多级渐进纹理过滤
多级渐进纹理由一组分辨率逐渐降低的纹理序列组成，每一级纹理宽度和高度都是上一级纹理宽度和高度的一半。宽和高不一定相等，也就是说，这些纹理不一定都是正方形。
Direct3D在纹理映射时，自动选择一幅与物体大小最接近的纹理进行渲染。当物体离投影平面较远时，Direct3D会选择一张尺寸较小、分辨率较低的纹理进行渲染；当物体离投影平面较近时，Direct3D会选择一张尺寸较大、分辨率较高的纹理进行渲染。Direct3D将纹理序列看成一条多级渐进纹理链。链头处纹理的分辨率最高，下一级往后依次递减，链尾处纹理的分辨率最低。
Direct3D能估计出多级渐进纹理链中哪幅纹理的分辨率最接近想要的输出结果，然后它将像素映射到纹理空间。当最终显示的图形大小介于任意两级纹理图形之间时，Direct3D将两级纹理的相应元素进行混合后显示。
多级渐进纹理过滤能够有效地提高图形渲染速度，当物体离投影平面较远时，Direct3D会选择一张尺寸较小的纹理进行渲染，而无需经过复杂的诸如各项异性纹理过滤，并且由于这时纹理需要的显存比不使用多级渐进纹理时小，因此能有效地减少纹理载入显存的时间。
生成多级渐进纹理
可以通过调用Direct3D扩展实用库函数D3DXCreateTextureFromFileEx()自动生成多级渐进纹理序列，该函数的声明如下：
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:
- 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.
- 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.
- 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.
参数Format是D3DFORMAT枚举类型，指定纹理图形的格式，还可以将它设置为D3DFMT_DXT1
~ D3DFMT_DXT5的值之一，表示生成DXT压缩纹理以节省空间。
Texture Constants
|
#define |
Description |
|
D3DFMT_FROM_FILE |
Take
the format exactly from a file. |
|
D3DX_DEFAULT |
A
default value. |
|
D3DX_DEFAULT_NONPOW2 |
Do not
round up numbers such as width or height to a power of two. |
|
D3DX_FROM_FILE |
Take
the texture dimensions exactly from a file. |
These #defines are declared in d3dx9.h.
D3DXIMAGE_INFO
Returns a description of the original contents of an
image file.
typedef struct D3DXIMAGE_INFO {
UINT Width;
UINT Height;
UINT Depth;
UINT MipLevels;
D3DFORMAT Format;
D3DRESOURCETYPE ResourceType;
D3DXIMAGE_FILEFORMAT ImageFileFormat;
} D3DXIMAGE_INFO, *LPD3DXIMAGE_INFO;
Members
- Width
- Width of original image in pixels.
- Height
- Height of original image in pixels.
- Depth
- Depth of original image in pixels.
- MipLevels
- Number of mip levels in original image.
- Format
- A value from the D3DFORMAT enumerated type that
most closely describes the data in the original image.
- ResourceType
- Represents the type of the texture stored in the
file. It is either D3DRTYPE_TEXTURE, D3DRTYPE_VOLUMETEXTURE, or
D3DRTYPE_CubeTexture.
- ImageFileFormat
- Represents the format of the image file.
PALETTEENTRY
Specifies the color and usage of an entry in a logical
palette.
typedef struct PALETTEENTRY {
BYTE peRed;
BYTE peGreen;
BYTE peBlue;
BYTE peFlags;
} PALETTEENTRY, *LPPALETTEENTRY;
Members
- peRed
- The red intensity value for the palette entry.
- peGreen
- The green intensity value for the palette entry.
- peBlue
- The blue intensity value for the palette entry.
- peFlags
- The alpha intensity value for the palette entry.
Note that as of DirectX 8, this member is treated differently than
documented in the Platform SDK.
