Drawing a line with mouse

mahesh

Actually i want to connect to components with mouse by a line..

koahnig

[quote author="mahesh438" date="1327234224"]Actually i want to connect to components with mouse by a line..[/quote]
That is obvious. But how do you like to do it? Meaning the sequence of actions with the mouse.
One way is:

Move mouse to start point
Press and hold (left) mouse button
Move to end point
Release (left) mouse button
This should draw a line from point of pressing teh mouse button to the point where mouse button is released.
Is that the sequence you like to perform?

@
void Scene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if (mouseEvent->button() == Qt::LeftButton) {
lastPoint = mouseEvent->pos();
lineveriable = true;
}
}

void Scene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if ((mouseEvent->buttons() & Qt::LeftButton) && lineveriable)
moveTo(mouseEvent->pos());

}

void Scene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if (mouseEvent->button() == Qt::LeftButton && lineveriable) {
drawLineTo(mouseEvent->pos());
lineveriable = false;
}

}
void Scene::drawLineTo(const QPointF &endPoint)
{
QPainter painter;// may be wrong is here

     painter.drawLine(lastPoint, endPoint);
     lastPoint = endPoint;

}
void Scene::moveTo(const QPointF &endPoint)
{
lastPoint = endPoint;
}

@

[Edit] the painter handling does not seem to be right as you already anticipated.

koahnig

You need to tell the painter where to paint.
Have a look at "this":http://developer.qt.nokia.com/doc/qt-4.8/qpainter.html#QPainter-2

mahesh

i want to paint that line to the scene ....how can i add that corresponding line to the scene...

koahnig

Check out what your Scene is based on ( see "this":http://developer.qt.nokia.com/doc/qt-4.8/qpaintdevice.html#details ).

If it is derived from one of these classes than you should be fine with:
@
void Scene::drawLineTo(const QPointF &endPoint)
{
QPainter painter ( this );

     painter.drawLine(lastPoint, endPoint);
     lastPoint = endPoint;

}
@
Please read also the information provided in those links.

mahesh

if i given "QPainter painter(this);"..this scene class i derived from --QGraphicsscene
it showing error
no matching function call QPainter ::Qpainter(scene* const)
i have one doubt is it right way to paint on the scene

koahnig

QGraphicsScene has "an addLine":http://developer.qt.nokia.com/doc/qt-4.8/qgraphicsscene.html#addLine

mahesh

@
void Scene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if (mouseEvent->button() == Qt::LeftButton)
{
lastPoint = mouseEvent->scenePos();
line = new QGraphicsLineItem(QLineF(mouseEvent->scenePos(), mouseEvent->scenePos()));
addItem(line);
lineveriable = true;
}

void Scene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if ((mouseEvent->buttons() & Qt::LeftButton) && lineveriable){
QLineF newLine(lastPoint, mouseEvent->scenePos());
line->setLine(newLine);
}
}

void Scene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
{
if (mouseEvent->button() == Qt::LeftButton && lineveriable) {
QLineF newLine(lastPoint, mouseEvent->scenePos());
line->setLine(newLine);
lineveriable = false;
}

@
now also it is not adding...no errors but program is unexpectedly finishing.

cincirin

From what I see in your code is normal that you don't see any line. Also when you move the mouse (with one button clicked) you construct a new empty line ( with p1 == p2) for every new mouse movement. Is this what you want ?

mahesh

sorry i didn't saw that one i was interchanged mouse press and mouse release functions...thanks now it is drawing