Hi Carl,
Have you actually got this working in practice (I presume so). We were
going to have multiple locales in our project, but we read all the
documentation (not much, & a bit cryptic) and we still couldn't get
HiResCoord to work properly. I think if I recall properly it worked OK for
small numbers (where you don't really need HiResCoords), but for larger
values, which we needed to keep our locales sufficiently separated, we
couldn't get them to work. And if I recall correctly the larger numbers we
tried which didn't work weren't all that large. You mention something about
bit twiddling, can you elaborate on this, and why this is necessary? What
is the difference between a two's-complement fixed-point number and an
integer?
Anyone else who's successfully used HiResCoords or is familiar with bit
twiddling or computer number representations feel free to join in too and
enlighten me / save me from my ignorance. For our project, we ended
up using multiple VirtualUniverses, which I read somewhere is not the
recommended way of doing things (something about you shouldn't need more
than 1 universe). How have other people dealt with multiple independent
scenes in their programs?
Thanks,
Matt Pattison
Carl Smotricz ([EMAIL PROTECTED]) [001027 10:02]:
> Hi Mohammed,
>
> At 12:00 26.10.00 , you wrote:
> >how can I construct a Locale at Origine(x,y.z)?.I want to have two
> >locale under my universe. I read about the HiResCoord classe but I
> >didn't really understand how it works. let's say I want the origine at
> >(12,10,45) how do I come then to the following
> >Constructor parameters values:
> >public HiResCoord(int[] X,
> > int[] Y,
> > int[] Z)
> >
> > x - an eight element array specifying the x position
> > y - an eight element array specifying the y position
> > z - an eight element array specifying the z position
>
> I checked the documentation for HiResCoord (you DO have the JavaDocs for
> the J3D library, don't you?) and found this:
>
> (-----quote-----)
> The HiResCoord defines a point using a set of three high-resolution
> coordinates, each of which consists of three
> two's-complement fixed-point numbers. Each high-resolution number consists
> of 256 total bits with a binary point at bit 128, or
> between the integers at index 3 and 4. A high-resolution coordinate of 1.0
> is defined to be exactly 1 meter. This coordinate
> system is sufficient to describe a universe in excess of several billion
> light years across, yet still define objects smaller than a
> proton.
> (-----end quote-----)
>
> This isn't immediately obvious if you're not into binary math, but it can
> be worked out.
> Here is a picture of the first 3 of those 8 integers and the bytes
> contained therein.
> Note 1: I'm only showing part of the number because an email line is only
> so long.
> Note 2: Change the font of this text to Courier to look at it, or it will
> not be aligned right.
>
> Int index: -----0----- -----1----- -----2-----
> Contents (hex): 00 00 00 00 00 00 00 00 00 00 00 00
>
> So... an integer is 4 bytes = 32 bits.
> With all those bits, one integer can count up to 2 billion or so before the
> high bit flips and it becomes negative.
> The description says that we should imagine a binary point between the
> third and fourth integer. This means that the bits to the left of this
> position form a whole number and the bits to the right form a fraction. To
> show this, I'll zoom out of my picture a bit now, showing integers, not bytes:
>
> Index: ----0--- ----1--- ----2--- ----3--- . ----4--- ...
> Contents: 00000000 00000000 00000000 00000000 | 00000000 ...
>
> You said you wanted your X to be 12. All you have to do is make the
> decimal/binary point in your number (it's to the right of the 12) line up
> with the decimal/binary/whatever point in this 256-bit-long number
> describing your position. Your 12 is 0C in hex, if you line it up in the
> big number it looks like this (note where I put the 'C'):
>
> Index: ----0--- ----1--- ----2--- ----3--- . ----4--- ...
> Contents: 00000000 00000000 00000000 0000000C | 00000000 ...
>
> which tells you that to create a '12' as a HiResCoord all you have to do is
> put that 12, as an ordinary integer, into the 4th word (word index 3 in the
> array) of an array containing 8 zeroes. Bingo, done! This approach will
> take you all the way up to about 2 billion; after that you need to do some
> bit twiddling to get the right numbers into the right integers.
>
> If you want fractions behind the decimal point, say 0.25, then you need to
> set some bits in the 5th integer (word 4). To create 0.25, you need to put
> 0.25 of 0x100000000 into that integer, or roughly 1 billion.
>
> So... positioning a Locale is not so hard, especially if the position is a
> whole number less than 2 billion.
>
> Happy hacking, I hope it works out for you!
>
> -Carl-
>
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