The DirectX 8.0 DDI introduces a new mechanism for querying the driver for information. This mechanism extends the existing DdGetDriverInfo entry point to query for additional information from the driver. Currently, this mechanism is only used for querying for DX8 style D3D caps.
Note As you read the following you may question why the GetDriverInfo2 mechanism is necessary. It would seem preferable to simply define a new GetDriverInfo GUID that the driver would handle by returning a D3DCAP8 structure. GetDriverInfo2, introduced in the following paragraphs, is a mechanism to minimize the changes required to the Windows Operating Systems to enable DirectX 8.0 level functionality and thus make redistributing the DirectX 8.0 runtime practical.
This extension to GetDriverInfo takes the form of a DdGetDriverInfo call with GUID_GetDriverInfo2. When a DdGetDriverInfo call with that GUID is received by the driver, it must examine the data structure passed in the lpvData field of the DD_GETDRIVERINFODATA data structure to see what information is being requested. As described below, lpvData can point to either a DD_GETDRIVERINFO2DATA or DD_STEREOMODE structure.
The GUID_GetDriverInfo2 is the same GUID value as GUID_DDStereoMode. If your driver does not handle GUID_DDStereoMode, this is not an issue. However, if your DirectX 8.0 driver handles GUID_DDStereoMode, note that when a call to DdGetDriverInfo with the GUID_GetDriverInfo2(GUID_DDStereoMode) is made, the runtime sets the dwHeight field of the DD_STEREOMODE structure to the special value D3DGDI2_MAGIC. This field corresponds to the dwMagic field of the DD_GETDRIVERINFO2DATA structure. Therefore, by casting the lpvData pointer to either a pointer to a DD_STEREOMODE structure or a pointer to a DD_GETDRIVERINFO2DATA structure and checking the value of the corresponding field (dwHeight or dwMagic) for the value D3DGDI2_MAGIC, you can distinguish between a call to determine stereo mode capabilities or a request of Direct3D 8.0 capabilities.
Once the driver has determined that this is a call to GetDriverInfo2 it must then determine the type of information being requested by the runtime. This type is contained in the dwType field of the DD_GETDRIVERINFO2DATA data structure.
Finally, the driver copies the requested data into the supplied buffer. It is important to note that the lpvData field of the DD_GETDRIVERINFODATA data structure points to the buffer to which to copy the requested data. lpvData also points to the DD_GETDRIVERINFO2DATA structure. This means that the data returned by the driver overwrites the DD_GETDRIVERINFO2DATA structure (and, therefore, that the DD_GETDRIVERINFO2DATA structure occupies the first few DWORDs of the buffer).
In order to be called with GetDriverInfo2, and report DirectX 8.0 capabilities, it is necessary for the driver to set the new flag DDHALINFO_GETDRIVERINFO2 in the dwFlags field of the DD_HALINFO structure returned by the driver. If this flag is not set, the runtime does not send GetDriverInfo2 calls to the driver and the driver is not recognized as a DirectX 8.0 level driver.
The runtime uses GetDriverInfo2 with type D3DGDI2_TYPE_DXVERSION to notify the driver of the current DX runtime version being used by the application. The runtime provides a pointer to a DD_DXVERSION structure in the lpvData field of DD_GETDRIVERINFODATA.