D3D中的Alpha颜色混合（3）

鼯鼠

本篇是D3D中的Alpha颜色混合（2）的后续篇。

另一种实现实现背景透明显示的简便方法是直接应用渲染管道流水线的Alpha测试功能进行，D3D中的Alpha颜色混合（2）介绍的接口方法实际就是对Alpha测试的一个包装。Alpha测试是对需要写入绘图表面的像素颜色Alpha值进行测试，判断该Alpha值是否满足预先设定的条件，如果满足条件，则将该像素颜色值写入绘图表面，否则不写入。



如上图所示，瞄准器的背景色为标准绿色，为了使瞄准镜可以背景透明地显示在其他图象的上面，需要把瞄准镜的绿色部分镂空。为此，可调用 D3DXCreateTextureFromFileEx函数，相应的创建一个背景为黑色的纹理对象，这个黑色的Alpha值为 0，它的RGBA颜色值则为(0, 0, 0, 0)。然后，开启渲染管道流水线的Alpha测试，并使Alpha测试仅对Alpha值大于或等于某个值的像素颜色值进行写入，以使Alpha值为0的瞄准镜背景黑色不能写入绘图表面，从而使得瞄准镜图象贴在老虎背景画面上时，背景可透明地显示出来。

来看看 D3DXCreateTextureFromFileEx的具体使用说明：

Creates a texture from a file. This is a more advanced function than D3DXCreateTextureFromFile.

HRESULT D3DXCreateTextureFromFileEx(

		LPDIRECT3DDEVICE9
		pDevice,

		LPCTSTR
		pSrcFile,

		UINT
		Width,

		UINT
		Height,

		UINT
		MipLevels,

		DWORD
		Usage,

		D3DFORMAT
		Format,

		D3DPOOL
		Pool,

		DWORD
		Filter,

		DWORD
		MipFilter,

		D3DCOLOR
		ColorKey,

		D3DXIMAGE_INFO *
		pSrcInfo,

		PALETTEENTRY *
		pPalette,

		LPDIRECT3DTEXTURE9 *
		ppTexture
);

Parameters

pDevice

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

pSrcFile

[in] Pointer to a string that specifies the filename. If the compiler settings require Unicode, the data type LPCTSTR resolves to LPCWSTR. Otherwise, the string data type resolves to LPCSTR. See Remarks.

Width

[in] Width in pixels. If this value is zero or D3DX_DEFAULT, the dimensions are taken from the file and rounded up to a power of two. If the device supports non-power of 2 textures and D3DX_DEFAULT_NONPOW2 is specified, the size will not be rounded.

Height

[in] Height, in pixels. If this value is zero or D3DX_DEFAULT, the dimensions are taken from the file and rounded up to a power of two. If the device supports non-power of 2 textures and D3DX_DEFAULT_NONPOW2 is sepcified, the size will not be rounded.

MipLevels

[in] Number of mip levels requested. If this value is zero or D3DX_DEFAULT, a complete mipmap chain is created. If D3DX_FROM_FILE, the size will be taken exactly as it is in the file, and the call will fail if this violates device capabilities.

Usage

[in] 0, D3DUSAGE_RENDERTARGET, or D3DUSAGE_DYNAMIC. Setting this flag to D3DUSAGE_RENDERTARGET indicates that the surface is to be used as a render target. The resource can then be passed to the pNewRenderTarget parameter of the IDirect3DDevice9::SetRenderTarget method. If either D3DUSAGE_RENDERTARGET or D3DUSAGE_DYNAMIC is specified, Pool must be set to D3DPOOL_DEFAULT, and the application should check that the device supports this operation by calling IDirect3D9::CheckDeviceFormat. D3DUSAGE_DYNAMIC indicates that the surface should be handled dynamically. See Using Dynamic Textures.

Format

[in] Member of the D3DFORMAT enumerated type, describing the requested pixel format for the texture. The returned texture might have a different format from that specified by Format. Applications should check the format of the returned texture. If D3DFMT_UNKNOWN, the format is taken from the file. If D3DFMT_FROM_FILE, the format is taken exactly as it is in the file, and the call will fail if this violates device capabilities.

