_class, PROP_PERIOD, pspec);
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/**
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* CbPageFoldEffect:angle:
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*
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* The angle of the page fold, in degrees, between 0.0 and 180.0
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*/
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pspec = g_param_spec_double ("angle",
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"Angle",
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"The angle of the page fold, in degrees",
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0.0, 180.0,
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0.0,
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G_PARAM_READWRITE);
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obj_props[PROP_ANGLE] = pspec;
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g_object_class_install_property (gobject_class, PROP_ANGLE, pspec);
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}
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static void
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cb_page_fold_effect_init (CbPageFoldEffect *self)
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{
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CbPageFoldEffectPrivate *priv;
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priv = self->priv = CB_PAGE_FOLD_EFFECT_GET_PRIVATE (self);
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priv->period = 0.0;
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priv->angle = 0.0;
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}
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/* public API */
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ClutterEffect *
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cb_page_fold_effect_new (gdouble angle,
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gdouble period)
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{
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return g_object_new (CB_TYPE_PAGE_FOLD_EFFECT,
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"angle", angle,
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"period", period,
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NULL);
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}
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/**
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* cb_page_fold_effect_set_period:
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* @effect: a #CbPageFoldEffect
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* @period: the period of the page fold, between 0.0 and 1.0
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*
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* Sets the period of the page fold, between 0.0 (no fold)
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* and 1.0 (fully folded)
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*/
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void
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cb_page_fold_effect_set_period (CbPageFoldEffect *effect,
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gdouble period)
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{
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g_return_if_fail (CB_IS_PAGE_FOLD_EFFECT (effect));
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g_return_if_fail (period >= 0.0 && period <= 1.0);
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effect->priv->period = period;
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clutter_deform_effect_invalidate (CLUTTER_DEFORM_EFFECT (effect));
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}
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/**
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* cb_page_fold_effect_get_period:
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* @effect: a #CbPageFoldEffect
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*
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* Retrieves the value set using cb_page_fold_effect_get_period()
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*
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* Return value: the period of the page fold
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*/
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gdouble
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cb_page_fold_effect_get_period (CbPageFoldEffect *effect)
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{
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g_return_val_if_fail (CB_IS_PAGE_FOLD_EFFECT (effect), 0.0);
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return effect->priv->period;
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}
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/**
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* cb_page_fold_effect_set_angle:
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* @effect: #CbPageFoldEffect
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* @angle: the angle of the page fold, in degrees
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*
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* Sets the angle of the page fold, in degrees; must be a value between
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* 0.0 and 180.0
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*/
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void
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cb_page_fold_effect_set_angle (CbPageFoldEffect *effect,
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gdouble angle)
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{
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g_return_if_fail (CB_IS_PAGE_FOLD_EFFECT (effect));
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g_return_if_fail (angle >= 0.0 && angle <= 180.0);
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effect->priv->angle = angle;
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clutter_deform_effect_invalidate (CLUTTER_DEFORM_EFFECT (effect));
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}
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/**
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* cb_page_fold_effect_get_angle:
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* @effect: a #CbPageFoldEffect:
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*
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* Retrieves the angle of the page fold, in degrees
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*
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* Return value: the angle of the page fold
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*/
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gdouble
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cb_page_fold_effect_get_angle (CbPageFoldEffect *effect)
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{
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g_return_val_if_fail (CB_IS_PAGE_FOLD_EFFECT (effect), 0.0);
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return effect->priv->angle;
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}
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