For Widgets I can call 'raise' which keeps the widget on top of anything else, but this doesn't seem to work for any QPixmap's that are rendered.
How can I ensure that a QPixmap remains on top of anything else?
In my paintEvent function:
QPainter objPainter(this);
if ( strImage.isEmpty() != true ) {
qint16 int16NudgeImageX = mpobjNode->int16GetAttr(clsXML::mscszAttrNudgeImageX)
,int16NudgeImageY = mpobjNode->int16GetAttr(clsXML::mscszAttrNudeImageY);
QPixmap pmImage(":/" + strImage);
QSize szImage = pmImage.size();
QPoint ptImage(rctGeom.center().x() - (szImage.width() / 2) + int16NudgeImageX
,rctGeom.center().y() - (szImage.height() / 2) + int16NudgeImageY);
QRect rctImage(ptImage, szImage);
objPainter.drawPixmap(rctImage, pmImage);
}
A QPixmap is not a widget (no parent, nor layout).
The QPixmap class is an off-screen image representation that can be used as a paint device.
Use a QLabel for use with a parent (and layout)
QLabel* label = new QLabel(parent);
label->setPixmap(pixmap);
If you want to make sure that your QPixmap is painted on top of everything else inside your widget, simply paint it last.
Keep in mind that other widgets may be painted above your widget.
Related
QT Paintevent is not painting the required image, instead paints black screen. this paintevent is called for each time interval of 2 seconds using SLOT(update).
I have tried with triggering PaintImage method that is Implemented to draw QImage supplied, but didnt work either.
void Client::paintEvent(QPaintEvent *event)
{
//qWarning() << image.isNull() << image.width()<< image.height();
QPainter painter(&image);
painter.end();
QPixmap pixMap;//(image);
//painter.drawImage(1280, 639, image);
bool b = pixMap.convertFromImage(image);
QLabel w;
w.setPixmap(pixMap);
w.show();
}
Expected actual Image to be displayed but ending up blank screen.
Add QLabel as a member of class (Client) ... lets give it name m_my_label.
Then in paintEvent say just m_my_label.setPixmap(pixMap) and m_my_label.show().
Problem is that QLabel is local variable and will cease to exist when you go out of paintEvent function.
I'm trying to get a custom scrolling widget in QT, and I'm getting redraw errors on scroll. Alt-tab or other redrawing events redraw correctly.
I'm basing it on the example at http://doc.qt.io/qt-5/qtwidgets-widgets-charactermap-example.html
repeatingwidget.cpp (excerpt):
QSize RepeatingWidget::sizeHint() const {
return QSize(500, itemHeight * displayItems.size() + 1);
}
void RepeatingWidget::paintEvent(QPaintEvent *event) {
QPainter painter(this);
painter.fillRect(event->rect(), QBrush(Qt::white));
painter.setFont(displayFont);
QRect itemRect = event->rect();
int top = itemRect.top();
QFontMetrics fontMetrics(*displayFont);
for (auto item : displayItems) {
painter.setPen(QPen(Qt::gray));
painter.drawRect(itemRect.left(), top, itemRect.right(), itemHeight);
painter.setPen(QPen(Qt::black));
painter.drawText(8, 4 + top + fontMetrics.ascent(), item.name);
top += itemHeight;
}
}
mainwindow.cpp (excerpt):
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
QMenu *filemenu = menuBar()->addMenu(tr("File"));
filemenu->addAction(tr("Quit"), this, &QWidget::close);
auto *centralWidget = new QWidget;
scrollArea = new QScrollArea;
repeatingArea = new RepeatingWidget();
scrollArea->setWidget(repeatingArea);
auto *centralLayout = new QVBoxLayout;
centralLayout->addWidget(scrollArea, 1);
centralWidget->setLayout(centralLayout);
setCentralWidget(centralWidget);
setWindowTitle(tr("Widget Test"));
}
This seems to match the example, but I'm getting redraw errors that don't happen in charmap.
I've tried setGeometry, setWidgetResizable, and different size policies, but I'm still getting these redraw errors.
After scrolling:
I don't know what I'm doing wrong because it's largely identical in important ways to the example code from the charmap.
This is the full code: https://gist.github.com/jonasbuckner/2acc1a960e457946ce4756199de3fb57
QPaintEvent is a method that allows you to make an intelligent painting, that is, to paint where necessary, thus saving resources, for example it gives us the information of the rectangle that must be painted through event->rect(), with this we can calculate the items that have to be painted since others will be hidden and therefore it is not necessary to paint them:
void RepeatingWidget::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.fillRect(event->rect(), QBrush(Qt::white));
painter.setFont(displayFont);
QFontMetrics fontMetrics(displayFont);
int i = std::max(event->rect().top()/itemHeight, 0);
int j = std::min(event->rect().bottom()/itemHeight+1, displayItems.size());
QRect itemRect(0, i*itemHeight, width(), itemHeight);
for(; i < j; i++){
painter.setPen(QPen(Qt::gray));
painter.drawRect(itemRect);
painter.setPen(QPen(Qt::black));
painter.drawText(8, 4 + itemRect.top() + fontMetrics.ascent(), displayItems[i].name);
itemRect.translate(0, itemHeight);
}
}
Your original code didn't work because you were drawing all of the items, but using the event->rect, which may only be part of the RepeatingWidget.
