1218991 - Initial zoom constraints can be dropped

Status: RESOLVED FIXED

(Core :: Widget, defect)

Description

[James Willcox (:snorp) ([e-mail]) (he/him)]

Because the compositor and APZCTreeManager are lazily created when we do the first paint, it's possible that zoom constraints will be dropped since we have nowhere for them to go.

Comment 1

[James Willcox (:snorp) ([e-mail]) (he/him)]

Attachment: Save initial zoom constraints to be used once compositor is created

Comment 2

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

Comment on attachment 8679660 [details] [diff] [review]
Save initial zoom constraints to be used once compositor is created

Review of attachment 8679660 [details] [diff] [review]:
-----------------------------------------------------------------

r+ with the change described below. I'm still a little uneasy about this but I don't have any better suggestions.

::: widget/nsBaseWidget.cpp
@@ +937,5 @@
>    if (!mCompositorParent || !mAPZC) {
> +    if (aConstraints) {
> +      // We have some constraints, but the compositor and APZC aren't created yet.
> +      // Save these so we can use them later.
> +      mInitialZoomConstraints = Some(InitialZoomConstraints(aPresShellId, aViewId, aConstraints.ref()));

I'm assuming that UpdateZoomConstraints can get called multiple times before the compositor is created. Technically this should get stashed into a map of (presShellId, viewId) -> ZoomConstraints. But in practice I'm thinking this will only happen in a limited set of cases, so we can get away with what you're doing here. However I still want to assert that we don't run into the other scenarios. So do this instead:

if (!mCompositorParent || !mAPZC) {
  if (mInitialZoomConstraints) {
    MOZ_ASSERT(mInitialZoomConstraints->mPresShellID == aPresShellId);
    MOZ_ASSERT(mInitialZoomConstraints->mViewID == aViewId);
    if (!aConstraints) {
      mInitialZoomConstraints.reset();
    }
  }
  if (aConstraints) {
    ... // what you have now
  }
  return;

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/5978297efa48

Comment 4

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/5978297efa48