QGraphicsView ugly distortion yuck

[genjix]

Hey.

I've made a bug report but searching around I could not find any similar questions so I thought maybe I'm doing something wrong?


That's QGraphicsView::scale(0.9, 0.9)... The distortion is really bad.
(I wrote a little demo app demonstrating this)

Now if I screenshot the app and then scale it using QImage (example), it's suddenly fine.

My idea is to draw QGraphicsScene onto a custom buffer and then scale that using a QImage for display. Unfortunately I can't find any way to get the rendered scene.

Can anyone give me any pointers how to do this?

---

Added after 52 minutes:

C++ Example
I just wrote that test to show what I mean for anyone who doesn't use PySide.

#include <QtGui>
 
 #include "dialog.h"
 
 Dialog::Dialog()
 {
     setWindowTitle(tr("Basic Layouts"));
    QGraphicsScene *scene = new QGraphicsScene(this);
    QPixmap *pic = new QPixmap("table.png");
    scene->addPixmap(*pic);
    view = new QGraphicsView();
    view->setScene(scene);
 
    view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    view->setAlignment(Qt::AlignLeft|Qt::AlignTop);
 
    view->setRenderHints(QPainter::Antialiasing|QPainter::SmoothPixmapTransform);
 
    QPixmap *p = new QPixmap("seat_empty.png");
    QGraphicsPixmapItem *d = scene->addPixmap(*p);
    d->setPos(400,30);
    d = scene->addPixmap(*p);
    d->setPos(80,220);
    d = scene->addPixmap(*p);
    d->setPos(60,30);
    d = scene->addPixmap(*p);
    d->setPos(20,120);
    d = scene->addPixmap(*p);
    d->setPos(460,120);
    p = new QPixmap("other_cards.png");
    d = scene->addPixmap(*p);
    d->setPos(120,50);
    d = scene->addPixmap(*p);
    d->setPos(80,130);
    d = scene->addPixmap(*p);
    d->setPos(120,200);
    d = scene->addPixmap(*p);
    d->setPos(440,120);
    p = new QPixmap("6.png");
    d = scene->addPixmap(*p);
    d->setPos(540,330);
    p = new QPixmap("50.png");
    d = scene->addPixmap(*p);
    d->setPos(600,330);
 
    setCentralWidget(view);
    show();
 }
void Dialog::resizeEvent(QResizeEvent* event)
{
}
void Dialog::keyPressEvent(QKeyEvent* event)
{
    if (event->key() == Qt::Key_Equal)
        view->scale(1.1, 1.1);
    else if (event->key() == Qt::Key_Minus)
        view->scale(0.9, 0.9);
}

#include <QtGui>

 #include "dialog.h"

 Dialog::Dialog()
 {
     setWindowTitle(tr("Basic Layouts"));
    QGraphicsScene *scene = new QGraphicsScene(this);
    QPixmap *pic = new QPixmap("table.png");
    scene->addPixmap(*pic);
    view = new QGraphicsView();
    view->setScene(scene);

    view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    view->setAlignment(Qt::AlignLeft|Qt::AlignTop);

    view->setRenderHints(QPainter::Antialiasing|QPainter::SmoothPixmapTransform);

    QPixmap *p = new QPixmap("seat_empty.png");
    QGraphicsPixmapItem *d = scene->addPixmap(*p);
    d->setPos(400,30);
    d = scene->addPixmap(*p);
    d->setPos(80,220);
    d = scene->addPixmap(*p);
    d->setPos(60,30);
    d = scene->addPixmap(*p);
    d->setPos(20,120);
    d = scene->addPixmap(*p);
    d->setPos(460,120);
    p = new QPixmap("other_cards.png");
    d = scene->addPixmap(*p);
    d->setPos(120,50);
    d = scene->addPixmap(*p);
    d->setPos(80,130);
    d = scene->addPixmap(*p);
    d->setPos(120,200);
    d = scene->addPixmap(*p);
    d->setPos(440,120);
    p = new QPixmap("6.png");
    d = scene->addPixmap(*p);
    d->setPos(540,330);
    p = new QPixmap("50.png");
    d = scene->addPixmap(*p);
    d->setPos(600,330);

    setCentralWidget(view);
    show();
 }
void Dialog::resizeEvent(QResizeEvent* event)
{
}
void Dialog::keyPressEvent(QKeyEvent* event)
{
    if (event->key() == Qt::Key_Equal)
        view->scale(1.1, 1.1);
    else if (event->key() == Qt::Key_Minus)
        view->scale(0.9, 0.9);
}

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[Lykurg]

I just wrote that test to show what I mean for anyone who doesn't use PySide.

That was a good idea, but posting images from a 3rd party side isn't. Please attach them on the board that your thread stays valid a long time and not depend on other sides.

To your problem. When scaling images one will always loose informations. Sure. If you want to ensure a clear border of the cards, you have to do the painting yourself and use a cosmetic pen to draw the border. That's the only way to enforce that and also have in mind Qt (and its classes) aren't a graphics program so the transformation might be a little worser than in a real graphics problem (which also has more time to do the transformations).

Anyway, if you use QGraphicsPixmapItem::setTransformationMode() with smooth transformation your problem should be gone.

[genjix]

Aha Thank you. That was exactly what I needed, and was a great help.

Sorry about the images; I didn't realise and will remember that in the future. I've tried re-attaching those images to this thread, but whenever I click "Manage Attachments", I just get a blank window pop-up in Firefox.

[wysota]

Sorry about the images; I didn't realise and will remember that in the future. I've tried re-attaching those images to this thread, but whenever I click "Manage Attachments", I just get a blank window pop-up in Firefox.

You might want to try disabling AdBlock for QtCentre. We don't have any ads anyway...

[genjix]

OK, This is not my computer but the problem was 2 add-ons for firefox:
Torbutton 1.2.5 and GameBox 1.0.0
Individually they work fine, but when they're both on together then the Manage Attachments form is blank.distortion1.jpgdistortion2.jpg