On Wed, Dec 5, 2012 at 8:28 PM, Adam Barth <aba...@webkit.org> wrote: > On Wed, Dec 5, 2012 at 7:16 AM, Alexander Pavlov <apav...@chromium.org> wrote: >> I'm working on emulating the device scale factor with Web Inspector. My goal >> is to let web developers see their pages on "normal" (device pixel ratio == >> 1) monitors the way they would look on e.g. retina screens. >> Page::setDeviceScaleFactor() is not something we can use, since it will have >> the reverse effect when used by platform-specific compositor code (which I >> saw on Chromium, and its compositor is far from being ready for such >> abnormal treatment.) > > I'm not sure I fully understand what you're trying to accomplish. Is > the developer using a high density screen or a low density screen? > > Chromium has a command line option for setting a fake device pixel > ratio. For example, if you're using a low density screen, you can > pass something like --device-pixel-ratio 2 to ask Chromium to render > as if your device has a high density display. The net effect is that > the glyphs get really big (since they use 2x the pixels in each > dimension). > > Alternatively, I can imagine that the developer is using a high > density screen but wants to develop a web site that looks good on a > low density screen. In that case, they want to set a > --device-pixel-ratio 1 but then render the web page pixel doubled > (i.e., rasterizing each pixel as a 2x2 quad). I don't think there's a > command line option for that in Chromium, but it's something you might > reasonably do in the compositor. > > In general, though, trying to shim this feature into WebCore isn't > likely the right approach. For WebKit2, for example, both the UI > process and the web process need to agree about the device pixel ratio > or else the system gets confused about how big various regions of > memory ought to be. If you look at how we test high density rendering > on low density machines, you'll see that we override the device's > actual pixel density via the WebKit/WebKit2 API. That's to avoid this > confusion. > >> I took the approach of instrumenting the WebCore/css and WebCore/page code >> relying on the page->deviceScaleFactor() value. This worked pretty well, and >> you can see the respective patch at >> https://bugs.webkit.org/attachment.cgi?id=172046&action=prettypatch >> (https://bugs.webkit.org/show_bug.cgi?id=100762), but now I'm wondering if >> there are better ways to implement this without instrumenting lots of >> page->deviceScaleFactor() call sites. >> >> Comments, ideas, suggestions, please? > > If you want to see how this is done in Chromium, you might want to > study the --device-pixel-ratio command line flag. In general, I don't > think you want to try to implementing this feature by hacking WebCore > as it requires coordination beyond WebCore to do correctly.
I think Adam is refering to the --force-device-scale-factor=2 flag for chromium. To try it out, you may need to build with the use_ash=1 flag. > Adam > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > http://lists.webkit.org/mailman/listinfo/webkit-dev _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo/webkit-dev
