Feasability study: Displaying a graph with QML ?

Zaxy

Hello guys,

I am starting working with QML and want to know if the following is feasable:

I want to display a graph with QML in the following way:

nodes are represented by an icon (image file)
you can right click on an node and do some simple stuff like rename the node's name
nodes are connected with lines and the graph is drawn in a suitable easy to visualize way

I saw that there is GridView in QML, but not sure that you can draw lines between the elements or arrange them on the screen in a suitable way.

Can you please give me an oppinion if this is feaseable with QML and which elements should I use ?

Many thanks in advance !

Zaxy

P.S. I want to create the graph with C++ and display (visualize) it with QML.

sierdzio

GridView is not suitable. In QML2, there is QML Canvas element and Paths can also be used. For your use case, though, I think some very custom implementation is more suitable, or even transfer to QGraphicsView.

Zaxy

So which elements should I use - QGraphicsView or Canvas + Paths ?

Is it better to do it entierly with Qt instead ? Maybe will be simplier ?

Thanks

sierdzio

QML is integral part of Qt. Better to differentiate between QtWidgets and QtQuick/QML.

The answer is: I don't know. Try making test projects using both technologies and then decide. There is no built-in mechanism that will allow you to create this in a couple lines of code. I would personally recommend QML, as it's easy and fast but you have to judge yourself.

You can also take a look at Qwt, maybe Uwe has some classes there that would help you. I think it's a charting library, but have never tried - it's quite probable there is some graphing stuff there, too.

Zaxy

Why do you recommend QML ? Is it easier to be done with QML ? For QML, which elements you could advise me to use or even if you have a simular tutorial on that ?

Thanks again

sierdzio

"QML, as it's easy and fast" :) It's a pure pleasure to code in. Lame reason, I know, but a valid one for me. There are components like Image, Transform and various Paths that can make it quite straightforward to code, although there are caveats, too. That is why I'm not sure what to recommend to you.

No I don't have any tutorials at hand. Search the documentation.

Zaxy

Thanks a lot, sierdzio !

Anyone else has an idea ?

nizeguy

Try porting some small js library that already does that to html canvas and tell us about it.

If it can't be done easily in javascript qml for some reason, it can surely be done in QtQuick in C++ .

ps: just found this one in reddit/programming : http://tenxer.github.com/xcharts/examples/

Zaxy

Hello,

I have the following example - a QList of Nodes in ConfigurationModel .
I want to bind the properties "QString nodeID" and "QString iconFilePath" beween the QML component Node and the C++ class Node.

Unfortunetly the binding is not working - when you create the Node instances from C++, the properties of the correspondingly generated QML objects don't have the given values. They are empty. I cannot find where the issue comes from ... Could you please advise me, what I do wrong ?

main.qml
@import QtQuick 1.0

Rectangle {
width: 500
height: 500

Repeater {
    anchors.fill: parent
    model: configModel
    delegate: Node {}
}

}
@

Node.qml
@import QtQuick 1.0
import NodeLib 1.0

Node {
id: nodeDelegate

Image{
    id : nodeIcon
    source: nodeDelegate.iconFilePath
}

Text {
   anchors.top: nodeIcon.bottom
   text: nodeDelegate.nodeID
}

MouseArea {
   anchors.fill: parent
}

}
@

main.cpp
@#include <QApplication>
#include "qmlapplicationviewer.h"
#include <QDeclarativeContext>
#include <QtDeclarative>

#include "ConfigurationModel.h"

Q_DECL_EXPORT int main(int argc, char *argv[])
{
QScopedPointer<QApplication> app(createApplication(argc, argv));

QDeclarativeView    declarativeView;
qmlRegisterType<Node>("NodeLib", 1, 0, "Node");

ConfigurationModel* p_configModel = ConfigurationModel::GetConfigModelInstance();
p_configModel->addNodeInConfigurationModel(new Node("PanelXXXX", PLUG_IN, EVALUATION_BLOCK, "./ui-images/cutetube.png"));
p_configModel->addNodeInConfigurationModel(new Node("PanelYYYY", PLUG_IN, EVALUATION_BLOCK, "./ui-images/cutetube.png"));
Node *p_nodeZ = new Node("PanelZZZZ", PLUG_IN, EVALUATION_BLOCK, "./ui-images/cutetube.png");
p_nodeZ->setNodeID("NODE ZZZZ");
p_configModel->addNodeInConfigurationModel(p_nodeZ);

// if the configuration has been changed, you need to call setContextProperty() again to update the QML view

declarativeView.rootContext()->setContextProperty("configModel", ConfigurationModel::GetConfigModelInstance());

declarativeView.setSource(QUrl::fromLocalFile&#40;"qml/ConfigurationView/main.qml"&#41;);
declarativeView.show();

return app->exec&#40;&#41;;

}
@

Zaxy

Node.h
@#ifndef NODE_H
#define NODE_H

#include <QString>
#include <QList>
#include <QDeclarativeItem>

#include "GlobalDeclarations.h"

