feat: Added glow effect using maskFilter

[dipakp2726]

Description

A new paint effect for glowing effects using maskFilter.

Checklist

• The title of my PR starts with a [Conventional Commit] prefix (fix:, feat:, docs: etc).
• I have followed the [Contributor Guide] when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• No, this PR is not a breaking change.

Related Issues

Closes #1027

[munsterlander]

How do I change the size and color of the glow effect? Glow is supposed to be like a neon light, right?

[dipakp2726]

Screen.Recording.2022-10-28.at.10.02.01.PM.mov

Screen.Recording.2022-10-28.at.10.19.04.PM.mov

[munsterlander]

Awesome!

[st-pasha]

Very nice addition!

But it seems like this needs to have a well-considered documentation. For example, the effect applies to shapes but not sprites. It makes a certain paint glow -- so the component has to be drawing something with a paint. We need to investigate how it would apply to "stroke" paints, or to transparent paints (say, can I draw a transparent outline of a sprite and make that outline glow?)

[dipakp2726]

We need to investigate how it would apply to "stroke" paints

example on stroke paints

Screen.Recording.2022-10-29.at.9.09.28.AM.mov

[dipakp2726]

say, can I draw a transparent outline of a sprite and make that outline glow?)

example on outline.
ps: it not exact outline.

Screen.Recording.2022-10-29.at.9.24.47.AM.mov

[spydon]

There should also be tests and docs for it (with an interactive example), but other than that it looks good!

[dipakp2726]

Screen.Recording.2022-10-29.at.4.25.12.PM.mov

[st-pasha]

Oh lol -- I just realized that this filter replaces the color with a glow. So if you had a shape with a solid color before, that color will now disappear and there will only be glow.

Perhaps we could mark this effect as @experimental for now, and then figure out whether we need a different approach, or just document this behavior carefully?

[dipakp2726]

if we use BlurStyle.solid then both color and glow will stay.

[st-pasha]

Yeah, but it would hardly look like a glow then -- more like a blurred-out shape.
For a "real" glow I think we need a second paint.

[spydon]

Oh lol -- I just realized that this filter replaces the color with a glow. So if you had a shape with a solid color before, that color will now disappear and there will only be glow.

Perhaps we could mark this effect as @experimental for now, and then figure out whether we need a different approach, or just document this behavior carefully?

We should make the effect target a color then right? So that the component can have several colors defined.
It doesn't really fit that well in with how the PaintProvider is created in this PR.
Any ideas of how to improve on this?

[st-pasha]

I guess the first thing we have to acknowledge is that "glow effect" is not an Effect. We use the term "Effect" to describe a change in some property over time. At the same time, a glow "effect" is a static change in appearance of the target.
A more appropriate term here would probably be Decoration

[spydon]

Maybe it could be modified to be pulsating or such? But yeah, maybe this shouldn't have been an effect at all.