Add star seek adaptive difficulty

[K-Meech]

For #16

As discussed with David (see new info on the issue), adaptive difficulty for this game is focused on changes to the overall time limit.

• Adds progression of time limit from 1 minute, up to a maximum of 3 minutes
• Currently can only increase (no criteria for decreasing), but I will check if this is needed by David
• I also fixed the issue with the left / right stars appearing offscreen for certain screen sizes - as noted by @thompson318 on the last PR

[mmcleod89]

Adaptive difficulty looks good to me; potentially an additional useful parameter is to keep track of something like a "streak". We might not want the difficulty to change with every game, but maybe you complete the current difficult 3 times or something like that. It should be quite easy to do with the save data and we can always initially default it to 1 so we're changing difficulty every time, but it would just give them some extra options in play-testing (especially if they're ending up with weirdly small increments between difficulty levels it might work better to have a 15 or 30 second increment but ask for a short streak instead of updating every time).

[mmcleod89]

The screen limits seem to be working nicely, but it also means that there are only 4 locations that are being spawned; is this the desired behaviour? I got the impression from the original document that the stars could appear anywhere within the field of play (except presumably where we have UI elements in the way!)

[K-Meech]

I'm going to put this back to draft while I add the features we discussed in the meeting today 👍

[K-Meech]

@mmcleod89 @thompson318 - I think this PR is ready to review again now. In addition to the changes mentioned above, I've added:

• the player must meet the upgrade rate for 3 games in a row for the time limit to increase. This should mean the time limit upgrade is fully configurable from the unity editor now - you can set: the time limit increment, the required star collection rate + the number of games in a row that must meet that rate.

• stars are now spawned on a configurable grid (with a certain number of rows / columns), and each spawned star will be a minimum distance apart. To avoid spawning stars under UI elements, I've added a configurable list of 'gridPositionsToExclude', so we can adapt this as needed. (I tested this with a 1920 x 1080 screen + a surface sized screen, and seems the current exclusion values work well for both)

[thompson318]

Looks good and plays well. All stars were on screen for me and in different positions. One question about if/how we should control for people putting silly values in for the parameters that would be good to look at before merging.

[K-Meech]

Thanks @thompson318 - I think I've addressed all your comments now. I removed the un-needed if else statement + added an allowable range to the min distance variable. I've set this to 0-9 for the moment, as I found a distance of 10 could fail if the initial star spawned near the middle of the screen.

It's tough to ensure these values are always valid, as they will also depend on what edge offset is set to. With a large edge offset, the area stars can spawn in is much smaller and hence a smaller min distance is required to allow correct spawning. Due to this, I also added a check in spawnStar which will throw a more informative error if no valid spawn locations are available.

[thompson318]

Looks good.