slicers.lock("BC_Xfer::xfer_slices");
for( int i=0; i<slices1; y0=y1 ) {
Slicer *slicer = slicers.get_slicer(this);
slicers.lock("BC_Xfer::xfer_slices");
for( int i=0; i<slices1; y0=y1 ) {
Slicer *slicer = slicers.get_slicer(this);
active[i] = slicer;
y1 = out_h * ++i / slices;
slicer->slice(this, y0, y1);
active[i] = slicer;
y1 = out_h * ++i / slices;
slicer->slice(this, y0, y1);