1.關于創建Direct3D設備對象
   創建Direct3D設備對象時，需要先創建Direct3D對象，然后再調用Direct3D對象的接口函數IDirect3D9：：CreateDevice創建Direct3D設備對象。通過同一個Direct3D對象創建的所有Direct3D設備對象共享相同的物理資源（顯卡）。因為共享同一硬件，所以如果通過一個Direct3D對象創建多個Direct3D渲染設備對象會明顯降低系統性能。
   在創建Direct3D設備對象之前，還需要先初始化D3DPRESENT_PARAMENTERS結構，該結構用于創建Direct3D設備對象。此結構將會影響Direct3D設備的顯示方法。
      

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。