From: "Jason Smithwick" <jets@soton.ac.uk>
To: <efg2@efg2.com>
Subject: ComputerLab Feedback
Date: Wed, 20 Jun 2001 14:29:52 +0100

Dear Earl,

I have been working on a Plotting Prgram for graphs etc. and found most of
the Newsgroups posted solutions for Dotted/Dashed lines types for a line
thickness>1 in Delphi unsatisfactory.

I was wondering if you would like my solution to the problem. This works for
2 to N Point Lines.

Basically define the Pen for your canvas first (e.g. Pen.Width=6,
Pen.Style:=psDot etc.) and then pass the Canvas, TPoint array, and number of
points to the following procedure:

Best regards,

Jason
----------------------------------------------------------------------------
-------

Const
 MaxNumPlotData=500;

type
    PlotPointArray = Array [1..MaxNumPlotData] of TPoint;



procedure DrawPolyLine(Canvas : TCanvas; PP : PlotPointArray; numpts :
integer);
var
   dist,m,r,dx,dy,xa,ya : real;
   i,pl,numps : integer;
   space : boolean;
   LP : TPoint;
   ps : array[1..6] of integer;
   tempps : TPenStyle;
   DashDist,SpaceDist,DotDist : integer;
begin
     DashDist:=15;
     DotDist:=5;
     SpaceDist:=5;
     tempps:=Canvas.Pen.Style;
     Case Canvas.Pen.Style of
          psSolid : begin
                  Canvas.PolyLine(Slice(PP,numpts));
                  exit;
          end;
          psDash : begin
                 numps:=2;
                 ps[1]:=DashDist;
                 ps[2]:=-SpaceDist
          end;
          psDot : begin
                    numps:=2;
                    ps[1]:=DotDist;
                    ps[2]:=-SpaceDist;
          end;
          psDashDot : begin
                    numps:=4;
                    ps[1]:=DashDist;
                    ps[2]:=-SpaceDist;
                    ps[3]:=DotDist;
                    ps[4]:=-SpaceDist;
          end;
          psDashDotDot : begin
                    numps:=6;
                    ps[1]:=DashDist;
                    ps[2]:=-SpaceDist;
                    ps[3]:=DotDist;
                    ps[4]:=-SpaceDist;
                    ps[5]:=DotDist;
                    ps[6]:=-spacedist;
          end;
          psClear : exit;
     end;
     Canvas.Pen.Style:=psSolid;
     dist:=0;
     space:=false;
     if numpts>=1 then begin
        Canvas.MoveTo(PP[1].X,PP[1].Y);
        LP.X:=PP[1].X;
        LP.Y:=PP[1].Y;
     end;
     i:=1;
     pl:=1;
     while i<numpts do begin
           dx:=PP[i+1].X-LP.X;
           dy:=PP[i+1].Y-LP.Y;
           dist:=dist+Sqrt(dx*dx+dy*dy);
           if dist<abs(ps[pl]) then begin
              if space then Canvas.MoveTo(PP[i+1].X,PP[i+1].Y)
              else Canvas.LineTo(PP[i+1].X,PP[i+1].Y);
              LP.X:=PP[i+1].X;
              LP.Y:=PP[i+1].Y;
              i:=i+1;
           end
           else begin
                r:=Sqrt(dx*dx+dy*dy)-(dist-abs(ps[pl]));
                if abs(dx)>0 then begin
                   m:=dy/dx;
                   if dx>=0 then xa:=LP.X+sqrt(r*r/(1+m*m))
                   else xa:=LP.X-sqrt(r*r/(1+m*m));
                   ya:=LP.Y+m*(xa-LP.X);
                end
                else begin
                     xa:=LP.X;
                     if dy>0 then ya:=LP.Y-r
                     else ya:=LP.Y-r;
                end;
                LP.X:=round(xa);
                LP.Y:=round(ya);
                if Space then Canvas.MoveTo(LP.X,LP.Y)
                else Canvas.LineTo(LP.X,LP.Y);
                pl:=pl+1;
                if pl>numps then pl:=1;
                dist:=0;
                space:=ps[pl]<0;
           end;
     end;
     Canvas.Pen.Style:=tempps;
end;


*********************************************
Dr Jason Smithwick
Wolfson Unit M.T.I.A.
University of Southampton
Southampton, SO17 1BJ, U.K.
*********************************************
Tel: +44 (0)23 8058 5044
Fax: +44 (0)23 8067 1532
e-mail: jets@soton.ac.uk
URL: www.soton.ac.uk/~wumtia
*********************************************