Sometimes it is not easy to calculate which items are in the event->rect as #eyllanesc shows. In these cases, just use clientRect instead - Qt will clip the drawing for you.
I have an issue with pixmaps created for drag events. For drag events of my derived QGraphicsRectItem I create a semi-transparent pixmap from that item.
In the debug build everything looks fine.
But in the release build the drag pixmap has some periodic and random artefacts
here is the code:
QPixmap MyGraphicsRectItem::toPixmap() const
{
QRect r = boundingRect().toRect();
QPixmap pixmap(r.width(), r.height());
QColor dragColor(color);
dragColor.setAlphaF(0.5);
QPainter painter;
painter.begin(&pixmap);
painter.fillRect(pixmap.rect(), dragColor);
painter.setPen(Qt::white);
QFont font("SegoeUI");
font.setBold(true);
painter.setFont(font);
painter.drawText(pixmap.rect(), QString(" ") + textItem->toPlainText());
if (pixItem != nullptr) {
painter.setOpacity(0.5);
painter.drawPixmap(pixItem->pos(), pixItem->pixmap());
}
painter.end();
return pixmap;
}
Could that be a kind of memory issue?
The QPixmap is initialized with uninitialized data. In Debug, this is often set to a fixed pattern, but in Release it is garbage.
You should fill the pixmap with transparent color before using it.
QPixmap::QPixmap(int width, int height)
Constructs a pixmap with the given width and height. If either width or height is zero, a null pixmap is constructed.
Warning: This will create a QPixmap with uninitialized data. Call fill() to fill the pixmap with an appropriate color before drawing onto it with QPainter.
(From Qt Docs)
I have been messing with this problem for hours, and decided it's time to ask SO :)
I have a Qt program that rotates an image and then updates the size of the widget. Here is the code I'm using to do this currently.
void VideoSubWindow::showFrame(const QImage& frame)
{
QPixmap pixmap = QPixmap::fromImage(frame);
ui->videoFrameLabel->setPixmap(pixmap);
resizeWidgets(pixmap.size());
}
void VideoSubWindow::resizeWidgets(const QSize &size)
{
if(frameSize != size)
{
frameSize = size;
ui->videoFrameLabel->setFixedSize(size);
ui->scrollArea->setMinimumSize(size.width() + 2, size.height() + 2);
}
}
The widgets are structured as follows:
VideoSubWindow (QMainWindow)
-> centralWidget (QWidget) (Vertical layout is set on this)
-> scrollArea (QScrollArea)
-> videoFrameLabel (QLabel)
-> statusBar (QStatusBar)
-> menuBar (QMenuBar)
When the code above is executed, like rotating the image 90 degrees, the image will be rotated, but the window doesn't resize to fit the new pixmap size. I have tried to call adjustSize() and updateGeometry() on SubWindow and centralWidget, but those seem to have zero effect. But, if I manually resize the window with my mouse, the window snaps to the minimum size that was set for the scrollArea, so that seems to be taking effect.
Does anyone have experience with this? Thanks!
Try with the resize(...) function : Qt documentation
adjustSize() used sizeHint() function, so calling adjustSize() on SubWindow and centralWidget cannot have any effet
I'm working on a basic image viewer/tagger that will need a thumbnail view to select an image. So far, I've used a QDockWidget enclosing a QScrollArea with a QHBoxLayout to contain a series of QLabels, each of which has its QPixMap set.
This seems very inelegant, and it only gets uglier to consider how I might implement auto-scaling of the thumbnails when the QDockWidget is resized. It's further complicated by the additional need to resize the thumbnails when the scroll bar appears and disappears.
There must be a better way to do this?
I've ran into a similar problem when trying to animate resizing a qlabel with a qpixmap. The method I found that worked best was to use a QWidget instead and re-implement the paintEvent function. Then your QWidget image will automatically be scaled if it's resized. Here is an example:
In my case I had the private variables in a private object called private_:
bool image_set_;
QImage image_;
QBrush paintbrush_;
void MyClass::paintEvent( QPaintEvent* event )
{
// if the QWidget has an image set, then we use our custom painting.
if( this->private_->image_set_ )
{
//I've made it so that my QWidget has a 1px white border
this->private_->paintbrush_.setTextureImage( this->private_->image_.scaled(QSize( this->width() - 2, this->height() - 2 ) ) );
QPainter painter( this );
QRect temp_rect = QRect( 1, 1, this->width()-2, this->height() - 2 );
painter.fillRect( this->rect(), Qt::white );
painter.fillRect( temp_rect, this->private_->paintbrush_ );
}
else
{
QWidget::paintEvent( event );
}
}