I have referenced this code to draw points on my widget.
OverLay::OverLay(std::vector<int> &points, QWidget *parent) :
QWidget(parent),
m_points(points)
{
setAttribute(Qt::WA_NoSystemBackground, true);
setAttribute(Qt::WA_TransparentForMouseEvents, true);
}
void OverLay::paintEvent(QPaintEvent *)
{
QPainter painter(this);
painter.setPen(QPen(Qt::red,2));
//painter.eraseRect( this->rect() );
int y_pos = height()/2;
for(int i=0; i<m_points.size();i++){
int x_pos = m_points[i];
QPointF p1 = QPointF(x_pos,y_pos);
painter.drawPoint(p1);
}
}
Here am creating new Overlay Widget and drawing
void Dialog::draw_points(std::vector<int> points)
{
OverLay *m_overlay = new OverLay(points,ui->view->parentWidget());
m_overlay->setGeometry(ui->view->geometry());
m_overlay->show();
}
So, everytime, Whenever I call draw_points functions, old drawing will be there. I want to clear the canvas everytime before drawing again.
painter.eraseRect( this->rect() ); will clear points. But, it will also clear underlying view.
Well, I always do it always specific:
painter.setBrush(Qt::NoBrush);
painter.setPen(Qt::NoPen);
painter.drawRect(rect());
I did not know it was so simple ..
Simply deleting instance of m_overlay worked.
if(m_overlay!=NULL){
delete m_overlay;
}
Related
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'm trying to draw on QLabel in Qt like this:
paintscene.h:
class PaintScene : public QWidget
{
Q_OBJECT
public:
PaintScene(QWidget* parent = NULL);
QVector<QLabel*> _layers;
QColor _color;
int _width;
void mousePressEvent(QMouseEvent* event);
private slots:
void updateWidth();
};
paintscene.cpp:
PaintScene::PaintScene(QWidget* parent) : QWidget(parent)
{
_width = 10;
_color = Qt::red;
QLabel* inital = new QLabel(this);
inital->setStyleSheet("QLabel { background-color : white; }");
_layers.push_back(inital);
QGridLayout* layout = new QGridLayout();
layout->addWidget(inital, 1, 1, 1, 1);
this->setLayout(layout);
}
void PaintScene::mousePressEvent(QMouseEvent *event)
{
QImage tmp = _layers.back()->pixmap()->toImage();
QPainter painter(&tmp);
QPen paintpen(_color);
paintpen.setWidth(_width);
painter.setPen(paintpen);
painter.drawPoint(event->x(), event->y());
_layers.back()->setPixmap(QPixmap::fromImage(tmp));
}
The list is needed because I want to implement the work with layers (QLabel - a separate layer).
However, I get an error, the program terminates. The error occurs on the line QImage tmp = _layers.back()->pixmap()->toImage();.
What makes this happen? How can this be fixed? Maybe for a layer to use something different, not QLabel?
#Jeremy Friesner is right about the reason for the error, not having a QPixmap this will be null, in my answer I will show a possible solution
void PaintScene::mousePressEvent(QMouseEvent *event)
{
QLabel *label = _layers.back();
const QPixmap *pix= label->pixmap();
QPixmap pixmap;
if(pix)
pixmap = *pix;
else{
pixmap = QPixmap(label->size());
pixmap.fill(Qt::transparent);
}
QPainter painter(&pixmap);
QPen paintpen(_color);
paintpen.setWidth(_width);
painter.setPen(paintpen);
painter.drawPoint(event->pos());
painter.end();
label->setPixmap(pixmap);
}
From the Qt docs for QLabel::pixmap():
This property holds the label's pixmap
If no pixmap has been set this will return 0.
... so when you do this:
QImage tmp = _layers.back()->pixmap()->toImage();
pixmap() is returning NULL (because the QLabel has never had any QPixmap set on it yet), and then you try to dereference that NULL pointer to call toImage() on it, hence the crash.
To avoid crashing, don't try to create a QImage from a NULL QPixmap pointer.
I suspect you wanted to be calling grab() instead of pixmap() -- grab() will create a QPixmap for you that contains the visual appearance of the QLabel. However, an even better approach would be to avoid messing about with QPixmaps at all; instead, make your own subclass of the QLabel class, and override its paintEvent(QPaintEvent *) method to first call up to QLabel::paintEvent(e) and then use a QPainter to draw the additional point afterwards. That will be easier to implement and also more efficient at runtime.
