Have you tried confirming that the value you enter in a knob is even stored
as-is to begin with? I think that's the piece you're missing. For example, I
created a Roto, added a shape, and set its 'center.x' value to your input
float (1054.123456). Upon closing reopening the control panel, the knob
displays the exact value you're seeing: 1054.12341309.
In other words, what you're seeing appears to be standard floating-point
precision loss, occurring when the text entered by the user is converted and
stored. I would guess that the closing and reopening is what causes Nuke to
pull that value back out of the knob's storage memory to display in the bin.
Also, 43b40000 should translate to 360.0. Your value (or the floating-point
approximation of it) is stored as 4483c3f3.
Hope this helps.
-Nathan
-----Original Message-----
From: Magno Borgo
Sent: Wednesday, May 08, 2013 11:09 AM
To: nuke-python@support.thefoundry.co.uk
Subject: [Nuke-python] Parsing hex float values - precision loss
Hello.
I working on a script parser that takes the raw .nk file and do some magic.
The v7 roto format stores the animated float values using hexadecimal
literals
(http://docs.thefoundry.co.uk/nuke/70/ndkdevguide/advanced/rotoformat.html),
something like this:
x41200000 (this is 10)
x43b40000 (this is 1054.123456)
after some research on the interwebs I managed to found a way to convert
these back to float using this function:
def hex2float(s):
#s is a string like x4000000, we need only the 4000000 part:
s = str(s.group().lstrip()[1:])
bins = ''.join(chr(int(s[x:x+2], 16)) for x in range(0, len(s), 2))
return str(struct.unpack('>f', bins)[0])
But I'm running into some precision loss after the conversion, for example
x43b40000 is originally 1054.123456, after conversion using the function
above 1054.12341309
Any tips on this kind of conversions?
Thanks in advance,
--
Magno Borgo
www.boundaryvfx.com
www.borgo.tv
Brasil:Curitiba:GMT= -3
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