Listing 3 


/*
    fillOval() = draws an oval centered at (x,y) with    
                 radius in y direction of 'b' with       
                 aspect ratio 'aspect' and fills it      
                 with color 'color'.                     
                                                         
*/



void fillOval(float x_cen, float y_cen, float radius, 
    int color, float aspect)
{
    union REGS reg;

    #define seq_out(index,val)  {outp(0x3C4,index);\
                     outp(0x3C5,val);}
    #define graph_out(index,val)  {outp(0x3CE,index);\
                     outp(0x3CF,val);}

    unsigned int offset;
    char far * mem_address;
    float a,b,aspect_square;
    int x,y,col,row,dummy,mask,start_x, start_y,end_x,end_y;
    float a_square,b_square,b_test;

    a = radius/aspect;
    a_square = a*a;
    b = .729*radius;
    b_square = b*b;
    x = x_cen;;
    y = y_cen);
    start_x = max(0,x-a);
    end_x = min (639,x+a);
    start_y = max(0,y-b);
    end_y = min(349,y+b);

    for (col=start_x; col<=end_x; col++)
    {
        b_test = b_square - (b_square*(col-x)*(col-x))/a_square;
        mask = 0x80 >> ((col) % 8);
        graph_out(8,mask);
        seq_out(2,0x0F);
        for (row=start_y; row<=end_y; row++)
            if ((long)(row-y)*(row-y) <= b_test)
            {
                offset = (long)row*80L + ((long)(col)/8L);
                mem_address = (char far *) 0xA0000000L +
                    offset;
                dummy = *mem_address;
                *mem_address = 0;
                seq_out(2,color);
                *mem_address = 0xFF;
                seq_out(2,0x0F);
            }
    }
    graph_out(3,0);
    graph_out(8,0xFF);
}