Unpack Color

The other side of packcolor: one number becomes four again

mediumYou need: A colour as one number, Properties of buildings

A packed colour is one number, and it cannot be read by eye. unpackcolor lays it back out into four channels.

steptick 0

Sensor0

=

 in

Unpack Color1

= unpack

Operation2

=

*

Operation3

=

*

Operation4

=

*

Operation5

= floor

Operation6

= floor

Operation7

= floor

Print8

Print9

Print10

Print11

Print12

Print13

Print Flush14

Stop15

@counter0number

colournullnull

Rnullnull

Gnullnull

Bnullnull

Anullnull

The program asks copper for its colour and prints it channel by channel: the board shows copper colour: 217 157 115.

sensor colour @copper @color
unpackcolor R G B A colour

Field	What is in it
the first four	where to put red, green, blue and alpha
fifth	the packed colour

Note

The channels come back as fractions from zero to one — the same ones packcolor takes. The familiar 0–255 are obtained by multiplying: op mul R R 255. In the example the multiplication is followed by op floor, because dividing and multiplying by 255 leaves a tail like 217.00000000000003.

Why take a colour apart

Taking one apart is rarely needed for its own sake — colours are usually assembled rather than read. There is one real use: learning a colour somebody else chose.

• an item’s, liquid’s or block’s colour — sensor @color, and the display draws ore in its own colour;
• a team’s colour — sensor @color @crux, so markers on the map match what the player sees around them;
• a colour that arrived from a memory cell or a neighbouring processor and needs a small change — dimming it by halving the channels and packing it back, for instance.

unpackcolor R G B A colour
op div R R 2
op div G G 2
op div B B 2
packcolor dim R G B A

That is the usual way of working with colour: take apart, adjust the channels, pack again. The packed number itself must not be touched with arithmetic.

Remember

• unpackcolor R G B A colour lays a packed colour out into four channels.
• The channels are fractions from zero to one; 0–255 comes from multiplying.
• The main source of other people’s colours is sensor @color on content and teams.
• To change a colour you take it apart, adjust the channels and pack it back with packcolor.

Task

Change @copper in the example to @graphite and run it: the numbers come out different — graphite is grey, and all three channels end up close to one another.

Then remove the three op floor lines and look at the board: instead of round numbers there are tails. That is not a fault of the unpacking but the ordinary imprecision of fractional numbers — there is a lesson of its own about it.