Solved Paint to QWidget but not main window
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Hi
I am using the scribble example as a template and starting point. What i want to do is create a second window that will copy whatever is drawn on the scribble application.
I have modified the paintEvent to copy the output to a second window.
void ScribbleArea::paintEvent(QPaintEvent *event) //! [13] //! [14] { QPainter painter(this); QRect dirtyRect = event->rect(); painter.drawImage(dirtyRect, image, dirtyRect); QPainter painter2(secondDisplay); // QRect dirtyRect2 = event->rect(); // painter2.drawImage(dirtyRect, image, dirtyRect); } //! [14]
The second blank window shows but i get the following error when i start drawing
QWidget::paintEngine: Should no longer be called QPainter::begin: Paint device returned engine == 0, type: 1 QWidget::paintEngine: Should no longer be called QPainter::begin: Paint device returned engine == 0, type: 1 QWidget::paintEngine: Should no longer be called
My second window is created in the scribblearea.cpp file
ScribbleArea::ScribbleArea(QWidget *parent) : QWidget(parent) { setAttribute(Qt::WA_StaticContents); modified = false; scribbling = false; myPenWidth = 1; myPenColor = Qt::blue; // projector = new ScribbleArea; // create the display for the projector secondDisplay= new QWidget; secondDisplay->setWindowFlags(Qt::FramelessWindowHint); secondDisplay->resize(800,480); secondDisplay->show(); }
and a pointer created in the header
private: void drawLineTo(const QPoint &endPoint); void resizeImage(QImage *image, const QSize &newSize); QWidget *secondDisplay; bool modified; bool scribbling; int myPenWidth; QColor myPenColor; QImage image; QPoint lastPoint;
Steve
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@supersteve
every widget is only allowed to paint to itself in the paintEvent() handler
You you need to change your design.When the data changes and a repaint is needed you should notify
secondDisplay
about the change and set the necessary data and let it repaint itself. -
Thanks for the response, i have attempted what you suggested with not much luck.
I created a function within the ScribbleArea class that returns the QImage image.
I then used then used the existing Help menu button (just for testing) to update the Widget but i still get the same error.
/**************************************************************************** ** ** Copyright (C) 2016 The Qt Company Ltd. ** Contact: https://www.qt.io/licensing/ ** ** This file is part of the examples of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:BSD$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. For further ** information use the contact form at https://www.qt.io/contact-us. ** ** BSD License Usage ** Alternatively, you may use this file under the terms of the BSD license ** as follows: ** ** "Redistribution and use in source and binary forms, with or without ** modification, are permitted provided that the following conditions are ** met: ** * Redistributions of source code must retain the above copyright ** notice, this list of conditions and the following disclaimer. ** * Redistributions in binary form must reproduce the above copyright ** notice, this list of conditions and the following disclaimer in ** the documentation and/or other materials provided with the ** distribution. ** * Neither the name of The Qt Company Ltd nor the names of its ** contributors may be used to endorse or promote products derived ** from this software without specific prior written permission. ** ** ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE." ** ** $QT_END_LICENSE$ ** ****************************************************************************/ #include <QtWidgets> #include "mainwindow.h" #include "scribblearea.h" //! [0] MainWindow::MainWindow() { screen = new ScribbleArea; // create the screen setCentralWidget(screen); createActions(); createMenus(); setWindowTitle(tr("Scribble")); resize(800, 480); secondDisplay = new QWidget; secondDisplay->setWindowFlags(Qt::FramelessWindowHint); secondDisplay->resize(800,480); secondDisplay->show(); } //! [0] //! [1] void MainWindow::closeEvent(QCloseEvent *event) //! [1] //! [2] { if (maybeSave()) { event->accept(); } else { event->ignore(); } } //! [2] //! [3] void MainWindow::open() //! [3] //! [4] { if (maybeSave()) { QString fileName = QFileDialog::getOpenFileName(this, tr("Open File"), QDir::currentPath()); if (!fileName.isEmpty()) screen->openImage(fileName); } } //! [4] //! [5] void MainWindow::save() //! [5] //! [6] { QAction *action = qobject_cast<QAction *>(sender()); QByteArray fileFormat = action->data().toByteArray(); saveFile(fileFormat); } //! [6] //! [7] void MainWindow::penColor() //! [7] //! [8] { QColor newColor = QColorDialog::getColor(screen->penColor()); if (newColor.isValid()) screen->setPenColor(newColor); } //! [8] //! [9] void MainWindow::penWidth() //! [9] //! [10] { bool ok; int newWidth = QInputDialog::getInt(this, tr("Scribble"), tr("Select pen width:"), screen->penWidth(), 1, 50, 1, &ok); if (ok) screen->setPenWidth(newWidth); } //! [10] //! [11] void MainWindow::about() //! [11] //! [12] { QMessageBox::about(this, tr("About Scribble"), tr("<p>The <b>Scribble</b> example shows how to use QMainWindow as the " "base widget for an application, and how to reimplement some of " "QWidget's event handlers to receive the events generated for " "the application's widgets:</p><p> We reimplement the mouse event " "handlers to facilitate drawing, the paint event handler to " "update the application and the resize event handler to optimize " "the application's appearance. In addition we reimplement the " "close event handler to intercept the close events before " "terminating the application.