inkscape/src/sp-object.cpp

	sp-object.cpp revision 258e7ba7fabc54ebb7fc844437eaf36231066ef5
#define __SP_OBJECT_C__
/** \file
 * SPObject implementation.
 *
 * Authors:
 *   Lauris Kaplinski <lauris@kaplinski.com>
 *   bulia byak <buliabyak@users.sf.net>
 *   Stephen Silver <sasilver@users.sourceforge.net>
 *
 * Copyright (C) 1999-2008 authors
 * Copyright (C) 2001-2002 Ximian, Inc.
 *
 * Released under GNU GPL, read the file 'COPYING' for more information
 */

/** \class SPObject
 *
 * SPObject is an abstract base class of all of the document nodes at the
 * SVG document level. Each SPObject subclass implements a certain SVG
 * element node type, or is an abstract base class for different node
 * types.  The SPObject layer is bound to the SPRepr layer, closely
 * following the SPRepr mutations via callbacks.  During creation,
 * SPObject parses and interprets all textual attributes and CSS style
 * strings of the SPRepr, and later updates the internal state whenever
 * it receives a signal about a change. The opposite is not true - there
 * are methods manipulating SPObjects directly and such changes do not
 * propagate to the SPRepr layer. This is important for implementation of
 * the undo stack, animations and other features.
 *
 * SPObjects are bound to the higher-level container SPDocument, which
 * provides document level functionality such as the undo stack,
 * dictionary and so on. Source: doc/architecture.txt
 */

#include <cstring>
#include <string>

#include "helper/sp-marshal.h"
#include "xml/node-event-vector.h"
#include "attributes.h"
#include "document.h"
#include "style.h"
#include "sp-object-repr.h"
#include "sp-root.h"
#include "sp-style-elem.h"
#include "sp-script.h"
#include "streq.h"
#include "strneq.h"
#include "xml/repr.h"
#include "xml/node-fns.h"
#include "debug/event-tracker.h"
#include "debug/simple-event.h"
#include "debug/demangle.h"
#include "util/share.h"
#include "util/format.h"
#include "util/longest-common-suffix.h"

using std::memcpy;
using std::strchr;
using std::strcmp;
using std::strlen;
using std::strstr;

#define noSP_OBJECT_DEBUG_CASCADE

#define noSP_OBJECT_DEBUG

#ifdef SP_OBJECT_DEBUG
# define debug(f, a...) { g_print("%s(%d) %s:", \
                                  __FILE__,__LINE__,__FUNCTION__); \
                          g_print(f, ## a); \
                          g_print("\n"); \
                        }
#else
# define debug(f, a...) /**/
#endif

static void sp_object_class_init(SPObjectClass *klass);
static void sp_object_init(SPObject *object);
static void sp_object_finalize(GObject *object);

static void sp_object_child_added(SPObject *object, Inkscape::XML::Node *child, Inkscape::XML::Node *ref);
static void sp_object_remove_child(SPObject *object, Inkscape::XML::Node *child);
static void sp_object_order_changed(SPObject *object, Inkscape::XML::Node *child, Inkscape::XML::Node *old_ref, Inkscape::XML::Node *new_ref);

static void sp_object_release(SPObject *object);
static void sp_object_build(SPObject *object, SPDocument *document, Inkscape::XML::Node *repr);

static void sp_object_private_set(SPObject *object, unsigned int key, gchar const *value);
static Inkscape::XML::Node *sp_object_private_write(SPObject *object, Inkscape::XML::Document *doc, Inkscape::XML::Node *repr, guint flags);

/* Real handlers of repr signals */

static void sp_object_repr_attr_changed(Inkscape::XML::Node *repr, gchar const *key, gchar const *oldval, gchar const *newval, bool is_interactive, gpointer data);

static void sp_object_repr_content_changed(Inkscape::XML::Node *repr, gchar const *oldcontent, gchar const *newcontent, gpointer data);

static void sp_object_repr_child_added(Inkscape::XML::Node *repr, Inkscape::XML::Node *child, Inkscape::XML::Node *ref, gpointer data);
static void sp_object_repr_child_removed(Inkscape::XML::Node *repr, Inkscape::XML::Node *child, Inkscape::XML::Node *ref, void *data);

static void sp_object_repr_order_changed(Inkscape::XML::Node *repr, Inkscape::XML::Node *child, Inkscape::XML::Node *old, Inkscape::XML::Node *newer, gpointer data);

static gchar *sp_object_get_unique_id(SPObject *object, gchar const *defid);

guint update_in_progress = 0; // guard against update-during-update

Inkscape::XML::NodeEventVector object_event_vector = {
    sp_object_repr_child_added,
    sp_object_repr_child_removed,
    sp_object_repr_attr_changed,
    sp_object_repr_content_changed,
    sp_object_repr_order_changed
};

// A friend class used to set internal members on SPObject so as to not expose settors in SPObject's public API
class SPObjectImpl
{
public:

/**
 * Null's the id member of an SPObject without attempting to free prior contents.
 */
    static void setIdNull( SPObject* obj ) {
        if (obj) {
            obj->id = 0;
        }
    }

/**
 * Sets the id member of an object, freeing any prior content.
 */
    static void setId( SPObject* obj, gchar const* id ) {
        if (obj && (id != obj->id) ) {
            if (obj->id) {
                g_free(obj->id);
                obj->id = 0;
            }
            if (id) {
                obj->id = g_strdup(id);
            }
        }
    }
};


static GObjectClass *parent_class;

/**
 * Registers the SPObject class with Gdk and returns its type number.
 */
GType
sp_object_get_type(void)
{
    static GType type = 0;
    if (!type) {
        GTypeInfo info = {
            sizeof(SPObjectClass),
            NULL, NULL,
            (GClassInitFunc) sp_object_class_init,
            NULL, NULL,
            sizeof(SPObject),
            16,
            (GInstanceInitFunc) sp_object_init,
            NULL
        };
        type = g_type_register_static(G_TYPE_OBJECT, "SPObject", &info, (GTypeFlags)0);
    }
    return type;
}

/**
 * Initializes the SPObject vtable.
 */
static void
sp_object_class_init(SPObjectClass *klass)
{
    GObjectClass *object_class;

    object_class = (GObjectClass *) klass;

    parent_class = (GObjectClass *) g_type_class_ref(G_TYPE_OBJECT);

    object_class->finalize = sp_object_finalize;

    klass->child_added = sp_object_child_added;
    klass->remove_child = sp_object_remove_child;
    klass->order_changed = sp_object_order_changed;

    klass->release = sp_object_release;

    klass->build = sp_object_build;

    klass->set = sp_object_private_set;
    klass->write = sp_object_private_write;
}

/**
 * Callback to initialize the SPObject object.
 */
static void
sp_object_init(SPObject *object)
{
    debug("id=%x, typename=%s",object, g_type_name_from_instance((GTypeInstance*)object));

    object->hrefcount = 0;
    object->_total_hrefcount = 0;
    object->document = NULL;
    object->children = object->_last_child = NULL;
    object->parent = object->next = NULL;
    object->repr = NULL;
    SPObjectImpl::setIdNull(object);

    object->_collection_policy = SPObject::COLLECT_WITH_PARENT;

    new (&object->_release_signal) sigc::signal<void, SPObject *>();
    new (&object->_modified_signal) sigc::signal<void, SPObject *, unsigned int>();
    new (&object->_delete_signal) sigc::signal<void, SPObject *>();
    new (&object->_position_changed_signal) sigc::signal<void, SPObject *>();
    object->_successor = NULL;

