Path: chuka.playstation.co.uk!news
From: rs108@mdx.ac.uk (Robert Swan)
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: Textures are skewed.
Date: Tue, 10 Mar 1998 02:51:15 GMT
Organization: PlayStation Net Yaroze (SCEE)
Lines: 64
Message-ID: <3504a5f5.4576890@news.playstation.co.uk>
References: <3504949A.95F1D356@cybec.com.au>
NNTP-Posting-Host: stu-dialup10.mdx.ac.uk
X-Newsreader: Forte Free Agent 1.11/32.235

On Tue, 10 Mar 1998 11:17:14 +1000, Toby Hutton <thutton@cybec.com.au>
wrote:
>Anyway, I have some textured quads.  The texture I'm using is a grid, a
>whole lot of squares.  When I put this texture on the quad, it'll go all
>skewwy when viewed from an angle.
>
>Toby.

As far as I'm aware, that happens to all of us and our textured
polugons. Its as a result of the graphics chip taking loads of
shortcuts (including not doing very good perspective correction) to
keep the speed up. There are several ways around this...

1) keep your viewpoint further up and away from all textured polygons.
This may sound silly, but take a look at hover (latest jap demo) and
you realise thats why it can do so much without distortion, or

2) you can force the playstation to divide your polygon into smaller
areas (as the smaller the polygon, the less distortion can occur as it
is a factor of size and orientation). Good point = can correct your
problems. Bad point = slows game down. If you subdivide a polygon into
four smaller polygons then this puts more calculations through the
yaroze. The best compromise is to only subdivide those textures which
are near the viewer. How to do this requires you to code in a routine
to check distances as this isn't done by hardware, and its
effectiveness becomes a function of your programming skill. If you can
easily subdivide your world into a grid system, whereby each object is
attached to a cell in the grid, then you can force subdivision only on
those objects in the cells nearest the viewpoint. (In simplified
theory). Anyway, to actually set the factor of subdivision you
manipulate the attribute member of GsDOBJ2 as shown below:-


typedef struct
{
// any other variables you want to associate with a model, such as
// speed, health, whatver
GsDOBJ2	Obj_Handler;
} modelInfo;

modelInfo	DemoObject[6];

DemoObject[0].Obj_Handler.attribute = 0;
DemoObject[1].Obj_Handler.attribute = GsDIV1;
DemoObject[2].Obj_Handler.attribute = GsDIV2;
DemoObject[3].Obj_Handler.attribute = GsDIV3;
DemoObject[4].Obj_Handler.attribute = GsDIV4;
DemoObject[5].Obj_Handler.attribute = GsDIV5;

// when these objects get registered to be drawn with an ordering
// table using GsSortObject4(), they will be drawn with each of the
// polygons in the model (textured or otherwise) affected as follows
// automatically-

// DemoObject[0] - drawn as normal
// DemoObject[1] - subdivided into 4 smaller polygons
// DemoObject[2] - subdivided into 16 smaller polygons
// DemoObject[3] - subdivided into 64 smaller polygons
// DemoObject[4] - subdivided into 256 smaller polygons
// DemoObject[5] - subdivided into 1024 smaller polygons


I've never had the courage to use GsDIV5 :)