Opacity

Opacity (and its inverse, transparency) are properties of blocks which affect how the game renders it and other nearby blocks, as well as how occlusion culling is handled.

The primary purpose of opacity is to tell the game engine if it needs to render other blocks behind that block; an opaque block completely obscures the view behind it, while a transparent block does not. Therefore, transparency applies not only to solid blocks like ice and glass, but also to blocks like cacti, stairs, chests, and single slabs, which are not considered full blocks. By this definition, transparency does not imply that a block is actually see-through, which is a quality of the item texture specified by the game or resource pack.

In Bedrock Edition, most transparent blocks become opaque when located far away from the player. This is especially noticeable when looking long distances with the spyglass. The distance at which blocks become opaque is proportional to the render distance.