Printing QGraphicsScene cuts objects in half - qt

I want to print everything what's on QGraphicsScene:
void MainWindow::on_print_clicked()
{
if (template_ptr != Q_NULLPTR) {
QPrinter printer(QPrinter::HighResolution);
if (QPrintDialog(&printer, this).exec() == QDialog::Accepted) {
if (QPageSetupDialog(&printer, this).exec() == QDialog::Accepted) {
QPainter painter(&printer);
painter.setRenderHint(QPainter::Antialiasing);
painter.setRenderHint(QPainter::TextAntialiasing);
qreal x, _y, h, w, fake;
ui->graphicsView->sceneRect().getRect(&x, &_y, &w, &fake);
h = template_ptr->page_height*2.0;
qint32 page = 0;
while (true) {
qreal y = _y + h*page;
QRectF leftRect(x, y, w, template_ptr->page_height*2.0*template_ptr->max_pages - h*page);
if (ui->graphicsView->scene()->items(leftRect).length() <= 0) {
break;
}
QRectF sourceRect(x, y, w, h);
ui->graphicsView->scene()->render(&painter, printer.pageRect(), sourceRect);
printer.newPage();
page++;
}
}
}
}
}
That's the effect (PDF file):
Every point on the lists is a single QGraphicsItem and I don't know what's the easiest way to move the items that doesn't fit within a page, to the next page... I probably could do some error-prone mathematics to achieve that but I'm pretty sure this can be resolved in some elegant way.

What I would do...
Step 1: I would first create a copy of the scene (a new QGraphicsScene with the same size as your original) and move all items there.
Step 2: Create a temporary scene for each new page, with a sceneRect equal to the section you wish to print.
Step 3: Move to it the items from the scene copy, that are contained in the sceneRect of the temp scene.
Step 4: After printing, move the printed items to the original scene...
Step 5: Shorten your copy scene bounding rect to the bounding rect of the items still left inside it. (to allow step 4 to place items exactly in place, change the x/y coordinates as well as change the w/h)
Repeat steps 3 to 5 till the copy scene is empty.

Related

How to scale the contents of a QGraphicsView using the QPinchGesture?

I'm implementing an image viewer on an embedded platform. The hardware is a sort of tablet and has a touch screen as input device. The Qt version I'm using is 5.4.3.
The QGraphicsView is used to display a QGraphicsScene which contains a QGraphicsPixmapItem. The QGraphicsPixmapItem containts the pixmap to display.
The relevant part of the code is the following:
void MyGraphicsView::pinchTriggered(QPinchGesture *gesture)
{
QPinchGesture::ChangeFlags changeFlags = gesture->changeFlags();
if (changeFlags & QPinchGesture::ScaleFactorChanged) {
currentStepScaleFactor = gesture->totalScaleFactor();
}
if (gesture->state() == Qt::GestureFinished) {
scaleFactor *= currentStepScaleFactor;
currentStepScaleFactor = 1;
return;
}
// Compute the scale factor based on the current pinch level
qreal sxy = scaleFactor * currentStepScaleFactor;
// Get the pointer to the currently displayed picture
QList<QGraphicsItem *> listOfItems = items();
QGraphicsItem* item = listOfItems.at(0);
// Scale the picture
item.setScale(sxy);
// Adapt the scene to the scaled picture
setSceneRect(scene()->itemsBoundingRect());
}
As result of the pinch, the pixmap is scaled starting from the top-left corner of the view.
How to scale the pixmap respect to the center of the QPinchGesture?
From The Docs
The item is scaled around its transform origin point, which by default is (0, 0). You can select a different transformation origin by calling setTransformOriginPoint().
That function takes in a QPoint so you would need to find out your centre point first then set the origin point.
void QGraphicsItem::setTransformOriginPoint(const QPointF & origin)