设置多级渐进纹理过滤方式
当最终显示的纹理贴图大小介于任意两级纹理之间时，Direct3D能够取得两级纹理元素进行混合后显示，具体的混合方式由指定的多级渐进纹理过滤方式决定。可以调用函数IDirect3DDevice9::SetSamplerState()设置多级渐进纹理过滤方式，将第一个参数设为纹理层序号，第二个参数设为D3DSAMP_MIPFILTER表示多级渐进纹理过滤，第三个参数设为在相邻纹理级之间的过滤方式，可取枚举类型D3DTEXTUREFILTERTYPE的任意值。下面的示例代码设置相邻纹理级之间的过滤方式为线性过滤。
g_device->SetSamplerState(0,
D3DSAMP_MIPFILTER, D3DTEXF_LINEAR);
如果将第三个参数设为D3DTEXF_NONE，那么就会一直使用最高一级的纹理，即禁用多级渐进纹理过滤。如果将其设为D3DTEXF_POINT，就会只使用与图元大小最匹配的一级纹理。如果将其设为D3DTEXF_LINEAR，Direct3D就将与图元大小最匹配的两级纹理以线性方式混合。
需要注意的是，多级纹理过滤是缩小和放大过滤器的结合。例如，如果将缩小和方法过滤器设为线性过滤，但是多级纹理过滤方式设为最近点采样，Direct3D就会选择与要显示的纹理贴图大小最接近的纹理级别，在该级纹理上完成双线性纹理过滤，并将结果作为像素的值。如果将缩小、放大过滤器和多级渐进纹理都设置为线性过滤，则Direct3D就会在两个最接近的纹理级别上都进行双线性纹理过滤，然后再对相邻两级纹理图形上对应的两个纹理颜色进行加权平均，最后的结果作为单个像素值。这种为了图元中的一个像素，而结合了两幅纹理，共8个像素的技术，称为“三线性过滤”，因为它在纹理的三个方向----u、
v和纹理级别上都进行了线性过滤。
可以通过IDirect3DDevice9::SetSamplerState()函数设置实际渲染时纹理过滤的最大级数，其中需要将第二个参数设为D3DSAMP_MAXMIPLEVEL，第三个参数设为实际渲染时纹理过滤的最大级数。下面的示例代码设置纹理层0的最大多级纹理过滤级数为16。
g_device->SetSamplerState(0,
D3DSAMP_MAXMIPLEVEL, 16);
还可以通过将IDirect3DDevice9::SetSamplerState()的第二个参数设为D3DSAMP_MIPMAPLODBIAS，设置多级纹理映射级数偏移值。如果对某个纹理映射设置正偏移值，得到的图形结果就会比原来的更清晰，但锯齿更多；反之设为负偏移值，得到的图形结果就会更模糊。
多级渐进纹理过滤示例程序
该程序创建了一幅多级渐进纹理和一幅单级别纹理，按下数字键“1”则使用多级渐进纹理，按下数字键“2”则使用单级别纹理。按下“↓”和“↑”则缩小和放大显示的图形，仔细观察图像的变化，可以看到多级渐进纹理的效果。
使用MipMap纹理过滤
使用单级纹理过滤（即禁用多级纹理过滤）
源程序：
#include <d3dx9.h>
#pragma warning(disable : 4127)
#define CLASS_NAME "GameApp"
#define release_com(p) do { if(p) { (p)->Release(); (p) = NULL; } } while(0)
IDirect3D9* g_d3d;
IDirect3DDevice9* g_device;
IDirect3DVertexBuffer9* g_vertex_buffer;
IDirect3DTexture9* g_texture;
IDirect3DTexture9* g_mip_texture;
float g_distance = -10; // distance from camera to image
bool g_use_mip_texture = true;
struct sCustomVertex
{
float x, y, z;
float u, v;
};
#define D3DFVF_CUSTOM_VERTEX (D3DFVF_XYZ | D3DFVF_TEX1)
void setup_matrices()
{
// build world matrix
D3DXMATRIX mat_world;
D3DXMatrixIdentity(&mat_world);
g_device->SetTransform(D3DTS_WORLD, &mat_world);
// setup view matrix
D3DXVECTOR3 eye(0.0f, 0.0f, g_distance);
D3DXVECTOR3 at(0.0f, 0.0f, 0.0f);
D3DXVECTOR3 up(0.0f, 1.0f, 0.0f);
D3DXMATRIX mat_view;
D3DXMatrixLookAtLH(&mat_view, &eye, &at, &up);
g_device->SetTransform(D3DTS_VIEW, &mat_view);
// setup projection matrix
D3DXMATRIX mat_proj;
D3DXMatrixPerspectiveFovLH(&mat_proj, D3DX_PI/4, 1.0f, 1.0f, 100.0f);
g_device->SetTransform(D3DTS_PROJECTION, &mat_proj);
}
bool init_graphics()
{
/*
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
);
*/
// create mipmap texture object
if(FAILED(D3DXCreateTextureFromFileEx(g_device, "texture.jpg", 0, 0, 0, 0, D3DFMT_X8R8G8B8, D3DPOOL_MANAGED,
D3DX_DEFAULT, D3DX_DEFAULT, 0xFF000000, NULL, NULL, &g_mip_texture)))
{
MessageBox(NULL, "Create mipmap texture failed!", "ERROR", MB_OK);
return false;
}
// create normal texture object, set MipLevels as 1, disable mipmap.
