To compute the bounding box of an element, you have to place it in the DOM, because you can't do CSS selector matching on an element otherwise. You have to do selector matching on it to know which CSS rules will be applicable, because CSS rules affect the bounding box.
We defer the actual rendering process as much as possible, so if you're doing a bunch of DOM operations just to compute bounding boxes we'll do layout a lot but won't actually render it until your script returns control to the event loop. Don't all the major browsers do that, though? On Sat, Nov 12, 2016, 9:50 AM Emilio Cobos Álvarez <ecoa...@gmail.com> wrote: > I'm posting this message in the name of Rod McGuire, who got his message > rejected apparently. > > --- > > [ I apologize for knowing nothing of current Servo internals ] > > For precise layout of things like math equations or SVG diagrams a > Javascrpt application may need to know the width and height extent of > component elements. > > Currently in browsers the only way to find this information is with > .getBoundingClientRect() which only works after an element has been > rendered and also returns x and y position information. > > The current way to kludge around this is by rendering each element > twice - on the first pass width and height information is collected > to determine the layout in the final render pass. > > [ MathJax does this though I think they are moving towards an > external font table approach ] > > I've heard that to just get width and height information without > rendering would require a major rewrite of the work flow for most > current browsers. > > Has there been any effort in Servo to make available this information > for non-rendered elements? > > I think most developers affected by this would be somewhat happy with > width and height just for textual elements. They also might like some > exposure of the actual selected font so that font table information can > be used in layout. > > I haven't been able to find any discussion of this issue though there > seems to be some on performance of the full blown > .getBoundingClientRect(). > > [1]: > https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect > [2]: Recent Improvements to Functions like getClientBoundingRect - > https://groups.google.com/forum/#!searchin/mozilla.dev.servo/getBoundingClientRect/mozilla.dev.servo/fpY49KCQ_64/0Mq7fnn4OMIJ > _______________________________________________ > dev-servo mailing list > dev-servo@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-servo > _______________________________________________ dev-servo mailing list dev-servo@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-servo
