1759958 - ScrollAnimationMSDPhysics::ApplyContentShift() implementation is incorrect

Status: RESOLVED FIXED

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

Description

[Botond Ballo [:botond]]

GenericScrollAnimation overrides HandleScrollOffsetUpdate() to handle relative scroll offset updates without interrupting the animation.

The implementation calls ScrollAnimationPhysics::ApplyContentShift(). This is intended to shift both the current position and the destination of the animation by the provided argument.

ScrollAnimationPhysics has two implementations, ScrollAnimationBezierPhysics and ScrollAnimationMSDPhysics.

The Bezier implementation of ApplyContentShift() is correct: it adjusts mStartPos and mDestination, and then PositionAt() interpolates between those two values.

The MSD implementation, however, is incorrect. It too adjusts mStartPos and mDestination, but these adjustments have no impact on the result of PositionAt(), which is instead based on state inside the AxisPhysicsMSDModels.

Comment 1

[Botond Ballo [:botond]]

Attachment: Bug 1759958 - Add comments to clarify the purpose of ScrollAnimationPhysics::Update() and ApplyContentShift(). r=hiro

These methods seem somewhat similar but they have two important differences:

1. Update() only changes the destination, not the current position.
2. ApplyContentShift() does not recompute the shape of the animation curve.

Comment 2

[Botond Ballo [:botond]]

Attachment: Bug 1759958 - Implement ScrollAnimationMSDPhysics::ApplyContentShift() correctly. r=hiro

The previous implementation did not actually change what PositionAt() returns.

Depends on D141318

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/43758c2e591d
Add comments to clarify the purpose of ScrollAnimationPhysics::Update() and ApplyContentShift(). r=hiro
https://hg.mozilla.org/integration/autoland/rev/692d1b656c58
Implement ScrollAnimationMSDPhysics::ApplyContentShift() correctly. r=hiro

Comment 4

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/43758c2e591d
https://hg.mozilla.org/mozilla-central/rev/692d1b656c58