[PD] data structures - color?

[Mathieu Bouchard]

On Wed, 29 Mar 2006, Frank Barknecht wrote:

> My GEM patches OTOH have a lot of [unpack $1 $2 $3] constructs. Btw: It
> would be nice if the GEM color objects would accept lists instead of
> being forced to [unpack 0 0 0] in front of every colorRGB object.

Someone else implemented that.

It's called GridFlow.

BTW, Jitter has got the same problem, just worse. You've got to pass your
list through a messagebox like "aoutline $1, routline $2, goutline $3,
boutline $4" if it's for setting the outline colour of some figure, for
example.

> Encoding RGB color in one float is hard enough, but how to encode RGBA
> into one float?

Take the RGB value as an integer 0..0xFFFFFF. If it's less than 0x800000, 
substract 0x1000000. Then multiply by 1<<(alpha-104).

To decode, compute alpha = int(log(abs($1))/log(2)+104). Then divide by 
1<<(alpha-104). If it's less than 0, add 0x1000000. That gives you an 
integer 0..0xFFFFFF which is your RGB triplet.

Sorry, but it's really the easiest way (and almost the only way) to encode
32-bit RGBA in a 32-bit float.

If you want to encode it in 24 bits, use 6+6+6+6 bits, and if you want it 
to fit in 19 bits (because of Pd's... features) then use 5+5+5+4 or 
something.

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| Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
| Freelance Digital Arts Engineer, Montréal QC Canada