🚀 go-pugleaf

In article <1991Apr16.033639.11295@rti.rti.org> bcw@rti.rti.org (Bruce
Wright) writes:

   You might have been seeing aliasing caused by having the mapping mode
   not match the display resolution.  If you are setting the loop up
   properly the aliasing shouldn't be cumulative (as seems to have been
   the case with your problem from your description), but some lines
   would appear to be a pixel or two off.  (Although this doesn't seem
   like a lot, for screens with a lot of horizontal or vertical lines
   the eye can often zero in on those that are a bit "off", even if the
   line isn't really very far off).

The distortion from scaling from a mapping mode world coordinate
system to the screen pixels was definitely a factor, but I don't think
it was the major problem.

If you look at the diagram in the Petzold book where he explains the
tmHeight, tmInternalLeading, and tmExternalLeading, you can see that
the area you have to play with in terms of drawing a line, is
somewhere in the tmExternalLeading region.  So as plan B, I tried to
trigger the line drawing off of a fractional relationship like this:


/* this is declared somewhere in the code */
yChar = tmHeight + tmInternalLeading + tmExternalLeading;


/* now for the loop to draw the line between rows of text */
for (y = 1; y <= someMaxNum; y++)
{
  /* location to draw line */
  yLine = (yChar + .3 * tmExternalLeading) * y;
  
  /* then draw the line at yLine */
}



This routine draws the line below the row of text.  So to get the
proper position, you have to go down the height of the character plus
some fraction of the external leading.  I choose 0.3 off the top of my
head as I was typing this msg.  The result of the multiplication will
also have to be converted to an integer.

What I could not home in on was the proper fraction.  If you choose a
mapping mode other than MM_TEXT, the coordinate conversion distortion
you mention will rear its head and byte you :)

This approach also leads to major verticle offset problems when you
have lots of rows.  Eventually the lines will overlap the text; once
again, due to the fraction rounding error and the mapping mode
coordinate distortion.
     

Any thoughts on a better approach?
--

                                          A new world record
                                          in the javalin throw
                                                
    /                                          /
   /                                          I
-------------------------------------------------


David Sampson                                         Harris Corporation
dsampson@x102a.ess.harris.com                   Gov't Aerospace Systems Divison
uunet!x102a!dsampson                                  Melbourne, Florida

-------------------------------------------------------------------------------