This article is from the Mac Programming FAQ, by Jon Watte email@example.com with numerous contributions by others.
On 68k Macs, NOT SetCPixel()! Assuming you have the correct ForeColor()
set, you can set the pen size to (1,0) and call Line (0,1)
I have heard PaintRect is good for this but requires slightly more code.
Using PaintRect eliminates a trap call.