Qt painting without clearing the background

Question

I'm using a QPainter to get some graphics on a window. Unfortunately every time the paintEvent() function is called, the whole window is cleared. How can I draw without clearing? I.e. how do I leave the stuff from previous paint event untouched?

I'm using Qt4

Which Qt version are you using? – Frerich Raabe Oct 29 '09 at 15:35 — Frerich Raabe, Oct 29 '09 at 15:35

score 5 · Answer 1 · answered Aug 09 '13 at 11:37

5

Since both replies are for Qt3 only, here is the solution for Qt4. You need to call

setAttribute(Qt::WA_OpaquePaintEvent);

(for example in the constructor) following the documentation here.

answered Aug 09 '13 at 11:37

hochl

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score 4 · Accepted Answer · answered Oct 29 '09 at 15:44

4

You need to set the backgroundMode by using the setBackgroundMode setter. The Qt::NoBackground enum is what you are searching for.

answered Oct 29 '09 at 15:44

Patrice Bernassola

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Frerich Raabe · Answer 3 · 2009-10-29T15:48:44.313

1

In Qt3, set the Qt::WNoAutoErase flag from the WidgetFlags enum to avoid that the window is cleared on each paint event.

You can set this flag by passing it to the QWidget constructor.

edited Oct 29 '09 at 15:48

answered Oct 29 '09 at 15:30

Frerich Raabe

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Qt Documentation says it no longer needed. So he should not use it – Patrice Bernassola Oct 29 '09 at 15:33
@Patrice: Ah, yes - in Qt4 it does not work anymore. This is a Qt3 solution. – Frerich Raabe Oct 29 '09 at 15:49

Qt painting without clearing the background

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