unsigned long* smoke_rays = NULL;

    smoke_rays = new unsigned long[num_nondupe_words];

// IMPROVEMENTS:
// Smoke will now only block LOS after two cells of smoke. This is
// done by updating with a second array.

    int quadrant_x[4] = {  1, -1, -1,  1 };
    int quadrant_y[4] = {  1,  1, -1, -1 };

    const int quadrant_x[4] = {  1, -1, -1,  1 };
    const int quadrant_y[4] = {  1,  1, -1, -1 };

    for ( int i = 0; i < 19; ++i )
        for ( int j = 0; j < 19; ++j )
            sh[i][j] = 0;

    sh.init(0);

        memset( (void*)dead_rays, 0, sizeof(unsigned long) * num_words);

        memset( (void*)dead_rays,  0, sizeof(unsigned long) * num_words);
        memset( (void*)smoke_rays, 0, sizeof(unsigned long) * num_words);

                if ( grid_is_opaque(gr[realx][realy]) ||
                     is_opaque_cloud(env.cgrid[realx][realy]) )

                if ( grid_is_opaque(gr[realx][realy]) )

                }
                else if ( is_opaque_cloud(env.cgrid[realx][realy]) )
                {
                    // block rays which have already seen a cloud
                    for ( unsigned int i = 0; i < num_words; ++i )
                    {
                        dead_rays[i] |= (smoke_rays[i] & inptr[i]);
                        smoke_rays[i] |= inptr[i];
                    }