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// -*- c++ -*-
/* $Id$ */
/* Copyright 2002 The gtkmm Development Team
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library 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
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free
* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <glibmm/property.h>
#include <glibmm/object.h>
#include <cstddef>
// Temporary hack till GLib gets fixed.
#undef G_STRLOC
#define G_STRLOC __FILE__ ":" G_STRINGIFY(__LINE__)
namespace
{
// OK guys, please don't kill me for that. Let me explain what happens here.
//
// The task:
// ---------
// a) Autogenerate a property ID number for each custom property. This is an
// unsigned integer, which doesn't have to be assigned continuously. I.e.,
// it can be everything but 0.
// b) If more than one object of the same class is instantiated, then of course
// the already installed properties must be used. That means, a property ID
// must not be associated with a single Glib::Property<> instance. Rather,
// the ID has to be associated with the class somehow.
// c) With only a GObject pointer and a property ID (and perhaps GParamSpec*
// if necessary), it must be possible to acquire a reference to the property
// wrapper instance.
//
// The current solution:
// ---------------------
// a) Assign an ID to a Glib::PropertyBase by calculating its offset in bytes
// relative to the beginning of the object's memory. dynamic_cast<void*>
// is used to retrieve a pointer to the very beginning of an instance.
// b) Recalculate a specific PropertyBase pointer by adding the property ID
// (i.e. the byte offset) to the object start pointer. The result is then
// just casted to PropertyBase*.
//
// Drawbacks:
// ----------
// a) It's a low-level hack. Should be portable, yes, but we can only do very
// limited error checking.
// b) All Glib::Property<> instances are absolutely required to be direct data
// members of the class that implements the property. That seems a natural
// thing to do, but it's questionable whether it should be a requirement.
//
// Advantages:
// -----------
// a) Although low-level, it's extremely easy to implement. The nasty code is
// concentrated in only two non-exposed utility functions, and it works
// just fine.
// b) It's efficient, and the memory footprint is very small too.
// c) I actually tried other ways, too, but ran into dead-ends everywhere.
// It's probably possible to implement this without calculating offsets,
// but it'll be very complicated, and involve a lot of qdata pointers to
// property tables andwhatnot.
//
// We can reimplement this later if necessary.
unsigned int property_to_id(Glib::ObjectBase& object, Glib::PropertyBase& property)
{
void *const base_ptr = dynamic_cast<void*>(&object);
void *const prop_ptr = &property;
const ptrdiff_t offset = static_cast<guint8*>(prop_ptr) - static_cast<guint8*>(base_ptr);
g_return_val_if_fail(offset > 0 && offset < G_MAXINT, 0);
return static_cast<unsigned int>(offset);
}
Glib::PropertyBase& property_from_id(Glib::ObjectBase& object, unsigned int property_id)
{
void *const base_ptr = dynamic_cast<void*>(&object);
void *const prop_ptr = static_cast<guint8*>(base_ptr) + property_id;
return *static_cast<Glib::PropertyBase*>(prop_ptr);
}
} // anonymous namespace
namespace Glib
{
void custom_get_property_callback(GObject* object, unsigned int property_id,
GValue* value, GParamSpec* param_spec)
{
if(Glib::ObjectBase *const wrapper = Glib::ObjectBase::_get_current_wrapper(object))
{
PropertyBase& property = property_from_id(*wrapper, property_id);
if((property.object_ == wrapper) && (property.param_spec_ == param_spec))
g_value_copy(property.value_.gobj(), value);
else
G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, param_spec);
}
}
void custom_set_property_callback(GObject* object, unsigned int property_id,
const GValue* value, GParamSpec* param_spec)
{
if(Glib::ObjectBase *const wrapper = Glib::ObjectBase::_get_current_wrapper(object))
{
PropertyBase& property = property_from_id(*wrapper, property_id);
if((property.object_ == wrapper) && (property.param_spec_ == param_spec))
{
g_value_copy(value, property.value_.gobj());
g_object_notify(object, g_param_spec_get_name(param_spec));
}
else
G_OBJECT_WARN_INVALID_PROPERTY_ID(object, property_id, param_spec);
}
}
/**** Glib::PropertyBase ***************************************************/
PropertyBase::PropertyBase(Glib::Object& object, GType value_type)
:
object_ (&object),
value_ (),
param_spec_ (0)
{
value_.init(value_type);
}
PropertyBase::~PropertyBase()
{
if(param_spec_)
g_param_spec_unref(param_spec_);
}
bool PropertyBase::lookup_property(const Glib::ustring& name)
{
g_assert(param_spec_ == 0);
param_spec_ = g_object_class_find_property(G_OBJECT_GET_CLASS(object_->gobj()), name.c_str());
if(param_spec_)
{
g_assert(G_PARAM_SPEC_VALUE_TYPE(param_spec_) == G_VALUE_TYPE(value_.gobj()));
g_param_spec_ref(param_spec_);
}
return (param_spec_ != 0);
}
void PropertyBase::install_property(GParamSpec* param_spec)
{
g_return_if_fail(param_spec != 0);
const unsigned int property_id = property_to_id(*object_, *this);
g_object_class_install_property(G_OBJECT_GET_CLASS(object_->gobj()), property_id, param_spec);
param_spec_ = param_spec;
g_param_spec_ref(param_spec_);
}
const char* PropertyBase::get_name_internal() const
{
const char *const name = g_param_spec_get_name(param_spec_);
g_return_val_if_fail(name != 0, "");
return name;
}
Glib::ustring PropertyBase::get_name() const
{
return Glib::ustring(get_name_internal());
}
void PropertyBase::notify()
{
g_object_notify(object_->gobj(), g_param_spec_get_name(param_spec_));
}
} // namespace Glib
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