</p><p> The example also demonstrates " "how to use QPainter to draw an image in real time, as well as " "to repaint widgets.</p>")); secondDisplay->update(); } //! [12] void MainWindow::paintEvent(QPaintEvent *event){ QPainter painter(secondDisplay); painter.drawImage(800,480, screen->updateProjector()); } //! [13] void MainWindow::createActions() //! [13] //! [14] { openAct = new QAction(tr("&Open..."), this); openAct->setShortcuts(QKeySequence::Open); connect(openAct, SIGNAL(triggered()), this, SLOT(open())); foreach (QByteArray format, QImageWriter::supportedImageFormats()) { QString text = tr("%1...").arg(QString(format).toUpper()); QAction *action = new QAction(text, this); action->setData(format); connect(action, SIGNAL(triggered()), this, SLOT(save())); saveAsActs.append(action); } printAct = new QAction(tr("&Print..."), this); connect(printAct, SIGNAL(triggered()), screen, SLOT(print())); exitAct = new QAction(tr("E&xit"), this); exitAct->setShortcuts(QKeySequence::Quit); connect(exitAct, SIGNAL(triggered()), this, SLOT(close())); penColorAct = new QAction(tr("&Pen Color..."), this); connect(penColorAct, SIGNAL(triggered()), this, SLOT(penColor())); penWidthAct = new QAction(tr("Pen &Width..."), this); connect(penWidthAct, SIGNAL(triggered()), this, SLOT(penWidth())); clearScreenAct = new QAction(tr("&Clear Screen"), this); clearScreenAct->setShortcut(tr("Ctrl+L")); connect(clearScreenAct, SIGNAL(triggered()), screen, SLOT(clearImage())); aboutAct = new QAction(tr("&About"), this); connect(aboutAct, SIGNAL(triggered()), this, SLOT(about())); aboutQtAct = new QAction(tr("About &Qt"), this); connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt())); } //! [14] //! [15] void MainWindow::createMenus() //! [15] //! [16] { saveAsMenu = new QMenu(tr("&Save As"), this); foreach (QAction *action, saveAsActs) saveAsMenu->addAction(action); fileMenu = new QMenu(tr("&File"), this); fileMenu->addAction(openAct); fileMenu->addMenu(saveAsMenu); fileMenu->addAction(printAct); fileMenu->addSeparator(); fileMenu->addAction(exitAct); optionMenu = new QMenu(tr("&Options"), this); optionMenu->addAction(penColorAct); optionMenu->addAction(penWidthAct); optionMenu->addSeparator(); optionMenu->addAction(clearScreenAct); helpMenu = new QMenu(tr("&Help"), this); helpMenu->addAction(aboutAct); helpMenu->addAction(aboutQtAct); menuBar()->addMenu(fileMenu); menuBar()->addMenu(optionMenu); menuBar()->addMenu(helpMenu); } //! [16] //! [17] bool MainWindow::maybeSave() //! [17] //! [18] { if (screen->isModified()) { QMessageBox::StandardButton ret; ret = QMessageBox::warning(this, tr("Scribble"), tr("The image has been modified.\n" "Do you want to save your changes?"), QMessageBox::Save | QMessageBox::Discard | QMessageBox::Cancel); if (ret == QMessageBox::Save) { return saveFile("png"); } else if (ret == QMessageBox::Cancel) { return false; } } return true; } //! [18] //! [19] bool MainWindow::saveFile(const QByteArray &fileFormat) //! [19] //! [20] { QString initialPath = QDir::currentPath() + "/untitled." + fileFormat; QString fileName = QFileDialog::getSaveFileName(this, tr("Save As"), initialPath, tr("%1 Files (*.%2);;All Files (*)") .arg(QString::fromLatin1(fileFormat.toUpper())) .arg(QString::fromLatin1(fileFormat))); if (fileName.isEmpty()) { return false; } else { return screen->saveImage(fileName, fileFormat.constData()); } } //! [20]
/**************************************************************************** ** ** Copyright (C) 2016 The Qt Company Ltd. ** Contact: https://www.qt.io/licensing/ ** ** This file is part of the examples of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:BSD$ ** Commercial License Usage ** Licensees holding valid commercial Qt licenses may use this file in ** accordance with the commercial license agreement provided with the ** Software or, alternatively, in accordance with the terms contained in ** a written agreement between you and The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. For further ** information use the contact form at https://www.qt.io/contact-us. ** ** BSD License Usage ** Alternatively, you may use this file under the terms of the BSD license ** as follows: ** ** "Redistribution and use in source and binary forms, with or without ** modification, are permitted provided that the following conditions are ** met: ** * Redistributions of source code must retain the above