1400167 - investigate why animating between matched transform lists with singular matrix is not discrete in Gecko

Status: NEW

(Core :: CSS Parsing and Computation, defect, P4)

Description

[Jeremy Chen ([e-mail])]

In bug 1394284, we added 3 wpt tests to verify that we always discretely animate transform with singular matrix. The tests get passed in Stylo, but somehow one of the tests gets failed in Gecko.

Following is the error log while running wpt tests with
'./mach wpt --setpref layout.css.servo.enabled=false ./testing/web-platform/tests/web-animations/animation-model/animation-types/interpolation-per-property.html':

```
transform: non-invertible matrices in matched transform lists
-------------------------------------------------------------
Expected PASS, got FAIL
assert_approx_equals: expected matrix(0,-1,1,0,250,0) but got matrix(0.705995, -0.708217, 0.708217, 0.705995, 274.95, 0): The value should be matrix(0,-1,1,0,250,0) at 499ms but got matrix(0.705995, -0.708217, 0.708217, 0.705995, 274.95, 0) expected 0 +/- 0.0001 but got 0.705995
```

Note that the value at 0ms is correct, it somehow gets weird at 499ms. So, this is not a ReadTransforms issue I guess. Not sure if Gecko handles  matched transform lists any different with Stylo...

Comment 1

[Hiroyuki Ikezoe (:hiro)]

I haven't looked the test case, the test case has an singular matrix in a transform list? If so, Gecko does handle the transform list as interpolable?

Comment 2

[Jeremy Chen ([e-mail])]

(In reply to Hiroyuki Ikezoe (:hiro) from comment #1)
> I haven't looked the test case, the test case has an singular matrix in a
> transform list? If so, Gecko does handle the transform list as interpolable?

Yes, a singular matrix in one of the transform list.

The failing test is:
```
From: translate(50px)  matrix(-1, 0, 0, -1, 200, 0) rotate(90deg)  // matrix(0, -1, 1, 0, 250, 0)
To: translate(100px) matrix( 1, 1, 0,  0, 0, 100) rotate(180deg)  // matrix(-1, -1, 0, 0, 100, 100)
```