Dragged QGraphicsItem not visible in items() function

I have created a QGraphicsScene scene and added some graphcis items (lines, rectangles) etc to the scene.
I can loop through them using this list :
QList<QGraphicsItem*> all = items();
I enabled movement for these items and I am able to drag them by click selecting them. But after an element has been dragged, it stops showing up in the call to items() function of the QGraphicsScene.
QList<QGraphicsItem*> all = items();
None of the dragged items show up in the above list, while non-dragged ones do show up.
Does dragging the QGraphicScene elements change their parent ? or any other reason somebody could suggest for such an issue ?
{P.S. Code is too very big to share}
Edit 1 :
I am using the flags QGraphicsItem::ItemIsSelectable and QGraphicsItem::ItemIsMovable for making the items movable.
foreach(QGraphicsItem* itemInVisualScene, items())
{
itemInVisualScene->setFlag(QGraphicsItem::ItemIsSelectable, itemsMovable);
itemInVisualScene->setFlag(QGraphicsItem::ItemIsMovable, itemsMovable);
}
By default I add few rectangle to the scene. Then in the 'move mode' I drag them around. Then in the 'add mode' I click on screen to add new rectangles. I have written a logic to check if I am clicking on any existing drawn rectangle :
void Scene::mousePressEvent(QGraphicsSceneMouseEvent * event)
{
if(eDrawLines == sceneMode)
{
dragBeginPoint = event->scenePos();
dragEndPoint = dragBeginPoint;
QList<QGraphicsItem*> all = items();
for (int i = 0; i < all.size(); i++)
{
QGraphicsItem *gi = all[i];
// Clicked point lies inside existing rect
if( QGraphicsRectItem::Type == gi->type() && gi->contains(dragBeginPoint))
{
std::cout << "Pressed inside existing rect" << std::endl;
return;
}
}
std::cout << "Point not found, add new rectangle" << std::endl;
}
QGraphicsScene::mousePressEvent(event);
}
This adding of rectangles work fine for rects which were not dragged in the 'move mode'. But rects which were moved do not seem to recognize the click anymore. My control comes out of the loop even when I click on an existing rectangle which was dragged earlier.
QGraphicsItem's transform is changed after dragging and therefore need to transform the point to item's local coordinates.
gi->contains(gi->mapFromScene(dragBeginPoint))
To convert or get item's position in scene coordinates, use
gi->mapToScene(0,0) or gi->scenePos()

How do I clear certain lines/paths from a QWidget but not others, then redraw separate lines/paths on top?

I'm trying to optimize line drawings on a QWidget. I basically have a grid in the background and drawings on top of the grid. Currently I'm redrawing the background and grid lines every time the paint event is called. This works fine if the grid lines are far enough apart so I don't have to draw that many lines, but if the scale gets changed, the lines must be redrawn at that new scale. Also, if the window is resized, then more of the grid is displayed, hurting the performance even more.
Here is the code for drawing the grid:
// draw grid
painter.fillRect(0,0,areaWidth, areaHeight, QColor(255,255,255));
painter.setPen(QPen(QBrush(QColor(240,240,255)), 1, Qt::SolidLine, Qt::FlatCap));
int numXLines = areaWidth/mSIToPixelScale + 1;
int numYLines = areaHeight/mSIToPixelScale + 1;
double width = areaWidth;
double height = areaHeight;
for (int x=0; x<numXLines;x++)
{
for (int y=0; y<numYLines; y++)
{
painter.drawLine(0,y*mSIToPixelScale,width, y*mSIToPixelScale);
painter.drawLine(x*mSIToPixelScale,0,x*mSIToPixelScale,height);
}
}
So when numXLines and numYLines in the above code reach higher values, the performance drops very hard, which makes sense. The grid will always have to be redrawn if the scale changes, but if the scale does not change, then only the drawing on top of the grid should change. How can I accomplish this?
The QWidget::paintEvent( QPaintEvent* aEvent ) is called by the framework not just when you want it. So if you want to remove some lines from the widget than you need draw them conditionally in your function.
For example:
if ( numXLines < 25 && numYLines < 25 )
{
// Draw only every second lines for example.
}
else
{
// Draw all lines.
}
But this is not the best way. Maybe you shall use larger steps between the grid lines if there too many of them.
I found where I went wrong, I was redrawing the y lines every x iteration. I fixed it by creating two separate for loops:
// add grid lines to a painter path
QPainterPath grid;
for (int x=0; x<numXLines;x++)
{
grid.moveTo(x*mSIToPixelScale, 0);
grid.lineTo(x*mSIToPixelScale, height);
}
for (int y=0; y<numYLines; y++)
{
grid.moveTo(0, y*mSIToPixelScale);
grid.lineTo(width,y*mSIToPixelScale);
}
painter.drawPath(grid);
painter.end();
Also, I think drawing onto a QImage first then drawing that image inside the paintEvent would make code more organized, so all your doing in the paintEvent is drawing from a high level.

