[Oberon] SystemV - Simple Graph

[Tomas Kral]

Hi,

Currently pursuing the idea of `Ellipse Solid Fill'.
I borrow this algo, believe is Bresenham, and use two pairs
of horizontal lines.

  PROCEDURE Ellipse*(col, x0, y0, a, b, mode: INTEGER);
    VAR x, y, y1, aa, bb, d, g, h: INTEGER;
  BEGIN aa := a*a; bb := b*b;
    h := (aa DIV 4) - b*aa + bb; g := (9*aa DIV 4) - 3*b*aa + bb; x := 0; y := b;
    WHILE g < 0 DO

      (*Dots - Bresenham algo*)
      (*D.Dot(col, x0+x, y0+y, mode);
      D.Dot(col, x0-x, y0+y, mode);
      D.Dot(col, x0-x, y0-y, mode);
      D.Dot(col, x0+x, y0-y, mode);*)

      (*Fills - TODO replace with ReplConst() and optimise*)
      Line(col, x0-x, y0+y, x0+x, y0+y, mode);
      Line(col, x0-x, y0-y, x0+x, y0-y, mode);

      IF h < 0 THEN d := (2*x+3)*bb; INC(g, d)
      ELSE d := (2*x+3)*bb - 2*(y-1)*aa; INC(g, d + 2*aa); DEC(y)
      END ;
      INC(h, d); INC(x)
    END ;
    y1 := y; h := (bb DIV 4) - a*bb + aa; x := a; y := 0;
    WHILE y <= y1 DO

      (*Dots - Bresenham algo*)
      (*D.Dot(col, x0+x, y0+y, mode);
      D.Dot(col, x0-x, y0+y, mode);
      D.Dot(col, x0-x, y0-y, mode);
      D.Dot(col, x0+x, y0-y, mode);*)

      (*Fills - TODO replace with ReplConst() and optimise*)
      Line(col, x0-x, y0+y, x0+x, y0+y, mode);
      Line(col, x0-x, y0-y, x0+x, y0-y, mode);

      IF h < 0 THEN INC(h, (2*y+3)*aa) ELSE INC(h, (2*y+3)*aa - 2*(x-1)*bb); DEC(x) END ;
      INC(y)
    END
  END Ellipse;

I feel up to replacing `Line' with `ReplConst', but cannot optimise
further. I have got this nice algo for Circle from Joerg (gladly keeping similar algos from the list on file), looking for simplicity.

  PROCEDURE CircleFill*(col, x0, y0, r, mode: INTEGER);
    VAR x, y, r2, lim: INTEGER;
  BEGIN r2 := r*r;
    FOR y := 0 TO r DO
      lim := r2 - y*y; x := 0; WHILE x*x <(*[=]*) lim DO INC(x) END;
      D.ReplConst(col, x0-x, y0+y, 2*x, 1, mode);
      D.ReplConst(col, x0-x, y0-y, 2*x, 1, mode)
    END
  END CircleFill;

Many thanks.

-- 
Tomas Kral <thomas.kral at email.cz>