Animate spreading colour in a Line

[Plecra]

Description
I would like a way to draw a line, then fill it with a colour (blue) starting at one end and progressing to the other over time.

This would be an alternative to manually drawing this animation:

  const filled = createSignal(0);
  // (I couldn't figure out how to render Lines, they kept complaining with errors in vite :P)
  view.add(<Rect width={420} height={20} x={0} fill="white"/>)
  view.add(<Rect width={() => filled() * 420} height={20} x={() => (filled() - 1) * 210} fill="blue"/>)
  
  yield* filled(1, 2);

I would hope that a proper API would allow us to floodfill objects without rebuilding them with manual size/pos calculations.

Proposed solution

Nothing yet! I haven't got far enough into the app's guts to know how we'd need to implement this. It's easy if we can use shaders, but a bit of a PITA with html/css. The best option would be using gradients across the rendered boxes

[Plecra]

Oh, I see we're rendering on canvases for the shapes! Gradient should be perfect for this, but I can't figure out how to make it work :/

[Plecra]

Hahah!

const filled = createSignal(0);
const myRect = createRef<Rect>();
view.add(<Rect ref={myRect} width={420} height={20} x={0} fill={() => new Gradient({
  from: myRect().cacheRect().topLeft,
  to: myRect().cacheRect().topRight,
  stops: [{ color: "blue", offset: filled() }, { color: "white", offset: filled() }]
})}/>);
yield* filled(1, 2, linear);

That's lovely, pretty much what I wanted :) I'll leave it here in case you want to pop it on the docs for Gradient?

[Plecra]

(Related feature request: It'd be rlly awesome to be able to use absolute positions with Gradient so I can use it across multiple nodes)

[Plecra]

That would be to simplify this:

const filled = createSignal(0);
const space = createSignal<Bounds>();

const layout = <Layout layout direction="column" gap={40} alignItems="center">
  {[[300, 100], [420, 20]].map(([w, h]) => {
    const rect = <Rect width={w} height={h}/> as Rect;
    rect.fill(() => {
      const bounds = space();
      return new Gradient({
        from: bounds.center.transformAsPoint(rect.worldToLocal()),
        to: bounds.center.transformAsPoint(rect.worldToLocal()),
        type: "radial",
        toRadius: Math.sqrt(bounds.width**2 + bounds.height**2) / 2,
        stops: [{ color: "blue", offset: filled() }, { color: "white", offset: filled() }]
      })
    })
    return rect;
  })}
</Layout>;
space(() => layout.cacheRect().transform(layout.localToWorld()));
view.add(layout);

yield* filled(1, 2, linear);

too um 🤔

const filled = createSignal(0);
const space = createSignal<Bounds>();
const gradient = createSignal(() => new Gradient({
    from: space().center,
    to: space().center,
    type: "absolute-radial",
    toRadius: Math.sqrt(space().width**2 + space().height**2) / 2,
    stops: [{ color: "blue", offset: filled() }, { color: "white", offset: filled() }]
}))

const layout = <Layout layout direction="column" gap={40} alignItems="center">
  {[[300, 100], [420, 20]].map(([w, h]) => <Rect width={w} height={h} fill={gradient}/>)}
</Layout>;
space(() => layout.cacheRect().transform(layout.localToWorld()));
view.add(layout);

yield* filled(1, 2, linear);

[aarthificial]

I think the best solution would be to turn Gradient into a node so that it could be placed in the scene:

const gradient = createRef<Gradient>();

view.add(
  <>
    <Gradient ref={gradient} />
    <Rect fill={gradient()} />
  </>
);

It wouldn't render anything, but moving it around would move the gradient from/to points. This way you could not only have absolute gradients but also parent them to other nodes.

[brandonpelfrey]

One possible solution to this might be something like...

<Rect radius={10} width={200} height={20} clip >
  <Rect fill={gradient} {/* Other props */} />
</Rect>

So the outer Rect is the actual line being filled, specified with clip properties so that none of the child Rect is drawn outside. Meanwhile the child Rect can be resized or style animated in order to get the style to animate within that line. Would this work? Agreed having a nicer integration with Gradient would be nice.

[Plecra]

Hmm could the sizes be specified as percentages of the parent? I don't want to have to manually scale filled

[aarthificial]

If by "percentages of the parent" you mean its scale, then yes. After turning Gradient into a Node, putting it inside of another node would make it scale together with it:

const gradient = createRef<Gradient>();

view.add(
  <Rect fill={gradient()}>
    <Gradient ref={gradient} />
  </Rect>
);

But if you mean the size, then no. It's difficult to imagine how something like this would work since the gradient doesn't have to be aligned with the node - it could be diagonal, for example.

[Plecra]

Oh, that was confusing of me! :D I'd only seen @brandonpelfrey's comment when I sent that.

As for Gradient as a Node, I don't really understand what you're proposing. Gradients have N stops, they need colour information; and what I'm looking for is being able to build a gradient relative to the Node we're drawing it in, which I can't see the Gradient nodes' solution for. What do you imagine we'd write to render progress bar?

[chris-findlay]

Regarding progress along a Line, it'd be nice if a line had start% and end% props, as then we could render a line with start% = filled() and a clone with end% = filled(). Same for splines when we get them.