    // FIXME: now we create style for all objects, but per SVG, only the following can have style attribute:
    // vg, g, defs, desc, title, symbol, use, image, switch, path, rect, circle, ellipse, line, polyline,
    // polygon, text, tspan, tref, textPath, altGlyph, glyphRef, marker, linearGradient, radialGradient,
    // stop, pattern, clipPath, mask, filter, feImage, a, font, glyph, missing-glyph, foreignObject
    object->style = sp_style_new_from_object(object);

    object->_label = NULL;
    object->_default_label = NULL;
}

/**
 * Callback to destroy all members and connections of object and itself.
 */
static void
sp_object_finalize(GObject *object)
{
    SPObject *spobject = (SPObject *)object;

    g_free(spobject->_label);
    g_free(spobject->_default_label);
    spobject->_label = NULL;
    spobject->_default_label = NULL;

    if (spobject->_successor) {
        sp_object_unref(spobject->_successor, NULL);
        spobject->_successor = NULL;
    }

    if (((GObjectClass *) (parent_class))->finalize) {
        (* ((GObjectClass *) (parent_class))->finalize)(object);
    }

    spobject->_release_signal.~signal();
    spobject->_modified_signal.~signal();
    spobject->_delete_signal.~signal();
    spobject->_position_changed_signal.~signal();
}

namespace {

namespace Debug = Inkscape::Debug;
namespace Util = Inkscape::Util;

typedef Debug::SimpleEvent<Debug::Event::REFCOUNT> BaseRefCountEvent;

class RefCountEvent : public BaseRefCountEvent {
public:
    RefCountEvent(SPObject *object, int bias, Util::ptr_shared<char> name)
    : BaseRefCountEvent(name)
    {
        _addProperty("object", Util::format("%p", object));
        _addProperty("class", Debug::demangle(g_type_name(G_TYPE_FROM_INSTANCE(object))));
        _addProperty("new-refcount", Util::format("%d", G_OBJECT(object)->ref_count + bias));
    }
};

class RefEvent : public RefCountEvent {
public:
    RefEvent(SPObject *object)
    : RefCountEvent(object, 1, Util::share_static_string("sp-object-ref"))
    {}
};

class UnrefEvent : public RefCountEvent {
public:
    UnrefEvent(SPObject *object)
    : RefCountEvent(object, -1, Util::share_static_string("sp-object-unref"))
    {}
};

}

gchar const* SPObject::getId() const {
    return id;
}

/**
 * Increase reference count of object, with possible debugging.
 *
 * \param owner If non-NULL, make debug log entry.
 * \return object, NULL is error.
 * \pre object points to real object
 */
SPObject *
sp_object_ref(SPObject *object, SPObject *owner)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);
    g_return_val_if_fail(!owner || SP_IS_OBJECT(owner), NULL);

    Inkscape::Debug::EventTracker<RefEvent> tracker(object);
    g_object_ref(G_OBJECT(object));
    return object;
}

/**
 * Decrease reference count of object, with possible debugging and
 * finalization.
 *
 * \param owner If non-NULL, make debug log entry.
 * \return always NULL
 * \pre object points to real object
 */
SPObject *
sp_object_unref(SPObject *object, SPObject *owner)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);
    g_return_val_if_fail(!owner || SP_IS_OBJECT(owner), NULL);

    Inkscape::Debug::EventTracker<UnrefEvent> tracker(object);
    g_object_unref(G_OBJECT(object));
    return NULL;
}

/**
 * Increase weak refcount.
 *
 * Hrefcount is used for weak references, for example, to
 * determine whether any graphical element references a certain gradient
 * node.
 * \param owner Ignored.
 * \return object, NULL is error
 * \pre object points to real object
 */
SPObject *
sp_object_href(SPObject *object, gpointer /*owner*/)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);

    object->hrefcount++;
    object->_updateTotalHRefCount(1);

    return object;
}

/**
 * Decrease weak refcount.
 *
 * Hrefcount is used for weak references, for example, to determine whether
 * any graphical element references a certain gradient node.
 * \param owner Ignored.
 * \return always NULL
 * \pre object points to real object and hrefcount>0
 */
SPObject *
sp_object_hunref(SPObject *object, gpointer /*owner*/)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);
    g_return_val_if_fail(object->hrefcount > 0, NULL);

    object->hrefcount--;
    object->_updateTotalHRefCount(-1);

    return NULL;
}

/**
 * Adds increment to _total_hrefcount of object and its parents.
 */
void
SPObject::_updateTotalHRefCount(int increment) {
    SPObject *topmost_collectable = NULL;
    for ( SPObject *iter = this ; iter ; iter = SP_OBJECT_PARENT(iter) ) {
        iter->_total_hrefcount += increment;
        if ( iter->_total_hrefcount < iter->hrefcount ) {
            g_critical("HRefs overcounted");
        }
        if ( iter->_total_hrefcount == 0 &&
             iter->_collection_policy != COLLECT_WITH_PARENT )
        {
            topmost_collectable = iter;
        }
    }
    if (topmost_collectable) {
        topmost_collectable->requestOrphanCollection();
    }
}

/**
 * True if object is non-NULL and this is some in/direct parent of object.
 */
bool
SPObject::isAncestorOf(SPObject const *object) const {
    g_return_val_if_fail(object != NULL, false);
    object = SP_OBJECT_PARENT(object);
    while (object) {
        if ( object == this ) {
            return true;
        }
        object = SP_OBJECT_PARENT(object);
    }
    return false;
}

namespace {

bool same_objects(SPObject const &a, SPObject const &b) {
    return &a == &b;
}

}

/**
 * Returns youngest object being parent to this and object.
 */
SPObject const *
SPObject::nearestCommonAncestor(SPObject const *object) const {
    g_return_val_if_fail(object != NULL, NULL);

    using Inkscape::Algorithms::longest_common_suffix;
    return longest_common_suffix<SPObject::ConstParentIterator>(this, object, NULL, &same_objects);
}

SPObject const *AncestorSon(SPObject const *obj, SPObject const *ancestor) {
    if (obj == NULL || ancestor == NULL)
        return NULL;
    if (SP_OBJECT_PARENT(obj) == ancestor)
        return obj;
    return AncestorSon(SP_OBJECT_PARENT(obj), ancestor);
}

/**
 * Compares height of objects in tree.
 *
 * Works for different-parent objects, so long as they have a common ancestor.
 * \return \verbatim
 *    0    positions are equivalent
 *    1    first object's position is greater than the second
 *   -1    first object's position is less than the second   \endverbatim
 */
int
sp_object_compare_position(SPObject const *first, SPObject const *second)
{
    if (first == second) return 0;

    SPObject const *ancestor = first->nearestCommonAncestor(second);
    if (ancestor == NULL) return 0; // cannot compare, no common ancestor!

