Explanation of 1200DPI confusion (mentioned in brlaser.drv.in)

[ahydronous]

// The 1200dpi mode is weird: we need to send 1200x1200dpi raster
// data, but Brother only advertises 1200x600dpi. I wonder what
// is going on there.

There are actually two separate 1200dpi modes. 1200dpi and 1200hq.
1200dpi is true 1200x1200, whereas 1200hq simulates (and gets pretty close to) 1200dpi by printing 2400x600 mixed with a few tricks like interpolation.