DirectX and video cards Question

Okay, so we have the GF4 which are directx 8 generation right? So they can't
display directx 9 effects? Then why do directx 9 games tell me to install
directx9 if my card is directx8?

Because your game is going to make use of some DX9 routines. While your
card may not fully support DX9, it will make an approximation of the effects
to the best of its abilities. The overall effect with a DX8 compatible card
is not bad, but without DX9 your game is likely to drop out with errors if
it runs at all.

Ron

"() ()" wrote in message
...
Okay, so we have the GF4 which are directx 8 generation right? So they
can't
display directx 9 effects? Then why do directx 9 games tell me to install
directx9 if my card is directx8?

On Mon, 07 Jul 2003 07:05:37 GMT
"Ron Merts" wrote:

Because your game is going to make use of some DX9 routines. While
your card may not fully support DX9, it will make an approximation of
the effects to the best of its abilities. The overall effect with a
DX8 compatible card is not bad, but without DX9 your game is likely to
drop out with errors if it runs at all.

No. The board does not "make an approximation to the best of its
abilities". If the feature is not supported by the hardware then it is
implemented in software, which simply runs more slowly.

A game written for DX9, running under DX9, should run equally reliably
or unreliably on any board supported by DX9, regardless of whether any
particular feature is implemented in software or hardware. That does
not mean that particular boards or drivers won't have defects which will
result in problems, but this would be because of defects in design or
implementation and not to lack of any particular feature.

What _will_ happen though is that programs which make heavy use of
DX9 features that were not present in DX8 will run more slowly on a
board which requires that the software implementation of those features
be used.

Ron

"() ()" wrote in message
...
Okay, so we have the GF4 which are directx 8 generation right? So
they
can't
display directx 9 effects? Then why do directx 9 games tell me to
install directx9 if my card is directx8?

The answer to this question is that a program written to run under
DirectX 9 needs to have DirectX 9 installed on the computer. DirectX 9
is a software product from Microsoft, it is not a hardware device, and
provides a particular set of system calls which are called the
Application Program Interface or API--DirectX 9 has new calls that were
not present in DirectX 8. Programs written to run under DirectX 9 make
use of those new calls, which, since they are not provided with DirectX
8 will result in an error condition. DirectX 9 works with
many existing video boards, however there is a new generation of boards
which are designed to provide hardware acceleration for all features of
DirectX 9. Those board will in principle provide the best performance
under DirectX 9 but they are not required in order to run it.

It's not a matter of "displaying DirectX 9 effects"--such "effects" are
simply patterns of color on a screen and any board that provides the
necessary color depth can display them once the necessary calculations
have been performed to establish what those patterns should be. What a
board which does not have hardware acceleration for DirectX 9 cannot do
is perform in hardware the necessary calculations to figure out what to
display in order to achieve those effects, hence those calculations have
to be done in software instead. This means that using DirectX 9 effects
will result in slower video performance with such a board than with one
which supports those features in hardware. Whether this is a problem or
not depends on how heavily the particular feature is used, how much
calculation it requires, how fast your processor is, and what other
routines are competing for CPU time. Results can range from not
noticeable to totally unusable, and the only way to tell which is the
case in your particular situation is to experiment.



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--John
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(was jclarke at eye bee em dot net)