16.16 integer fixed-point line drawer :)

[paul_nicholls]

Hi all,
If any of you are interested, I have created a very simple and fast 16.16 integer based fixed-point 2d line drawer.

This means the code uses numbers with 16 bit integer part, and 16 bit fractional part.

The idea is definitely not new and I didn't invent it but here it is for anyone to use

Type
{...........................................................................}
    TFixed = LongInt;
    TInterpolant = Record
        Value : TFixed;
        Delta : TFixed;
    End;
{..............................................................................}

{..............................................................................}
Function  CalculateInterpolant(v1,v2,span : LongInt) : TInterpolant;
Begin
    Result.Value := v1 * 65536;
    Result.Delta := 0;
    If span > 0 Then Result.Delta := ((v2 - v1) * 65536) Div span;
End;
{..............................................................................}

{..............................................................................}
Procedure SDLSurface_DrawLine2d(Const s           : PSDL_Surface;
                                      x1,y1,x2,y2 : Integer;
                                Const r,g,b,a     : Byte;
                                Const SetPixel    : TSetPixel);
Var
    x,y   : Integer;
    dx,dy : Integer;
    span  : Integer;
    i     : Integer;
    ix,iy : TInterpolant;
Begin
    dx := Abs(x2 - x1);
    dy := Abs(y2 - y1);
    Case dx >= dy Of
        False : span := dy;
        True  : span := dx;
    End;
    ix := CalculateInterpolant(x1,x2,span);
    iy := CalculateInterpolant(y1,y2,span);
    For i := 0 To span Do
    Begin
        x := ix.Value Shr 16;
        y := iy.Value Shr 16;
        SetPixel(s,x,y,r,g,b,a);
        Inc(ix.Value,ix.Delta);
        Inc(iy.Value,iy.Delta);
    End;
End;

Enjoy
cheers,
Paul