mixster

const
  init_force = 100; // Initial acceleration - ms^-2 (same as force in newtons assuming 1 kg projectile)
  init_angle = 30; // Initial angle in degrees, with horizontal being 0 and vertical being 90
  grav = 9.81; // Gravity, x ms^-2
  res = 1; // Resistance, x ms^-2

var
  r_for, x_for, y_for, cur_ang, x_pos, y_pos: Extended; // resultant force; x and y components of resultant force; current angle of projectile
  i: Integer; // Timer
  arc: TPointArray;
  tb: TBox;

begin
  r_for := init_force;
  x_pos := 0;
  y_pos := 0;
  cur_ang := Radians(init_angle);
  i := 0;
  repeat
    SetLength(arc, i + 1);
    arc[i] := Point(Round(x_pos), Round(y_pos));

    r_for := r_for - res;
    x_for := r_for * Cos(cur_ang);
    x_pos := x_pos + x_for;

    y_for := (r_for * Sin(cur_ang)) - grav;
    y_pos := y_pos + y_for;
    if (y_pos < 0) then
      y_pos := 0;

    cur_ang := ArcTan(y_for / x_for);
    r_for := x_for / Cos(cur_ang);

    i := i + 1;
  until y_pos = 0;

  SetLength(arc, i + 1);
  arc[i] := Point(Round(x_pos), Round(y_pos));
  tb := GetTPABounds(arc);

  tb.y2 := tb.y2 + 5;

  DisplayDebugImgWindow(tb.x2, tb.y2 + 5);
  Wait(50);
  GetDebugCanvas.Brush.Color := clWhite;
  GetDebugCanvas.Rectangle(0, 0, tb.x2, tb.y2 + 5);
  GetDebugCanvas.MoveTo(0, tb.x2);
  GetDebugCanvas.Pen.Color := clBlack;

  for i := 0 to High(arc) do
    GetDebugCanvas.LineTo(arc[i].x, tb.y2 - arc[i].y);
end.