lesson13.txt

#color 0xffc3e1fe
#coord 305 17
#title The Subframe Lessons
#title 113: BRAY Annihilation

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#section 13.1 INWR-Mode DRAY

When activated with any conductor other than PSCN, DRAY will not
overwrite or delete particles in the copy destination area.

When activated by INWR, DRAY will additionally not copy diagonally.

#space 20

#section 13.2 FILT to SPRK

Using BRAY annihilation, we can translate FILT data into a SPRK bit.

One way is to use BRAY to spark a conductor directly.
However, this creates a SPRK with life = 4, which can't
be used to activate other circuits within the same frame.

A better way is to use DRAY in INWR mode.

For example, this circuit activates an ARAY only if
the input FILT's ctype is even.

This works by checking if the last bit (representing "1" in binary)
is set. Specifically, A & 1 = 0 only if A is even.

If the last bit isn't set, the BRAY is annihilated, and the INWR-mode
DRAY copies a SPRK with life = 3 into the spot where the BRAY
would otherwise have gone. We call this spot the BRAY output zone.

As usual, the BRAY (if the input is odd) or SPRK (if the input is even)
needs to be cleared every frame. This DRAY handles both cases.

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#color 0xffbefcc4
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#section Activity #13.1

In an effort to save space, a fellow
subframer tried the following design
for the even/odd detector:

#space 20

Instead of copying a SPRK into the
BRAY output zone, this design copies
in the ARAY.

However, as you can see, the ARAY
fails to activate even if the input
ctype is even. What's wrong?

#answer
When the ARAY is copied in, the game
assigns the newly created ARAY an ID.

This ID does not come before the IDs of
the CONV stack. The CONVs reset the
PSCN before the ARAY's update function
is run, so the ARAY is not activated.

Always remember that particle ID order
does not necessarily follow subframe
order, unless you have just reloaded
particle order.
#answer

As a rule of thumb, you should avoid
copying activated particles like ARAY
and DRAY into empty space.