> Dear Qt developers, > I got a new toy at work -- a 27" LCD with some crazy resolution > (2560x1440 IIRC), i,e. its pixel density is roughly 109 PPI. The LCD I > use at home has got a 94 PPI grid. I frequently move my laptop between > these two places and I have yet to make my KDE 4.9 use fonts which look > great no matter which display I switched to at runtime. The current > state is driving me nuts; I have to constantly adjust the font size in > KDE's preferences *and* restart the applications afterwards, so that > they pick up the new font preferences. That's not the first thing I want > to do when I get to work in the morning. > > It looks like Qt 4.8.3 doesn't provide dynamic updates to the DPI value > to the applications. The attached patch does just that; it simply > updates the value which is returned by QX11Info::appDpiX() and appDpiY > when XRandR informs about new geometry. No fancy signalling is done. > > The results are actually pretty funny; it looks like a QTreeView would > use the new font size only for text items whose font previously did not > fit the column width while those which fit will remain in the previous > size; there are also no changes to stuff like height of the menu bars, > the layouts won't change, and so on. On the other hand, it's now enough > to reopen the current file in Qt Creator and the font size reflects the > new DPI. > > I don't know anything about Qt internals (and I suspect that this is not > exactly an area a newcomer should dive into), so I'll appreciate some > pointers about what else would need changing in order for dynamic DPI to > work. Or is this a futile attempt which is doomed to failure anyway? Are > there any chances of getting this accepted, eventually?
Yes and no (depending). There are several approaches to DPI scaling. I'm working on a patch to Qt 5 that implements the "retina" or "web bowser" type of scaling that creates a distinction between device independent pixels and device pixels. Detecting and reacting to DPI changes would be a natural addition to the patch, but it's for Qt 5 only so it won't help you right away. (I have a smaller mac-only patch for Qt 4). This approach has the following characteristics: - Everything is scaled: fonts, layouts and all. There should be no "funny" results. - Scaling means that Qt apps see a smaller desktop geometry. The graphics backing store and OpenGL contexts are full resolution. - A 2x scale factor (around 200 PPI) works best, since there are no "misaligned" pixels then. - How well it works outside of Mac OS X is uncertain. We're adapting the new fusion style to work in high-dpi mode and I'm optimistic that it can be useful. Morten _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
