lesson12.txt

#color 0xffc3e1fe
#coord 305 17
#title The Subframe Lessons
#title 112: FILT Modes

#font 7px
#color 0xfffbfbbb
#coord 37 46
#section 12.1 Bitwise Operations

FILT allows you to apply logic gates to
all 30 bits of its ctype at once.

These are called bitwise operations.

For example, we say that 19 AND 26 is 18.

You can check this by writing them out in binary
and taking the AND of every pair of bits.

#section 12.2 FILT Modes

You can perform bitwise operations by setting FILT's tmp.

FILT with tmp = 1 performs the AND operation. When a BRAY is
sent into it, the ctype of the BRAY coming out will be the
AND of the incoming BRAY's ctype and the FILT's ctype.

Other operations include OR (tmp = 2), XOR (tmp = 7) and
"subtract color" (tmp = 3). The "subtract color" gate outputs
ON only if the first input (i.e. bits from the incoming BRAY)
is ON and the second input (i.e. bits from FILT) is OFF.

By default, FILT has tmp = 0, which overwrites the BRAY's ctype
with its own ctype. FILT with tmp = 6 does nothing.

We will use the symbol "&" for AND, "|" for OR, "^" for XOR
and "\" for "subtract color".

#color 0xffeee561

  19 & 26 = 18    19 | 26 = 27    19 ^ 26 = 9    19 \ 26 = 1

#font 5px
#color 0xffbefcc4
#coord 410 48
#section Activity #12.1

You can tell what mode a FILT is in
from the HUD.

Mouseover this FILT to see what
operation it performs.

#section Activity #12.2

What happens when you take the XOR of
a number with itself?

#answer
You get zero! XOR outputs zero
if both inputs are the same.
#answer

Try using FILT to take the XOR of a
number with itself. What happens?

#answer
Nothing comes out!
#answer

This effect is called "BRAY annihilation".
Whenever the result of a bitwise operation
is zero, no BRAY will come out of the FILT.

#section Activity #12.3

Without changing the tmp of these FILTs,
compute their XOR within the same frame.

#hint
Use ARAY/DTEC to transfer one of the
FILT's ctype to a new FILT with tmp = 7.
#hint

#answer 150 10

Challenge: Do the same thing but
without using tmp = 7.