Oh man, so I totally just realized something.
The game is always rendering at 400x240, and then scaling up appropriately. It explains why screenshots taken at 1080p always seem to look slightly blurred, and has those odd edges on it. I knew it looked off and now i finally understand why, and how to fix it.
So, I learned that the best way to play the game with those perfectly crisp, hard lined edges is to play at any multiple of 400x240.
For example,
- 400x240
- 800x480
- 1200x720
- 1600x960
- 2000x1200
- 2400x1440
...