Pool

[in] Member of the D3DPOOL enumerated type, describing the memory class into which the texture should be placed.

Filter

[in] A combination of one or more D3DX_FILTER constants controlling how the image is filtered. Specifying D3DX_DEFAULT for this parameter is the equivalent of specifying D3DX_FILTER_TRIANGLE | D3DX_FILTER_DITHER.

MipFilter

[in] A combination of one or more D3DX_FILTER constants controlling how the image is filtered. Specifying D3DX_DEFAULT for this parameter is the equivalent of specifying D3DX_FILTER_BOX. In addition, use bits 27-31 to specify the number of mip levels to be skipped (from the top of the mipmap chain) when a .dds texture is loaded into memory; this allows you to skip up to 32 levels.

ColorKey

[in] D3DCOLOR value to replace with transparent black, or 0 to disable the color key. This is always a 32-bit ARGB color, independent of the source image format. Alpha is significant and should usually be set to FF for opaque color keys. Thus, for opaque black, the value would be equal to 0xFF000000.

pSrcInfo

[in, out] Pointer to a D3DXIMAGE_INFO structure to be filled in with a description of the data in the source image file, or NULL.

pPalette

[out] Pointer to a PALETTEENTRY structure, representing a 256-color palette to fill in, or NULL.

ppTexture

[out] Address of a pointer to an IDirect3DTexture9 interface, representing the created texture object.

Return Values

If the function succeeds, the return value is D3D_OK. If the function fails, the return value can be one of the following: D3DERR_INVALIDCALL.

D3DERR_NOTAVAILABLED3DERR_OUTOFVIDEOMEMORYD3DXERR_INVALIDDATAE_OUTOFMEMORY

Remarks

The compiler setting also determines the function version. If Unicode is defined, the function call resolves to D3DXCreateTextureFromFileExW. Otherwise, the function call resolves to D3DXCreateTextureFromFileExA because ANSI strings are being used.

Use D3DXCheckTextureRequirements to determine if your device can support the texture given the current state.

This function supports the following file formats: .bmp, .dds, .dib, .hdr, .jpg, .pfm, .png, .ppm, and .tga. See D3DXIMAGE_FILEFORMAT.

Mipmapped textures automatically have each level filled with the loaded texture. When loading images into mipmapped textures, some devices are unable to go to a 1x1 image and this function will fail. If this happens, then the images need to be loaded manually.

For the best performance when using D3DXCreateTextureFromFileEx:

1. Doing image scaling and format conversion at load time can be slow. Store images in the format and resolution they will be used. If the target hardware requires power of 2 dimensions, then create and store images using power of 2 dimensions.
2. For mipmap image creation at load time, filter using D3DX_FILTER_BOX. A box filter is much faster than other filter types such as D3DX_FILTER_TRIANGLE.
3. Consider using DDS files. Since DDS files can be used to represent any Direct3D 9 texture format, they are very easy for D3DX to read. Also, they can store mipmaps, so any mipmap-generation algorithms can be used to author the images.

When skipping mipmap levels while loading a .dds file, use the D3DX_SKIP_DDS_MIP_LEVELS macro to generate the MipFilter value. This macro takes the number of levels to skip and the filter type and returns the filter value, which would then be passed into the MipFilter parameter.

鼯鼠

再来看看参数Usage可以使用的枚举类型D3DUSAGE_RENDERTARGET的详细说明：

Usage options that identify how resources are to be used.

Usages

The following table summarizes the available usage options.

