Can someone clue me in on the usage of bitwise operators when declaring the cardinal direction variables (NSWE)? I can't make sense of it -- those values don't seem to make use of any bitwise operations further down the line, unless I'm missing something, which is very possible.
Is this just a stylistic choice to signal the uses for those variables? (Though I confess I still don't know what that signal would be, anyway.)
Any illumination would be appreciated, but should MBostock still be following this, thanks so much for your work! So inspiring.
The maze is defined as a rectangular grid of cells, where each cell is bit field specifying whether you can navigate from that cell to each of its four neighbors: the cell above (N), the cell below (S), the cell to the right (E), and the cell to the left (W). The bit masks are powers of two (N = 1 << 0 = 1, S = 1 << 1 = 2, W = 1 << 2 = 4, E = 1 << 3 = 8) to uniquely assign each bit to each of the four directions.
For example, say that you have a cell that’s open to the north and the south, as part of a vertical passage. The bit field therefore is 0011. To check whether you can go south from the cell, you use the bitwise AND (&) operator: 0011 & S = 0011 & 0010 = 0010 = truthy. To likewise check whether you can go east from the cell: 0011 & E = 0011 & 1000 = 0000 = falsey.
Is this just a stylistic choice to signal the uses for those variables? (Though I confess I still don't know what that signal would be, anyway.)
Any illumination would be appreciated, but should MBostock still be following this, thanks so much for your work! So inspiring.