I've been struggling with this problem for the past couple of days. I want to be able to grow and shrink whatever the assigned Pixmap is in a QLabel as the user resizes the window. The issue is preserving the aspect ratio and image quality. Another user on here suggested that I reimplement the paint event for the label - but I'm still very lost. I'm not even sure if I have overridden the paintEvent correctly. I would kill for a bit of sample code here.
This is where I'm at:
void MyLabel::paintEvent(QPaintEvent * event)
{
//if this widget is assigned a pixmap
//paint that pixmap at the size of the parent, aspect ratio preserved
//otherwise, nothing
}
Here is a possible implementation of a QLabel subclass that scales its pixmap content while keeping its aspect ratio. It is implemented based on the way QLabel::paintEvent is implemented.
If you are using it in a layout you can also set its size policy to QSizePolicy::Expanding, so that additional space in the layout is taken up by the QLabel for a larger display of the pixmap content.
#include <QApplication>
#include <QtWidgets>
class PixmapLabel : public QLabel{
public:
explicit PixmapLabel(QWidget* parent=nullptr):QLabel(parent){
//By default, this class scales the pixmap according to the label's size
setScaledContents(true);
}
~PixmapLabel(){}
protected:
void paintEvent(QPaintEvent* event);
private:
//QImage to cache the pixmap()
//to avoid constructing a new QImage on every scale operation
QImage cachedImage;
//used to cache the last scaled pixmap
//to avoid calling scale again when the size is still at the same
QPixmap scaledPixmap;
//key for the currently cached QImage and QPixmap
//used to make sure the label was not set to another QPixmap
qint64 cacheKey{0};
};
//based on the implementation of QLabel::paintEvent
void PixmapLabel::paintEvent(QPaintEvent *event){
//if this is assigned to a pixmap
if(pixmap() && !pixmap()->isNull()){
QStyle* style= PixmapLabel::style();
QPainter painter(this);
drawFrame(&painter);
QRect cr = contentsRect();
cr.adjust(margin(), margin(), -margin(), -margin());
int align= QStyle::visualAlignment(layoutDirection(), alignment());
QPixmap pix;
if(hasScaledContents()){ //if scaling is enabled
QSize scaledSize= cr.size() * devicePixelRatioF();
//if scaledPixmap is invalid
if(scaledPixmap.isNull() || scaledPixmap.size()!=scaledSize
|| pixmap()->cacheKey()!=cacheKey){
//if cachedImage is also invalid
if(pixmap()->cacheKey() != cacheKey){
//reconstruct cachedImage
cachedImage= pixmap()->toImage();
}
QImage scaledImage= cachedImage.scaled(
scaledSize, Qt::KeepAspectRatio, Qt::SmoothTransformation);
scaledPixmap= QPixmap::fromImage(scaledImage);
scaledPixmap.setDevicePixelRatio(devicePixelRatioF());
}
pix= scaledPixmap;
} else { // no scaling, Just use pixmap()
pix= *pixmap();
}
QStyleOption opt;
opt.initFrom(this);
if(!isEnabled())
pix= style->generatedIconPixmap(QIcon::Disabled, pix, &opt);
style->drawItemPixmap(&painter, cr, align, pix);
} else { //otherwise (if the label is not assigned to a pixmap)
//call base paintEvent
QLabel::paintEvent(event);
}
}
//DEMO program
QPixmap generatePixmap(QSize size) {
QPixmap pixmap(size);
pixmap.fill(Qt::white);
QPainter p(&pixmap);
p.setRenderHint(QPainter::Antialiasing);
p.setPen(QPen(Qt::black, 10));
p.drawEllipse(pixmap.rect());
p.setPen(QPen(Qt::red, 2));
p.drawLine(pixmap.rect().topLeft(), pixmap.rect().bottomRight());
p.drawLine(pixmap.rect().topRight(), pixmap.rect().bottomLeft());
return pixmap;
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QPixmap pixmap= generatePixmap(QSize(1280, 960));
PixmapLabel label;
label.setPixmap(pixmap);
label.setAlignment(Qt::AlignCenter);
label.setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
label.setMinimumSize(320, 240);
label.show();
return a.exec();
}
I think this is better than the solution in this answer, as the QLabel here takes care of resizing its pixmap. So, there is no need to resize it manually every time the parent widget is resized and everytime a new pixmap is set on it.
First of all I wanted to say thanks to Mike.
Additionally I would like to add to his answer from 21.10.2016 - however I am not able to add a comment as of yet - thus here is a full fledged answer. [If anyone is able to move this to the comment section, feel free.]
