Improved collision filter test

[eoineoineoin]

Minor improvements to collision filter test:

SharedPhysicsSystem was doing an O(n*m) test for every possible fixture pair when testing two FixturesComponents for collision. But because it's not doing any narrowphase collisions, the same result can be calculated in O(n+m) steps, just by summing up the collision layers/masks.

Added an interface to check IsHardCollidable() using just the fixtures components. I wanted this when checking collision with an EntityPrototype, so didn't have an Entity yet.

[moonheart08]

Tentative approval, I'm iffy on the idea of encouraging people to do physics checks without a real entity, but the logic looks fine. Please double-check your logic in-game if this code path doesn't have any tests.

[eoineoineoin]

Tentative approval, I'm iffy on the idea of encouraging people to do physics checks without a real entity, but the logic looks fine. Please double-check your logic in-game if this code path doesn't have any tests.

Pretty confident that it's equivalent - have written a few physics engines in my time :). Robust.Shared.Tests/Physics is pretty light on tests, but happy to write some if you like?

The code before was effectively doing:

for every fixtureA in A
     for every fixtureB in B
           if fixtureA.Mask & fixtureB.Layer != 0 || fixtureA.Layer & fixtureB.Mask != 0
                        return true
return false

So I'm just transforming this to get rid of the n^2 loop, by combining all the layers/masks and testing them once:

allLayersA = A[0].Layer | A[1].Layer | A[2].Layer | ....
allMasksA = A[0].Mask | A[1].Mask | A[2].Mask | ....
allLayersB = B[0].Layer | B[1].Layer | B[2].Layer | ....
allMasksB = B[0].Mask | B[1].Mask | B[2].Mask | ....

if allLayersA & allMasksB != 0 || allMasksA & allLayersB != 0
      return true;
return false;