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Mr Cucumber

Modern 3D engines

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quote:
Original post by Mr Cucumber
Does modern 3D engines handle the transformations themselves or do they let for example Direct3D handle it for them?


Yes.






- Zorak - Neat Fella.

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Guest Anonymous Poster

For PS2 development, you must do all the transformations
and lighting yourself.

For XBox and GameCube, you do a few transformations, but
the hardware takes care of a majority of them.

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AP:

Depends on what the original poster means by "handling the transformations themselves"

- if he meant doing it with plain CPU instructions rather than letting the graphics hardware do it, then on the platforms you mention, then it''s not usually true.

- if instead he meant putting your own transformation maths and operations into the graphics hardware, then yes thats the case (VU and vertex shader asm to program for PS2 and XBox respectively). The vertex processing on the GC is much more fixed function (lovely TEV wirability and nippy 1TSRAM redress the balance though).


Regardless of how much the API or hardware does though - it''s still useful to know the principles and mathematics behind the whole pipeline. You''re unlikely to end up writing a transform pipe on general hardware professionally (read: for base CPU) nowadays, but knowing how gives important insight.

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Guest Anonymous Poster
quote:
Original post by S1CA
AP:

Depends on what the original poster means by "handling the transformations themselves"



Very true.

quote:

- if he meant doing it with plain CPU instructions rather than letting the graphics hardware do it, then on the platforms you mention, then it''s not usually true.



With regards to the PS2, at least this is how i thought it
worked (Im not one of the engine guys, but i know quite a bit
on how the system works), its just like the PSone in respect
that the hardware expects polygons to be sent to it in
screenspace, with the PS2 wanting a little more info per
polygon. so either the main cpu or the vector units must
do the transformations.

Then again..maybe i was thinking Dreamcast, with its weird
planar projection "z-buffer replacement" tile system that
couldnt handle changing combine modes on the fly.
Yay PowerVR chipset..

quote:

Regardless of how much the API or hardware does though - it''s still useful to know the principles and mathematics behind the whole pipeline. You''re unlikely to end up writing a transform pipe on general hardware professionally (read: for base CPU) nowadays, but knowing how gives important insight.


My thoughts exactly.


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quote:
Original post by Anonymous Poster

[quote]
- if he meant doing it with plain CPU instructions rather than letting the graphics hardware do it, then on the platforms you mention, then it''s not usually true.



With regards to the PS2, at least this is how i thought it
worked (Im not one of the engine guys, but i know quite a bit
on how the system works), its just like the PSone in respect
that the hardware expects polygons to be sent to it in
screenspace, with the PS2 wanting a little more info per
polygon. so either the main cpu or the vector units must
do the transformations.
quote:


Yep you are right, - my point was that the T&L is handled away from the main CPU these days, by co-processors specialised to that job (e.g. PSOne''s GTE or PS2''s VUs [admitted the PS2''s VUs are much more general, but you are always going to be using at least one of them for T&L unless you''re mad]).

Posters asking how engines handle transformations tend to be thinking about old school non-parallel engines where only the main system CPU is running, doing all the transforms and doing all the feeding of the rasteriser - I was trying to put the point across that it''s not the way things are done these days (unless you were coding for a say a GBA )

[quote]
Then again..maybe i was thinking Dreamcast, with its weird
planar projection "z-buffer replacement" tile system that
couldnt handle changing combine modes on the fly.
Yay PowerVR chipset..


Yeah, but it does makes sort independent alpha possible...

--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

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