A heap of nasty grid system bugs have been ironed out.
I've put together a little intro area to play around in. Everything feels quite nice. I'm still using placeholder sprites and whatnot, though, so it doesn't look good at the moment. It includes bounce pads, a newly implemented feature, which I think are necessary for the intro level because the player character does not have much vertical mobility at the beginning.
I am considering bringing back the imaginary floor mechanic from SS2 and LoGM -- the thing where you can stand on the bottom of the screen for a moment after entering a room -- but I might not need it this time.
There were weird issues where, when connecting rooms in certain ways, blocks couldn't line up properly. To fix this, I made every room be an integer number of blocks wide. This means that I had to increase the standard 1x1 room size slightly to 864x480. The window remains 853x480 in order to stay in the proper proportion for widescreen. The discrepancy is no problem because the camera code I have happily scrolls the screen the extra 11 pixels automatically, just like it scrolls in larger rooms.