Make object hover & selection colors brighter and more pronounced

[emilk]

What

Problem

The outline colors of things that are hovered and/or selected in spatial space views has always been way too dark.
Can you quickly spot what is hovered and what is selected in this scene?

The problem with the selection color is that it is the dark blue used for selection of other things, e.g. ListItems:

Using the same color for selections everywhere makes sense, except one cannot really use the same color for a thin stroke as one uses for a massive background.

Solution

This PR introduces two new ContextExt methods: hover_stroke and selection_stroke.

The hover stroke is very bright, making it directly obvious what is being hovered.
The selection stroke is a brighter version of the blue background selection color. The result:

This is a vast improvement in practice (though the anti-aliasing leaves a little something to be desired…)

Other

I also chose to reuse the same colors for other thing things, like the rays show out in the 2D->3D projection:

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
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[Wumpf]

A very unfortuante sideeffect is that this now looks a quite bad on WebGL where we do even less antialiasing of the outlines - this is one of our few hidden WebGL differences: since it's not possible to sample multisampled textures, we don't do any antialiasing at all. On Native and WebGPU we do some (although still with lots to be desired).

WebGL:

WebGPU:

[Wumpf]

The "ugly dna" screenshot I can't repro actually, I guess you ramped up the thickness again after taking that?

(screenshot: chrome Webgpu)

[Wumpf]

Reducing the sharpness parameter in composite.wgsl helps a bit.

WebGL: Left 0.7, right 1.0 (status quo)

[Wumpf]

mechanics lgtm and it's a net win. In favor of going with sharpness of 0.7 as suggested above since it makes the antialiasing issues less pronounced. drawback is the slightly darker appearance again

[emilk]

The "ugly dna" screenshot I can't repro actually, I guess you ramped up the thickness again after taking that? (screenshot: chrome Webgpu)

This is how the current state of the PR looks like on my machine with pixels_per_points=1:

[Wumpf]

I guess github scaled it because the screenshot was too big to fit, making the lines look thinner

you didn't like the sharpness change?