// Inherit from QDeclarativeItem in order to override paint() method and to display links to parent nodes
class Node : public QDeclarativeItem
{
Q_OBJECT
Q_PROPERTY(QString iconFilePath READ getIconFilePath WRITE setIconFilePath NOTIFY iconFilePathChanged)
Q_PROPERTY(QString nodeID READ getNodeID WRITE setNodeID NOTIFY nodeIDchanged)

public:
// Constructors
Node();
Node(QString nodeID, NodeType nodeType, PlugInType plugInType, QString iconFilePath);

 QHash<int, QByteArray> roleNames() const;
// Destructor
~Node();

QString getNodeID() const;
Q_INVOKABLE bool setNodeID(const QString &nodeID);

QString  getIconFilePath() const;
Q_INVOKABLE bool setIconFilePath(const QString &iconFilePath);

void hide();
void show();

void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0);

signals:
void nodeIDchanged(QString data);
void iconFilePathChanged(QString data);
void dataChanged();

private:
QString _nodeID;
NodeType _nodeType;
PlugInType _plugInType;
QString _iconFilePath;

QList<Node*>    _parents;
QList<Node*>    _children;

};

#endif // NODE_H
@

Zaxy

ConfigurationModel.h
@#ifndef CONFIGURATIONVIEW_H
#define CONFIGURATIONVIEW_H

#include <QList>
#include <QDeclarativeItem>
#include <QAbstractListModel>

#include "Node.h"

// This class is implemented as Singleton
class ConfigurationModel : public QAbstractListModel
{

Q_OBJECT

public:

// Destructor
~ConfigurationModel();

static ConfigurationModel* GetConfigModelInstance ();

void addNodeInConfigurationModel(Node *p_node);
QList< Node* >&  accessAllNodes();
const QList< Node* >&  getAllNodes() const;
void removeNodeFromConfigurationModel(Node *p_node);

QModelIndex indexFromItem(const Node *item) const;

// Functions from QAbstractListModel that should be implemented
int rowCount(const QModelIndex &parent) const;
QVariant data(const QModelIndex &index, int role) const;

signals:
void dataChanged();

private slots:
void handleItemChange();

private:
// Constructor
explicit ConfigurationModel(QObject* parent = 0);

// Copy constructor
ConfigurationModel(const ConfigurationModel& sourceConfView) {}

// Assignment operator
ConfigurationModel& operator=(const ConfigurationModel& sourceConfView) {}

static ConfigurationModel*       _pConfigModelInstance;

QList< Node* >                  _rootNodes;
QList< Node* >                  _standAloneNodes;
QList< Node* >                  _allNodes;

};

#endif // CONFIGURATIONVIEW_H
@

Zaxy

Node.cpp
@#include <Node.h>

// Constructors
Node::Node() : _nodeID(""), _nodeType(NOT_DEFINED), _plugInType(NOT_DEFINEDD), _iconFilePath("")
{
setFlag(ItemHasNoContents, false);
}

Node::Node(QString nodeID, NodeType nodeType, PlugInType plugInType, QString iconFilePath) :
QDeclarativeItem (), _nodeID(nodeID), _nodeType(nodeType), _plugInType(plugInType), _iconFilePath(iconFilePath)
{
emit nodeIDchanged(_nodeID);
emit iconFilePathChanged(_iconFilePath);
emit dataChanged();

setFlag(ItemHasNoContents, false);

}

// Destructor
Node::~Node()
{
}

QHash<int, QByteArray> Node::roleNames() const
{
QHash<int, QByteArray> names;
names[Qt::UserRole + 1] = "name";
return names;
}

QString Node::getNodeID() const
{
return _nodeID;
}

bool Node::setNodeID(const QString &nodeID)
{
_nodeID = nodeID;
emit nodeIDchanged(_nodeID);
emit dataChanged();

return true;

}

QString Node::getIconFilePath() const
{
return _iconFilePath;
}

bool Node::setIconFilePath(const QString &iconFilePath)
{
_iconFilePath = iconFilePath;
emit iconFilePathChanged(_iconFilePath);
emit dataChanged();

return true;

}
@

Zaxy

ConfigurationModel.cpp
@#include "ConfigurationModel.h"

// The global static instance of the Singleton
ConfigurationModel* ConfigurationModel::_pConfigModelInstance = NULL;

// Constructor
ConfigurationModel::ConfigurationModel(QObject *parent) :
QAbstractListModel(parent)
{
}

// Destructor
ConfigurationModel::~ConfigurationModel()
{

// free memory allocated for all nodes of the given configuration
for (QList<Node*>::iterator itAllNodesList = _pConfigModelInstance->_allNodes.begin();
     itAllNodesList != _pConfigModelInstance->_allNodes.end();
     itAllNodesList++)
{
    delete  *itAllNodesList;
    *itAllNodesList = NULL;
}

// free memory of the ConfigurationView instance itself
delete _pConfigModelInstance;
_pConfigModelInstance = NULL;

