Codechange: Use vehicle viewport hash to find clicked vehicle.

[PeterN]

Motivation / Problem

Clicking on a vehicle in a viewport needs to find the which vehicle was clicked on. This is done by iterating through all vehicles that exist to find the nearest one.

On a game with a lot of vehicles this can take some time (but only in the order of milliseconds.)

Description

Use the existing vehicle viewport hash instead.

This avoids having to iterate all vehicles, which can be a minor performance improvement when there are many vehicles.

Performance measurements with the old stalwart wentbourne game:

version	release	debug
master	avg 1100µs (1.1ms)	avg 6500µs (6.5ms)
this pull request	5-20µs	10-30µs

Limitations

The code is more complex as it duplicates the viewport hash loop from ViewportAddVehicles(). While that could be abstracted out to allow reuse, it would then be slightly detrimental to viewport drawing performance.

This is a fairly unnecessary performance change, as a user cannot click on vehicles fast enough to notice an issue.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[TrueBrain]

I assume you tested it :)

[PeterN]

I assume you tested it :)

"It's so quick you don't even see the window appear..."