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Dark GDK / D3D Device Flags

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jezza
16
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Joined: 8th Mar 2008
Location: Bham, UK
Posted: 28th Jul 2008 12:31
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I have a problem whereby my calculations are not precise enough, because when a D3D device is created, by default DirectX limits the CPU's calculations to float values, but this is ot good enough for me. You can stop this by using a CreateFlags.FpuPreserve option when creating the device, but of course this cannot be done when using GDK. Or can it? I need it.
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Mahoney
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Posted: 28th Jul 2008 20:18
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So, if I call an outside function that uses doubles from a DarkGDK app, will they be used as floats?

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jezza
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Posted: 28th Jul 2008 21:02
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I think so yeah. in calculations
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Mahoney
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Posted: 28th Jul 2008 21:15
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v.v

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pirogoth
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Posted: 29th Jul 2008 02:30 Edited at: 29th Jul 2008 02:35
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That isn't quite correct. DirectX does not limit your CPU calculations to floats or doubles or anything else. You will however notice that all DirectX functions/methods use floats however. The reason for this being the GPU (Video Card) is highly optimized for floating point calculations. Naturally DirectX will internally do everything with floating point values and offload anything it can onto the GPU. This simply makes sense.

However this does not limit you on the CPU in the slightest. Also as a quick note, the issue of changing the runtime to default to floating point over double precision only affects users of Managed DirectX (.NET/CLR). So as a user of the DarkGDK or DarkGDK.NET, this should not affect you. Source: http://msdn.microsoft.com/en-us/library/bb322733(VS.85).aspx

-Piro

One last Edit: While I'm seeing references to this affecting standard DirectX as well, I can't actually find anything on it on the MSDN, or any code samples that are not in .NET languages (C# specifically). So it's possible it does affect you, but I find it unlikely.
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jezza
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Posted: 29th Jul 2008 11:07
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well, I ran this:

in a GDK program and i get:


exactly the same thing in a normal command line app:


the difference seen in the GDK one really does make a difference to me when using radians on a large scale.
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Morcilla
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Posted: 30th Jul 2008 12:44 Edited at: 30th Jul 2008 12:45
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Quote: "when a D3D device is created, by default DirectX limits the CPU's calculations to float values"


Uh, I never heard of this. Perhaps you could post the whole code so we can run it ourselves in different machines.
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jezza
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Posted: 30th Jul 2008 18:22
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Ummm, no because the thing I really need it for uses physX so that would be pointless, unless you have the physX SDK installed
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Mahoney
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Posted: 30th Jul 2008 18:46
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I am curious about this issue, though.

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