copyright ** notice, this list of conditions and the following disclaimer. ** * Redistributions in binary form must reproduce the above copyright ** notice, this list of conditions and the following disclaimer in ** the documentation and/or other materials provided with the ** distribution. ** * Neither the name of The Qt Company Ltd nor the names of its ** contributors may be used to endorse or promote products derived ** from this software without specific prior written permission. ** ** ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE." ** ** $QT_END_LICENSE$ ** ****************************************************************************/ #include <QtWidgets> #ifndef QT_NO_PRINTER #include <QPrinter> #include <QPrintDialog> #endif #include "scribblearea.h" #include "mainwindow.h" //! [0] ScribbleArea::ScribbleArea(QWidget *parent) : QWidget(parent) { setAttribute(Qt::WA_StaticContents); modified = false; scribbling = false; myPenWidth = 1; myPenColor = Qt::blue; } //! [0] //! [1] bool ScribbleArea::openImage(const QString &fileName) //! [1] //! [2] { QImage loadedImage; if (!loadedImage.load(fileName)) return false; QSize newSize = loadedImage.size().expandedTo(size()); resizeImage(&loadedImage, newSize); image = loadedImage; modified = false; update(); return true; } //! [2] //! [3] bool ScribbleArea::saveImage(const QString &fileName, const char *fileFormat) //! [3] //! [4] { QImage visibleImage = image; resizeImage(&visibleImage, size()); if (visibleImage.save(fileName, fileFormat)) { modified = false; return true; } else { return false; } } //! [4] //! //! QImage ScribbleArea::updateProjector(){ QImage returnImage = image; return returnImage; } //! [5] void ScribbleArea::setPenColor(const QColor &newColor) //! [5] //! [6] { myPenColor = newColor; } //! [6] //! [7] void ScribbleArea::setPenWidth(int newWidth) //! [7] //! [8] { myPenWidth = newWidth; } //! [8] //! [9] void ScribbleArea::clearImage() //! [9] //! [10] { image.fill(qRgb(255, 255, 255)); modified = true; update(); } //! [10] //! [11] void ScribbleArea::mousePressEvent(QMouseEvent *event) //! [11] //! [12] { if (event->button() == Qt::LeftButton) { lastPoint = event->pos(); scribbling = true; } } void ScribbleArea::mouseMoveEvent(QMouseEvent *event) { if ((event->buttons() & Qt::LeftButton) && scribbling) drawLineTo(event->pos()); } void ScribbleArea::mouseReleaseEvent(QMouseEvent *event) { if (event->button() == Qt::LeftButton && scribbling) { drawLineTo(event->pos()); scribbling = false; } } //! [12] //! [13] void ScribbleArea::paintEvent(QPaintEvent *event) //! [13] //! [14] { QPainter painter(this); QRect dirtyRect = event->rect(); painter.drawImage(dirtyRect, image, dirtyRect); // QPainter painter2(projector); // QRect dirtyRect2 = event->rect(); // painter2.drawImage(dirtyRect, image, dirtyRect); } //! [14] //! [15] void ScribbleArea::resizeEvent(QResizeEvent *event) //! [15] //! [16] { if (width() > image.width() || height() > image.height()) { int newWidth = qMax(width() + 128, image.width()); int newHeight = qMax(height() + 128, image.height()); resizeImage(&image, QSize(newWidth, newHeight)); update(); } QWidget::resizeEvent(event); } //! [16] //! [17] void ScribbleArea::drawLineTo(const QPoint &endPoint) //! [17] //! [18] { QPainter painter(&image); painter.setPen(QPen(myPenColor, myPenWidth, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin)); painter.drawLine(lastPoint, endPoint); modified = true; int rad = (myPenWidth / 2) + 2; update(QRect(lastPoint, endPoint).normalized() .adjusted(-rad, -rad, +rad, +rad)); lastPoint = endPoint; } //! [18] //! [19] void ScribbleArea::resizeImage(QImage *image, const QSize &newSize) //! [19] //! [20] { if (image->size() == newSize) return; QImage newImage(newSize, QImage::Format_RGB32); newImage.fill(qRgb(255, 255, 255)); QPainter painter(&newImage); painter.drawImage(QPoint(0, 0), *image); *image = newImage; } //! [20] //! [21] void ScribbleArea::print() { #if !defined(QT_NO_PRINTER) && !defined(QT_NO_PRINTDIALOG) QPrinter printer(QPrinter::HighResolution); QPrintDialog printDialog(&printer, this); //! [21] //! [22] if (printDialog.exec() == QDialog::Accepted) { QPainter painter(&printer); QRect rect = painter.viewport(); QSize size = image.size(); size.scale(rect.size(), Qt::KeepAspectRatio); painter.setViewport(rect.x(), rect.y(), size.width(), size.height()); painter.setWindow(image.rect()); painter.drawImage(0, 0, image); } #endif // QT_NO_PRINTER } //! [22]
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@supersteve
because you keep doing the same mistake!void MainWindow::paintEvent(QPaintEvent *event){ QPainter painter(secondDisplay); painter.drawImage(800,480, screen->updateProjector()); }
As i said: A widget is only allowed to paint to itself in it's paintEvent() handler.
You need a custom class and reimplement the paintEvnet() handler and do the painting there. Or you simply use a QLabel and set a pixmap on it. -
Thanks for your help, using your advice i used QLabel and converted the first screen to pixmap and now i can get the image on my second screen.