My environment is the following:
Qt 5.4, build from source with -platform win32-msvc2013 -opengl desktop -no-icu -skip webkit
Visual Studio 2013
Windows 7 x64
Consider the following setup (A QScrollArea containing a centered widget with fixed size):
QScrollArea scrollArea;
scrollArea.setAlignment(Qt::AlignCenter);
scrollArea.setWidgetResizable(false);
QWidget scrollAreaWidgetContents;
scrollArea.setWidget(scrollAreaWidgetContents);
Now, I want to resize that widget within my program like the following:
int w = 200, h = 200;
scrollAreaWidgetContents.setGeometry(0, 0, w, h);
And here comes the strange behavior:
If w and h are equal to the current width and height (i.e. nothing changes), the widget jumps to the upper left corner.
If w and h are different from the current width and height, the widgets stays at its centered position and changes its size correctly.
I have written a little demo application that demonstrates the issue. If you click the pushButton_Stay button, the widgets jumps to the upper left corner.
#include <QtWidgets/QApplication>
#include <QPushButton>
#include <QVBoxLayout>
#include <QScrollArea>
QScrollArea *scrollArea;
QWidget *scrollAreaWidgetContents;
QPushButton *pushButton_Up;
QPushButton *pushButton_Down;
QPushButton *pushButton_Stay;
QVBoxLayout *layout;
int w = 200, h = 200;
void sizeUp() {
w += 10;
h += 10;
scrollAreaWidgetContents->setGeometry(0, 0, w, h);
}
void sizeDown() {
w -= 10;
h -= 10;
scrollAreaWidgetContents->setGeometry(0, 0, w, h);
}
void sizeStay() {
scrollAreaWidgetContents->setGeometry(0, 0, w, h);
}
int main(int argv, char **args)
{
QApplication app(argv, args);
// Scroll area
scrollArea = new QScrollArea;
scrollArea->setWidgetResizable(false);
scrollArea->setAlignment(Qt::AlignCenter);
scrollAreaWidgetContents = new QWidget();
scrollAreaWidgetContents->setGeometry(QRect(0, 0, w, h));
scrollAreaWidgetContents->setAutoFillBackground(true);
QPalette Pal(scrollAreaWidgetContents->palette());
Pal.setColor(QPalette::Background, Qt::black);
scrollAreaWidgetContents->setPalette(Pal);
scrollArea->setWidget(scrollAreaWidgetContents);
// Buttons
pushButton_Up = new QPushButton(scrollAreaWidgetContents);
pushButton_Up->setGeometry(QRect(85, 50, 31, 23));
pushButton_Up->setText("+");
pushButton_Down = new QPushButton(scrollAreaWidgetContents);
pushButton_Down->setGeometry(QRect(85, 110, 31, 23));
pushButton_Down->setText("-");
pushButton_Stay = new QPushButton(scrollAreaWidgetContents);
pushButton_Stay->setGeometry(QRect(85, 80, 31, 23));
pushButton_Stay->setText("0");
QObject::connect(pushButton_Up, &QPushButton::clicked, sizeUp);
QObject::connect(pushButton_Stay, &QPushButton::clicked, sizeStay);
QObject::connect(pushButton_Down, &QPushButton::clicked, sizeDown);
// Central layout
layout = new QVBoxLayout;
layout->addWidget(scrollArea);
// Main window
QWidget window;
window.setGeometry(200, 200, 400, 400);
window.setLayout(layout);
window.show();
return app.exec();
}
Clicking the pushButton_Up button:
Clicking the pushButton_Stay button:
Questions:
What's going wrong here?
Is it a bug? An if and yes, can anyone confirm it?
If it's not a bug, how can I make it that the widget always stays centered?
What's going wrong here?
Is it a bug? An if and yes, can anyone confirm it?
It seems the second call of setGeometry with the same arguments use different origin, and the coordinates (0, 0) make the widget move to top-left corner. You can use other coordinates such as setGeometry(100, 50, w, h) to see the difference.
