D3DPRESENT_PARAMETERS

Describes the presentation parameters.

typedef struct D3DPRESENT_PARAMETERS {
    UINT BackBufferWidth, BackBufferHeight;
    D3DFORMAT BackBufferFormat;
    UINT BackBufferCount;
    D3DMULTISAMPLE_TYPE MultiSampleType;
    DWORD MultiSampleQuality;
    D3DSWAPEFFECT SwapEffect;
    HWND hDeviceWindow;
    BOOL Windowed;
    BOOL EnableAutoDepthStencil;
    D3DFORMAT AutoDepthStencilFormat;
    DWORD Flags;
    UINT FullScreen_RefreshRateInHz;
    UINT PresentationInterval;
} D3DPRESENT_PARAMETERS, *LPD3DPRESENT_PARAMETERS;

Members

BackBufferWidth, BackBufferHeight

Width and height of the new swap chain's back buffers, in pixels. If Windowed is FALSE (the presentation is full-screen), these values must equal the width and height of one of the enumerated display modes found through IDirect3D9::EnumAdapterModes. If Windowed is TRUE and either of these values is zero, the corresponding dimension of the client area of the hDeviceWindow (or the focus window, if hDeviceWindow is NULL) is taken.

BackBufferFormat

The back buffer format. For more information about formats, see D3DFORMAT. This value must be one of the render-target formats as validated by IDirect3D9::CheckDeviceType. You can use IDirect3DDevice9::GetDisplayMode to obtain the current format.

In fact, D3DFMT_UNKNOWN can be specified for the BackBufferFormat while in windowed mode. This tells the runtime to use the current display-mode format and eliminates the need to call IDirect3DDevice9::GetDisplayMode.

For windowed applications, the back buffer format no longer needs to match the display-mode format because color conversion can now be done by the hardware (if the hardware supports color conversion). The set of possible back buffer formats is constrained, but the runtime will allow any valid back buffer format to be presented to any desktop format. (There is the additional requirement that the device be operable in the desktop mode; devices typically do not operate in 8 bits per pixel modes.)

Full-screen applications cannot do color conversion.

BackBufferCount

This value can be between 0 and D3DPRESENT_BACK_BUFFERS_MAX (or D3DPRESENT_BACK_BUFFERS_MAX_EX when using Direct3D 9Ex). Values of 0 are treated as 1. If the number of back buffers cannot be created, the runtime will fail the method call and fill this value with the number of back buffers that could be created. As a result, an application can call the method twice with the same D3DPRESENT_PARAMETERS structure and expect it to work the second time.

The method fails if one back buffer cannot be created. The value of BackBufferCount influences what set of swap effects are allowed. Specifically, any D3DSWAPEFFECT_COPY swap effect requires that there be exactly one back buffer.

MultiSampleType

Member of the D3DMULTISAMPLE_TYPE enumerated type. The value must be D3DMULTISAMPLE_NONE unless SwapEffect has been set to D3DSWAPEFFECT_DISCARD. Multisampling is supported only if the swap effect is D3DSWAPEFFECT_DISCARD.

MultiSampleQuality

Quality level. The valid range is between zero and one less than the level returned by pQualityLevels used by IDirect3D9::CheckDeviceMultiSampleType. Passing a larger value returns the error D3DERR_INVALIDCALL. Paired values of render targets or of depth stencil surfaces and D3DMULTISAMPLE_TYPE must match.

SwapEffect

Member of the D3DSWAPEFFECT enumerated type. The runtime will guarantee the implied semantics concerning buffer swap behavior; therefore, if Windowed is TRUE and SwapEffect is set to D3DSWAPEFFECT_FLIP, the runtime will create one extra back buffer and copy whichever becomes the front buffer at presentation time.

D3DSWAPEFFECT_COPY requires that BackBufferCount be set to 1.

D3DSWAPEFFECT_DISCARD will be enforced in the debug runtime by filling any buffer with noise after it is presented.

Differences between Direct3D9 and Direct3D9Ex In Direct3D9Ex, D3DSWAPEFFECT_FLIPEX is added to designate when an application is adopting flip mode. That is, whan an application's frame is passed in window's mode (instead of copied) to the Desktop Window Manager(DWM) for composition. Flip mode provides more efficient memory bandwidth and enables an application to take advantage of full-screen-present statistics. It does not change full screen behavior. Flip mode behavior is available beginning with Windows 7.

hDeviceWindow

The device window determines the location and size of the back buffer on screen. This is used by Direct3D when the back buffer contents are copied to the front buffer during IDirect3DDevice9::Present.

• For a full-screen application, this is a handle to the top window (which is the focus window).

  For applications that use multiple full-screen devices (such as a multimonitor system), exactly one device can use the focus window as the device window. All other devices must have unique device windows.

• For a windowed-mode application, this handle will be the default target window for IDirect3DDevice9::Present. If this handle is NULL, the focus window will be taken.

Note that no attempt is made by the runtime to reflect user changes in window size. The back buffer is not implicitly reset when this window is reset. However, the IDirect3DDevice9::Present method does automatically track window position changes.

Windowed

TRUE if the application runs windowed; FALSE if the application runs full-screen.

EnableAutoDepthStencil

If this value is TRUE, Direct3D will manage depth buffers for the application. The device will create a depth-stencil buffer when it is created. The depth-stencil buffer will be automatically set as the render target of the device. When the device is reset, the depth-stencil buffer will be automatically destroyed and recreated in the new size.

