gamedevlists-windows

[GD-Windows] graphics cards texture offset thing

[Richard F. <gd...@th...>]

Hi, i'm pretty new to rendering code, and have stumbled upon a problem i
have never thought about before: how do you write games that "know"
whether the textures are offset by a pixel or not?

I use textures for fonts, and this is where artefacts show up most.
How do you go about determining what UVs to give the characters when the
values you give may be hardware transposed to somewhere unknown?

------------------
On the other hand
I may be talking
complete drivel.
------------------ 

Re: [GD-Windows] graphics cards texture offset thing

[Javier A. <ja...@py...>]

Richard Fabian wrote:
> How do you go about determining what UVs to give the characters when
> the values you give may be hardware transposed to somewhere unknown?

There are sub-pixel accuracy issues regarding the location of the pixel
center, which are usually solved by using point filtering and adding .5f / W
or .375f / W to the UV coordinates (W is the width / height of the texture).

Other than that, no the hardware doesn't magically change your UVs unless
there's a bug somewhere.

-- 
  Javier Arevalo
  Pyro Studios

RE: [GD-Windows] graphics cards texture offset thing

[Richard F. <gd...@th...>]

thats what i meant, i have an app that runs fine on my ATI 9800, but
looks like the UVs are shifted down by 1/W  in both dimensions when
running on my GeForce 5800.

when i run the app on a PSP, the same UVs generate correct looking
text... I am assuming that it is GeForces that get it wrong... is this a
known thing? and how do you detect when to fix it and when its "just
works" as in the case of the ATI card.

------------------
On the other hand
I may be talking
complete drivel.
------------------ 

> -----Original Message-----
> From: gam...@li... 
> [mailto:gam...@li...] On 
> Behalf Of Javier Arevalo
> Sent: 18 June 2004 12:36 PM
> To: gam...@li...
> Subject: Re: [GD-Windows] graphics cards texture offset thing
> 
> 
> Richard Fabian wrote:
> > How do you go about determining what UVs to give the 
> characters when 
> > the values you give may be hardware transposed to somewhere unknown?
> 
> There are sub-pixel accuracy issues regarding the location of 
> the pixel center, which are usually solved by using point 
> filtering and adding .5f / W or .375f / W to the UV 
> coordinates (W is the width / height of the texture).
> 
> Other than that, no the hardware doesn't magically change 
> your UVs unless there's a bug somewhere.
> 
> -- 
>   Javier Arevalo
>   Pyro Studios
> 
> 
> 
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