Here is the source code of QWidget::setGeometry:
if (testAttribute(Qt::WA_WState_Created)) {
d->setGeometry_sys(r.x(), r.y(), r.width(), r.height(), true);
d->setDirtyOpaqueRegion();
} else {
data->crect.setTopLeft(r.topLeft());
// ^^^^^^^^^ Could be the reason why (0, 0) move to top-left
data->crect.setSize(r.size().boundedTo(maximumSize()).expandedTo(minimumSize()));
setAttribute(Qt::WA_PendingMoveEvent);
setAttribute(Qt::WA_PendingResizeEvent);
}
Personally I think it's a bug, but more evidences need to be provided until we can confirm it.
If it's not a bug, how can I make it that the widget always stays
centered?
Actually you don't have to call setGeometry if you just want to resize the widget. Use resize instead:
void sizeStay() {
scrollAreaWidgetContents->resize(w, h);
}
It solves the problem in your case.
Related
I would like to programmatically scroll a scene to the left / right, but I am not sure how to do that properly. Note that I do not want to have (visible) scroll bars.
I use a standard QGraphicsView + QGraphicsScene + QGraphicsItem setup. I have downsized it to the minimum, with one single QGraphicsItem (a QGraphicsRectItem) in the scene.
I have managed to achieve programmatic scrolling by setting my view like this:
// view setup
view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
and then, in another part of the code:
// programmatic scrolling
QScrollBar* const sb = view->horizontalScrollBar();
sb->setRange(0, 1000); // some values for experimenting
sb->setValue(sb->value() + 100 or -100); // some increment for experimenting
This works, but... scrolling through invisible scrollbars doesn't feel right.
I tried this more straightforward approach:
// programmatic scrolling - doesn't quite work
view->viewport()->scroll(100 or -100, 0); // some increment for experimenting
This code does scroll, but when the rectangle goes off the left edge of the view, and I reverse the scrolling direction (increment changed from 100 to -100 in the call to scroll()), the uncovered part of the rectangle is not repainted. The reason is that QGraphicsRectItem::paint() is not called in that case (it is called when using the scrollbar method).
So, is there a way to get viewport()->scroll() work? Or some other simple way to achieve programmatic scrolling? Or is the artificial scrollbar method just the way to go?
Moving the view assumes that it's smaller than its scene. If they're the same size, it won't move.
QGraphicsView can be set to centerOn any position in scene coordinates. Use a timer to call centerOn to move the view one frame at a time.
Here's a working example: -
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QTimer>
class MyView : public QGraphicsView
{
private:
public:
MyView(QGraphicsScene* pScene)
: QGraphicsView(pScene, NULL)
{}
void AnimateBy(int x)
{
float updateFrequency = (1000/30.0); // ~30 frames per second
QPointF currScenePos = sceneRect().center();
int curX = currScenePos.x();
int endPos = curX + x;
int distanceToAnimate = (endPos - curX);
// speed = dist / time
float updatePosInterval = (float)distanceToAnimate / updateFrequency;
printf("updatePosInterval: %f \n", updatePosInterval);
static float newXPos = sceneRect().center().x();
QTimer* pTimer = new QTimer;
QObject::connect(pTimer, &QTimer::timeout, [=](){
newXPos += updatePosInterval;
centerOn(newXPos, sceneRect().center().y());
// check for end position or time, then....
if(newXPos >= endPos)
{
pTimer->stop();
pTimer->deleteLater();
}
});
pTimer->start(updateFrequency);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene scene(0, 0, 10000, 20000);
MyView* view = new MyView(&scene);
QGraphicsRectItem* pRect = new QGraphicsRectItem(0, 0, 100, 100);
pRect->setPos(scene.width()/2, scene.height()/2);
scene.addItem(pRect);
// timer to wait for the window to appear, before starting to move
QTimer* pTimer = new QTimer;
pTimer->setSingleShot(true);
QObject::connect(pTimer, &QTimer::timeout,[=](){
view->centerOn(pRect); // centre on the rectangle
view->AnimateBy(100);
pTimer->deleteLater();
});
pTimer->start(1000);
view->show();
return a.exec();
}
So, we create the animation by moving the view frame-by-frame using the call to centerOn.
