Category : Science and Education
Archive   : SURF1311.ZIP
Filename : STORLINE.PAS

procedure STORLINE (X1, Y1, X2, Y2: integer; var Xpt, Ypt: points;
var Npts: integer);

{ Store the line from (X1,Y1) to (X2,Y2) in an internal buffer array }

var X, Y: integer; { current point being stored }
Xfact: real; { factor for (X,Y) interpolation }
Ylow, Yhigh: integer; { range of for loop }
First: boolean; { flag first dot of line }

begin
First := TRUE;
if (Y2 = Y1) then
Xfact := 0.0
else
Xfact := (X2-X1) / (Y2-Y1);
if (Y1 > Y2) then begin
Ylow := Y2;
Yhigh := Y1;
end else begin
Ylow := Y1;
Yhigh := Y2;
end;
if (Ylow < Gymin) then
Ylow := Gymin;
if (Yhigh > Gymax) then
Yhigh := Gymax;

{ Store the line segment, making sure there is not more than one X
value for any given Y (unless Y1 = Y2, in which case only the two
endpoints should be saved).
}
{ Make sure the entire line isn't out of bounds }
if (Ylow <= Gymax) and (Yhigh >= Gymin) then begin
for Y := Ylow to Yhigh do begin
if (Xfact = 0.0) then
if (First) then begin
X := X1;
First := FALSE;
end else
X := X2
else
X := X1 + round((Y-Y1) * Xfact);
Npts := Npts + 1;
if (Npts <= MAXPTS) then begin
Xpt[Npts] := X;
Ypt[Npts] := Y;
end;
end; { for Y }
end; { if Ylow... }

{ Flag error condition if array dimension exceeded }
if (Npts > MAXPTS) then
Npts := -1;
end; { procedure STORLINE }