Path: chuka.playstation.co.uk!news
From: "Alex Herbert" <alex@herbs.dabsol.co.uk>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Newbie needs basic help
Date: Mon, 19 Nov 2001 13:19:46 -0000
Organization: PlayStation Net Yaroze (SCEE)
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References: <9t4jt2$ob41@www.netyaroze-europe.com> <01c16fc2$8b592ba0$2f3be4d5@pal-s-omnibook> <9t76in$ob42@www.netyaroze-europe.com>
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Hi Greg,

> GsOT_TAG WorldTags[2][NO_OF_SPRITES*sizeof(GsSPRITE)];

This is nonsense and is not the way to define the OTs.  OT_TAGs should be
defined:

GsOT_TAG WorldTags[2][1<<OT_LENGTH];

where OT_LENGTH is the bit depth of your ordering table.

The OT is used to represent the z-axis with each array element representing
a point or plane along the z-axis, 0 being closest to the screen.  So, if
your OT_LENGTH is defined as 4, then you'll have a 4-bit z-axis giving a
range of 0 to 15.  Similarly, an OT_LENGTH of 14 will yield a z-axis depth
of 16384.

If you're working in 2D then the z-axis is used for sprite priorities.  I.e.
sprites with lower priorities appear in front of sprites with higher
priorities.  If several sprites are sorted at the same priority then the
first one sorted will appear on top.

The reason the array is 2 dimensional is because an OT (being a table) is a
1 dimensional array, and you've got 2 of them - the one you're preparing and
the one the GPU is drawing.  Note that when calling GsClearOt and GsDrawOt,
a pointer to either WorldTags[0] or WorldTags[1] is used to select which of
the 2 OTs should be cleared/drawn.

Check out pages 17-18 of the Library Reference which sort of give an
explanation - ish.  Also look at the source code for the 'check' program on
the Yaroze CD.

Hope this helps.

Alex


"Greg Cook" <gjc53@student.canterbury.ac.nz> wrote in message
news:9t76in$ob42@www.netyaroze-europe.com...
> Thanks for the explanation of the struct stuff, thats great..
>
> as for the second part.. i think i asked the question wrong.
>
> From looking at the reference manual how did you know to define the code
> below?
>
> GsOT_TAG WorldTags[2][NO_OF_SPRITES*sizeof(GsSPRITE)];
>
> looking at the reference manual theres not example of how to define/use
the
> structure, so how did you know to define it as 2d? i know the example code
> that sony has supplied shows it define like what is abo ve, but apart from
> seeing that would anyone of known how to define/use the structure.
>
> again not sure if im putting the question the right way, all im trying to
> say is i wouldnt of known to write the code like above from just looking
at
> the reference manual ( i wouldnt of known to use 2 dimensions etc ) the
only
> way i know how to do it is because theres a sample bit of code provided by
> sony..
>
> anyways i'll keep playing
>
> Greg
>
>