    // we have an object and its ancestor (should not happen when sorting selection)
    if (ancestor == first)
        return 1;
    if (ancestor == second)
        return -1;

    SPObject const *to_first = AncestorSon(first, ancestor);
    SPObject const *to_second = AncestorSon(second, ancestor);

    g_assert(SP_OBJECT_PARENT(to_second) == SP_OBJECT_PARENT(to_first));

    return sp_repr_compare_position(SP_OBJECT_REPR(to_first), SP_OBJECT_REPR(to_second));
}


/**
 * Append repr as child of this object.
 * \pre this is not a cloned object
 */
SPObject *
SPObject::appendChildRepr(Inkscape::XML::Node *repr) {
    if (!SP_OBJECT_IS_CLONED(this)) {
        SP_OBJECT_REPR(this)->appendChild(repr);
        return SP_OBJECT_DOCUMENT(this)->getObjectByRepr(repr);
    } else {
        g_critical("Attempt to append repr as child of cloned object");
        return NULL;
    }
}

/**
 * Retrieves the children as a GSList object, optionally ref'ing the children
 * in the process, if add_ref is specified.
 */
GSList *SPObject::childList(bool add_ref, Action) {
    GSList *l = NULL;
    for (SPObject *child = sp_object_first_child(this) ; child != NULL; child = SP_OBJECT_NEXT(child) ) {
        if (add_ref)
            g_object_ref (G_OBJECT (child));

        l = g_slist_prepend (l, child);
    }
    return l;

}

/** Gets the label property for the object or a default if no label
 *  is defined.
 */
gchar const *
SPObject::label() const {
    return _label;
}

/** Returns a default label property for the object. */
gchar const *
SPObject::defaultLabel() const {
    if (_label) {
        return _label;
    } else {
        if (!_default_label) {
            gchar const *id=SP_OBJECT_ID(this);
            if (id) {
                _default_label = g_strdup_printf("#%s", id);
            } else {
                _default_label = g_strdup_printf("<%s>", SP_OBJECT_REPR(this)->name());
            }
        }
        return _default_label;
    }
}

/** Sets the label property for the object */
void
SPObject::setLabel(gchar const *label) {
    SP_OBJECT_REPR(this)->setAttribute("inkscape:label", label, false);
}


/** Queues the object for orphan collection */
void SPObject::requestOrphanCollection() {
    g_return_if_fail(document != NULL);

    // do not remove style or script elements (Bug #276244)
    if (SP_IS_STYLE_ELEM(this)) {
        // leave it
    } else if (SP_IS_SCRIPT(this)) {
        // leave it
    } else if (SP_IS_PAINT_SERVER(this) && static_cast<SPPaintServer*>(this)->isSwatch() ) {
        // leave it
    } else {
        document->queueForOrphanCollection(this);

        /** \todo
         * This is a temporary hack added to make fill&stroke rebuild its
         * gradient list when the defs are vacuumed.  gradient-vector.cpp
         * listens to the modified signal on defs, and now we give it that
         * signal.  Mental says that this should be made automatic by
         * merging SPObjectGroup with SPObject; SPObjectGroup would issue
         * this signal automatically. Or maybe just derive SPDefs from
         * SPObjectGroup?
         */

        this->requestModified(SP_OBJECT_CHILD_MODIFIED_FLAG);
    }
}

/** Sends the delete signal to all children of this object recursively */
void
SPObject::_sendDeleteSignalRecursive() {
    for (SPObject *child = sp_object_first_child(this); child; child = SP_OBJECT_NEXT(child)) {
        child->_delete_signal.emit(child);
        child->_sendDeleteSignalRecursive();
    }
}

/**
 * Deletes the object reference, unparenting it from its parent.
 *
 * If the \a propagate parameter is set to true, it emits a delete
 * signal.  If the \a propagate_descendants parameter is true, it
 * recursively sends the delete signal to children.
 */
void
SPObject::deleteObject(bool propagate, bool propagate_descendants)
{
    sp_object_ref(this, NULL);
    if (propagate) {
        _delete_signal.emit(this);
    }
    if (propagate_descendants) {
        this->_sendDeleteSignalRecursive();
    }

    Inkscape::XML::Node *repr=SP_OBJECT_REPR(this);
    if (repr && sp_repr_parent(repr)) {
        sp_repr_unparent(repr);
    }

    if (_successor) {
        _successor->deleteObject(propagate, propagate_descendants);
    }
    sp_object_unref(this, NULL);
}

/**
 * Put object into object tree, under parent, and behind prev;
 * also update object's XML space.
 */
void
sp_object_attach(SPObject *parent, SPObject *object, SPObject *prev)
{
    g_return_if_fail(parent != NULL);
    g_return_if_fail(SP_IS_OBJECT(parent));
    g_return_if_fail(object != NULL);
    g_return_if_fail(SP_IS_OBJECT(object));
    g_return_if_fail(!prev || SP_IS_OBJECT(prev));
    g_return_if_fail(!prev || prev->parent == parent);
    g_return_if_fail(!object->parent);

    sp_object_ref(object, parent);
    object->parent = parent;
    parent->_updateTotalHRefCount(object->_total_hrefcount);

    SPObject *next;
    if (prev) {
        next = prev->next;
        prev->next = object;
    } else {
        next = parent->children;
        parent->children = object;
    }
    object->next = next;
    if (!next) {
        parent->_last_child = object;
    }
    if (!object->xml_space.set)
        object->xml_space.value = parent->xml_space.value;
}

/**
 * In list of object's siblings, move object behind prev.
 */
void
sp_object_reorder(SPObject *object, SPObject *prev) {
    g_return_if_fail(object != NULL);
    g_return_if_fail(SP_IS_OBJECT(object));
    g_return_if_fail(object->parent != NULL);
    g_return_if_fail(object != prev);
    g_return_if_fail(!prev || SP_IS_OBJECT(prev));
    g_return_if_fail(!prev || prev->parent == object->parent);

    SPObject *const parent=object->parent;

    SPObject *old_prev=NULL;
    for ( SPObject *child = parent->children ; child && child != object ;
          child = child->next )
    {
        old_prev = child;
    }

    SPObject *next=object->next;
    if (old_prev) {
        old_prev->next = next;
    } else {
        parent->children = next;
    }
    if (!next) {
        parent->_last_child = old_prev;
    }
    if (prev) {
        next = prev->next;
        prev->next = object;
    } else {
        next = parent->children;
        parent->children = object;
    }
    object->next = next;
    if (!next) {
        parent->_last_child = object;
    }
}

/**
 * Remove object from parent's children, release and unref it.
 */
void
sp_object_detach(SPObject *parent, SPObject *object) {
    g_return_if_fail(parent != NULL);
    g_return_if_fail(SP_IS_OBJECT(parent));
    g_return_if_fail(object != NULL);
    g_return_if_fail(SP_IS_OBJECT(object));
    g_return_if_fail(object->parent == parent);

    object->releaseReferences();

    SPObject *prev=NULL;
    for ( SPObject *child = parent->children ; child && child != object ;
          child = child->next )
    {
        prev = child;
    }

    SPObject *next=object->next;
    if (prev) {
        prev->next = next;
    } else {
        parent->children = next;
    }
    if (!next) {
        parent->_last_child = prev;
    }

    object->next = NULL;
    object->parent = NULL;

    parent->_updateTotalHRefCount(-object->_total_hrefcount);
    sp_object_unref(object, parent);
}

