if(!bv) return 0;
for(ty = FFMAX(y - c->range, 0); ty < FFMIN(y + c->range, c->avctx->height - bh); ty++){
for(tx = FFMAX(x - c->range, 0); tx < FFMIN(x + c->range, c->avctx->width - bw); tx++){
if(tx == x && ty == y) continue; // we already tested this block
dx = tx - x;
dy = ty - y;
if(!bv) return 0;
for(ty = FFMAX(y - c->range, 0); ty < FFMIN(y + c->range, c->avctx->height - bh); ty++){
for(tx = FFMAX(x - c->range, 0); tx < FFMIN(x + c->range, c->avctx->width - bw); tx++){
if(tx == x && ty == y) continue; // we already tested this block
dx = tx - x;
dy = ty - y;