For simplicity, the code just deals with moving in one axis. To move in 2 axis, use 2D vector maths to calculate the interval position.
Try to change the view transformation with the QGraphicsView::translate() or QGraphicsView::setTransform().
But keep in mind that you can't move the viewport "outside" the scene, so make sure that your scene rectangle is large enough.
If I got your question correctly, there is a dojo classes library with such class as PanWebView that allow QWebView to scroll smoothly with mouse without any scrollbars. Take a look at sources. It supports panning and can be suitable for mobile apps, but maybe it'll help you too.
PanWebView class looks like this
#include <QWebView>
#include <QWebFrame>
#include <QMouseEvent>
#include <QApplication>
class PanWebView : public QWebView
{
Q_OBJECT
private:
bool pressed;
bool scrolling;
QPoint position;
QPoint offset;
QList<QEvent*> ignored;
public:
PanWebView(QWidget *parent = 0): QWebView(parent), pressed(false), scrolling(false) {
QWebFrame *frame = page()->mainFrame();
frame->setScrollBarPolicy(Qt::Vertical, Qt::ScrollBarAlwaysOff);
frame->setScrollBarPolicy(Qt::Horizontal, Qt::ScrollBarAlwaysOff);
}
protected:
void mousePressEvent(QMouseEvent *mouseEvent) {
if (ignored.removeAll(mouseEvent))
return QWebView::mousePressEvent(mouseEvent);
if (!pressed && !scrolling && mouseEvent->modifiers() == Qt::NoModifier)
if (mouseEvent->buttons() == Qt::LeftButton) {
pressed = true;
scrolling = false;
position = mouseEvent->pos();
QWebFrame *frame = page()->mainFrame();
int x = frame->evaluateJavaScript("window.scrollX").toInt();
int y = frame->evaluateJavaScript("window.scrollY").toInt();
offset = QPoint(x, y);
QApplication::setOverrideCursor(Qt::OpenHandCursor);
return;
}
return QWebView::mousePressEvent(mouseEvent);
}
void mouseReleaseEvent(QMouseEvent *mouseEvent) {
if (ignored.removeAll(mouseEvent))
return QWebView::mouseReleaseEvent(mouseEvent);
if (scrolling) {
pressed = false;
scrolling = false;
QApplication::restoreOverrideCursor();
return;
}
if (pressed) {
pressed = false;
scrolling = false;
QMouseEvent *event1 = new QMouseEvent(QEvent::MouseButtonPress,
position, Qt::LeftButton,
Qt::LeftButton, Qt::NoModifier);
QMouseEvent *event2 = new QMouseEvent(*mouseEvent);
ignored << event1;
ignored << event2;
QApplication::postEvent(this, event1);
QApplication::postEvent(this, event2);
QApplication::restoreOverrideCursor();
return;
}
return QWebView::mouseReleaseEvent(mouseEvent);
}
void mouseMoveEvent(QMouseEvent *mouseEvent) {
if (scrolling) {
QPoint delta = mouseEvent->pos() - position;
QPoint p = offset - delta;
QWebFrame *frame = page()->mainFrame();
frame- >evaluateJavaScript(QString("window.scrollTo(%1,%2);").arg(p.x()).arg(p.y()));
return;
}
if (pressed) {
pressed = false;
scrolling = true;
return;
}
return QWebView::mouseMoveEvent(mouseEvent);
}
};
And usage:
PanWebView web;
web.setUrl(QUrl("http://news.google.com"));
web.setWindowTitle("Web View - use mouse to drag and pan around");
web.show();
Also did you check this and this topics? I think it can be usefull.
I want to somehow paint a selection rectangle on scene, to show selected items (not he item bounding rectangle, but the bounding rectangle mapped to scene - and if multiple selection, the selection bounding rectangle).
I would like to try something like, on mouse press, to show the rectangle (and update based on current selection), and on mouse release, to hide it.