}

// The class ConfigurationView is implemented as Singleton.
// GetConfigModelInstance() is a static method.
ConfigurationModel* ConfigurationModel::GetConfigModelInstance ()
{
if (_pConfigModelInstance == NULL)
{

    _pConfigModelInstance = new ConfigurationModel();
}

return _pConfigModelInstance;

}

void ConfigurationModel::addNodeInConfigurationModel(Node *p_node)
{
beginInsertRows(QModelIndex(), rowCount(QModelIndex()), rowCount(QModelIndex())); // QModelIndex() is a dummy parameter, not used actually
connect(p_node, SIGNAL(dataChanged()),this, SLOT(handleItemChange()));

_allNodes.append(p_node);

endInsertRows();

// ...
refreshView();

}

QList<Node*>& ConfigurationModel::accessAllNodes()
{
return _allNodes;
}

const QList<Node*>& ConfigurationModel::getAllNodes() const
{
return _allNodes;
}

void ConfigurationModel::removeNodeFromConfigurationModel(Node *p_node)
{
// ...
refreshView();
}

QModelIndex ConfigurationModel::indexFromItem(const Node *item) const
{
Q_ASSERT(item);
for(int row = 0; row < _allNodes.size(); row++) {
if(_allNodes.at(row) == item) return index(row);
}
return QModelIndex();
}

void ConfigurationModel::handleItemChange()
{
Node* node = static_cast<Node*>(sender());
QModelIndex index = indexFromItem(node);
if(index.isValid())
emit dataChanged();
}

// Functions from QAbstractListView that should be implemented
int ConfigurationModel::rowCount(const QModelIndex &parent) const
{
Q_UNUSED(parent);
return _allNodes.size();
}

QVariant ConfigurationModel::data(const QModelIndex &index, int role) const
{
if(index.row() < 0 || index.row() >= _allNodes.size())
return QVariant();

if(role == (Qt::UserRole + 1))
    return _allNodes.at(index.row())->getNodeID();
return QVariant();

}
@

sierdzio

I'm sorry, but are you insane? Do you really expect me to read all this?

@
Node {
id: nodeDelegate

Image{
    id : nodeIcon
    source: nodeDelegate.iconFilePath // no need for referencing nodeDelegate
}

Text {
   anchors.top: nodeIcon.bottom
   text: nodeDelegate.nodeID // no need for referencing nodeDelegate
}

}
@

I suspect you must feed the delegate with entries from the model. Debug, or better - create a small, dumb example to get the hang of Repeater.

Also, I would suggest making node connections separately, not by overriding ::paint().

Zaxy

Exactly, I want to feed the delegate with entries from the model by using the Q_Property binding in Node.h

The example is not complicated, but the binding is not working, and I cannot find why.

If I have Q_PROPERTIes like this:

@class Node : public QDeclarativeItem
{
Q_OBJECT
Q_PROPERTY(QString iconFilePath READ getIconFilePath WRITE setIconFilePath NOTIFY iconFilePathChanged)
Q_PROPERTY(QString nodeID READ getNodeID WRITE setNodeID NOTIFY nodeIDchanged)
@

How should I refer to them in the QML component Node ?
Is the following correct:

@import QtQuick 1.0
import NodeLib 1.0

Node {
id: nodeDelegate

Image{
    id : nodeIcon
    source: nodeDelegate.iconFilePath
}

Text {
   anchors.top: nodeIcon.bottom
   text: nodeDelegate.nodeID
}

MouseArea {
   anchors.fill: parent
}

}
@

sierdzio

You inherit from Node.h, so the properties are visible in QML without refering to the id. Instead of "source: nodeDelegate.iconFilePath" you can just write "iconFilePath". But that has nothing to do with the model - that just assigns the value set in c++.

To access the model, you need to use variables declared in the model. See "this page":http://doc-snapshot.qt-project.org/4.8/qdeclarativemodels.html for reference.

Zaxy

Hi Sierdzio,

Thanks for the article. I implemented a model with nodeID and iconFilePath roles and now I can display the Node objects in a GridView for example or in a Repeater.

But I need a way to draw the graph on the screen:
- order the Node objects in a suitable way on the screen - how could I place the objects in a custom way ? Is there something like currentNode.left = previousNode.right etc. ?
- draw connection lines between some nodes - for that could I use the paint function ?

Thanks again for the help !

sierdzio

I would use QML Rectangle for that. If you want to detect things like previousnode.right, you need to implement it yourself. You could base this on meta object's parent and children properties if you wish.

Or, of course, you can use your own paint function.

Zaxy

So , to use the paint function to draw a line between two nodes.

And about displaying the QList<Node*> in a customized way - for example in a tree view, what could I do ? I think, whan a new node is added to the list, it is automatically displayed, but I want somehow to re-order the graphical representation. I have also additional llist, containing the root Node(s), so I could visit all tree nodes, but don't know how to display them node by node and place them on the screen.

Thanks