Improvements to Gradient2D Editor

[MewPurPur]

A few small tweaks to the GradientTexture2D editor.

• Modifies snap_size into snap_count, which everyone I asked seemed to prefer for Gradient in Overhaul the Gradient Editor #70760. I think it does make more sense here too, as we're representing fractions and not pixels. But feel free to discuss
  
• If two handles are overlapping and the user clicks the area where they overlap, picks the handle that's closer, instead of always the FROM handle.
• Remembers snapping options between sessions on a per-GradientTexture2D basis.

Improvements to Undo/Redo

• Only leaves a message in the output when you release a handle to prevent spam
• Fixes occasions in which it used to break
• Doesn't leave a message if you leave the handle where you grabbed it

All of these Undo/Redo behaviors match how it is done in the CanvasItem editor.

[MewPurPur]

This hasn't been receiving much attention, I thought I'd do a follow-up but I might as well just finish the job of polishing it now.

• Added hover indication for the handles
• Added axis snapping with Shift
• Added temporary grid snapping with Ctrl

These are pretty expected functionalities from a 2D editor, I don't think I need to justify them

[KoBeWi]

Added temporary grid snapping with Ctrl

I think the editor should update as soon as you press Ctrl. Right now it has no effect until you drag.
EDIT:
Ah, I see it's implemented, but doesn't work 🙃

[MewPurPur]

A bit short on time, sorry, but I think I addressed most of the remarks. Just not the static variable one, I'm not familiar with this feature, sorry-

[KoBeWi]

Example is here:

godot/scene/resources/packed_scene.h

Line 224 in 14c582b

static const String META_POINTER_PROPERTY_BASE;

It's static const, so that it's a constant that's allocated only once for the whole class (without static it's once per instance).
You need to initialize it in cpp file.

[MewPurPur]

I think the editor should update as soon as you press Ctrl. Right now it has no effect until you drag.

I removed the implementation, I actually found it very odd when the grid appeared when you do stuff like Ctrl+Z, so I think it is reasonable to only show when you are dragging.

Implement the static const thing too. Also moved drawing to a _draw() function.

[MewPurPur]

Very weird, I have no idea what could possibly be causing this, but I'll try to debug it now. The only thing relating to those functions I remember doing was using the static var and meta suggestions...

[MewPurPur]

The GradientTexture2D now gets rebuilt every time I press the snap button. I'm 90% sure this has to do with the added editor metadata causing the property tree to be updated, rebuilding this editor plugin, which shouldn't happen.

Busy now but I'll fix this soon. (Unless someone fixes the underlying cause - the pointless property tree rebuilding. pls...)

[KoBeWi]

#76814
Although there is a faulty logic there, because you are storing the default value (true). Otherwise the button would be correctly unpressed after update...

[MewPurPur]

Ah that's true. Thanks for pointing it out. I just saw that the code for the "READY" notif was running and rebuilding the editor, so I thought this might be the problem.

[KoBeWi]

I removed the implementation, I actually found it very odd when the grid appeared when you do stuff like Ctrl+Z, so I think it is reasonable to only show when you are dragging.

But it could at least update when you press Ctrl while dragging (without any movement). That's what I meant.

[Calinou]

But it could at least update when you press Ctrl while dragging (without any movement). That's what I meant.

Note that this also needs to be done in the Gradient editor PR. That said, I don't consider it a blocker for either PR.

[Calinou]

Tested locally (rebased against latest master 06ccbfe), it works.

Code looks good to me at a glance.

[akien-mga]

Thanks!