/**
 * Return object's child whose node pointer equals repr.
 */
SPObject *
sp_object_get_child_by_repr(SPObject *object, Inkscape::XML::Node *repr)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);
    g_return_val_if_fail(repr != NULL, NULL);

    if (object->_last_child && SP_OBJECT_REPR(object->_last_child) == repr)
        return object->_last_child;   // optimization for common scenario
    for ( SPObject *child = object->children ; child ; child = child->next ) {
        if ( SP_OBJECT_REPR(child) == repr ) {
            return child;
        }
    }

    return NULL;
}

/**
 * Callback for child_added event.
 * Invoked whenever the given mutation event happens in the XML tree.
 */
static void
sp_object_child_added(SPObject *object, Inkscape::XML::Node *child, Inkscape::XML::Node *ref)
{
    GType type = sp_repr_type_lookup(child);
    if (!type) {
        return;
    }
    SPObject *ochild = SP_OBJECT(g_object_new(type, 0));
    SPObject *prev = ref ? sp_object_get_child_by_repr(object, ref) : NULL;
    sp_object_attach(object, ochild, prev);
    sp_object_unref(ochild, NULL);

    sp_object_invoke_build(ochild, object->document, child, SP_OBJECT_IS_CLONED(object));
}

/**
 * Removes, releases and unrefs all children of object.
 *
 * This is the opposite of build. It has to be invoked as soon as the
 * object is removed from the tree, even if it is still alive according
 * to reference count. The frontend unregisters the object from the
 * document and releases the SPRepr bindings; implementations should free
 * state data and release all child objects.  Invoking release on
 * SPRoot destroys the whole document tree.
 * \see sp_object_build()
 */
static void sp_object_release(SPObject *object)
{
    debug("id=%x, typename=%s", object, g_type_name_from_instance((GTypeInstance*)object));
    while (object->children) {
        sp_object_detach(object, object->children);
    }
}

/**
 * Remove object's child whose node equals repr, release and
 * unref it.
 *
 * Invoked whenever the given mutation event happens in the XML
 * tree, BEFORE removal from the XML tree happens, so grouping
 * objects can safely release the child data.
 */
static void
sp_object_remove_child(SPObject *object, Inkscape::XML::Node *child)
{
    debug("id=%x, typename=%s", object, g_type_name_from_instance((GTypeInstance*)object));
    SPObject *ochild = sp_object_get_child_by_repr(object, child);
    g_return_if_fail (ochild != NULL || !strcmp("comment", child->name())); // comments have no objects
    if (ochild)
        sp_object_detach(object, ochild);
}

/**
 * Move object corresponding to child after sibling object corresponding
 * to new_ref.
 * Invoked whenever the given mutation event happens in the XML tree.
 * \param old_ref Ignored
 */
static void sp_object_order_changed(SPObject *object, Inkscape::XML::Node *child, Inkscape::XML::Node */*old_ref*/,
                                    Inkscape::XML::Node *new_ref)
{
    SPObject *ochild = sp_object_get_child_by_repr(object, child);
    g_return_if_fail(ochild != NULL);
    SPObject *prev = new_ref ? sp_object_get_child_by_repr(object, new_ref) : NULL;
    sp_object_reorder(ochild, prev);
    ochild->_position_changed_signal.emit(ochild);
}

/**
 * Virtual build callback.
 *
 * This has to be invoked immediately after creation of an SPObject. The
 * frontend method ensures that the new object is properly attached to
 * the document and repr; implementation then will parse all of the attributes,
 * generate the children objects and so on.  Invoking build on the SPRoot
 * object results in creation of the whole document tree (this is, what
 * SPDocument does after the creation of the XML tree).
 * \see sp_object_release()
 */
static void
sp_object_build(SPObject *object, SPDocument *document, Inkscape::XML::Node *repr)
{
    /* Nothing specific here */
    debug("id=%x, typename=%s", object, g_type_name_from_instance((GTypeInstance*)object));

    sp_object_read_attr(object, "xml:space");
    sp_object_read_attr(object, "inkscape:label");
    sp_object_read_attr(object, "inkscape:collect");

    for (Inkscape::XML::Node *rchild = repr->firstChild() ; rchild != NULL; rchild = rchild->next()) {
        GType type = sp_repr_type_lookup(rchild);
        if (!type) {
            continue;
        }
        SPObject *child = SP_OBJECT(g_object_new(type, 0));
        sp_object_attach(object, child, object->lastChild());
        sp_object_unref(child, NULL);
        sp_object_invoke_build(child, document, rchild, SP_OBJECT_IS_CLONED(object));
    }
}

void sp_object_invoke_build(SPObject *object, SPDocument *document, Inkscape::XML::Node *repr, unsigned int cloned)
{
    debug("id=%x, typename=%s", object, g_type_name_from_instance((GTypeInstance*)object));

    g_assert(object != NULL);
    g_assert(SP_IS_OBJECT(object));
    g_assert(document != NULL);
    g_assert(repr != NULL);

    g_assert(object->document == NULL);
    g_assert(object->repr == NULL);
    g_assert(object->getId() == NULL);

    /* Bookkeeping */

    object->document = document;
    object->repr = repr;
    if (!cloned)
        Inkscape::GC::anchor(repr);
    object->cloned = cloned;

    if (!SP_OBJECT_IS_CLONED(object)) {
        object->document->bindObjectToRepr(object->repr, object);

        if (Inkscape::XML::id_permitted(object->repr)) {
            /* If we are not cloned, and not seeking, force unique id */
            gchar const *id = object->repr->attribute("id");
            if (!document->isSeeking()) {
                {
                    gchar *realid = sp_object_get_unique_id(object, id);
                    g_assert(realid != NULL);

                    object->document->bindObjectToId(realid, object);
                    SPObjectImpl::setId(object, realid);
                    g_free(realid);
                }

                /* Redefine ID, if required */
                if ((id == NULL) || (strcmp(id, object->getId()) != 0)) {
                    object->repr->setAttribute("id", object->getId());
                }
            } else if (id) {
                // bind if id, but no conflict -- otherwise, we can expect
                // a subsequent setting of the id attribute
                if (!object->document->getObjectById(id)) {
                    object->document->bindObjectToId(id, object);
                    SPObjectImpl::setId(object, id);
                }
            }
        }
    } else {
        g_assert(object->getId() == NULL);
    }

    /* Invoke derived methods, if any */
    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->build) {
        (*((SPObjectClass *) G_OBJECT_GET_CLASS(object))->build)(object, document, repr);
    }

    /* Signalling (should be connected AFTER processing derived methods */
    sp_repr_add_listener(repr, &object_event_vector, object);
}

void SPObject::releaseReferences() {
    g_assert(this->document);
    g_assert(this->repr);

    sp_repr_remove_listener_by_data(this->repr, this);

    this->_release_signal.emit(this);
    SPObjectClass *klass=(SPObjectClass *)G_OBJECT_GET_CLASS(this);
    if (klass->release) {
        klass->release(this);
    }

    /* all hrefs should be released by the "release" handlers */
    g_assert(this->hrefcount == 0);

    if (!SP_OBJECT_IS_CLONED(this)) {
        if (this->id) {
            this->document->bindObjectToId(this->id, NULL);
        }
        g_free(this->id);
        this->id = NULL;

        g_free(this->_default_label);
        this->_default_label = NULL;

        this->document->bindObjectToRepr(this->repr, NULL);

