func (f *Field) flushLine(j int) bool {
	for i := 0; i < fieldBlockNumX; i++ {
		if f.blocks[i][j] == BlockTypeNone {
			return false
		}
	}
	for j2 := j; 1 <= j2; j2-- {
		for i := 0; i < fieldBlockNumX; i++ {
			f.blocks[i][j2] = f.blocks[i][j2-1]
		}
	}
	for i := 0; i < fieldBlockNumX; i++ {
		f.blocks[i][0] = BlockTypeNone
	}
	return true
}
func (f *Field) flushLine(j int) bool {
	for i := 0; i < fieldBlockNumX; i++ {
		if f.blocks[i][j] == BlockTypeNone {
			return false
		}
	}
	for j2 := j; 1 <= j2; j2-- {
		for i := 0; i < fieldBlockNumX; i++ {
			f.blocks[i][j2] = f.blocks[i][j2-1]
		}
	}
	for i := 0; i < fieldBlockNumX; i++ {
		f.blocks[i][0] = BlockTypeNone
	}
	return true
}
// flushLine flushes the line j if possible, and if the line is flushed,
// the other lines above the line go down.
//
// flushLine returns a boolean value indicating whether
// the line is actually flushed.