Draw big things with Painter outside main window.

BD9a

Hey, is it possible to draw things outside main window? I have an really big pattern to draw but I cant because of it's too big / window is too small. Is it possible?

jsulm

@BD9a You can only draw on a widget, so, no you can't draw outside of your window. Why would you need to draw outside of the window? Just draw what currently fits in your window.

mrjj

Hi
Yes it is possible if you use a QPixmap.

https://forum.qt.io/topic/108442/how-to-paint-to-pixmap/2

But if it is to show to the user, then you should either use a ScrollArea so the user can scroll around to see if all
or simply draw in a scaled version that fits the window.

BD9a

@jsulm The problem is that sometimes my pattern is a lot bigger than window (I have an "ScrollArea / Drag option to see it all)

@mrjj Will test this QPixmap, thanks. As I said I have an "ScrollArea / Drag option to see it all, but what about "scaled version"? I saw there's Painter->setScale(), but it doesnt work for me properly(?) (cant see "image" after that option)

mrjj

@BD9a

Hi
How do you currently draw the pattern

BD9a

@mrjj

Im using painter->drawPoint(row, col); in loop (looping through file containing data) in a paint() function (from QQuickPaintedItem).

mrjj

@BD9a
Hi
Well drawpoint is affected by scale() so maybe the scale values was just too much

virtual void paintEvent(QPaintEvent *event) override
    {
        QPainter p(this);
        QPointF list[] = {{0,0}, {20,20}, {30,30}};
        p.setPen(QPen(Qt::red));
        p.scale(0.5,0.5);
        p.drawPoints(list,3);
    }

clearly makes the half the size but maybe your use case if differnt.

BD9a

@mrjj
In QQuickPaintedItem there's no paintEvent that I can override. If it does matter, Im using C++ Object in QML to display it.

mrjj

@BD9a

I'm don't think it matter since QQuickPaintedItem has paint.

But did you try to with like scale (0.5,0.5) and see if that affects it ?

BD9a

@mrjj
Yeah, when I had problem with this I placed painter->scale(0.5, 0.5); in loop, I dont know why. Now I placed it before loop and it's working, but the problem is when the pattern is small. When I tried to "back" to original scale in QML (from 0.5 in C++ to 2.0 in QML) the image is blurry. I will try to do pattern size detection and then - if pattern is big scale is down, if pattern is small then do nothing / scale it up.