1280518 - Displayport shown on APZ minimap is inconsistent with what is rendered

Status: RESOLVED DUPLICATE of bug 1604280

(Core :: Panning and Zooming, defect, P3)

Description

[Botond Ballo [:botond]]

STR:
  1. Turn on apz.minimap.enabled in about:config
  2. Navigate to https://bugzilla.mozilla.org/show_bug.cgi?id=1234158
  3. Press "End" to scroll to the bottom
  4. Press "Up" a few times to scroll up a bit, by less than a page.
  5. Wheel-scroll back down to the bottom.

At the end of the wheel-scroll, the displayport rect shown on the minimap does not extend down to the bottom of the page, while the viewport does, as if we were checkerboarding, but we are not in fact checkerboarding - the bottom of the page is rendered in full.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

I can sort of repro on OS X. It's most likely a regression from bug 1257641, because the empty transaction updates the scroll offset in the frame metrics, which changes where the minimap draws the displayport. However the displayport hasn't actually moved.

Presumably this means anywhere we're computing the page-relative displayport in the compositor it might be a little off, so we should fix this.

Comment 2

[Kartikaya Gupta (email:[e-mail])]

I took a look through the users of FrameMetrics::GetDisplayPort and other than the minimap the only other call site that looks like it would be affected is the one that calls SyncFrameMetrics to sync the displayport to java-land on Fennec. So it probably doesn't impact user-visible correctness as much as I thought it might.

Comment 3

[Milan Sreckovic [:milan] (needinfo for best results)]

Doesn't sound like we'd uplift a fix to beta, so wontfix for 48.

Comment 4

[Botond Ballo [:botond]]

This issue no longer occurs with the WebRender implementation of the minimap added in bug 1604280.