[silentbil]

Summary

Smoother vertical scrolling in the Netflix-style TV Home.

Moving down used to resize every card of two rails at once: the row being left shrank while the row being entered grew, along with their headings and descriptions. That re-measured the whole list on every frame of the vertical scroll.

• The row being left now keeps its expanded layout while the scroll carries it out the top, then collapses in one frame once it is off screen. Moving up is unchanged, since the row being left stays visible below.
• Row headings scale with graphicsLayer instead of animating their font size, so the text is no longer re-measured each frame.
• A row held expanded while it leaves no longer moves the channel preview.
• Cards get their morph size at layout time instead of reading the animated width and height in composition, so every card of the two morphing rows is re-measured each frame instead of recomposed. MediaCard gains fillArtworkHeight so its artwork follows the height the parent gives it.

Testing

Release (R8) builds on a Xiaomi Mi Box 4 (Android 9). Frame times come from dumpsys gfxinfo over 20 Down presses from the top of Home; the two builds were alternated, 3 runs each, on the same rows.

1. Keep the leaving row expanded (first commit) vs main, one press every ~1.4 s and every ~0.9 s:

	~1.4 s: main	~1.4 s: branch	~0.9 s: main	~0.9 s: branch
Median frame	15 ms	16 ms	17 ms	18 ms
90th percentile	54 ms	48 ms	57 ms	53 ms
95th percentile	77 ms	60 ms	82 ms	58 ms
99th percentile	133 ms	81 ms	113 ms	82 ms

2. Morph size at layout time (ca7ac54d) vs the first commit, one press every ~0.5 s:

	first commit	+ ca7ac54d
Janky frames	51%	46%
Median frame	21 ms	17 ms
90th percentile	104 ms	76 ms
95th percentile	134 ms	102 ms
99th percentile	194 ms	131 ms

Together, the stutters that are visible on the box (90th–99th percentile) are roughly a quarter to a third shorter at each step. Unit tests (Netflix home and card components) and NetflixVerticalNavigationDeviceTest pass.

[ProdigyV21]

I think we can also make horizontal smoother, especially when holding down right or left it can be improved a lot, think you can do that as well?

[silentbil]

I think we can also make horizontal smoother, especially when holding down right or left it can be improved a lot, think you can do that as well?

@ProdigyV21 i dont have any issues in horizontal scrolling, i checked old devices too.
this is the first phase, on next one i want to upgrade compose which suppose to improve a lot