I also added an overwrite of the other constructor of QLabel and the window flags [with default arguments as in QLabel] and added the Q_OBJECT macro, as to be compatible to the Qt framework:
Header:
class PixmapLabel : public QLabel
{
Q_OBJECT
public:
explicit PixmapLabel(QWidget* parent=nullptr, Qt::WindowFlags f = Qt::WindowFlags());
explicit PixmapLabel(const QString &text, QWidget *parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags());
...
}
Module:
PixmapLabel::PixmapLabel(QString const & text, QWidget * parent, Qt::WindowFlags f) :
QLabel(text, parent, f)
{
//By default, this class scales the pixmap according to the label's size
setScaledContents(true);
}
I want to show a pixmap on Qt and make able to zoom, I'm using a QWidget inside a QScrollArea, but the ScrollBars of the area are not working, when I zoom on the image, the image gets bigger, but there is no scrollbars so i can move, let me show you some code :
Here is how I'm declaring the Widgets :
_scroll = new QScrollArea(_frame);
_image_widget = new QImageWidget(_scroll);
_scroll->setBackgroundRole(QPalette::Dark);
_scroll->setWidget(_image_widget);
_scroll->setWidgetResizable(true);
_frame is the area where i should show the hole thing, _image_widget is an object of QImageWidget which is inheriting from QWidget
if I dont use this : _scroll->setWidgetResizable(true); the image is just too small
And here is how I deal with the Zoom :
void QImageWidget::paintEvent(QPaintEvent *ev) {
QPainter p(this);
if(pixmap() != NULL){
int w = pixmap()->width();
int h = pixmap()->height();
QPixmap map = pixmap()->scaled(w*zoom,h*zoom,Qt::KeepAspectRatio);
p.drawPixmap(0, 0, map );
}
}
void QImageWidget::wheelEvent ( QWheelEvent * e )
{
int x = e->pos( ).x();
int y = e->pos( ).y();
if (e->delta() > 0)
zoom *= 2;
else
if(zoom > 1)
zoom /= 2;
}
SO the problem is as I said, the image keeps getting bigger when i'm zooming until it takes the hole area of the QScrollArea and then when I keep zooming, the zoom is working but there is no ScrollBars so i can see the other part of the Image.
Tell me if i'm not understandable !
thanks !
I found the answer to my question, all i had to do is add this resize(sizeHint()*zoom); before drawing the pixmap :
void QImageWidget::paintEvent(QPaintEvent *ev) {
QPainter p(this);
if(pixmap() != NULL){
int w = pixmap()->width();
int h = pixmap()->height();
QPixmap map = pixmap()->scaled(w*zoom,h*zoom,Qt::KeepAspectRatio);
resize(sizeHint()*zoom);
p.drawPixmap(0, 0, map );
}
}
the pixels were updated but not the size of the widget !
I'm facing an annoying issue using Qt QGraphicsView framework.
I write a basic image viewer to display large B&W tiff images.
Images are displayed using a QGraphicsPixmapItem and added to the scene.
I also need to draw a colored rectangle around the viewport.
void ImageView::drawForeground( QPainter * painter, const QRectF & rect )
{
if( m_image ) {
qDebug() << "drawForeground(), rect = " << rect;
QBrush br(m_image->isValidated() ? Qt::green : Qt::red);
qreal w = 40. / m_scaleFactor;
QPen pen(br, w);
painter->save();
painter->setOpacity(0.5);
painter->setPen(pen);
painter->drawRect(rect);
painter->restore();
}
}
It works fine, at first glance.
But when I scroll the viewport content, things are getting ugly.
drawForeground() method is effectively called but it seems the content of the viewport is not erased before. So the drawing becomes horrible on screen.
Is there a better way to achieve it?
EDIT
As leems mentioned it, Qt internals don't alow me to achieve it with drawForeground().
I found a workaround by using a QGraphicsRectItem which gets resized in the viewportEvent().
Loos like:
bool ImageView::viewportEvent(QEvent *ev)
{
QRect rect = viewport()->rect();
if( m_image ) {
QPolygonF r = mapToScene(rect);
QBrush br2(m_image->isValidated() ? Qt::green : Qt::red);
qreal w2 = 40. / m_scaleFactor;
QPen pen2(br2, w2);
m_rect->setPen(pen2);
m_rect->setOpacity(0.5);
m_rect->setRect(r.boundingRect());
}
return QGraphicsView::viewportEvent(ev);
}
The code is not finalized but will basically looks like that.
It works fine, though it blinks a little bit when scrolling too fast...