z_order_debug renders are cubes black

[mrk-its]

Bevy version
current master

Operating system & version

Ubuntu 20.04

What you did
Ran z_order_debug example

What you expected to happen

cubes should have different color depending on distance

What actually happened

All cubes are black

It seems this behavior is introduced by 7d065ee#diff-ee5fac51976cada9d968631feef5cb2bbfdbdb4c2057c08e1a1a2e743fa7f4ae

cc: @jamadazi

[DJMcNab]

Reintroducing the square root does fix it. That is, converting:

bevy/examples/3d/z_sort_debug.rs

Line 37 in 3475a64

let value = 1.0 - (visible_entity.order.0 - 10.0) / 7.0;

to

let value = 1.0 - (visible_entity.order.0.sqrt() - 10.0) / 7.0;

That being said, it doesn't seem like we should encourage relying on what order actually means

Since there is the possibility we'd want to change it again in the future (e.g. normalise it to a certain power of 2 to speed up comparisons, as a potential example)