#define	Description
D3DUSAGE_AUTOGENMIPMAP	The resource will automatically generate mipmaps. See Automatic Generation of Mipmaps (Direct3D 9). Automatic generation of mipmaps is not supported for volume textures and depth stencil surfaces/textures. This usage is not valid for a resource in system memory (D3DPOOL_SYSTEMMEM).
D3DUSAGE_DEPTHSTENCIL	The resource will be a depth stencil buffer. D3DUSAGE_DEPTHSTENCIL can only be used with D3DPOOL_DEFAULT.
D3DUSAGE_DMAP	The resource will be a displacement map.
D3DUSAGE_DONOTCLIP	Set to indicate that the vertex buffer content will never require clipping. When rendering with buffers that have this flag set, the D3DRS_CLIPPING render state must be set to false.
D3DUSAGE_DYNAMIC	Set to indicate that the vertex buffer requires dynamic memory use. This is useful for drivers because it enables them to decide where to place the buffer. In general, static vertex buffers are placed in video memory and dynamic vertex buffers are placed in AGP memory. Note that there is no separate static use. If you do not specify D3DUSAGE_DYNAMIC, the vertex buffer is made static. D3DUSAGE_DYNAMIC is strictly enforced through the D3DLOCK_DISCARD and D3DLOCK_NOOVERWRITE locking flags. As a result, D3DLOCK_DISCARD and D3DLOCK_NOOVERWRITE are valid only on vertex buffers created with D3DUSAGE_DYNAMIC. They are not valid flags on static vertex buffers. For more information, see Managing Resources (Direct3D 9). For more information about using dynamic vertex buffers, see Performance Optimizations (Direct3D 9). D3DUSAGE_DYNAMIC and D3DPOOL_MANAGED are incompatible and should not be used together. See D3DPOOL. Textures can specify D3DUSAGE_DYNAMIC. However, managed textures cannot use D3DUSAGE_DYNAMIC. For more information about dynamic textures, see Using Dynamic Textures.
D3DUSAGE_NPATCHES	Set to indicate that the vertex buffer is to be used for drawing N-patches.
D3DUSAGE_POINTS	Set to indicate that the vertex or index buffer will be used for drawing point sprites. The buffer will be loaded in system memory if software vertex processing is needed to emulate point sprites.
D3DUSAGE_RENDERTARGET	The resource will be a render target. D3DUSAGE_RENDERTARGET can only be used with D3DPOOL_DEFAULT.
D3DUSAGE_RTPATCHES	Set to indicate that the vertex buffer is to be used for drawing high-order primitives.
D3DUSAGE_SOFTWAREPROCESSING	If this flag is used, vertex processing is done in software. If this flag is not used, vertex processing is done in hardware. The D3DUSAGE_SOFTWAREPROCESSING flag can be set when mixed-mode or software vertex processing (D3DCREATE_MIXED_VERTEXPROCESSING / D3DCREATE_SOFTWARE_VERTEXPROCESSING) is enabled for that device. D3DUSAGE_SOFTWAREPROCESSING must be set for buffers to be used with software vertex processing in mixed mode, but it should not be set for the best possible performance when using hardware index processing in mixed mode (D3DCREATE_HARDWARE_VERTEXPROCESSING). However, setting D3DUSAGE_SOFTWAREPROCESSING is the only option when a single buffer is used with both hardware and software vertex processing. D3DUSAGE_SOFTWAREPROCESSING is allowed for mixed and software devices. D3DUSAGE_SOFTWAREPROCESSING is used with IDirect3D9::CheckDeviceFormat to find out if a particular texture format can be used as a vertex texture during software vertex processing. If it can, the texture must be created in D3DPOOL_SCRATCH.
D3DUSAGE_WRITEONLY	Informs the system that the application writes only to the vertex buffer. Using this flag enables the driver to choose the best memory location for efficient write operations and rendering. Attempts to read from a vertex buffer that is created with this capability will fail. Buffers created with D3DPOOL_DEFAULT that do not specify D3DUSAGE_WRITEONLY might suffer a severe performance penalty.

Usage and Resource Combinations

Usages are either specified when a resource is created, or specified with IDirect3D9::CheckDeviceType to test the capability of an existing resource. The following table identifies which usages can be applied to which resource types.

