``````{1)  An efficient/optimised line-drawing routine (in Pascal
or Asm) based on (or better than) the Bres. Line algorithm.
}

{\$R-,S-}

Uses
Crt, Dos;

Procedure PutPixel(X, Y : Word; Color : Byte);
begin
Mem[\$A000:Y*320+X] := Color
end;

Procedure Switch(Var First, Second : Integer);
{ Exchange the values of First and second }
Var
Temp : Integer;
begin
Temp := First;
First := Second;
Second := Temp;
end; { Switch }

Procedure Line(X1, Y1, X2, Y2, Color : Integer);
{ Uses Bressenham's algorithm For drawing a line }
Var
LgDelta, ShDelta, LgStep, ShStep, Cycle, PointAddr : Integer;

begin
LgDelta := X2 - X1;
ShDelta := Y2 - Y1;
if LgDelta < 0 then
begin
LgDelta := -LgDelta;
LgStep := -1;
end
else
LgStep := 1;
if ShDelta < 0 then
begin
ShDelta := -ShDelta;
ShStep := -1;
end
else
ShStep := 1;
if LgDelta > ShDelta then
begin
Cycle := LgDelta shr 1; { LgDelta / 2 }
While X1 <> X2 do
begin
Mem[\$A000:Y1*320+X1] := Color; { PutPixel(X1, Y1, Color); }
Inc(X1, LgStep);
Inc(Cycle, ShDelta);
if Cycle > LgDelta then
begin
Inc(Y1, ShStep);
Dec(Cycle, LgDelta);
end;
end;
end
else
begin
Cycle := ShDelta shr 1; { ShDelta / 2 }
Switch(LgDelta, ShDelta);
Switch(LgStep, ShStep);
While Y1 <> Y2 do
begin
Mem[\$A000:Y1*320+X1] := Color; { PutPixel(X1, Y1, Color); }
Inc(Y1, LgStep);
Inc(Cycle, ShDelta);
if Cycle > LgDelta then
begin
Inc(X1, ShStep);
Dec(Cycle, LgDelta);
end;
end;
end;
end; { Line }

Procedure SetMode(Mode : Byte);
{ Interrupt \$10, sub-Function 0 - Set video mode }
Var
Regs : Registers;
begin
With Regs do
begin
AH := 0;
AL := Mode;
end;
Intr(\$10, Regs);
end; { SetMode }

Var
x,y,d:Word;
r:Real;

begin   { example }
SetMode(\$13);  { 320x200 256 color mode For VGA and MCGA cards }
For d := 0 to 360 * 10 do
begin
r := (d * PI) * 0.1 / 180;
x := round(sin(r * 5) * 90) + 160;
y := round(cos(r) * 90) + 100;
line(160,100,x,y,x div 4);
end;
Repeat Until port[\$60] = 1;    { hit esc to end }

SetMode(\$03) { Text mode }
end.

``````