本篇是D3D中的Alpha顏色混合（1）的后續篇，主要講利用ID3DXSprite來實現圖片間的顏色透明效果。

在一幅圖象上透明的顯示另一幅圖象，是Alpha顏色混合的一個典型應用，如下圖所示，瞄準鏡圖象背景透明地顯示在老虎背景圖象上。



實現瞄準鏡的背景透明顯示，首先需要準備如下兩張圖：

                                               
  瞄準鏡源圖  （圖1）                                    瞄準鏡Alpha通道（屏蔽圖）（圖2）

Alpha通道圖（屏蔽圖）的黑色像素對應的源圖像素不被顯示出來，Alpha通道圖（屏蔽圖）的白色像素對應的源圖像素會顯示出來。

Alpha 通道圖（屏蔽圖）的像素顏色值是作為DirectX顏色結構體的alpha分量值來使用的。圖2所示的黑色像素將產生一個為0的Alpha值，而白色像素將產生一個為1的Alpha值。如果此時將渲染管道流水線的D3DRS_SRCBLEND源混合因子參數設置為D3DBLEND_SRCALPHA，目標混合因子參數設置為D3DBLEND_INVSRCALPHA，然后先繪制圖1所示的紋理圖，再繪制圖2所示的紋理圖，那么混合后的結果將是圖1所示的白色背景不被顯示出來，僅顯示一個圓和一個十字形，正因為Alpha通道圖具有以上的屏蔽效果，因此圖2所示的Alpha通道圖也稱為屏蔽圖。

如果直接采用上面的方法實現圖形間的透明效果，那么需要進行3次紋理貼圖，并設置好相應的混合參數。第一次先繪制出老虎背景圖，接著繪制瞄準鏡源圖，最后繪制瞄準鏡Alpha通道圖。這樣做顯然是比較繁瑣的，因此可用DirectX提供的ID3DXSprite接口進行繪制。

首先，在DirectX安裝目錄下的Utilities目錄下執行DxTex.exe，這是DirectX提供的用于生成紋理圖象的Alpha通道圖的工具。

（注：如果你執行DxTex.exe時系統提示如下信息：

Unable to create Direct3D Device. Please make sure your desktop color depth is 16 or 32 bit, and that d3dref.dll is installed.

請參考解決方案 運行DxTex.exe碰到的問題）

首先執行"File - Open"菜單，將圖1所示的瞄準鏡源圖打開，然后執行"Change Surface Format ..." 菜單，重新設置bmp圖象的像素顏色格式為A8R8G8B8，即添加一個Alpha顏色值。

              

執行新增加的"File - Open onto alpha channel of this texture..."菜單，彈出一個文件打開對話框，選擇圖2所示的瞄準鏡Alpha通道圖并打開，DxTex將自動把Alpha通道圖的屏蔽信息插入圖象中。如下圖所示，DxTex默認的淡藍色背景色表示該像素顏色已為透明色。最后，執行"File - Save"菜單，將同時具有源圖信息和Alpha通道信息的圖象保存為DDS格式的gun.dds。



生成瞄準鏡的DDS文件后，就可以利用d3dx9.lib庫的ID3DXSprite提供的方法，將瞄準鏡背景透明地顯示出來。ID3DXSprite接口對象是通過D3DXCreateSprite函數進行創建的，來看看該函數的具體使用信息：

Creates a sprite object which is associated with a particular device. Sprite objects are used to draw 2D images to the screen.

HRESULT D3DXCreateSprite(
  LPDIRECT3DDEVICE9 pDevice,
  LPD3DXSPRITE * ppSprite
);

Parameters

pDevice

[in] Pointer to an IDirect3DDevice9 interface, the device to be associated with the sprite.

ppSprite

[out] Address of a pointer to an ID3DXSprite interface. This interface allows the user to access sprite functions.

Return Values

If the function succeeds, the return value is S_OK. If the function fails, the return value can be one of the following: D3DERR_INVALIDCALL, E_OUTOFMEMORY.

Remarks

This interface can be used to draw two dimensional images in screen space of the associated device.

再來看看SDK文檔提供的有關ID3DXSprite的使用說明:

The ID3DXSprite interface provides a set of methods that simplify the process of drawing sprites using Microsoft Direct3D.

