graphic output on a PC

Ellis Golub ellis at biochem.dental.upenn.edu
Sun Feb 18 10:42:42 EST 1996

In article <9602161742.AA03533 at aquila>, manion at AQUILA.RM.FCCC.EDU ("\"\"Frank J. Manion\"\"") writes:
|> Just fyi...
|> Graphics programs which output data as single "points" on devices often
|> implement some method to insure the point is actually visible to the human eye.
|> Dots of radius .0004 inches are not horribly visible with the naked eye.
|> Consequently you will see points rendered by some graphics programs
|> as either lines or filled boxes of small size. Quite often this type of
|> function is actually implemented in the graphics "driver".
|> This may be why the program functions in this way. I would hesitate to call
|> this a "problem". Reading the HPGL into CorelDraw is simply using the output in
|> a way the original authors never envisioned.
|> -- Frank

Hi Frank --

Your comments make sense when the output is directed to a display device, but
not to a plotter.  On a pen plotter (the native output device for HPGL) the dot
resolution is defined by the size of the pen, which the plotting language has no
control over.  When HPGL is used to emulate a screen, it usually does it by 
raising the pen, moving it to the appropriate coordinates and putting it down.
Instead, GCG really tries to draw lines.  Here is a sample of a dotplot output
I recently downloaded:


As you can see, the pen is raised (PU) moved to a coordinate, lowered (PD)
and then a line is drawn (PA).  Corel is not misinterpreting this data, it
is faithfully translating the HPGL as written.

I still think someone at GCG ought to have a look at this.

Good to hear from you.


Ellis Golub                            Phone: (215) 898-4629
Biochemistry Department                FAX:   (215) 898-3695
University of Pennsylvania             ellis at biochem.dental.upenn.edu
School of Dental Medicine             
4001 Spruce Street
Philadelphia, PA 19104-6003

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