If EnableAutoDepthStencil is TRUE, then AutoDepthStencilFormat must be a valid depth-stencil format.

AutoDepthStencilFormat

Member of the D3DFORMAT enumerated type. The format of the automatic depth-stencil surface that the device will create. This member is ignored unless EnableAutoDepthStencil is TRUE.

Flags

One of the D3DPRESENTFLAG constants.

FullScreen_RefreshRateInHz

The rate at which the display adapter refreshes the screen. The value depends on the mode in which the application is running:

• For windowed mode, the refresh rate must be 0.
• For full-screen mode, the refresh rate is one of the refresh rates returned by IDirect3D9::EnumAdapterModes.

PresentationInterval

The maximum rate at which the swap chain's back buffers can be presented to the front buffer. For a detailed explanation of the modes and the intervals that are supported, see D3DPRESENT.

Requirements

Header: Declared in D3D9Types.h. 
      幾個重要的參數加以解釋說明一下，其中BackBufferWidth和BackBufferHeight指定后臺緩存區的寬高（以像素為單位）。如果圖形以窗口方式顯示并且該成員變量被設置為0，則系統自動使用顯示窗口客戶區的寬高作為后臺緩沖區的寬高。BackBufferCount指定后臺緩沖區的數量。該值可以為0、1、2、3，其中0和1時都表示創建一個后臺緩沖區。通常使用一個后臺緩沖區和一個主緩存，主緩存將其顯示在屏幕上。

BOOL CD3DCameraViewWnd::GetImageInfo(DWORD* pPixelBuffer, int& width,int& height)
{
	BOOL result = FALSE;

	IDirect3DSurface9 *_surfaceback = NULL; 
	if (FAILED(m_pDevice->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &_surfaceback)))
	{
		result = FALSE;
	}
	  

	D3DSURFACE_DESC surfaceDesc; 
	if (!FAILED(_surfaceback->GetDesc(&surfaceDesc)))
	{
		width = surfaceDesc.Width;
		height = surfaceDesc.Height;
	}

	D3DLOCKED_RECT lockedRect; 
	HRESULT hr = _surfaceback->LockRect( &lockedRect,0, 0); /* pointer to receive locked data指向申請到的內存區域*/ /* lock entire surface*/// no lock flags specified 

	if (!FAILED(hr))
	{
		pPixelBuffer = (DWORD*)lockedRect.pBits;
		result = TRUE;
	}

	_surfaceback->UnlockRect();
	_surfaceback->Release();

	return result;
}

現在關鍵的問題就在于,資源鎖定的操作速度總是非常之慢.當然,你會跟我提, OpenGL似乎能夠快捷地完成這項任務.但是,在Direct3D中,資源鎖定操作確實是很慢的.這里面一個主要的原因是,API,驅動,以及硬件要處理一些不可回避的后臺操作.那就是GPU與CPU是并行運行的,若不加任何措施,將引起類似多線程程序同步時的競態條件的問題.

如果你試圖去修改的資源正同時被一個位于GPU處理序列中的指令使用,那么整個渲染流程就會因為你的資源鎖定而停頓或強制刷新(stalls and flushes).停頓(stall)會一直持續到你完成了對資源的修改并調用Unlock().而強制刷新(flush)則會要求GPU在你得到這個資源的訪問權之前完成目前所有的任務.

如何去解決這個問題？下面的參考資料中有一些解決方案，我沒有經過認真測試，我試了其中一個GetRenderTargetData 這樣的一種方法 ，感覺不太好用，why請看Reference3

下面給出我的解決方案

BOOL CD3DCameraViewWnd::GetImageInfo(DWORD* pPixelBuffer, int& width,int& height)
{
	BOOL result = FALSE;

	IDirect3DSurface9 *_surfaceback = NULL; 
	if (FAILED(m_pDevice->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &_surfaceback)))
	{
		result = FALSE;
	}
	  

	D3DSURFACE_DESC surfaceDesc; 
	if (!FAILED(_surfaceback->GetDesc(&surfaceDesc)))
	{
		width = surfaceDesc.Width;
		height = surfaceDesc.Height;
	}

	LPDIREC3DSURFACE9 surf;

	if(FAILED(m_pDevice->CreateOffscreenPlainSurface(width, height,D3DFMT_A8R8G8B8,D3DPOOL_SYSTEMMEM, &surf,NULL)))

	{

		result = FALSE;

	}

	D3DXLoadSurfaceFromSurface(surf, NULL,NULL,_surfaceback,NULL,NULL,D3DX_FILTER_NONE,0);

	D3DLOCKED_RECT lockedRect; 
	HRESULT hr = surf->LockRect( &lockedRect,0, 0); /* pointer to receive locked data指向申請到的內存區域*/ /* lock entire surface*/// no lock flags specified 

	if (!FAILED(hr))
	{
		pPixelBuffer = (DWORD*)lockedRect.pBits;
		result = TRUE;
	}

	surf->UnlockRect();

	surf->Release();
	_surfaceback->Release();

	return result;
}

參考資料：Reference1.http://www.cnblogs.com/mixiyou/archive/2010/02/25/1673060.html

   Reference 2.http://www.cnblogs.com/mixiyou/archive/2010/02/25/1673425.html

   Reference 3.http://blog.csdn.net/Nightmare/article/details/1707362

   Reference 4.http://www.cnblogs.com/lancidie/archive/2011/3/14.html