> But how was the region implemented?
The source code describes it as "an unpacked array of sorted inversion points". If you can read 68k assembly, here's the implementation of PtInRgn:
https://github.com/historicalsource/supermario/blob/9dd3c4be...
The source code describes it as "an unpacked array of sorted inversion points". If you can read 68k assembly, here's the implementation of PtInRgn:
https://github.com/historicalsource/supermario/blob/9dd3c4be...
It’s a sorted list of X coordinates (left to right). If you group them in couples, they are begin/end intervals of pixels within region (visibles), but it’s actually more useful to manipulate them as a flat array, as I described.
I studied a bit the code and each scanline is prefixed by the Y coordinates, and uses an out of bounds terminator (32767).
There's no such guarantee. The NEXTHOR loop only inverts for points which are to the absolute left of the point being tested ("IS HORIZ <= PT.H ? \\ NO, IGNORE THIS POINT").
Imagine that, for every point, there's a line of inversion that goes all the way down to the bottom of the bounding box. For a typical rectangular region, there's going to be four inversion points - one for each corner of the rectangle. The ones on the bottom cancel out the ones on the top. To add a second disjoint rectangle to the region, you'd simply include its four points as well; so long as the regions don't actually overlap, there's no need to keep track of whether they share any scan lines.