I am having trouble keeping the rectangle on the scene, and on mouse release it may be removing it, or maybe it was never there - and I get an error:
QGraphicsScene::removeItem: item 0x37828's scene (0x0) is different from this scene (0x1f57b68)
(The above error, and the fact that the item doesn't stay after mouse press, makes me think that it is not added properly but I don't understand why).
Here is a little sample code:
#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsRectItem>
class MyScene : public QGraphicsScene
{
public:
MyScene(qreal x, qreal y, qreal w, qreal h) {
setSceneRect(x, y, w, h);
m_selectionRectangle = new QGraphicsRectItem(0,0,1,1);
m_selectionRectangle->setBrush(Qt::magenta);
m_selectionRectangle->setOpacity(0.2);
}
~MyScene() {
if(m_selectionRectangle)
delete m_selectionRectangle;
}
protected:
virtual void mousePressEvent(QGraphicsSceneMouseEvent *event) {
QGraphicsScene::mousePressEvent(event);
if(!selectedItems().isEmpty()) {
QRectF selectionRect = QRectF();
foreach(QGraphicsItem* item, selectedItems())
selectionRect |= item->mapToScene(item->boundingRect()).boundingRect();
m_selectionRectangle->setRect(selectionRect);
addItem(m_selectionRectangle);
}
}
virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) {
QGraphicsScene::mouseReleaseEvent(event);
removeItem(m_selectionRectangle);
}
private:
QGraphicsRectItem* m_selectionRectangle;
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MyScene* s = new MyScene(0, 0, 800, 600);
QGraphicsView view(s);
view.setDragMode(QGraphicsView::RubberBandDrag);
view.show();
QGraphicsRectItem* xxx = new QGraphicsRectItem(200, 200, 100, 100);
QGraphicsEllipseItem* yyy = new QGraphicsEllipseItem(300, 300, 200, 100);
s->addItem(xxx);
s->addItem(yyy);
xxx->setFlags(QGraphicsItem::ItemIsMovable|QGraphicsItem::ItemIsFocusable|QGraphicsItem::ItemIsSelectable);
yyy->setFlags(QGraphicsItem::ItemIsMovable|QGraphicsItem::ItemIsFocusable|QGraphicsItem::ItemIsSelectable);
return app.exec();
}
What is the meaning of that error, what am I doing wrong in adding the selection rectangle, and why doesn't it stay there - and how can I fix it ?
The meaning of the error is literal: you're passing an item to removeItem that is not a child item of the scene you're trying to remove it from. It is nonsense to remove an item that is not in the scene to start with.
There is nothing that guarantees that the selection rectangle is on the scene when the mouse button is released, since there are paths through mousePressEvent that don't add the rectangle to the scene. I'm not even sure if you are guaranteed to get a press event preceding each release event at all.
You have to only remove the rectangle if it's on the scene (and virtual is not needed, but Q_DECL_OVERRIDE is!):
void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) Q_DECL_OVERRIDE {
QGraphicsScene::mouseReleaseEvent(event);
if (m_selectionRectangle.scene()) removeItem(m_selectionRectangle);
}
Also, the destructor of your custom scene is unnecessary. Simply add the item by value:
class MyScene : public QGraphicsScene
{
QGraphicsRectItem m_selectionRectangle;
public:
MyScene(qreal x, qreal y, qreal w, qreal h) :
m_selectionRectangle(0, 0, 1 1)
{
setSceneRect(x, y, w, h);
m_selectionRectangle.setBrush(Qt::magenta);
m_selectionRectangle.setOpacity(0.2);
}
protected:
void mousePressEvent(QGraphicsSceneMouseEvent *event) Q_DECL_OVERRIDE {
...
}
...
};
I'd appreciate help creating a top-level window in Qt with the following characteristics. The window must be:
Borderless, titleless and lie on top of all other windows on the desktop (easy)
Draggable by clicking and dragging anywhere inside it (this what I need help with)
Constrained to the top border of the desktop while dragging (relatively easy)
Basically, I'm trying to collapse our QT application to a top-level icon on the top border of the desktop.
