System mouse cursor: Web

[dkwingsmt]

Description

This PR adds system mouse cursor to the web engine.

This PR adds only a limited pool of system cursors. More will be added when the system is set up.

Related Issues

• Depends on System mouse cursors flutter#54171 to properly work, but neither one is required to build.
• Part of Add the ability to programmatically change mouse cursors. flutter#31952

Known issues

The mouse position flickers when the cursor changes.

Update: This is not a Flutter issue, but a general issue of macOS

Entering:

Leaving:

[dkwingsmt]

@yjbanov @ferhatb Can you take a look, also do you have an idea about the flickering?

[dkwingsmt]

It seems to me that this issue is not related to Flutter but a general issue (I noticed it on https://css-tricks.com/almanac/properties/c/cursor/).

[ferhatb]

Can you define kShapeCodeX/Y/Z in engine and then use those codes in rendering/mouse_cursor instead?

[dkwingsmt]

Is it possible to import engine code from framework at all? Also these constants have to be replicated to other platforms as well, including Android, macOS, GLFW, etc.

[ferhatb]

They would be part of dart:ui , just like StrokeJoin or other consts/enums. @gspencergoog : how do you typically handle consts across the 2 repos?

[gspencergoog]

Yeah, actually, I think Ferhat is right: we should define the codes just as contiguous integers, and define an enum that matches in the Dart code.

StrokeJoin defines an enum, and then in the C++/Java code, it defines constants that are used as indices into the StrokeJoin.values member.

Then the only things that need to be kept in sync are the enum (which is in the engine repo in dart:ui), and the constants (which are also in the engine repo).

You can also look at ImageByteFormat or TileMode, or any of the other enums we use that way in the engine.

[ferhatb]

I noticed that resize cursors are missing from codes which are used very frequently for things like resizing dividers etc. Are you planning to add more ? The web list of cursors is probably a good set to look at.

[dkwingsmt]

Yes, all cursors from CSS will be supported in an upcoming PR when the code styles are stabilized. This PR is a first step that aims to set up the infrastructure, and only include a small set of cursors to limit the scope of changes.

[dkwingsmt]

The described bug is actually from macOS, and not related to Web whatsoever.

[ferhatb]

Please dartfmt. Thx!

[nturgut]

I think Linux Fuchsia unit tests were a temporary breakage. I checked the LUCI , builds the current PRs are passing. May be we can sync to the head and re-run.

[ayushin]

Still present in master on Mac OSX Safari Version 13.1 (15609.1.20.111.8)

Overflow on channel: flutter/mousecursor. Messages on this channel are being discarded in FIFO fashion. The engine may not be running or you need to adjust the buffer size if of the channel. SE — channel_buffers.dart:144

[✓] Flutter (Channel master, 1.19.0-2.0.pre.143, on Mac OS X 10.15.4 19E287, locale en-CZ)