Thanks for the quick answer.
The concept of embedding three 8 bit components in one integer was
clear
to me, but I think that pd doesn't really use all 8 bits for the
colors.
Or maybe there is some issue with 2-complements or something.
For example, if I want to create three bang objects, in red
(#ff0000),
green (#00ff00) and blue (#0000ff), your formula gives values of:
16711680, 65280, 255 for the three colors.
But I insert them in a patch, like:
#N canvas 825 10 450 300 10;
#X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 16711680 0 0 ;
#X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 65280 0 0 ;
#X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 255 0 0 ;
I see the colors white, white, yellow.
Now, when I change the colors by hand, to really get red, blue and
green
on the bang objects and save the file, it reads:
#N canvas 825 10 450 300 10;
#X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 -258049 -1
-1 ;
#X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 -4033 -1 -1 ;
#X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 -64 -1 -1 ;
So it uses negative numbers, and -64 means "full blue".
Now, when I re-open the same file and look at the properties of
the blue
bang object, the color now reads: #0000fc instead of the #0000ff I
entered just before saving.
That's why I suspect some lower resolution going on. I tried to
browse
this part in the sources, but all the GUI code confuses me.
For your interest, this patch results for colors of #040000,
#000400 and
#000004 set by hand in the properties window:
#X obj 0 0 bng 15 200 50 0 target empty empty 0 0 0 8 -4097 -1 -1;
#X obj 0 15 bng 15 200 50 0 target empty empty 0 0 0 8 -65 -1 -1;
#X obj 0 30 bng 15 200 50 0 target empty empty 0 0 0 8 -2 -1 -1;
Setting colors to lower values, like #010000 results in getting them
rounded down to #000000.
So, the resolution is apparently 256/4 = 64 values, or 6 bits.
Indeed, if I replace the formula with:
color = (-([red]+1)/4*64*64) - (([green]+1)/4*64) - ([blue]+1)/4
I get the same values that Pure Data produces.
Hm, I might just have solved my problem.
It's still weird and some developer could check this our or change
the
documentation.
Cheers, Robert
On 02/13/2010 11:08 PM, Martin Peach wrote:
That formula should read:
color = ([red] * 65536) + ([green] * 256) + ([blue])
In binary the idea is to shift the 8 'red' bits 16 to the left,
then add
8 'green' bits shifted 8 bits, and finally 8 'blue' bits, so in
all 24
bits are occupied.
Multiplying the blue value by -1 in the original formula has the
effect
of setting the 16 bits to the left of it to 1, so you get different
shades of pure blue.
Martin
Robert Schwarz wrote:
Hi all,
I recently tried writing patches in a text editor (or from
scripts) and
had problems getting the color settings right, for bang elements.
There is some documentation at
http://puredata.info/docs/developer/fileformat
with the explanation:
Color: Some graphical elements have color attributes. Per color
only
one signed integer value is stored that contains the three 8-bit
color components (RGB). Formula to calculate color attribute
values:
color = ( [red] * -65536) + ( [green] * -256) + ( [blue] * -1)
Where [red], [green], [blue] obviously represent the three color
components, their values range from 0 to 255. They apply to the
attributes [background color], [front color], [label color] of
various elements.
I tried that, but it didn't work. Instead of showing the whole
spectrum
I just got different shades of blue. Also, when I opened one of my
handwritten patches in PureData, looked at the color settings
and saved,
the resulting numbers changed. I assume that some kind of
rounding is
happening, and colors are actually saved in lower resolution.
Do you have any ideas?
Also, my application is a 13x13 button matrix, each triggering
different
chords via MIDI. The buttons should be color coded. Obviously,
it's too
much work setting all colors individually and I might want to
create
several of these patches with different colors.
Maybe there is another obvious solution I didn't see.
Any help is appreciated!
(I'm using standard pd 0.42_5 on Arch Linux, but this shouldn't
make a
difference.)