ID3DXSprite Members

Method	Description
ID3DXSprite::Begin	Prepares a device for drawing sprites.
ID3DXSprite::Draw	Adds a sprite to the list of batched sprites.
ID3DXSprite::End	Calls ID3DXSprite::Flush and restores the device state to how it was before ID3DXSprite::Begin was called.
ID3DXSprite::Flush	Forces all batched sprites to be submitted to the device. Device states remain as they were after the last call to ID3DXSprite::Begin. The list of batched sprites is then cleared.
ID3DXSprite::GetDevice	Retrieves the device associated with the sprite object.
ID3DXSprite::GetTransform	Gets the sprite transform.
ID3DXSprite::OnLostDevice	Use this method to release all references to video memory resources and delete all stateblocks. This method should be called whenever a device is lost or before resetting a device.
ID3DXSprite::OnResetDevice	Use this method to re-acquire resources and save initial state.
ID3DXSprite::SetTransform	Sets the sprite transform.
ID3DXSprite::SetWorldViewLH	Sets the left-handed world-view transform for a sprite. A call to this method is required before billboarding or sorting sprites.
ID3DXSprite::SetWorldViewRH	Sets the right-handed world-view transform for a sprite. A call to this method is required before billboarding or sorting sprites.

Remarks

The ID3DXSprite interface is obtained by calling the D3DXCreateSprite function.

The application typically first calls ID3DXSprite::Begin, which allows control over the device render state, alpha blending, and sprite transformation and sorting. Then for each sprite to be displayed, call ID3DXSprite::Draw. ID3DXSprite::Draw can be called repeatedly to store any number of sprites. To display the batched sprites to the device, call ID3DXSprite::End or ID3DXSprite::Flush.

The LPD3DXSPRITE type is defined as a pointer to the ID3DXSprite interface.

typedef interface ID3DXSprite ID3DXSprite;
typedef interface ID3DXSprite *LPD3DXSPRITE;

Begin方法和End方法表明繪制精靈圖象的開始和結束，這是一對配套函數，必須用在IDirect3DDevice9::BeginScene和IDirect3DDevice9::EndScene的調用之間。

接著來看看Begin方法的使用說明:

Prepares a device for drawing sprites.

HRESULT Begin(
  DWORD Flags
);

Parameters

Flags

[in] Combination of zero or more flags that describe sprite rendering options. For this method, the valid flags are:

• D3DXSPRITE_ALPHABLEND
• D3DXSprite__BILLBOARD
• D3DXSPRITE_DONOTMODIFY_RENDERSTATE
• D3DXSPRITE_DONOTSAVESTATE
• D3DXSPRITE_OBJECTSPACE
• D3DXSprite__SORT_DEPTH_BACKTOFRONT
• D3DXSprite__SORT_DEPTH_FRONTTOBACK
• D3DXSprite__SORT_TEXTURE

For a description of the flags and for information on how to control device state capture and device view transforms, see D3DXSPRITE.

Return Values

If the method succeeds, the return value is S_OK. If the method fails, the return value can be one of the following: D3DERR_INVALIDCALL, D3DERR_OUTOFVIDEOMEMORY, D3DXERR_INVALIDDATA, E_OUTOFMEMORY.

Remarks

This method must be called from inside a IDirect3DDevice9::BeginScene . . . IDirect3DDevice9::EndScene sequence. ID3DXSprite::Begin cannot be used as a substitute for either IDirect3DDevice9::BeginScene or ID3DXRenderToSurface::BeginScene.

This method will set the following states on the device.

Render States:

Type (D3DRENDERSTATETYPE)	Value
D3DRS_ALPHABLENDENABLE	TRUE
D3DRS_ALPHAFUNC	D3DCMP_GREATER
D3DRS_ALPHAREF	0x00
D3DRS_ALPHATESTENABLE	AlphaCmpCaps
D3DRS_BLENDOP	D3DBLENDOP_ADD
D3DRS_CLIPPING	TRUE
D3DRS_CLIPPLANEENABLE	FALSE
D3DRS_COLORWRITEENABLE	D3DCOLORWRITEENABLE_ALPHA | D3DCOLORWRITEENABLE_BLUE | D3DCOLORWRITEENABLE_GREEN | D3DCOLORWRITEENABLE_RED
D3DRS_CULLMODE	D3DCULL_NONE
D3DRS_DESTBLEND	D3DBLEND_INVSRCALPHA
D3DRS_DIFFUSEMATERIALSOURCE	D3DMCS_COLOR1
D3DRS_ENABLEADAPTIVETESSELLATION	FALSE
D3DRS_FILLMODE	D3DFILL_SOLID
D3DRS_FOGENABLE	FALSE
D3DRS_INDEXEDVERTEXBLENDENABLE	FALSE
D3DRS_LIGHTING	FALSE
D3DRS_RANGEFOGENABLE	FALSE
D3DRS_SEPARATEALPHABLENDENABLE	FALSE
D3DRS_SHADEMODE	D3DSHADE_GOURAUD
D3DRS_SPECULARENABLE	FALSE
D3DRS_SRCBLEND	D3DBLEND_SRCALPHA
D3DRS_SRGBWRITEENABLE	FALSE
D3DRS_STENCILENABLE	FALSE
D3DRS_VERTEXBLEND	FALSE
D3DRS_WRAP0	0