        Inkscape::GC::release(this->repr);
    } else {
        g_assert(!this->id);
    }

    if (this->style) {
        this->style = sp_style_unref(this->style);
    }

    this->document = NULL;
    this->repr = NULL;
}


SPObject *SPObject::getNext()
{
    return next;
}

SPObject *SPObject::getPrev()
{
    return sp_object_prev(this);
}

/**
 * Callback for child_added node event.
 */
static void
sp_object_repr_child_added(Inkscape::XML::Node */*repr*/, Inkscape::XML::Node *child, Inkscape::XML::Node *ref, gpointer data)
{
    SPObject *object = SP_OBJECT(data);

    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->child_added)
        (*((SPObjectClass *)G_OBJECT_GET_CLASS(object))->child_added)(object, child, ref);
}

/**
 * Callback for remove_child node event.
 */
static void
sp_object_repr_child_removed(Inkscape::XML::Node */*repr*/, Inkscape::XML::Node *child, Inkscape::XML::Node */*ref*/, gpointer data)
{
    SPObject *object = SP_OBJECT(data);

    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->remove_child) {
        (* ((SPObjectClass *)G_OBJECT_GET_CLASS(object))->remove_child)(object, child);
    }
}

/**
 * Callback for order_changed node event.
 *
 * \todo fixme:
 */
static void
sp_object_repr_order_changed(Inkscape::XML::Node */*repr*/, Inkscape::XML::Node *child, Inkscape::XML::Node *old, Inkscape::XML::Node *newer, gpointer data)
{
    SPObject *object = SP_OBJECT(data);

    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->order_changed) {
        (* ((SPObjectClass *)G_OBJECT_GET_CLASS(object))->order_changed)(object, child, old, newer);
    }
}

/**
 * Callback for set event.
 */
static void
sp_object_private_set(SPObject *object, unsigned int key, gchar const *value)
{
    g_assert(key != SP_ATTR_INVALID);

    switch (key) {
        case SP_ATTR_ID:
            if ( !SP_OBJECT_IS_CLONED(object) && object->repr->type() == Inkscape::XML::ELEMENT_NODE ) {
                SPDocument *document=object->document;
                SPObject *conflict=NULL;

                gchar const *new_id = value;

                if (new_id) {
                    conflict = document->getObjectById((char const *)new_id);
                }

                if ( conflict && conflict != object ) {
                    if (!document->isSeeking()) {
                        sp_object_ref(conflict, NULL);
                        // give the conflicting object a new ID
                        gchar *new_conflict_id = sp_object_get_unique_id(conflict, NULL);
                        SP_OBJECT_REPR(conflict)->setAttribute("id", new_conflict_id);
                        g_free(new_conflict_id);
                        sp_object_unref(conflict, NULL);
                    } else {
                        new_id = NULL;
                    }
                }

                if (object->getId()) {
                    document->bindObjectToId(object->getId(), NULL);
                    SPObjectImpl::setId(object, 0);
                }

                if (new_id) {
                    SPObjectImpl::setId(object, new_id);
                    document->bindObjectToId(object->getId(), object);
                }

                g_free(object->_default_label);
                object->_default_label = NULL;
            }
            break;
        case SP_ATTR_INKSCAPE_LABEL:
            g_free(object->_label);
            if (value) {
                object->_label = g_strdup(value);
            } else {
                object->_label = NULL;
            }
            g_free(object->_default_label);
            object->_default_label = NULL;
            break;
        case SP_ATTR_INKSCAPE_COLLECT:
            if ( value && !strcmp(value, "always") ) {
                object->setCollectionPolicy(SPObject::ALWAYS_COLLECT);
            } else {
                object->setCollectionPolicy(SPObject::COLLECT_WITH_PARENT);
            }
            break;
        case SP_ATTR_XML_SPACE:
            if (value && !strcmp(value, "preserve")) {
                object->xml_space.value = SP_XML_SPACE_PRESERVE;
                object->xml_space.set = TRUE;
            } else if (value && !strcmp(value, "default")) {
                object->xml_space.value = SP_XML_SPACE_DEFAULT;
                object->xml_space.set = TRUE;
            } else if (object->parent) {
                SPObject *parent;
                parent = object->parent;
                object->xml_space.value = parent->xml_space.value;
            }
            object->requestDisplayUpdate(SP_OBJECT_MODIFIED_FLAG | SP_OBJECT_STYLE_MODIFIED_FLAG);
            break;
        case SP_ATTR_STYLE:
            sp_style_read_from_object(object->style, object);
            object->requestDisplayUpdate(SP_OBJECT_MODIFIED_FLAG | SP_OBJECT_STYLE_MODIFIED_FLAG);
            break;
        default:
            break;
    }
}

/**
 * Call virtual set() function of object.
 */
void
sp_object_set(SPObject *object, unsigned int key, gchar const *value)
{
    g_assert(object != NULL);
    g_assert(SP_IS_OBJECT(object));

    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->set) {
        ((SPObjectClass *) G_OBJECT_GET_CLASS(object))->set(object, key, value);
    }
}

/**
 * Read value of key attribute from XML node into object.
 */
void
sp_object_read_attr(SPObject *object, gchar const *key)
{
    g_assert(object != NULL);
    g_assert(SP_IS_OBJECT(object));
    g_assert(key != NULL);

    g_assert(object->repr != NULL);

    unsigned int keyid = sp_attribute_lookup(key);
    if (keyid != SP_ATTR_INVALID) {
        /* Retrieve the 'key' attribute from the object's XML representation */
        gchar const *value = object->repr->attribute(key);

        sp_object_set(object, keyid, value);
    }
}

/**
 * Callback for attr_changed node event.
 */
static void
sp_object_repr_attr_changed(Inkscape::XML::Node */*repr*/, gchar const *key, gchar const */*oldval*/, gchar const */*newval*/, bool is_interactive, gpointer data)
{
    SPObject *object = SP_OBJECT(data);

    sp_object_read_attr(object, key);

    // manual changes to extension attributes require the normal
    // attributes, which depend on them, to be updated immediately
    if (is_interactive) {
        object->updateRepr(0);
    }
}

/**
 * Callback for content_changed node event.
 */
static void
sp_object_repr_content_changed(Inkscape::XML::Node */*repr*/, gchar const */*oldcontent*/, gchar const */*newcontent*/, gpointer data)
{
    SPObject *object = SP_OBJECT(data);

    if (((SPObjectClass *) G_OBJECT_GET_CLASS(object))->read_content)
        (*((SPObjectClass *) G_OBJECT_GET_CLASS(object))->read_content)(object);
}

/**
 * Return string representation of space value.
 */
static gchar const*
sp_xml_get_space_string(unsigned int space)
{
    switch (space) {
        case SP_XML_SPACE_DEFAULT:
            return "default";
        case SP_XML_SPACE_PRESERVE:
            return "preserve";
        default:
            return NULL;
    }
}

