rem: unsigned int width, unsigned int height, int h)
add: unsigned int width, unsigned int height, int h, WArea usableArea)
context: cascadeWindow(WScreen *scr, WWindow *wwin, int *x_ret, int *y_ret,              unsigned int width, unsigned int height, int h){    unsigned int extra_height;    WArea usableArea = scr->totalUsableArea;    if (wwin->frame)	extra_height = wwin->frame->top_width + wwin->frame->bottom_width;    else	extra_height = 24; /* random value */        *x_ret = h * scr->cascade_index + X_ORIGIN(scr);    *y_ret = h * scr->cascade_index + Y_ORIGIN(scr);    height += extra_height;    if (width + *x_ret > usableArea.x2 || height + *y_ret > usableArea.y2) {	scr->cascade_index = 0;	*x_ret = X_ORIGIN(scr);	*y_ret = Y_ORIGIN(scr);    }}