Texture Stage States:

Stage Identifier	Type (D3DTEXTURESTAGESTATETYPE)	Value
0	D3DTSS_ALPHAARG1	D3DTA_TEXTURE
0	D3DTSS_ALPHAARG2	D3DTA_DIFFUSE
0	D3DTSS_ALPHAOP	D3DTOP_MODULATE
0	D3DTSS_COLORARG1	D3DTA_TEXTURE
0	D3DTSS_COLORARG2	D3DTA_DIFFUSE
0	D3DTSS_COLOROP	D3DTOP_MODULATE
0	D3DTSS_TEXCOORDINDEX	0
0	D3DTSS_TEXTURETRANSFORMFLAGS	D3DTTFF_DISABLE
1	D3DTSS_ALPHAOP	D3DTOP_DISABLE
1	D3DTSS_COLOROP	D3DTOP_DISABLE

Sampler States:

Sampler Stage Index	Type (D3DSAMPLERSTATETYPE)	Value
0	D3DSAMP_ADDRESSU	D3DTADDRESS_CLAMP
0	D3DSAMP_ADDRESSV	D3DTADDRESS_CLAMP
0	D3DSAMP_MAGFILTER	D3DTEXF_ANISOTROPIC if TextureFilterCaps includes D3DPTFILTERCAPS_MAGFANISOTROPIC; otherwise D3DTEXF_LINEAR
0	D3DSAMP_MAXMIPLEVEL	0
0	D3DSAMP_MAXANISOTROPY	MaxAnisotropy
0	D3DSAMP_MINFILTER	D3DTEXF_ANISOTROPIC if TextureFilterCaps includes D3DPTFILTERCAPS_MINFANISOTROPIC; otherwise D3DTEXF_LINEAR
0	D3DSAMP_MIPFILTER	D3DTEXF_LINEAR if TextureFilterCaps includes D3DPTFILTERCAPS_MIPFLINEAR; otherwise D3DTEXF_POINT
0	D3DSAMP_MIPMAPLODBIAS	0
0	D3DSAMP_SRGBTEXTURE	0

Note    This method disables N-patches.

參數Flags允許設置的D3DXSPRITE模式如下所示：

The following flags are used to specify sprite rendering options to the flags parameter in the ID3DXSprite::Begin method:

#define	Description
D3DXSPRITE_DONOTSAVESTATE	The device state is not to be saved or restored when ID3DXSprite::Begin or ID3DXSprite::End is called.
D3DXSPRITE_DONOTMODIFY_RENDERSTATE	The device render state is not to be changed when ID3DXSprite::Begin is called. The device is assumed to be in a valid state to draw vertices containing UsageIndex = 0 in the D3DDECLUSAGE_POSITION, D3DDECLUSAGE_TEXCOORD, and D3DDECLUSAGE_COLOR data.
D3DXSPRITE_OBJECTSPACE	The world, view, and projection transforms are not modified. The transforms currently set to the device are used to transform the sprites when the batched sprites are drawn (when ID3DXSprite::Flush or ID3DXSprite::End is called). If this flag is not specified, then world, view, and projection transforms are modified so that sprites are drawn in screen-space coordinates.
D3DXSPRITE_BILLBOARD	Each sprite will be rotated about its center so that it is facing the viewer. ID3DXSprite::SetWorldViewLH or ID3DXSprite::SetWorldViewRH must be called first.
D3DXSPRITE_ALPHABLEND	Enables alpha blending with D3DRS_ALPHATESTENABLE set to TRUE (for nonzero alpha). D3DBLEND_SRCALPHA will be the source blend state, and D3DBLEND_INVSRCALPHA will be the destination blend state in calls to IDirect3DDevice9::SetRenderState. See Alpha Blending State (Direct3D 9). ID3DXFont expects this flag to be set when drawing text.
D3DXSPRITE_SORT_TEXTURE	Sort sprites by texture prior to drawing. This can improve performance when drawing non-overlapping sprites of uniform depth. You may also combine D3DXSPRITE_SORT_TEXTURE with either D3DXSPRITE_SORT_DEPTH_FRONTTOBACK or D3DXSPRITE_SORT_DEPTH_BACKTOFRONT. This will sort the list of sprites by depth first and texture second.
D3DXSPRITE_SORT_DEPTH_FRONTTOBACK	Sprites are sorted by depth in front-to-back order prior to drawing. This procedure is recommended when drawing opaque sprites of varying depths. You may combine D3DXSPRITE_SORT_DEPTH_FRONTTOBACK with D3DXSPRITE_SORT_TEXTURE to sort first by depth, and second by texture.
D3DXSPRITE_SORT_DEPTH_BACKTOFRONT	Sprites are sorted by depth in back-to-front order prior to drawing. This procedure is recommended when drawing transparent sprites of varying depths. You may combine D3DXSPRITE_SORT_DEPTH_BACKTOFRONT with D3DXSPRITE_SORT_TEXTURE to sort first by depth, and second by texture.
D3DXSPRITE_DO_NOT_ADDREF_TEXTURE	Disables calling AddRef() on every draw, and Release() on Flush() for better performance.