/**
 * Callback for write event.
 */
static Inkscape::XML::Node *
sp_object_private_write(SPObject *object, Inkscape::XML::Document *doc, Inkscape::XML::Node *repr, guint flags)
{
    if (!repr && (flags & SP_OBJECT_WRITE_BUILD)) {
        repr = SP_OBJECT_REPR(object)->duplicate(doc);
        if (!( flags & SP_OBJECT_WRITE_EXT )) {
            repr->setAttribute("inkscape:collect", NULL);
        }
    } else {
        repr->setAttribute("id", object->getId());

        if (object->xml_space.set) {
            char const *xml_space;
            xml_space = sp_xml_get_space_string(object->xml_space.value);
            repr->setAttribute("xml:space", xml_space);
        }

        if ( flags & SP_OBJECT_WRITE_EXT &&
             object->collectionPolicy() == SPObject::ALWAYS_COLLECT )
        {
            repr->setAttribute("inkscape:collect", "always");
        } else {
            repr->setAttribute("inkscape:collect", NULL);
        }

        SPStyle const *const obj_style = SP_OBJECT_STYLE(object);
        if (obj_style) {
            gchar *s = sp_style_write_string(obj_style, SP_STYLE_FLAG_IFSET);
            repr->setAttribute("style", ( *s ? s : NULL ));
            g_free(s);
        } else {
            /** \todo I'm not sure what to do in this case.  Bug #1165868
             * suggests that it can arise, but the submitter doesn't know
             * how to do so reliably.  The main two options are either
             * leave repr's style attribute unchanged, or explicitly clear it.
             * Must also consider what to do with property attributes for
             * the element; see below.
             */
            char const *style_str = repr->attribute("style");
            if (!style_str) {
                style_str = "NULL";
            }
            g_warning("Item's style is NULL; repr style attribute is %s", style_str);
        }

        /** \note We treat object->style as authoritative.  Its effects have
         * been written to the style attribute above; any properties that are
         * unset we take to be deliberately unset (e.g. so that clones can
         * override the property).
         *
         * Note that the below has an undesirable consequence of changing the
         * appearance on renderers that lack CSS support (e.g. SVG tiny);
         * possibly we should write property attributes instead of a style
         * attribute.
         */
        sp_style_unset_property_attrs (object);
    }

    return repr;
}

/**
 * Update this object's XML node with flags value.
 */
Inkscape::XML::Node *
SPObject::updateRepr(unsigned int flags) {
    if (!SP_OBJECT_IS_CLONED(this)) {
        Inkscape::XML::Node *repr=SP_OBJECT_REPR(this);
        if (repr) {
            return updateRepr(repr->document(), repr, flags);
        } else {
            g_critical("Attempt to update non-existent repr");
            return NULL;
        }
    } else {
        /* cloned objects have no repr */
        return NULL;
    }
}

/** Used both to create reprs in the original document, and to create
 *  reprs in another document (e.g. a temporary document used when
 *  saving as "Plain SVG"
 */
Inkscape::XML::Node *
SPObject::updateRepr(Inkscape::XML::Document *doc, Inkscape::XML::Node *repr, unsigned int flags) {
    g_assert(doc != NULL);

    if (SP_OBJECT_IS_CLONED(this)) {
        /* cloned objects have no repr */
        return NULL;
    }
    if (((SPObjectClass *) G_OBJECT_GET_CLASS(this))->write) {
        if (!(flags & SP_OBJECT_WRITE_BUILD) && !repr) {
            repr = SP_OBJECT_REPR(this);
        }
        return ((SPObjectClass *) G_OBJECT_GET_CLASS(this))->write(this, doc, repr, flags);
    } else {
        g_warning("Class %s does not implement ::write", G_OBJECT_TYPE_NAME(this));
        if (!repr) {
            if (flags & SP_OBJECT_WRITE_BUILD) {
                repr = SP_OBJECT_REPR(this)->duplicate(doc);
            }
            /// \todo FIXME: else probably error (Lauris) */
        } else {
            repr->mergeFrom(SP_OBJECT_REPR(this), "id");
        }
        return repr;
    }
}

/* Modification */

/**
 * Add \a flags to \a object's as dirtiness flags, and
 * recursively add CHILD_MODIFIED flag to
 * parent and ancestors (as far up as necessary).
 */
void
SPObject::requestDisplayUpdate(unsigned int flags)
{
    g_return_if_fail( this->document != NULL );

    if (update_in_progress) {
        g_print("WARNING: Requested update while update in progress, counter = %d\n", update_in_progress);
    }

    /* requestModified must be used only to set one of SP_OBJECT_MODIFIED_FLAG or
     * SP_OBJECT_CHILD_MODIFIED_FLAG */
    g_return_if_fail(!(flags & SP_OBJECT_PARENT_MODIFIED_FLAG));
    g_return_if_fail((flags & SP_OBJECT_MODIFIED_FLAG) || (flags & SP_OBJECT_CHILD_MODIFIED_FLAG));
    g_return_if_fail(!((flags & SP_OBJECT_MODIFIED_FLAG) && (flags & SP_OBJECT_CHILD_MODIFIED_FLAG)));

    bool already_propagated = (!(this->uflags & (SP_OBJECT_MODIFIED_FLAG | SP_OBJECT_CHILD_MODIFIED_FLAG)));

    this->uflags |= flags;

    /* If requestModified has already been called on this object or one of its children, then we
     * don't need to set CHILD_MODIFIED on our ancestors because it's already been done.
     */
    if (already_propagated) {
        SPObject *parent = SP_OBJECT_PARENT(this);
        if (parent) {
            parent->requestDisplayUpdate(SP_OBJECT_CHILD_MODIFIED_FLAG);
        } else {
            sp_document_request_modified(SP_OBJECT_DOCUMENT(this));
        }
    }
}

/**
 * Update views
 */
void
SPObject::updateDisplay(SPCtx *ctx, unsigned int flags)
{
    g_return_if_fail(!(flags & ~SP_OBJECT_MODIFIED_CASCADE));

    update_in_progress ++;

#ifdef SP_OBJECT_DEBUG_CASCADE
    g_print("Update %s:%s %x %x %x\n", g_type_name_from_instance((GTypeInstance *) this), SP_OBJECT_ID(this), flags, this->uflags, this->mflags);
#endif

    /* Get this flags */
    flags |= this->uflags;
    /* Copy flags to modified cascade for later processing */
    this->mflags |= this->uflags;
    /* We have to clear flags here to allow rescheduling update */
    this->uflags = 0;

    // Merge style if we have good reasons to think that parent style is changed */
    /** \todo
     * I am not sure whether we should check only propagated
     * flag. We are currently assuming that style parsing is
     * done immediately. I think this is correct (Lauris).
     */
    if ((flags & SP_OBJECT_STYLE_MODIFIED_FLAG) && (flags & SP_OBJECT_PARENT_MODIFIED_FLAG)) {
        if (this->style && this->parent) {
            sp_style_merge_from_parent(this->style, this->parent->style);
        }
    }

    try
    {
        if (((SPObjectClass *) G_OBJECT_GET_CLASS(this))->update)
            ((SPObjectClass *) G_OBJECT_GET_CLASS(this))->update(this, ctx, flags);
    }
    catch(...)
    {
        /** \todo
        * in case of catching an exception we need to inform the user somehow that the document is corrupted
        * maybe by implementing an document flag documentOk
        * or by a modal error dialog
        */
        g_warning("SPObject::updateDisplay(SPCtx *ctx, unsigned int flags) : throw in ((SPObjectClass *) G_OBJECT_GET_CLASS(this))->update(this, ctx, flags);");
    }

    update_in_progress --;
}

/**
 * Request modified always bubbles *up* the tree, as opposed to
 * request display update, which trickles down and relies on the
 * flags set during this pass...
 */
void
SPObject::requestModified(unsigned int flags)
{
    g_return_if_fail( this->document != NULL );

