/************************************************************************/
/* Fill a base triangle using scan-line function                        */
/* and then fill a general triangle (using triangle fill routine)       */
/************************************************************************/

fill_triag()
        {

        /* Fill a base line triangle                                    */

        int     x0 = 100,x1 = 0, x2 = 300, y0 = 10, y1 = 100, y2 = 100;
        int     y, color = 15, start, end;
        for (y = y0; y <= y1; y++)      /* Loop over raster lines       */
                {                       /* Compute intercepts           */
                start = x0 + ((y - y0)*(x1 - x0))/(y1 - y0);
                end   = x0 + ((y - y0)*(x2 - x0))/(y2 - y0);
                scanline(start,end,y,color);    /* Fill next section    */
                }

        /* Fill a general triangle                                      */

        triangle(400,100, 500,0, 630,200, color);
        }

/************************************************************************/
/*                                                                      */
/*  triangle(x0,y0,x1,y1,x2,y2,color) - Fill a general triangle with    */
/*             color 'color'.  This routine will call the scanline      */
/*             procedure to fill scanlines between two edges of the     */
/*             triangle.                                                */
/*                                                                      */
/*             First vertices are ordered so that vertex 'a' is the     */
/*             left most top vertex, and 'b' is the left most bottom    */
/*             vertex.  Triangle is than split into two 'baseline'      */
/*             triangles, and each triangle is filled separately.       */
/*             One triangle is an upward pointing arrow and the second  */
/*             Triangle is a downward pointing arrow.                   */
/*                                                                      */
/************************************************************************/

triangle(x0,y0, x1,y1, x2,y2, color)
int     x0,y0, x1,y1, x2,y2,color;
        {
        int     x[4],y[4],a,b,c,temp;
        x[0] = x0;
        x[1] = x1;
        x[2] = x2;
        y[0] = y0;
        y[1] = y1;
        y[2] = y2;

        /* Order the vertices */
        a = 0;                                  /* Get lowest left in a */
        if (y[0] > y[1]) a = 1;
        if (y[a] > y[2]) a = 2;
        b = (a+1)%3;
        c = (b+1)%3;
        if (y[a] == y[b] && x[a] > x[b]) a = b;
        if (y[a] == y[c] && x[a] > x[c]) a = c;
        b = (a+1)%3;
        c = (b+1)%3;
        if (y[b] < y[c])                        /* Get highest left in b*/
                {
                temp = b;
                b = c;
                c = temp;
                }
        if (y[b] == y[c] && x[b] > x[c])
                {
                temp = b;
                b = c;
                c = temp;
                }
        /* fill 'base' triangles */
        if (y[a] == y[b])                       /* Fill degenerates     */
                {
                scanline(x[a],x[b],y[b],color);
                scanline(x[a],x[c],y[c],color);
                }
        else if (y[a] == y[c])                  /* Fill down arrow      */
                fill_dw(x[a],y[a],x[b],y[b],x[c],y[c],x[b],y[b],y[c],color);
        else if (y[b] == y[c])                  /* Fill up arrow        */
                fill_up(x[a],y[a],x[b],y[b],x[a],y[a],x[c],y[c],y[c],color);
        else
                {                               /* Split into two bases */
                y[3] = y[c];                    /* one up and one down  */
                x[3] = x[a] + ((y[3] - y[a])*(long int)(x[b] - x[a]))/(y[b] - y[a]);
                if (x[3] < x[c])                /* 'c' is to the right  */
                    {
                    fill_up(x[a],y[a],x[b],y[b],x[a],y[a],x[c],y[c],y[c],color);
                    fill_dw(x[a],y[a],x[b],y[b],x[c],y[c],x[b],y[b],y[c],color);
                    }
                else                            /* 'c' is to the left   */
                    {
                    fill_up(x[a],y[a],x[c],y[c],x[a],y[a],x[b],y[b],y[c],color);
                    fill_dw(x[c],y[c],x[b],y[b],x[a],y[a],x[b],y[b],y[c],color);
                    }
                }
        }

fill_up(ax,ay, bx,by, cx,cy, dx,dy,y0,color)    /* Fill up arrow        */
int     ax,ay,bx,by,cx,cy,dx,dy,y0,color;
        {
        int    dyab,dycd,y,d1,d2;
        dycd = dy - cy;
        dyab = by - ay;
        for (y = ay; y <= y0; y++)
                {
                d1 = ((y - ay)*(long)(bx - ax))/dyab;
                d2 = ((y - cy)*(long)(dx - cx))/dycd;
                scanline(ax+d1, cx+d2, y,color);
                }
        }
fill_dw(ax,ay, bx,by, cx,cy, dx,dy,y0,color)    /* Fill down arrow      */
int     ax,ay,bx,by,cx,cy,dx,dy,y0,color;
        {
        int    dyab,dycd,y,d1,d2;
        dycd = dy - cy;
        dyab = by - ay;
        for (y = dy; y >= y0; y--)
                {
                d1 = ((y - ay)*(long)(bx - ax))/dyab;
                d2 = ((y - cy)*(long)(dx - cx))/dycd;
                scanline(ax+d1, cx+d2, y, color);
                }
        }