Easy: when rendered, the two pixels on each respective coplanar surface will end up with the same Z value, if the distance between those surfaces ( what is usally called the thickness) is small.

• 这是因为在实时表现时，如果共面表面上间的距离很近（通常称为厚度），那么这些面上的两个重叠像素点的Z值就会是一样的。