(Qt) Rendering scene, different items in the same relative positions

I have a QSqlTableModel model that contains my data.
I have made a QGraphicsScene scene and a QGraphicsView view so the user can move around same myQGraphicsTextItem text items until the desired position.
Something like this:
myQWidget::myQWidget()
{
//these are member of my class
chequeScene = new QGraphicsScene();
chequeView = new QGraphicsView();
model = new QSQLTableModel();
//populate model, inialize things here...
//add predefined items to the scene
setScene();
}
there's a button to show the view and move the textitems of scene. It works well.
there's a button that calls the slot print that belongs to the class. It configures a QPrinter and then calls the following paint method myQWidget::paint(), after that scene->render() is called.
The porpoise of the method below is to print data on a paper that is configured to have the same size than the scene while printing the data in the same relative position the textItem had on the scene. Can't do it with QList it doesn't order the items in the same way I added them to the scene.
Here is my code below, it prints with overlapping of some fields doe to QList order items as they appear on the scene.
void myQWidget::paint()
{
qreal dx = 0;
qreal dy = 0;
QList<QGraphicsItem*> L = chequeScene->items();
for (int j=0; j<model->columnCount(); j++) {
if(!L.isEmpty())
{
//Saves the position on dx, dy
dx = L.first()->scenePos().x();
dy = L.first()->scenePos().y();
chequeScene->removeItem( L.first() );
delete L.first();
L.removeFirst();
}
QString txt("");
//selecting printing formar for each column
switch(j)
{
case COLUMNADEFECHA:
txt = QDate::fromString(model->data(model->index(chequenum,j)).toString(), "yyyy/MM/dd").toString("dd/MM/yyyy");
break;
case COLUMNADECHEQUES:
break;
default:
txt = model->data(model->index(chequenum,j)).toString();
break;
}
//filtering not important columns
if(j!=COLUMNADECHEQUES)
{
//Supposubly item with the desired information is added to the scene
//on the same position it had before. Not working.
GraphicsTextItem *item=new GraphicsTextItem();
item->setPlainText(txt);
item->setPos(dx,dy);
chequeScene->addItem(item);
}
}
}
Any idea on how to get this working?
I think as you are getting the scenePos in dx and dy but are setting it using setPos function.
Also as you are using your GraphicsTextItem and not QGraphicsTextItem maybe a look at your paint method will help in understanding the problem.
Try using item->mapFromScene(dx, dy) and then use those coordinates to set the item position by item->setPos(..).
Hope This Helps..

Items in a QGraphicsScene near the mouse

I am trying to find the items under the mouse in a scene. The code I am using is as follows:
QPainterPath mousePath;
mousePath.addEllipse(mouseEvent -> pos(),5,5);
QList<QGraphicsItem *> itemsCandidate = this->items(mousePath);
if (!(itemsCandidate.contains(lastSelectedItem))) lastSelectedItem =itemsCandidate.first();
PS: this refers to a scene.
The code should find the items intersected by a small circle around the mouse position and keep the item pointer unchanged if the previous intersected one is still intersected, or take the first in the QList otherwise.
Unfortunately, this code does not work with items inside each other. For example, if I have a Rect side a Rect, the outer Rect is always intersecting the mouse position even when this one is near the inner Rect. How can i solve this?
UPDATE: This seems not to be a problem with polygons, but with Rect, Ellipses, etc.
UPDATE: This code is in the redefined scene::mouseMoveEvent
You can reimplement ‍mouseMoveEvent in ‍QGraphicsView‍ to capture mouse move events in view and track items near the mouse like:
void MyView::mouseMoveEvent(QMouseEvent *event)
{
QPointF mousePoint = mapToScene(event->pos());
qreal x = mousePoint.x();
qreal y = mousePoint.y();
foreach(QGraphicsItem * t , items())
{
int dist = qSqrt(qPow(t->pos().x()-x,2)+qPow(t->pos().y()-y,2));
if( dist<70 )
{
//do whatever you like
}
}
QGraphicsView::mouseMoveEvent(event);
}

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