Usage	Vertex buffer create	Index buffer create	Texture create	Cube texture create	Volume texture create	Surface create	Check device format
D3DUSAGE_AUTOGENMIPMAP			x	x			x
D3DUSAGE_DEPTHSTENCIL			x	x		x	x
D3DUSAGE_DMAP			x				x
D3DUSAGE_DONOTCLIP	x	x
D3DUSAGE_DYNAMIC	x	x	x	x	x		x
D3DUSAGE_NPATCHES	x	x
D3DUSAGE_POINTS	x	x
D3DUSAGE_RTPATCHES	x	x
D3DUSAGE_RENDERTARGET			x	x		x	x
D3DUSAGE_SOFTWAREPROCESSING	x	x	x	x	x		x
D3DUSAGE_WRITEONLY	x	x

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Use IDirect3D9::CheckDeviceFormat to check hardware support for these usages.

Each of the resource creation methods is listed here.

• IDirect3DDevice9::CreateCubeTexture
• IDirect3DDevice9::CreateDepthStencilSurface
• IDirect3DDevice9::CreateIndexBuffer
• IDirect3DDevice9::CreateOffscreenPlainSurface
• IDirect3DDevice9::CreateRenderTarget
• IDirect3DDevice9::CreateTexture
• IDirect3DDevice9::CreateVertexBuffer
• IDirect3DDevice9::CreateVolumeTexture

The D3DXCreatexxx texturing functions also use some of these constant values for resource creation.

For more information about pool types and their restrictions with certain usages, see D3DPOOL.

再来看看参数Pool的D3DPOOL枚举类型的详细信息:

Defines the memory class that holds the buffers for a resource.

typedef enum D3DPOOL
{
    D3DPOOL_DEFAULT = 0,
    D3DPOOL_MANAGED = 1,
    D3DPOOL_SYSTEMMEM = 2,
    D3DPOOL_SCRATCH = 3,
    D3DPOOL_FORCE_DWORD = 0x7fffffff,
} D3DPOOL, *LPD3DPOOL;

Constants

D3DPOOL_DEFAULT

Resources are placed in the memory pool most appropriate for the set of usages requested for the given resource. This is usually video memory, including both local video memory and AGP memory. The D3DPOOL_DEFAULT pool is separate from D3DPOOL_MANAGED and D3DPOOL_SYSTEMMEM, and it specifies that the resource is placed in the preferred memory for device access. Note that D3DPOOL_DEFAULT never indicates that either D3DPOOL_MANAGED or D3DPOOL_SYSTEMMEM should be chosen as the memory pool type for this resource. Textures placed in the D3DPOOL_DEFAULT pool cannot be locked unless they are dynamic textures or they are private, FOURCC, driver formats. To access unlockable textures, you must use functions such as IDirect3DDevice9::UpdateSurface, IDirect3DDevice9::UpdateTexture, IDirect3DDevice9::GetFrontBufferData, and IDirect3DDevice9::GetRenderTargetData. D3DPOOL_MANAGED is probably a better choice than D3DPOOL_DEFAULT for most applications. Note that some textures created in driver-proprietary pixel formats, unknown to the Direct3D runtime, can be locked. Also note that - unlike textures - swap chain back buffers, render targets, vertex buffers, and index buffers can be locked. When a device is lost, resources created using D3DPOOL_DEFAULT must be released before calling IDirect3DDevice9::Reset. For more information, see Lost Devices (Direct3D 9).

When creating resources with D3DPOOL_DEFAULT, if video card memory is already committed, managed resources will be evicted to free enough memory to satisfy the request.

D3DPOOL_MANAGED

Resources are copied automatically to device-accessible memory as needed. Managed resources are backed by system memory and do not need to be recreated when a device is lost. See Managing Resources (Direct3D 9) for more information. Managed resources can be locked. Only the system-memory copy is directly modified. Direct3D copies your changes to driver-accessible memory as needed.

D3DPOOL_SYSTEMMEM

Resources are placed in memory that is not typically accessible by the Direct3D device. This memory allocation consumes system RAM but does not reduce pageable RAM. These resources do not need to be recreated when a device is lost. Resources in this pool can be locked and can be used as the source for a IDirect3DDevice9::UpdateSurface or IDirect3DDevice9::UpdateTexture operation to a memory resource created with D3DPOOL_DEFAULT.

