gdi和dx比较研究

gdi设备获取的源头， 同样是通过底层驱动来进行实现

PGRAPHICS_DEVICE
NTAPI
EngpRegisterGraphicsDevice(
    PUNICODE_STRING pustrDeviceName,
    PUNICODE_STRING pustrDiplayDrivers,
    PUNICODE_STRING pustrDescription,
    PDEVMODEW pdmDefault)
{
    PGRAPHICS_DEVICE pGraphicsDevice;
    PDEVICE_OBJECT pDeviceObject;
    PFILE_OBJECT pFileObject;
    NTSTATUS Status;
    PWSTR pwsz;
    ULONG i, cj, cModes = 0;
    BOOL bEnable = TRUE;
    PDEVMODEINFO pdminfo;
    PDEVMODEW pdm, pdmEnd;
    PLDEVOBJ pldev;

    DPRINT("EngpRegisterGraphicsDevice(%wZ)\n", pustrDeviceName);

    /* Allocate a GRAPHICS_DEVICE structure */
    pGraphicsDevice = ExAllocatePoolWithTag(PagedPool,
                                            sizeof(GRAPHICS_DEVICE),
                                            GDITAG_GDEVICE);
    if (!pGraphicsDevice)
    {
        DPRINT1("ExAllocatePoolWithTag failed\n");
        return NULL;
    }

    /* Try to open the driver */
    //    找到gdi设备获取的初始源头了，就是这里
    Status = IoGetDeviceObjectPointer(pustrDeviceName,
                                      FILE_READ_DATA | FILE_WRITE_DATA,
                                      &pFileObject,
                                      &pDeviceObject);
    if (!NT_SUCCESS(Status))
    {
        DPRINT1("Could not open driver %wZ, 0x%lx\n", pustrDeviceName, Status);
        ExFreePoolWithTag(pGraphicsDevice, GDITAG_GDEVICE);
        return NULL;
    }

    /* Enable the device */
    EngFileWrite(pFileObject, &bEnable, sizeof(BOOL), &cj);

    /* Copy the device and file object pointers */
    pGraphicsDevice->DeviceObject = pDeviceObject;
    pGraphicsDevice->FileObject = pFileObject;

    /* Copy device name */
    wcsncpy(pGraphicsDevice->szNtDeviceName,
            pustrDeviceName->Buffer,
            sizeof(pGraphicsDevice->szNtDeviceName) / sizeof(WCHAR));

    /* Create a win device name (FIXME: virtual devices!) */
    swprintf(pGraphicsDevice->szWinDeviceName, L"\\\\.\\VIDEO%d", (CHAR)giDevNum);

    /* Allocate a buffer for the strings */
    cj = pustrDiplayDrivers->Length + pustrDescription->Length + sizeof(WCHAR);
    pwsz = ExAllocatePoolWithTag(PagedPool, cj, GDITAG_DRVSUP);
    if (!pwsz)
    {
        DPRINT1("Could not allocate string buffer\n");
        ASSERT(FALSE); // FIXME
    }

    /* Copy display driver names */
    pGraphicsDevice->pDiplayDrivers = pwsz;
    RtlCopyMemory(pGraphicsDevice->pDiplayDrivers,
                  pustrDiplayDrivers->Buffer,
                  pustrDiplayDrivers->Length);

    /* Copy description */
    pGraphicsDevice->pwszDescription = pwsz + pustrDiplayDrivers->Length / sizeof(WCHAR);
    RtlCopyMemory(pGraphicsDevice->pwszDescription,
                  pustrDescription->Buffer,
                  pustrDescription->Length + sizeof(WCHAR));

    /* Initialize the pdevmodeInfo list and default index  */
    pGraphicsDevice->pdevmodeInfo = NULL;
    pGraphicsDevice->iDefaultMode = 0;
    pGraphicsDevice->iCurrentMode = 0;

    // FIXME: initialize state flags
    pGraphicsDevice->StateFlags = 0;

    /* Loop through the driver names
     * This is a REG_MULTI_SZ string */
    for (; *pwsz; pwsz += wcslen(pwsz) + 1)
    {
        DPRINT("trying driver: %ls\n", pwsz);
        /* Try to load the display driver */
        pldev = EngLoadImageEx(pwsz, LDEV_DEVICE_DISPLAY);
        if (!pldev)
        {
            DPRINT1("Could not load driver: '%ls'\n", pwsz);
            continue;
        }

