Re: Drawing lines of variable widths

The demonstration program only works for lines in the first octant.

See the comment
"This version of the demo only supports the drawing of lines in the
first octant - where (X2-X1)>(Y2-Y1)>0. Drawing lines in other octants
is obtained by defining the 4 types of moves required by the loops."

In your examples, (X2-X1)<0 and so it does not work.

I originally coded the algorithm in 1976, but when I published the web
pages in 1999, I did not get round to extending the example algorithm
for the other octants. This is left as an exercise for the reader.

Alan Murphy

On 11 Jul 2006 08:58:53 -0700, george.lutz@xxxxxxxxx wrote:


Alan Murphy wrote:
On 10 Jul 2006 16:27:13 -0700, george.lutz@xxxxxxxxx wrote:

Is there an algorithm available to draw lines of variable thickness
(using a bare bones graphics library - not GDI, etc)? I can draws
lines of single thickness. I am looking for something similiar to the
GDI functionality that creates a pen of a certain thickness then draws
a line using the pen.

This is an easy thing to do when I want to draw a line of zero or no
slope (i just draw parallel lines using DrawLine() of course), however
when i need to draw thicker lines of variable slope, it becomes quite
complex. I assume this has been done before though.

Thank you for any advice!

George

You may like to look at an algorithm I invented in 1976. This is
published at:
http://homepages.enterprise.net/murphy/thickline/index.html

The algorithm supports non-integer pen thicknesses. The example on the
page, show how the pen thickness can be varied as a function of the
length drawn. (i.e. a tapered line).

As I am now retired and no longer work in this field I am not able to
answer questions on modern implementations, but I gather that this has
been done by others.

Alan Murphy

Mr. Murphy,
I have actually experimented with your algorithm already as it is the
only such algorithm I have been able to find. It seems to work for
about 80% of the lines I've drawn, however the problem I have found is
that certain lines are not drawing correctly. For example, take the 2
connecting lines below here, drawn at a width of 3 (or 4 or 5). The
lines do not appear to be the same widths.

POINT p0 = {159,25};
POINT p1 = {107,207};

POINT p0a = {107,207};
POINT p1a = {0,319};

Have you heard of such an issue? Are you aware of any modifications to
the posted algorithm?

Thank you very much for any advice, it is much appreciated.

.

Relevant Pages

  • Re: Drawing lines of variable widths
    ... Alan Murphy wrote: ... I originally coded the algorithm in 1976, but when I published the web ... This is an easy thing to do when I want to draw a line of zero or no ... The algorithm supports non-integer pen thicknesses. ...
    (comp.graphics.misc)
  • Re: Drawing lines of variable widths
    ... Alan Murphy wrote: ... I originally coded the algorithm in 1976, but when I published the web ... This is an easy thing to do when I want to draw a line of zero or no ... The algorithm supports non-integer pen thicknesses. ...
    (comp.graphics.misc)
  • Re: Drawing lines of variable widths
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