You'll find the answer to the first part in: Making a borderless window with for Qt, and the answer to the second part in Select & moving Qwidget in the screen.
Combining the two, and adding the last part is straightforward.
Here's how you could do it:
#include <QtGui>
class W: public QWidget
{
Q_OBJECT
Set up a borderless widget with a few buttons to lock/unlock and quit:
public:
W(QWidget *parent=0)
: QWidget(parent, Qt::FramelessWindowHint), locked(false)
{
QPushButton *lock = new QPushButton("Lock");
QPushButton *unlock = new QPushButton("Unlock");
QPushButton *quit = new QPushButton("&Quit");
connect(lock, SIGNAL(clicked()), this, SLOT(lock()));
connect(unlock, SIGNAL(clicked()), this, SLOT(unlock()));
connect(quit, SIGNAL(clicked()),
QApplication::instance(), SLOT(quit()));
QHBoxLayout *l = new QHBoxLayout;
l->addWidget(lock);
l->addWidget(unlock);
l->addWidget(quit);
setLayout(l);
}
public slots:
void lock() {
locked = true;
move(x(), 0); // move window to the top of the screen
}
void unlock() { locked = false; }
Do the mouse handling:
protected:
void mousePressEvent(QMouseEvent *evt)
{
oldPos = evt->globalPos();
}
void mouseMoveEvent(QMouseEvent *evt)
{
const QPoint delta = evt->globalPos() - oldPos;
if (locked)
// if locked, ignore delta on y axis, stay at the top
move(x()+delta.x(), y());
else
move(x()+delta.x(), y()+delta.y());
oldPos = evt->globalPos();
}
private:
bool locked;
QPoint oldPos;
};
I'm attempting to produce a widget that consists of a text display that can be resized by the user grabbing the lower right corner. So far I've been able to generate this:
I've applied a red background to the layout to make it more obvious what's going on. I've used the following code to generate this:
m_sizeGrip = new QSizeGrip( this );
m_layout = new QHBoxLayout( this );
m_label = new QLabel( this );
m_layout->setContentsMargins( QMargins() );
m_layout->setSpacing( 0 );
m_layout->addWidget( m_label );
m_layout->addWidget( m_sizeGrip, 0, Qt::AlignBottom | Qt::AlignRight );
setWindowFlags( Qt::SubWindow );
Basically, it's a horizontal layout with the label and grip added to it, which is then installed on a QWidget. My problem is that I'd like the grip to be on the lower right corner of the label, rather than the parent widget. I'd also like to make it invisible while keeping it enabled.
Or perhaps I'm going about this the wrong way. My ultimate goal is to have a textual display widget that can be resized by the user either horizontally or vertically, but doesn't have a visible grip that would obscure the text. Am I already on the right track with the code above, or is there a better way to achieve this?
You could create a custom QLabel for that. The idea would be to track mouse move events (which by default only fire when a mouse button is pressed), and resize based on how much the mouse traveled since the last event.
This allows you to control exactly how to display the "gripper" (if at all) and what shape it should have. You can constrain the resizing to vertical or horizontal (or not).
Here's a demo of how you could do that (resizes both ways). Warning: this might wreak havoc in your layout.
