Vector Imagery

[Josh Dersch]

Brad Parker wrote:
> I would guess that a simple parallel port adc on a PC could do very
> well displaying a reasonable number of dots on a scope with intensity
> control...  not very impressive given what fpga's do now shading polygons,
> but fun none the less.
>
>   
A couple of years ago I tried this -- I built two very (very) simple 
parallel-port DACs (one for X, the other for Y) and I had them connected 
to linux machine with two parallel ports.  I wrote a small test app to 
rapidly write data to the output pins on the parallel ports.  Plotting 
points on the oscilloscope worked OK (aside from the poor precision of 
my DACs), but drawing arbitrary vectors seemed to be impossible because 
I couldn't figure out a way to change the data sent to the parallel 
ports for X and Y at /exactly/ the same time.  Since X would be changed 
slightly before Y (or vice versa) I'd get a stairstep effect instead of 
a single line from point A to B.

Maybe a faster machine would be able to reduce this effect (I was using 
a Pentium Pro 200), or clever use of DMA...

Josh