[PD-dev] pd file format: color settings

[Martin Peach]

Yes but why? You can accurately represent every 32-bit int with a float, 
but Pd clips them by using the %g format specifier to print them, 
instead of %f.

In m_atom.c, at line 68, the function atom_string() converts atoms into 
strings, and in the case of float atoms, uses this line to do it:

sprintf(tbuf, "%g", a->a_w.w_float);

This prints both of the floats 16777215.0 and 16777214.0 as "167772e+7".
It seems to me that

sprintf(tbuf, "%f", a->a_w.w_float);

would be better, since it prints 16777215.000000, 16777214.000000.

Martin

Roman Haefeli wrote:
> I assume, this is because a 24bit integer cannot be saved with full
> precision with Pd, since Pd seems to strip off some bits when saving a
> floating point value (or when printing or displaying it). If the color
> would be encoded as RGB 8bpp, it would look different after saving and
> restoring it. So a smaller range had to be used. 
> 
> When sending 'color' messages to the iemguis directly, the full 24bit
> resolution can be used.
> 
> Roman
> 
> 
> 
> On Sat, 2010-02-13 at 18:32 -0500, Martin Peach wrote:
>> Ah yes, in g_all_guis.c line 281:
>>
>> void iemgui_all_colfromload(t_iemgui *iemgui, int *bflcol)
>> {
>>      if(bflcol[0] < 0)
>>      {
>>          bflcol[0] = -1 - bflcol[0];
>>          iemgui->x_bcol = ((bflcol[0] & 0x3f000) << 6)|((bflcol[0] & 
>> 0xfc0) << 4)|
>>              ((bflcol[0] & 0x3f) << 2);
>>      }
>>      else
>>      {
>>          bflcol[0] = iemgui_modulo_color(bflcol[0]);
>>          iemgui->x_bcol = iemgui_color_hex[bflcol[0]];
>>      }
>>
>> ...so if the colour is negative it's a negated (all bits flipped) 18-bit 
>> rgb value and if it's positive it's an indexed colour from the iemgui 
>> palette.
>> 111111RRRRRRGGGGGGBBBBBB
>> is bit-flipped to get:
>> 000000rrrrrrggggggbbbbbb
>> which is shifted into this:
>> rrrrrr00gggggg00bbbbbb00
>> so the 2 LSBs of each colour are set to 0. I don't know why.
>>
>> Martin
>>
>> Robert Schwarz wrote:
>>> 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.)
>>>>>
>>
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