I have a huge QgraphicsScene and a QGraphicsItem which changes its position according to pressed key arrows. I want the item to always be in the centre of the viewport. I used QGraphicsView::centerOn() and it's exactly what i need, but there is jittering problem - and as i read it's associated with the integer precision issue. So what's the way around? Another post says to use QGraphicsView::translate() and setTransformationAnchor(QGraphicsView::NoAnchor). But it doesnt seem to work.
Game::Game()
{
player = new QGraphicsRectItem();
m_view = new QGraphicsView(this);
m_view->setSceneRect(QRectF(0,0,11800,11600));
this->setBackgroundBrush(Qt::black);
m_view->setScene(this);
m_view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
m_view->setViewportUpdateMode(QGraphicsView::NoViewportUpdate);
m_view->show();
player->setRect(0,0,100,100);
player->setBrush(Qt::red);
player->setPos(400,300);
player->setFocus();
this->addItem(player);
player->setZValue(10);
player->setTransformOriginPoint(player->boundingRect().center());
customRect = new CustomRect;
customRect->setPos(400,300);
this->addItem(customRect);
}
void Game::advance()
{
m_view->centerOn(player);
}
Related
My LineItem inheriting from QGraphicsLineItem can change its pen width.
I have created a boundingRect that uses the QGraphicsLineItem::boundingRect adjusted by pads that get calculated based on pen width and arrows. It works.
void LineItem::calculateStuff() // called on any change including pen width
{
qreal padLeft, padRight, padT;
padLeft = 0.5 * m_pen.width(); // if no arrows
padT = padLeft;
padRight = padLeft;
m_boundingRect = QGraphicsLineItem::boundingRect().adjusted(-padLeft, -padT, padRight, padT);
update();
}
QRectF LineItem::boundingRect() const
{
return m_boundingRect;
}
QPainterPath LineItem::shape() const
{
QPainterPath p;
p.addRect(m_boundingRect);
return p;
}
There is only one artifact that I get:
if I increase the pen width, then decrease it, I get traces:
these of course disappear as soon as i move mouse or any action (I had a hard time getting the screen shots)
As pretty as they are (seriously I consider them a "feature :-) ) - I am trying to eliminate them. I tried to remember previous bounding rectangle, and update the item with the previous bounding rectangle - i thought that was what the option was for - but it didn't work.
QRectF oldRect = selectedItem->boundingRect();
item->setItemPenWidth(p);
selectedItem->update(oldRect);
selectedItem->update();
My viewport has
setViewportUpdateMode(BoundingRectViewportUpdate);
If I change to
setViewportUpdateMode(FullViewportUpdate);
I don't get artifacts - but I think this will impact performance which is a major constraint.
How can I fix these artifacts - that only occur in that specific situation, decreasing pen width / decreasing bounding rect of line, without impacting performance ?
Simple fix... I had to add
prepareGeometryChange();
in my calculateStuff() function.
I have not seen any changes from this before, it is the first time I change my boundingRect that it does not update seamlessly.
I have a number of classes that inherit from QGraphicsItem, that get to be arranged in a certain way. For simplicity of calculations, I made the scenes, and items, centered in (0, 0) (with the boundingRect() having +/- coordinates).
QGraphicsTextItem subclass defies me, its pos() is relative to top left point.
I have tried a number of things to shift it so it centers in the text center (for example, the suggested solution here - the code referenced actually cuts my text and only shows the bottom left quarter).
I imagined that the solution should be something simple, like
void TextItem::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
{
painter->translate( -boundingRect().width()/2.0, -boundingRect().height()/2.0 );
QGraphicsTextItem::paint(painter, option, widget );
}
the above "sort of" works - but as I increase the item scale -> increase the font, the displayed item is cut off...
I tried to set the pos() - but the problem is, I still need to track the actual position on the scene, so I cannot just replace it.
A slightly unpleasant side effect - centering the QGraphicsView on the element does not work either.
How can I make my QGraphicsTextItem show its position relative to the center of the text ?
Edit: one of the experiments of changing the boundingRect():
QRectF TextItem::boundingRect() const
{
QRectF rect = QGraphicsTextItem::boundingRect();
rect.translate(QPointF(-rect.width()/2.0, -rect.height()/2.0));
return rect;
}
I had to shift the initial position, as well as the resize, to trigger a new position - I was unable to do it in paint() because, as I thought from the start, any repaint would continuously recalculate the position.
Only the initial position needs to be adjusted - but as the font size (or style...) changes, its bounding rectangle also changes, so the position must be recalculated - based on previous position.
In the constructor,
setPos(- boundingRect().width()/2, - boundingRect().height()/2);
in the function that modifies item (font) size,
void TextItem::setSize(int s)
{
QRectF oldRect = boundingRect();
QFont f;
f.setPointSize(s);
setFont(f);
if(m_scale != s)
{
m_scale = s;
qreal x = pos().x() - boundingRect().width()/2.0 + oldRect.width()/2.0;
qreal y = pos().y() - boundingRect().height()/2.0 + oldRect.height()/2.0;
setPos(QPointF(x, y));
}
}
I would like to write a custom QLabel subclass with some more features for responsive design. In thisexample, I want to write a QLabel which scales the text based on the useable space. This is quite easy but also has some problems because of Qt-intern stuff. (I have to scale the text to 0.9 of the useable space, otherwise resizing the window / widget gets buggy)
Now I wan't to add a way to hide the label completely when the font size is bellow a specific threshold. However, this seems to be quite a complex task.
Here is what I have sofar in the classes resizeEvent(QResizeEvent *event) function.
