Developer : Vertex processing & D3DCREATE_FPU_PRESERVE

[alessandroborges1]

Hi Im a developer and Id like to ask some things about Vertex processing and D3DCREATE_FPU_PRESERVE.

1) Vertex processing

As the X3000 is HW-TnL capable, and all older intel cards are not, couldn't the code shown at
http://software.intel.com/en-us/articles/intel-gma-3000-and-x3000-developers-guide
Intel GMA 3000 and X3000 Developer's Guide
looks like below ?

DWORD SetVertexProcessingMode( LPDIRECT3D9 pD3D )
{
 // vertex processing mode - default is mixed for generic card
 DWORD vertexprocessingmode = D3DCREATE_MIXED_VERTEXPROCESSING; 
 
 D3DCAPS9 caps; // Device CAPs structure
 D3DADAPTER_IDENTIFIER9 adapterID; // Used to store device info

 // Retrieve device capabilities
 if( g_pD3D->GetDeviceCaps( 0, D3DDEVTYPE_HAL, &caps ) != D3D_OK ){
 return E_FAIL; // exit if reading caps fails...
 } 

 // Check if hardware T&L is supported...
 // - The D3DDEVCAPS_HWTRANSFORMANDLIGHT capability should
 // be enabled for GMA X3000
 if ( ( caps.DevCaps & D3DDEVCAPS_HWTRANSFORMANDLIGHT ) != 0 ){
 vertexprocessingmode = D3DCREATE_HARDWARE_VERTEXPROCESSING;
 }
 else{
 // Check vendor and device ID and enable software vertex
 // processing for Intel Graphics...
 // Gather the primary adapter's information...

 if( g_pD3D->GetAdapterIdentifier(0,0,&adapterID ) != D3D_OK ){
 return E_FAIL;
 } 
 // this is an Intel non HW-TnL vcard
 if ( (adapterID.VendorId == 0x8086 )) // Intel Architecture 
 {
 vertexprocessingmode = D3DCREATE_SOFTWARE_VERTEXPROCESSING;
 }
 else
 {
 // Chipset does not meet minimum requirements...
 return E_MINSPEC;
 }

 }
 // return default mode - mixed
 return vertexprocessingmode;
} 

2) D3DCREATE_FPU_PRESERVE

Our application does intensive FPU operations, so our engine should use D3DCREATE_FPU_PRESERVE,
to avoid Direct D3D reduce fpu precision to single, when we need double precision.
Does it has bad i mpact on 9x5 vcards ? what about X3000 ?

[wedamon]

RE: 1
I think it would be safer to use the recommended approach described by the article. You don't gain anything by leaving out the checks against the device IDs, really...

RE: 2
You could use the D3DCREATE_FPU_PRESERVE flag, certainly; but just be aware that it is a minor performance penalty (on any graphics solution). The runtime is what sets/clears the FPU flags. I haven't measured the hit, but if you're considering using the flag (as opposed to setting the FPU mode yourself when you know you need it in a certain state) you should set it and see if there is any measurable performance impact to your app.

just my 2c anyway