D3DPOOL_SCRATCH

Resources are placed in system RAM and do not need to be recreated when a device is lost. These resources are not bound by device size or format restrictions. Because of this, these resources cannot be accessed by the Direct3D device nor set as textures or render targets. However, these resources can always be created, locked, and copied.

D3DPOOL_FORCE_DWORD

Forces this enumeration to compile to 32 bits in size. Without this value, some compilers would allow this enumeration to compile to a size other than 32 bits. This value is not used.

Remarks

All pool types are valid with all resources. This includes: vertex buffers, index buffers, textures, and surfaces.

The following tables indicate restrictions on pool types for render targets, depth stencils, and dynamic and mipmap usages. An x indicates a compatible combination; lack of an x indicates incompatibility.

Pool	D3DUSAGE_RENDERTARGET	D3DUSAGE_DEPTHSTENCIL
D3DPOOL_DEFAULT	x	x
D3DPOOL_MANAGED
D3DPOOL_SCRATCH
D3DPOOL_SYSTEMMEM

Pool	D3DUSAGE_DYNAMIC	D3DUSAGE_AUTOGENMIPMAP
D3DPOOL_DEFAULT	x	x
D3DPOOL_MANAGED		x
D3DPOOL_SCRATCH
D3DPOOL_SYSTEMMEM	x

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For more information about usage types, see D3DUSAGE.

Pools cannot be mixed for different objects contained within one resource (mip levels in a mipmap) and, when a pool is chosen, it cannot be changed.

Applications should use D3DPOOL_MANAGED for most static resources because this saves the application from having to deal with lost devices. (Managed resources are restored by the runtime.) This is especially beneficial for unified memory architecture (UMA) systems. Other dynamic resources are not a good match for D3DPOOL_MANAGED. In fact, index buffers and vertex buffers cannot be created using D3DPOOL_MANAGED together with D3DUSAGE_DYNAMIC.

For dynamic textures, it is sometimes desirable to use a pair of video memory and system memory textures, allocating the video memory using D3DPOOL_DEFAULT and the system memory using D3DPOOL_SYSTEMMEM. You can lock and modify the bits of the system memory texture using a locking method. Then you can update the video memory texture using IDirect3DDevice9::UpdateTexture.

再来看看参数Filter与MipFilter可以使用的枚举类型D3DX_FILTER的详细说明:

The following flags are used to specify which channels in a texture to operate on.

#define	Description
D3DX_FILTER_NONE	No scaling or filtering will take place. Pixels outside the bounds of the source image are assumed to be transparent black.
D3DX_FILTER_POINT	Each destination pixel is computed by sampling the nearest pixel from the source image.
D3DX_FILTER_LINEAR	Each destination pixel is computed by sampling the four nearest pixels from the source image. This filter works best when the scale on both axes is less than two.
D3DX_FILTER_TRIANGLE	Every pixel in the source image contributes equally to the destination image. This is the slowest of the filters.
D3DX_FILTER_BOX	Each pixel is computed by averaging a 2x2(x2) box of pixels from the source image. This filter works only when the dimensions of the destination are half those of the source, as is the case with mipmaps.
D3DX_FILTER_MIRROR_U	Pixels off the edge of the texture on the u-axis should be mirrored, not wrapped.
D3DX_FILTER_MIRROR_V	Pixels off the edge of the texture on the v-axis should be mirrored, not wrapped.
D3DX_FILTER_MIRROR_W	Pixels off the edge of the texture on the w-axis should be mirrored, not wrapped.
D3DX_FILTER_MIRROR	Specifying this flag is the same as specifying the D3DX_FILTER_MIRROR_U, D3DX_FILTER_MIRROR_V, and D3DX_FILTER_MIRROR_W flags.
D3DX_FILTER_DITHER	The resulting image must be dithered using a 4x4 ordered dither algorithm.
D3DX_FILTER_SRGB_IN	Input data is in sRGB (gamma 2.2) color space.
D3DX_FILTER_SRGB_OUT	The output data is in sRGB (gamma 2.2) color space.
D3DX_FILTER_SRGB	Same as specifying D3DX_FILTER_SRGB_IN | D3DX_FILTER_SRGB_OUT.