Right now, my function only sets the text to "" when the size would be bellow the threshold.
void CustomLabel::resizeEvent (QResizeEvent * event ) {
if(autoFontResize) {
this->setSilentText(labelText); // just the normal setText function, I overwrote it for the subclass
QFont f = this->font();
int flags = Qt::TextDontClip|Qt::TextWordWrap;
QRect fontBoundRect = this->fontMetrics().boundingRect(this->rect(), flags, this->text());
float xFactor = (float)event->size().width() / (float)fontBoundRect.width();
float yFactor = (float)event->size().height() / (float)fontBoundRect.height();
float factor = xFactor < yFactor ? xFactor : yFactor;
f.setPointSizeF(f.pointSize()*factor*0.9); //
if(minimumFontSize != 0) { // 0 = no minimum Size for the font
if(f.pointSize() < minimumFontSize) {
if(hideFontOnMinimum) { // either Hide or set to the limit size
this->setSilentText(""); //replace text
} else {
f.setPointSizeF(minimumFontSize);
}
}
}
this->setFont(f);
}
QLabel::resizeEvent(event);
}
By the way, some parts of the code are found on stackoverflow, not mine. ;)
What I would like to do is to completely hide() the label. However the label doesn't know when It can show() again since the resizeEvent doesn't seem to be called after that.
Any ideas?
Thanks!
As you've noticed, if you call hide() on the widget it fails to receive a resize event. Since you're customising the class anyway, rather than calling hide(), you could just set a class variable to note that it's hidden and overload the paintEvent function, not to draw the widget if the variable is set: -
void CustomLabel::paintEvent(QPaintEvent * event)
{
if(m_hideOnMinimum)
return;
QLabel::paintEvent(event);
}
Note that by not painting the label, it will be hidden, but the user may still be able to interact with it, so you will need to disable it or overload keyboard / mouse events too.
I implemented QLabel much like Qt's ImageViewer example, except I use QGridLayout for positioning my widgets. I also implemented similar lines for scaling my QLabel using QScrollBar, but QLabel just doesn't scale like it should inside the QScrollArea. I am not sure if it is related to some kind of GridLayout management issue or something else. I have been reading everywhere and trying different things for 3 days now. Below I list the relevant portion of my code.
In my Viewer class constructor:
{
imageLabel1 = new QLabel;
imageLabel1->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
imageLabel1->setScaledContents(true);
scrollArea1 = new QScrollArea;
scrollArea1->setWidget(imageLabel1);
scrollArea1->setWidgetResizable(true);
....
QGridLayout *centralLayout = new QGridLayout;
centralLayout->addWidget(scrollArea1, 0, 0);
...}
and my scaleImage method:
void Viewer::scaleImage1(int factor)
{
Q_ASSERT(imageLabel1->pixmap());
scaleFactor *= (1 + factor);
//imageLabel1->resize(scaleFactor* imageLabel1->pixmap()->size());
imageLabel1->pixmap()->toImage().scaled(scaleFactor* imageLabel1->pixmap()->size(), Qt::KeepAspectRatio, Qt::FastTransformation);
imageLabel1->adjustSize();
adjustScrollBar(scrollArea1->horizontalScrollBar(), factor);
adjustScrollBar(scrollArea1->verticalScrollBar(), factor);
imageLabel1->update();
}
My scaleImage1 function is a public slot, and it receives signal from a scrollbar that goes between 0 and 2 so that, into the scaleFactor, the imageLabel1 is designed to be capable of being zoomed in up to 3 times its original size. But when I run the code, I don’t observe the imageLabel becoming enlarged inside the QScrollArea, which I saw in the imageViewer demo. The imageLabel1 simply retains the original size as it is loaded and does not respond to the valueChange() of scrollbar.
I'd appreciate your advice/tips very much.
I think is because you set QSizePolicy::Minimum to the imageLabel, try with MinimumExpanding or other that better fit your needs.
As seen in the pictures.
I have QWidget inside a QScrollArea.
QWidget act as a render widget for cell image and some vector based contour data.
User can performe zoom in/out and what simply happens is, it changes the QPainters scale and change the size of QWidget size accordinly.
Now I want to perform the zooming in/out on the point under the mouse. (like zooming action in GIMP).
How to calculate the new positions of the scrollbars according to the zoom level ?
Is it better to implement this using transformations without using a scrollarea?
One solution could be to derive a new class from QScrollArea and reimplementing wheelEvent for example so that zooming is performed with the mouse wheel and at the current mouse cursor position.
This method works by adjusting scroll bar positions accordingly to reflect the new zoom level. This means as long as there is no visible scroll bar, zooming does not take place under mouse cursor position. This is the behavior of most image viewer applications.
void wheelEvent(QWheelEvent* e) {
double OldScale = ... // Get old scale factor
double NewScale = ... // Set new scale, use QWheelEvent...
QPointF ScrollbarPos = QPointF(horizontalScrollBar()->value(), verticalScrollBar()->value());
QPointF DeltaToPos = e->posF() / OldScale - widget()->pos() / OldScale;
QPointF Delta = DeltaToPos * NewScale - DeltaToPos * OldScale;
widget()->resize(/* Resize according to new scale factor */);
horizontalScrollBar()->setValue(ScrollbarPos.x() + Delta.x());
verticalScrollBar()->setValue(ScrollbarPos.y() + Delta.y());
}
Will void QScrollArea::ensureVisible(int x, int y, int xmargin = 50, int ymargin = 50) do what you need?
You need to pick up the wheelEvent() on the QWidget, get the event.pos() and pass it into the QscrollArea.ensureVisible(), right after scaling your QWidget.
def wheelEvent(self, event):
self.setFixedSize(newWidth, newHeight)
self.parent().ensureVisible(event.pos())
That should more or less produce what you want.