libpipi/pipi/paint/aline_template.h

/*
 *  libpipi       Proper image processing implementation library
 *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
 *                2008 Jean-Yves Lamoureux <jylam@lnxscene.org
 *                All Rights Reserved
 *
 *  $Id$
 *
 *  This library is free software. It comes without any warranty, to
 *  the extent permitted by applicable law. You can redistribute it
 *  and/or modify it under the terms of the Do What The Fuck You Want
 *  To Public License, Version 2, as published by Sam Hocevar. See
 *  http://sam.zoy.org/wtfpl/COPYING for more details.
 */

/*
 * aline_template.c: antialiased (Wu) line rendering template
 */

    float x1 = s->x1, y1 = s->y1, x2 = s->x2, y2 = s->y2;
    float g, xd, yd, xgap, xend, yend, xf, yf, val1, val2;
    int x, y, ix1, ix2, iy1, iy2;

    xd = x2 - x1;
    yd = y2 - y1;

    /* "Horizontal" line (X greater than Y)*/
    if (fabsf(xd) > fabsf(yd))
    {
        if (x1 > x2)
        {
            float tmp;
            tmp = x1; x1 = x2; x2 = tmp;
            tmp = y1; y1 = y2; y2 = tmp;
            xd = (x2-x1);
            yd = (y2-y1);
        }
        g = yd/xd;

        xend = truncf(x1+0.5);
        yend = y1 + g*(xend-x1);
        xgap = fractinvf(x1+0.5);
        ix1 = (int)xend;
        iy1 = (int)yend;
        val1 = fractinvf(yend)*xgap;
        val2 = fractf(yend)*xgap;

        PLOT(ix1, iy1,   val1);
        PLOT(ix1, (iy1+1)<y1?(iy1+1):iy1, val2);

        yf = yend+g;
        xend = truncf(x2+0.5);
        yend = y2 + g*(xend-x2);
        xgap = fractinvf(x2-0.5);
        ix2 = (int)xend;
        iy2 = (int)yend;
        val1 = fractinvf(yend)*xgap;
        val2 = fractf(yend)*xgap;

        PLOT(ix2, iy2,   val1);
        PLOT(ix2, iy2+1<y2?iy2+1:iy2, val2);

        for (x = (ix1+1); x < ix2; x++)
        {
            float focus;

            val1 = fractinvf(yf);
            val2 = fractf(yf);
            focus = (1.0 - fabsf(val1-val2));
            val1 += 0.3*focus;
            val2 += 0.3*focus;

            PLOT(x, yf, val1);
            PLOT(x, (yf+1)<y1?(yf+1):yf, val2);

            yf = yf + g;
        }
    }
    /* "Vertical" line (Y greater than X)*/
    else
    {
        if (x1 > x2)
        {
            float tmp;
            tmp = x1; x1 = x2; x2 = tmp;
            tmp = y1; y1 = y2; y2 = tmp;
            xd = (x2-x1);
            yd = (y2-y1);
        }

        g = xd/yd;

        xend = truncf(x1+0.5);
        yend = y1 + g*(xend-x1);
        xgap = fractf(x1+0.5);
        ix1 = (int)xend;
        iy1 = (int)yend;
        val1 = fractinvf(yend)*xgap;
        val2 = fractf(yend)*xgap;

        PLOT(ix1, iy1, val1);
        PLOT(ix1, (iy1+1)<y1?(iy1+1):iy1, val2);

        xf = xend + g;

        xend = truncf(x2+0.5);
        yend = y2 + g*(xend-x2);
        xgap = fractinvf(x2-0.5);
        ix2 = (int)xend;
        iy2 = (int)yend;
        val1 = fractinvf(yend)*xgap;
        val2 = fractf(yend)*xgap;

        PLOT(ix2, iy2,   val1);
        PLOT(ix2, (iy2+1)<y2?(iy2+1):iy2, val2);


        for (y = (iy1+1); y < iy2; y++)
        {
            float focus;
            int   vx = xf;
            val1 = fractinvf(xf);
            val2 = fractf(xf);
            focus = (1.0 - fabsf(val1-val2));
            val1 += 0.3*focus;
            val2 += 0.3*focus;
            PLOT(vx, y, val1);
            vx++;
            PLOT(vx, y, val2);
            xf = xf + g;
        }
    }