再來看看End方法的使用信息：

Calls ID3DXSprite::Flush and restores the device state to how it was before ID3DXSprite::Begin was called.

HRESULT End();

Parameters

None.

Return Values

If the method succeeds, the return value is S_OK. If the method fails, the following value will be returned.

D3DERR_INVALIDCALL

Remarks

ID3DXSprite::End cannot be used as a substitute for either IDirect3DDevice9::EndScene or ID3DXRenderToSurface::EndScene.

Draw方法用來在指定位置繪制精靈，來看看它的使用說明：

Adds a sprite to the list of batched sprites.

HRESULT Draw(
  LPDIRECT3DTEXTURE9 pTexture,
  CONST RECT * pSrcRect,
  CONST D3DXVECTOR3 * pCenter,
  CONST D3DXVECTOR3 * pPosition,
  D3DCOLOR Color
);

Parameters

pTexture

[in] Pointer to an IDirect3DTexture9 interface that represents the sprite texture.

pSrcRect

[in] Pointer to a RECT structure that indicates the portion of the source texture to use for the sprite. If this parameter is NULL, then the entire source image is used for the sprite.

pCenter

[in] Pointer to a D3DXVECTOR3 vector that identifies the center of the sprite. If this argument is NULL, the point (0,0,0) is used, which is the upper-left corner.

pPosition

[in] Pointer to a D3DXVECTOR3 vector that identifies the position of the sprite. If this argument is NULL, the point (0,0,0) is used, which is the upper-left corner.

Color

[in] D3DCOLOR type. The color and alpha channels are modulated by this value. A value of 0xFFFFFFFF maintains the original source color and alpha data. Use the D3DCOLOR_RGBA macro to help generate this color.

Return Values

If the method succeeds, the return value is S_OK. If the method fails, the return value can be one of the following: D3DERR_INVALIDCALL, D3DXERR_INVALIDDATA.

Remarks

To scale, rotate, or translate a sprite, call ID3DXSprite::SetTransform with a matrix that contains the scale, rotate, and translate (SRT) values, before calling ID3DXSprite::Draw. For information about setting SRT values in a matrix, see Matrix Transforms.

 

---

好了，現在來看一個例子：

需要在工程中設置鏈接d3dx9.lib d3d9.lib dinput8.lib dxguid.lib。
由于文件中用到了GE_APP和GE_INPUT這兩個類，它的具體使用說明請參閱主窗口和DirectInput的封裝。

若發現代碼中存在錯誤，敬請指出。

源碼及素材下載

來看看shoot.h的定義：
 

/*************************************************************************************
 [Include File]

 PURPOSE: 
    Define for alpha blending test, use ID3DXSprit interface.
*************************************************************************************/

#ifndef SHOOT_H
#define SHOOT_H

class SHOOT
{
private:
    IDirect3D9* _d3d;
    IDirect3DDevice9* _d3d_device;
    IDirect3DTexture9* _texture_tiger;
    IDirect3DTexture9* _texture_gun;
    ID3DXSprite* _sprite_tiger;
    ID3DXSprite* _sprite_gun;

public:
    float m_gun_pos_x, m_gun_pos_y;

public:
    SHOOT();
    ~SHOOT();
    
    bool Create_D3D_Device(HWND hwnd, bool full_screen = true);
    bool Create_Sprite();
    bool Create_Sprite_Texture(IDirect3DTexture9** texture, const char* image_file);
    void Render();
    void Release_COM_Object();
};

#endif

再來看看shoot.cpp的定義：

 
Create_Sprite方法用來創建背景圖和瞄準鏡的ID3DXSprite精靈接口對象和紋理接口對象， Create_Sprite_Texture方法根據圖象文件創建精靈的紋理對象，這里使用DDS格式的文件創建出一個背景透明的瞄準器精靈對象。 Render方法調用ID3DXSprite接口的Begin，Draw，End方法繪制出背景圖和背景透明的瞄準鏡圖象。

再來看看測試代碼main.cpp：

   
閱讀下篇：D3D中的Alpha顏色混合（3）