Fix multiple issues with screenshake code

[in1tiate]

While working on an independent project, I found multiple issues with the screenshake function:

• Maximum deviation from origin did not work as expected (values frequently exceeded this so-called maximum)
• Random deviation was heavily biased toward positive values, resulting in screenshakes being visibly directed downwards and to the right
• X and Y deviation were calculated using the same randomly generated value, resulting in screenshakes being visibly locked into a linear set of positions
• Screenshake intensity was not scaled to the viewport - A larger viewport would have less intense shaking

I have ported my corrected version. Here are some example videos, so you can see the difference (viewport size 512x384)

Current screenshake:
https://user-images.githubusercontent.com/32779090/179497853-4b789143-2f11-4a61-9af6-f2002f1fd5cb.mp4

My screenshake:
https://user-images.githubusercontent.com/32779090/179497933-7da6037e-2640-4866-8d9d-573f935a71da.mp4

[Salanto]

Looks goot to me, might cause troubles when using older distros, but eh, that can be done later. CI passes and your demo shows the noticable improvement to the old system.

[Salanto]

We are probably gonna loose some precision during your implicit conversion from float to int, but the effect will likely be negligible.

[in1tiate]

This is purposeful, actually - this is used as the bounds for QRandomGenerator, which does not generate floating point numbers. Additionally, since this is a deviation from the origin in pixels, the maximum applicable precision is integer precision anyway.

Also the implicit conversion only happens to the end value, which means the loss of precision is negligible (and doing these calculations with integers noticeably affects the final value - a 480p viewport will have a max deviation of 14 when done with integer math, while using floats will bump it up to 17).

[in1tiate]

[Salanto]

I'm gonna need a stapler at this point to keep it approved.
The surprise tool looks like ass, but hoenstly, it seems to work a bit better.

[stonedDiscord]

i hate mickey mouse

[Salanto]

staple noises

[stonedDiscord]

you made me look at mickey mouse again 😭

[oldmud0]

Making the shake scale to viewport size is a welcome addition.