Re: Please Explain Graphics

[Roger Johnstone <rojaws@orcon.net.nz>]

In <1112047558.043919.250830@l41g2000cwc.googlegroups.com> Rex the 
Strange wrote:

> Oh really! That would probably be it and I do recall reading that
> somewhere, now that you mention it. Thanks - I'll try it tonight when 
> I get home and will let you know. Thanks.
>
> rts

Try a diagonal line too to see the effect colour has on the hires 
display.

This will produce a nice solid purple diagonal line

  HGR
  HCOLOR=2
  HPLOT 0,0 TO 279,159

But try this

  HPLOT 0,0 to 20,159

and you'll get a line with big chunks missing from it. As Charlie said 
the problem is that the Apple II produces colour by only plotting every 
second pixel, giving a horizontal resolution of 140 pixels. 
Unfortunately the HPLOT command doesn't take this into account. That's 
great for producing Moire effects, but not great for coloured diagonal 
lines, or vetical lines in the wrong column. There are replacement HPLOT 
programs which do work properly, though I can't remember their names 
offhand.

-- 
Roger Johnstone, Invercargill, New Zealand
http://vintageware.orcon.net.nz/
________________________________________________________________________
  No Silicon Heaven? Preposterous! Where would all the calculators go?

              Kryten, from the Red Dwarf episode "The Last Day"