    /* requestModified must be used only to set one of SP_OBJECT_MODIFIED_FLAG or
     * SP_OBJECT_CHILD_MODIFIED_FLAG */
    g_return_if_fail(!(flags & SP_OBJECT_PARENT_MODIFIED_FLAG));
    g_return_if_fail((flags & SP_OBJECT_MODIFIED_FLAG) || (flags & SP_OBJECT_CHILD_MODIFIED_FLAG));
    g_return_if_fail(!((flags & SP_OBJECT_MODIFIED_FLAG) && (flags & SP_OBJECT_CHILD_MODIFIED_FLAG)));

    bool already_propagated = (!(this->mflags & (SP_OBJECT_MODIFIED_FLAG | SP_OBJECT_CHILD_MODIFIED_FLAG)));

    this->mflags |= flags;

    /* If requestModified has already been called on this object or one of its children, then we
     * don't need to set CHILD_MODIFIED on our ancestors because it's already been done.
     */
    if (already_propagated) {
        SPObject *parent=SP_OBJECT_PARENT(this);
        if (parent) {
            parent->requestModified(SP_OBJECT_CHILD_MODIFIED_FLAG);
        } else {
            sp_document_request_modified(SP_OBJECT_DOCUMENT(this));
        }
    }
}

/**
 *  Emits the MODIFIED signal with the object's flags.
 *  The object's mflags are the original set aside during the update pass for
 *  later delivery here.  Once emitModified() is called, those flags don't
 *  need to be stored any longer.
 */
void
SPObject::emitModified(unsigned int flags)
{
    /* only the MODIFIED_CASCADE flag is legal here */
    g_return_if_fail(!(flags & ~SP_OBJECT_MODIFIED_CASCADE));

#ifdef SP_OBJECT_DEBUG_CASCADE
    g_print("Modified %s:%s %x %x %x\n", g_type_name_from_instance((GTypeInstance *) this), SP_OBJECT_ID(this), flags, this->uflags, this->mflags);
#endif

    flags |= this->mflags;
    /* We have to clear mflags beforehand, as signal handlers may
     * make changes and therefore queue new modification notifications
     * themselves. */
    this->mflags = 0;

    g_object_ref(G_OBJECT(this));
    SPObjectClass *klass=(SPObjectClass *)G_OBJECT_GET_CLASS(this);
    if (klass->modified) {
        klass->modified(this, flags);
    }
    _modified_signal.emit(this, flags);
    g_object_unref(G_OBJECT(this));
}

gchar const *
sp_object_tagName_get(SPObject const *object, SPException *ex)
{
    /* If exception is not clear, return */
    if (!SP_EXCEPTION_IS_OK(ex)) {
        return NULL;
    }

    /// \todo fixme: Exception if object is NULL? */
    return object->repr->name();
}

gchar const *
sp_object_getAttribute(SPObject const *object, gchar const *key, SPException *ex)
{
    /* If exception is not clear, return */
    if (!SP_EXCEPTION_IS_OK(ex)) {
        return NULL;
    }

    /// \todo fixme: Exception if object is NULL? */
    return (gchar const *) object->repr->attribute(key);
}

void
sp_object_setAttribute(SPObject *object, gchar const *key, gchar const *value, SPException *ex)
{
    /* If exception is not clear, return */
    g_return_if_fail(SP_EXCEPTION_IS_OK(ex));

    /// \todo fixme: Exception if object is NULL? */
    object->repr->setAttribute(key, value, false);
}

void
sp_object_removeAttribute(SPObject *object, gchar const *key, SPException *ex)
{
    /* If exception is not clear, return */
    g_return_if_fail(SP_EXCEPTION_IS_OK(ex));

    /// \todo fixme: Exception if object is NULL? */
    object->repr->setAttribute(key, NULL, false);
}

/* Helper */

static gchar *
sp_object_get_unique_id(SPObject *object, gchar const *id)
{
    static unsigned long count = 0;

    g_assert(SP_IS_OBJECT(object));

    count++;

    gchar const *name = object->repr->name();
    g_assert(name != NULL);

    gchar const *local = strchr(name, ':');
    if (local) {
        name = local + 1;
    }

    if (id != NULL) {
        if (object->document->getObjectById(id) == NULL) {
            return g_strdup(id);
        }
    }

    size_t const name_len = strlen(name);
    size_t const buflen = name_len + (sizeof(count) * 10 / 4) + 1;
    gchar *const buf = (gchar *) g_malloc(buflen);
    memcpy(buf, name, name_len);
    gchar *const count_buf = buf + name_len;
    size_t const count_buflen = buflen - name_len;
    do {
        ++count;
        g_snprintf(count_buf, count_buflen, "%lu", count);
    } while ( object->document->getObjectById(buf) != NULL );
    return buf;
}

/* Style */

/**
 * Returns an object style property.
 *
 * \todo
 * fixme: Use proper CSS parsing.  The current version is buggy
 * in a number of situations where key is a substring of the
 * style string other than as a property name (including
 * where key is a substring of a property name), and is also
 * buggy in its handling of inheritance for properties that
 * aren't inherited by default.  It also doesn't allow for
 * the case where the property is specified but with an invalid
 * value (in which case I believe the CSS2 error-handling
 * behaviour applies, viz. behave as if the property hadn't
 * been specified).  Also, the current code doesn't use CRSelEng
 * stuff to take a value from stylesheets.  Also, we aren't
 * setting any hooks to force an update for changes in any of
 * the inputs (i.e., in any of the elements that this function
 * queries).
 *
 * \par
 * Given that the default value for a property depends on what
 * property it is (e.g., whether to inherit or not), and given
 * the above comment about ignoring invalid values, and that the
 * repr parent isn't necessarily the right element to inherit
 * from (e.g., maybe we need to inherit from the referencing
 * <use> element instead), we should probably make the caller
 * responsible for ascending the repr tree as necessary.
 */
gchar const *
sp_object_get_style_property(SPObject const *object, gchar const *key, gchar const *def)
{
    g_return_val_if_fail(object != NULL, NULL);
    g_return_val_if_fail(SP_IS_OBJECT(object), NULL);
    g_return_val_if_fail(key != NULL, NULL);

    gchar const *style = object->repr->attribute("style");
    if (style) {
        size_t const len = strlen(key);
        char const *p;
        while ( (p = strstr(style, key))
                != NULL )
        {
            p += len;
            while ((*p <= ' ') && *p) p++;
            if (*p++ != ':') break;
            while ((*p <= ' ') && *p) p++;
            size_t const inherit_len = sizeof("inherit") - 1;
            if (*p
                && !(strneq(p, "inherit", inherit_len)
                     && (p[inherit_len] == '\0'
                         || p[inherit_len] == ';'
                         || g_ascii_isspace(p[inherit_len])))) {
                return p;
            }
        }
    }
    gchar const *val = object->repr->attribute(key);
    if (val && !streq(val, "inherit")) {
        return val;
    }
    if (object->parent) {
        return sp_object_get_style_property(object->parent, key, def);
    }

    return def;
}

/**
 * Lifts SVG version of all root objects to version.
 */
void
SPObject::_requireSVGVersion(Inkscape::Version version) {
    for ( SPObject::ParentIterator iter=this ; iter ; ++iter ) {
        SPObject *object=iter;
        if (SP_IS_ROOT(object)) {
            SPRoot *root=SP_ROOT(object);
            if ( root->version.svg < version ) {
                root->version.svg = version;
            }
        }
    }
}