#include <QtGui>
class GripLabel: public QLabel
{
Q_OBJECT
public:
GripLabel(QString const& title, QWidget* parent = 0)
: QLabel(title, parent),
resizing(false),
gripSize(10, 10)
{
// Prevent the widget from disappearing altogether
// Bare minimum would be gripSize
setMinimumSize(100, 30);
}
QSize sizeHint() const
{
return minimumSize();
}
protected:
bool mouseInGrip(QPoint mousePos)
{
// "handle" is in the lower right hand corner
return ((mousePos.x() > (width() - gripSize.width()))
&& (mousePos.y() > (height() - gripSize.height())));
}
void mousePressEvent(QMouseEvent *e)
{
// Check if we hit the grip handle
if (mouseInGrip(e->pos())) {
oldPos = e->pos();
resizing = true;
} else {
resizing = false;
}
}
void mouseMoveEvent(QMouseEvent *e)
{
if (resizing) {
// adapt the widget size based on mouse movement
QPoint delta = e->pos() - oldPos;
oldPos = e->pos();
setMinimumSize(width()+delta.x(), height()+delta.y());
updateGeometry();
}
}
void paintEvent(QPaintEvent *e)
{
QLabel::paintEvent(e);
QPainter p(this);
p.setPen(Qt::red);
p.drawRect(width()-gripSize.width(), height()-gripSize.height(),
gripSize.width(), gripSize.height());
}
private:
bool resizing;
QSize gripSize;
QPoint oldPos;
};
Sample main:
#include "griplabel.h"
int main(int argc, char **argv)
{
QApplication app(argc, argv);
QWidget *w = new QWidget;
QPushButton *b = new QPushButton("button");
GripLabel *l = new GripLabel("Hello");
QHBoxLayout *y = new QHBoxLayout;
y->addWidget(b);
y->addWidget(l);
y->setSizeConstraint(QLayout::SetFixedSize);
w->setLayout(y);
w->show();
return app.exec();
}
I need to create an alpha transparent widget, it's basically a navigation bar with a shadow and the widgets below need to be partially visible through the shadow. The widget loads a PNG then draws it on the paint event. The problem is that the shadow is all black and is not alpha-transparent.
This is the code I'm currently using:
NavigationBar::NavigationBar(QWidget *parent) : XQWidget(parent) {
backgroundPixmap_ = new QPixmap();
backgroundPixmap_->load(FilePaths::skinFile("NavigationBarBackground.png"), "png");
setAttribute(Qt::WA_NoBackground, true); // This is supposed to remove the background but there's still a (black) background
}
void NavigationBar::paintEvent(QPaintEvent* event) {
QWidget::paintEvent(event);
QPainter painter(this);
int x = 0;
while (x < width()) {
painter.drawPixmap(x, 0, backgroundPixmap_->width(), backgroundPixmap_->height(), *backgroundPixmap_);
x += backgroundPixmap_->width();
}
}
Does anybody know what I need to change to make sure the widget is really transparent?
You're doing too much work :-)
The setAttribute call is not necessary. By default, a widget will not draw anything on its background (assuming Qt >= 4.1). Calling QWidget::paintEvent is also unnecessary - you don't want it to do anything.
Rather than doing the pattern fill yourself, let Qt do it with a QBrush:
NavigationBar::NavigationBar(QWidget *parent) : XQWidget(parent) {
backgroundPixmap_ = new QPixmap();
backgroundPixmap_->load(FilePaths::skinFile("NavigationBarBackground.png"), "png");
// debug check here:
if (!backgroundPixmap_->hasAlphaChannel()) {
// won't work
}
}
void NavigationBar::paintEvent(QPaintEvent* event) {
QPainter painter(this);
painter.fillRect(0, 0, width(), height(), QBrush(*backgroundPixmap));
}
Adjust the height parameter if you don't want the pattern to repeat vertically.
Are you sure your PNG file is actually transparent? The following (which is essentially what you are doing) is working for me. If this fails on your machine, perhaps include what version of Qt you are using, and what platform.
#include <QtGui>
class TransparentWidget : public QWidget {
public:
TransparentWidget()
: QWidget(),
background_pixmap_(":/semi_transparent.png") {
setFixedSize(400, 100);
}
protected:
void paintEvent(QPaintEvent *) {
QPainter painter(this);
int x = 0;
while (x < width()) {
painter.drawPixmap(x, 0, background_pixmap_);
x += background_pixmap_.width();
}
}
private:
QPixmap background_pixmap_;
};
class ParentWidget : public QWidget {
public:
ParentWidget() : QWidget() {
QVBoxLayout *layout = new QVBoxLayout;
layout->addWidget(new TransparentWidget);
layout->addWidget(new QPushButton("Button"));
setLayout(layout);
setBackgroundRole(QPalette::Dark);
setAutoFillBackground(true);
}
};
int main(int argc, char **argv) {
QApplication app(argc, argv);
ParentWidget w;
w.show();
return app.exec();
}