The mobile session store saves the current document resolution in order to restore the previous zoom level when restoring a page. If the display width has changed since the session data was captured (e.g. because the device was rotated), the resolution might have to be scaled appropriately.
Currently, the session store does this scaling by itself by comparing the stored and current window widths, however this implementation is slightly simplified and doesn't cover all use cases, which means some pages can be restored at a wrong zoom level after rotation. To correctly cover all cases, the session store would have to compare viewport widths, too.
Because the MobileViewportManager doesn't wait for the session store to set the restore resolution, the latter has to call setRestoreResolution() as early as possible in order to guarantee that the restore resolution is set before the first paint of the document. Therefore the session store currently calls this after receiving a LocationChange notification. However at that time, the correct viewport for the current document is not yet available, which means the resolution cannot be recalculated by the session store at that point.
Therefore, this patch changes the approach taken and lets the MVM handle all resolution calculations instead. The session store now simply passes the stored previous display dimensions along with the previous document resolution to the MVM, which can then compare them to the current display and viewport widths and scale the resolution appropriately before using it during first paint.
MozReview-Commit-ID: IGxWw87yftK
We'll want to use this during first-paint, too, in order to correctly scale the resolution as received by the session store if we're restoring a previous tab. Therefore we extract this code into a separate helper function.
MozReview-Commit-ID: KCdvmyrP4mJ
The MobileViewportManager ("MVM") is responsible for setting the CSS viewport on
any of the following events:
- a page is painted for the first time (on the before-first-paint event)
- a meta-viewport tag is added (on the DOMMetaAdded event)
- the full-zoom is changed (on the FullZoomChanged event)
- if the window is resized (ResizeReflow gets called as part of normal layout
processing, and this will pick up a new CSS viewport from MVM)
If the CSS viewport changes or if it is the initial paint, the MVM additionally
calls SetResolutionAndScaleTo on the presShell to update the displayed zoom.
The APZ code in AsyncPanZoomController::NotifyLayersUpdated already has
corresponding code to accept this updated zoom when the CSS viewport changes.
The MobileViewportManager ("MVM") is responsible for setting the CSS viewport on
any of the following events:
- a page is painted for the first time (on the before-first-paint event)
- a meta-viewport tag is added (on the DOMMetaAdded event)
- the full-zoom is changed (on the FullZoomChanged event)
- if the window is resized (ResizeReflow gets called as part of normal layout
processing, and this will pick up a new CSS viewport from MVM)
If the CSS viewport changes or if it is the initial paint, the MVM additionally
calls SetResolutionAndScaleTo on the presShell to update the displayed zoom.
The APZ code in AsyncPanZoomController::NotifyLayersUpdated already has
corresponding code to accept this updated zoom when the CSS viewport changes.