/**
 * Returns previous object in sibling list or NULL.
 */
SPObject *
sp_object_prev(SPObject *child)
{
    SPObject *parent = SP_OBJECT_PARENT(child);
    for ( SPObject *i = sp_object_first_child(parent); i; i = SP_OBJECT_NEXT(i) ) {
        if (SP_OBJECT_NEXT(i) == child)
            return i;
    }
    return NULL;
}

/* Titles and descriptions */

/* Note:
   Titles and descriptions are stored in 'title' and 'desc' child elements
   (see section 5.4 of the SVG 1.0 and 1.1 specifications).  The spec allows
   an element to have more than one 'title' child element, but strongly
   recommends against this and requires using the first one if a choice must
   be made.  The same applies to 'desc' elements.  Therefore, these functions
   ignore all but the first 'title' child element and first 'desc' child
   element, except when deleting a title or description.
*/

/**
 * Returns the title of this object, or NULL if there is none.
 * The caller must free the returned string using g_free() - see comment
 * for getTitleOrDesc() below.
 */
gchar *
SPObject::title() const
{
    return getTitleOrDesc("svg:title");
}

/**
 * Sets the title of this object
 * A NULL first argument is interpreted as meaning that the existing title
 * (if any) should be deleted.
 * The second argument is optional - see setTitleOrDesc() below for details.
 */
bool
SPObject::setTitle(gchar const *title, bool verbatim)
{
    return setTitleOrDesc(title, "svg:title", verbatim);
}

/**
 * Returns the description of this object, or NULL if there is none.
 * The caller must free the returned string using g_free() - see comment
 * for getTitleOrDesc() below.
 */
gchar *
SPObject::desc() const
{
    return getTitleOrDesc("svg:desc");
}

/**
 * Sets the description of this object.
 * A NULL first argument is interpreted as meaning that the existing
 * description (if any) should be deleted.
 * The second argument is optional - see setTitleOrDesc() below for details.
 */
bool
SPObject::setDesc(gchar const *desc, bool verbatim)
{
    return setTitleOrDesc(desc, "svg:desc", verbatim);
}

/**
 * Returns the title or description of this object, or NULL if there is none.
 *
 * The SVG spec allows 'title' and 'desc' elements to contain text marked up
 * using elements from other namespaces.  Therefore, this function cannot
 * in general just return a pointer to an existing string - it must instead
 * construct a string containing the title or description without the mark-up.
 * Consequently, the return value is a newly allocated string (or NULL), and
 * must be freed (using g_free()) by the caller.
 */
gchar *
SPObject::getTitleOrDesc(gchar const *svg_tagname) const
{
    SPObject *elem = findFirstChild(svg_tagname);
    if (elem == NULL) return NULL;
    return g_string_free(elem->textualContent(), FALSE);
}

/**
 * Sets or deletes the title or description of this object.
 * A NULL 'value' argument causes the title or description to be deleted.
 *
 * 'verbatim' parameter:
 * If verbatim==true, then the title or description is set to exactly the
 * specified value.  If verbatim==false then two exceptions are made:
 *   (1) If the specified value is just whitespace, then the title/description
 *       is deleted.
 *   (2) If the specified value is the same as the current value except for
 *       mark-up, then the current value is left unchanged.
 * This is usually the desired behaviour, so 'verbatim' defaults to false for
 * setTitle() and setDesc().
 *
 * The return value is true if a change was made to the title/description,
 * and usually false otherwise.
 */
bool
SPObject::setTitleOrDesc(gchar const *value, gchar const *svg_tagname, bool verbatim)
{
    if (!verbatim) {
        // If the new title/description is just whitespace,
        // treat it as though it were NULL.
        if (value) {
            bool just_whitespace = true;
            for (const gchar *cp = value; *cp; ++cp) {
                if (!std::strchr("\r\n \t", *cp)) {
                    just_whitespace = false;
                    break;
                }
            }
            if (just_whitespace) value = NULL;
        }
        // Don't stomp on mark-up if there is no real change.
        if (value) {
            gchar *current_value = getTitleOrDesc(svg_tagname);
            if (current_value) {
                bool different = std::strcmp(current_value, value);
                g_free(current_value);
                if (!different) return false;
            }
        }
    }

    SPObject *elem = findFirstChild(svg_tagname);

    if (value == NULL) {
        if (elem == NULL) return false;
        // delete the title/description(s)
        while (elem) {
            elem->deleteObject();
            elem = findFirstChild(svg_tagname);
        }
        return true;
    }

    Inkscape::XML::Document *xml_doc = sp_document_repr_doc(document);

    if (elem == NULL) {
        // create a new 'title' or 'desc' element, putting it at the
        // beginning (in accordance with the spec's recommendations)
        Inkscape::XML::Node *xml_elem = xml_doc->createElement(svg_tagname);
        repr->addChild(xml_elem, NULL);
        elem = document->getObjectByRepr(xml_elem);
        Inkscape::GC::release(xml_elem);
    }
    else {
        // remove the current content of the 'text' or 'desc' element
        SPObject *child;
        while (NULL != (child = elem->firstChild())) child->deleteObject();
    }

    // add the new content
    elem->appendChildRepr(xml_doc->createTextNode(value));
    return true;
}

/**
 * Find the first child of this object with a given tag name,
 * and return it.  Returns NULL if there is no matching child.
 */
SPObject *
SPObject::findFirstChild(gchar const *tagname) const
{
    for (SPObject *child = children; child; child = child->next)
    {
        if (child->repr->type() == Inkscape::XML::ELEMENT_NODE &&
            !strcmp(child->repr->name(), tagname)) return child;
    }
    return NULL;
}

/**
 * Return the full textual content of an element (typically all the
 * content except the tags).
 * Must not be used on anything except elements.
 */
GString*
SPObject::textualContent() const
{
    GString* text = g_string_new("");

    for (const SPObject *child = firstChild(); child; child = child->next)
    {
        Inkscape::XML::NodeType child_type = child->repr->type();

        if (child_type == Inkscape::XML::ELEMENT_NODE) {
            GString * new_text = child->textualContent();
            g_string_append(text, new_text->str);
            g_string_free(new_text, TRUE);
        }
        else if (child_type == Inkscape::XML::TEXT_NODE) {
            g_string_append(text, child->repr->content());
        }
    }
    return text;
}

/*
  Local Variables:
  mode:c++
  c-file-style:"stroustrup"
  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
  indent-tabs-mode:nil
  fill-column:99
  End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:encoding=utf-8:textwidth=99 :