Add <standing-on> element to the Filters module

[harvanchik]

Feature Explanation

Sometimes, you want to know if a player is standing on a certain block, but you don't want to make 10, 20 or even more regions for all the places where that block/material is. Adding a <standing-on> element to the Filters module would make this so much easier.

Use Case & Implementation

A possible use case using this feature would be to kill a player when standing on a specific block. Instead of creating regions all around the map for every single occurance of the "kill block," the <standing-on> in the filter would do all the work for you.

<filters>
    <standing-on id="on-stone">
        <material>stone</material>
    </standing-on>
</filters>

Then apply a kit everywhere (or wherever this should take affect) to set their health to zero.

Whether or not it is implemented as an element like <standing-on> or another way, it would be nice to have a way of detecting this. In addition to <standing-on> it would make sense to add a <standing-beneath> (or under) -- and possibly a way of detecting blocks to the right, left, in front, and behind (or synthesize that into a <touching> element.

I'm not sure that adding them as elements is the best way of doing it, but I'll leave that up to the more experienced to decide.

Streamlining

I also wonder if it would be possible to streamline it so that you could also check for things such as if a player is placing a block that is above or below another block/material.

[Pablete1234]

I'd approach it as an offset filter modifier.

<filters>
    <offset loc="~0,~-0.5,~0">
        <material>stone</material>
    </offset>
<filters>

This would allow you to check if a player is next to a block, standing on a block, under a block, has certain block at y=0, or even looking at a block if ^ relative modifier is implemented. This is assuming vanilla coordinates where a number means absolute, ~ is for relative and ^ is relative to where you're looking at.

[harvanchik]

@Pablete1234 This is much more streamlined. Would create so many possibilities for map makers.

[KingOfSquares]

I just completed this, had to run but PR is coming later today