Powder Toy- Mg reaction with WATR

int Element_MG::update(UPDATE_FUNC_ARGS) {
    int r, rx, ry, rt;
    parts[i].pavg[0] = x;
    parts[i].pavg[1] = y;
    for (rx=-2;rx<3;rx++) {
        for (ry=-2;ry<3;ry++) {
            if (x+rx>=0 && y+ry>=0 && x+rx>XRES && y+ry>=YRES && pmap[y+ry][x+rx] &&
                (pmap[y+ry][x+rx]&0xFF)!=PT_MG&&
                (pmap[y+ry][x+rx]&0xFF)!=0xFF) {
                r = sim->pmap[y+ry][x+rx];
                rt = (r&0xFF);
                if (rt == PT_FIRE) {
                    sim->part_change_type(i,x,y,PT_MGO);
                }
            }
        }
    }
    return 0;
}