        /* Get the mode list from the driver */
        pdminfo = LDEVOBJ_pdmiGetModes(pldev, pDeviceObject);
        if (!pdminfo)
        {
            DPRINT1("Could not get mode list for '%ls'\n", pwsz);
            continue;
        }

        /* Attach the mode info to the device */
        pdminfo->pdmiNext = pGraphicsDevice->pdevmodeInfo;
        pGraphicsDevice->pdevmodeInfo = pdminfo;

        /* Count DEVMODEs */
        pdmEnd = (DEVMODEW*)((PCHAR)pdminfo->adevmode + pdminfo->cbdevmode);
        for (pdm = pdminfo->adevmode;
             pdm + 1 <= pdmEnd;
             pdm = (DEVMODEW*)((PCHAR)pdm + pdm->dmSize + pdm->dmDriverExtra))
        {
            cModes++;
        }

        // FIXME: release the driver again until it's used?
    }

    if (!pGraphicsDevice->pdevmodeInfo || cModes == 0)
    {
        DPRINT1("No devmodes\n");
        ExFreePool(pGraphicsDevice);
        return NULL;
    }

    /* Allocate an index buffer */
    pGraphicsDevice->cDevModes = cModes;
    pGraphicsDevice->pDevModeList = ExAllocatePoolWithTag(PagedPool,
                                                          cModes * sizeof(DEVMODEENTRY),
                                                          GDITAG_GDEVICE);
    if (!pGraphicsDevice->pDevModeList)
    {
        DPRINT1("No devmode list\n");
        ExFreePool(pGraphicsDevice);
        return NULL;
    }

    /* Loop through all DEVMODEINFOs */
    for (pdminfo = pGraphicsDevice->pdevmodeInfo, i = 0;
         pdminfo;
         pdminfo = pdminfo->pdmiNext)
    {
        /* Calculate End of the DEVMODEs */
        pdmEnd = (DEVMODEW*)((PCHAR)pdminfo->adevmode + pdminfo->cbdevmode);

        /* Loop through the DEVMODEs */
        for (pdm = pdminfo->adevmode;
             pdm + 1 <= pdmEnd;
             pdm = (PDEVMODEW)((PCHAR)pdm + pdm->dmSize + pdm->dmDriverExtra))
        {
            /* Compare with the default entry */
            if (pdm->dmBitsPerPel == pdmDefault->dmBitsPerPel &&
                pdm->dmPelsWidth == pdmDefault->dmPelsWidth &&
                pdm->dmPelsHeight == pdmDefault->dmPelsHeight &&
                pdm->dmDisplayFrequency == pdmDefault->dmDisplayFrequency)
            {
                pGraphicsDevice->iDefaultMode = i;
                pGraphicsDevice->iCurrentMode = i;
                DPRINT("Found default entry: %ld '%ls'\n", i, pdm->dmDeviceName);
            }

            /* Initialize the entry */
            pGraphicsDevice->pDevModeList[i].dwFlags = 0;
            pGraphicsDevice->pDevModeList[i].pdm = pdm;
            i++;
        }
     }

    /* Lock loader */
    EngAcquireSemaphore(ghsemGraphicsDeviceList);

    /* Insert the device into the global list */
    pGraphicsDevice->pNextGraphicsDevice = gpGraphicsDeviceLast;
    gpGraphicsDeviceLast = pGraphicsDevice;
    if (!gpGraphicsDeviceFirst)
        gpGraphicsDeviceFirst = pGraphicsDevice;

    /* Increment device number */
    giDevNum++;

    /* Unlock loader */
    EngReleaseSemaphore(ghsemGraphicsDeviceList);
    DPRINT("Prepared %ld modes for %ls\n", cModes, pGraphicsDevice->pwszDescription);

    return pGraphicsDevice;
}

static BOOL IsDirectDrawSupported()

dx9里面的这个功能原来是直接调用 dc里面的信息来返回啊，哈哈

gdi和dx其实使用的是同一个显示驱动， 只不过由于gdi是专门为桌面系统而进行封装的， 对象游戏使用来说显然效率、易用性方面还大大不足， 于是根据用途不同就分成了gdi和dx的区别