This mod adds compasses and special blocks. The compasses are attached to the block and point at it. Blocks and compasses have names.

1. Blocks and Items
2. Using
3. API

1. Point Block

   
   

2. Compass

   

1. Right click at point block and set name of block.
   
2. Left click at point block with compass.
3. Left click with compass in hand and its arrow will point at attached block.

The name and the coordinates of blocks are stored in mod_storage, key is "compasses".

Function changeCompass (line 161) starts when left click with compass in hand. If there is point block near, then compass gets attached to it.

Else function compassImg (line 106) starts. It controls the arrow.

In the drawing the red point is the point block, green is player. Blue line is direction of view. Yellow line built with two points - block point and player coordinates.

Blue and yellow lines are 2D vectors (x-z coordinates). Black is angle A between vectors. It calculates with formula:

ab=|a||b|cosA

Then use cross product of vectors to determine where block is located regarding player`s line of view. If it is on the right then add 180 to angle A.

The arrow of compass deviates by an angle A.