Place down the holographic projector, and right click (without any tools) to bring up the interface.
1 slot -- Place an item in here, and that is what the Hologram uses to create an image. Example: Place smoothstone, and the hologram is made of smoothstone. Place Cobble, etc you get the idea.
3 lines for settings, with numbers 1 though 9. This is Height and Width and depth. This tells you how big the projector's image will be. Example:
You choose 1x3x3, it creates a 1x3x3 wall of whatever material you placed in the item slot. (Not sure if this is do-able, if not, we'll need to figure out another way to size the thing).
Finally, theres a checkbox (or yes/no, or something) that determines whether the hologram is 'solid' or not. Solid holograms act just like normal MC blocks -- non solid holograms LOOK just like MC blocks, but you can walk right through them. (Perhaps toggle this with a redstone current?)
Requires 1eu/s per block. 2 eu/s per SOLID block (double energy cost to make image solid, aka can't walk through it).
Thoughts? 
... although it would be awesome to make something disappear (still hoping ...), turning it into a mountain would be pretty neat as well.
would support this. lol
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