Screen handling

[boriel]

nice, i got 11 secs for zxbasic and 7 secs for your function

ZX Basic uses ROMs PLOT (which is already somewhat optimized, BTW!), but uses a different entry point, to allow 192 scanlines.
On the other hand, DRAW has already been optimized and no longer uses PLOT, but PIXELADDR for the 1st point of a scan line (remaining points are computed relatively to the last plotted dot).

Also, keep en mind that ZX Basic/ROM PLOT routine also updates ATTR according to TEMP ATTRs and also take into account the SCREEN_ADDR variable (so you can draw/print in another memory/region like a temporary buffer).