ozone/wayland: Persist tablet tool axis state across frames [chromium/src : main]
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The Techromancer (Gerrit)
Aug 1, 2026, 2:38:07 PM (12 days ago) Aug 1
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File-level comment, Patchset 1 (Latest):
The Techromancer . resolved
Hi all,
This is my first Chromium contribution, and hopefully the first of several fixes to bugs I discovered while building darkly.art, an open source painting app.
This is a relatively small fix. I used Claude Opus 5 to assist in diagnosing and implementing it, but took the time to understand it, and fully compiled and tested it manually.
Here is a screenshot of the pen strokes, before and after:
https://issues.chromium.org/action/issues/497284918/attachments/80083491?download=false
Thanks for your help
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Thomas Anderson (Gerrit)
Aug 3, 2026, 10:49:45 AM (10 days ago) Aug 3
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Kramer Ge (Gerrit)
Aug 4, 2026, 2:28:30 PM (9 days ago) Aug 4
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Kramer Ge (Gerrit)
Aug 4, 2026, 2:28:53 PM (9 days ago) Aug 4
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| Commit-Queue | +2 |
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Kramer Ge . resolved
Thank you very much
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Kramer Ge (Gerrit)
Aug 5, 2026, 3:45:24 PM (8 days ago) Aug 5
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Chromium LUCI CQ (Gerrit)
Aug 5, 2026, 5:55:48 PM (7 days ago) Aug 5
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Chromium LUCI CQ submitted the change![]( "Open in Gerrit")
Change information
Commit message:
ozone/wayland: Persist tablet tool axis state across frames
zwp_tablet_tool_v2 sends an axis event (pressure, distance, tilt,
rotation, slider) only when the value changes. WaylandTabletTool
buffers axis values into frame_data_.pointer_details and dispatches on
frame, but ResetFrameData() rebuilt a fresh FrameData afterwards,
zeroing force, tilt, twist and tangential pressure. Any frame in which
the compositor did not re-send pressure therefore dispatched
force=0.0, producing intermittent pressure:0 samples on a pen held in
continuous contact with the surface.
pointer_type is already persisted across frames for exactly this
reason (crrev.com/c/6907510). This CL completes that pattern for the
analog axes by carrying the whole PointerDetails across the frame
reset instead of rebuilding it. The fields this class never writes
(radius_x, radius_y, id, offset) keep their defaults regardless, so
this is equivalent to persisting the axes individually, without
needing a cache member per axis that a future axis could forget to
update.
Persisting state across frames requires bounding its lifetime, so it
is cleared in two places:
- On proximity-in, since a tool entering proximity begins a new
interaction that must not inherit the previous one's axis values.
proximity_in is the first event in its frame, so a pressure event
arriving in that same frame still takes effect.
- On up, since the tip is no longer in contact and force is zero by
definition. Without this, a persisted force would survive into the
release event on compositors that omit a pressure event from the
frame carrying up.
continuous strokes on a canvas logging PointerEvent.pressure.
Mid-stroke zero-pressure samples: ~38 per stroke before, 0 after.
Bug: 497284918
Test: Manual, ELAN9008:00 04F3:4359 stylus under Sway, drawing
Change-Id: Ie7e5c58bccdddded997f1a45d9cc94e6f367d348
Commit-Queue: Kramer Ge <fang...@chromium.org>
Reviewed-by: Kramer Ge <fang...@chromium.org>
Reviewed-by: Thomas Anderson <thomasa...@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1674519}
Files:
- M AUTHORS
- M ui/ozone/platform/wayland/host/wayland_tablet_tool.cc
Change size: S
Delta: 2 files changed, 16 insertions(+), 1 deletion(-)
Branch: refs/heads/main
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Code-Review: +1 by Thomas Anderson, +1 by Kramer Ge
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