if(FAILED(D3DXCreateTextureFromFileEx(g_device, "texture.jpg", 0, 0, 1, 0, D3DFMT_X8R8G8B8, D3DPOOL_MANAGED,
D3DX_DEFAULT, D3DX_DEFAULT, 0xFF000000, NULL, NULL, &g_texture)))
{
MessageBox(NULL, "Create texture failed!", "ERROR", MB_OK);
return false;
}
sCustomVertex vertices[] =
{
{ -3, -3, 0.0f, 0.0f, 1.0f},
{ -3, 3, 0.0f, 0.0f, 0.0f},
{ 3, -3, 0.0f, 1.0f, 1.0f},
{ 3, 3, 0.0f, 1.0f, 0.0f }
};
g_device->CreateVertexBuffer(sizeof(vertices), 0, D3DFVF_CUSTOM_VERTEX, D3DPOOL_MANAGED, &g_vertex_buffer, NULL);
void* ptr;
g_vertex_buffer->Lock(0, 0, (void**)&ptr, 0);
memcpy(ptr, vertices, sizeof(vertices));
g_vertex_buffer->Unlock();
return true;
}
bool init_d3d(HWND hwnd)
{
g_d3d = Direct3DCreate9(D3D_SDK_VERSION);
if(g_d3d == NULL)
return false;
D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory(&d3dpp, sizeof(d3dpp));
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.BackBufferFormat = D3DFMT_UNKNOWN;
if(FAILED(g_d3d->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hwnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING,
&d3dpp, &g_device)))
{
return false;
}
if(! init_graphics())
return false;
g_device->SetRenderState(D3DRS_LIGHTING, FALSE);
g_device->SetSamplerState(0, D3DSAMP_MIPFILTER, D3DTEXF_LINEAR);
return true;
}
void cleanup()
{
release_com(g_texture);
release_com(g_mip_texture);
release_com(g_vertex_buffer);
release_com(g_device);
release_com(g_d3d);
}
void render()
{
setup_matrices();
g_device->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(5, 5, 5), 1.0f, 0);
g_device->BeginScene();
g_device->SetTexture(0, g_use_mip_texture ? g_mip_texture : g_texture);
g_device->SetStreamSource(0, g_vertex_buffer, 0, sizeof(sCustomVertex));
g_device->SetFVF(D3DFVF_CUSTOM_VERTEX);
g_device->DrawPrimitive(D3DPT_TRIANGLESTRIP, 0, 2);
g_device->EndScene();
g_device->Present(NULL, NULL, NULL, NULL);
}
LRESULT WINAPI WinProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_KEYDOWN:
switch(wParam)
{
case VK_ESCAPE:
DestroyWindow(hwnd);
break;
case 49: // press key "1", use mipmap texture filter mode
g_use_mip_texture = true;
break;
case 50: // press key "2", use normal texture filter mode
g_use_mip_texture = false;
break;
case VK_DOWN:
g_distance -= 0.1f;
break;
case VK_UP:
g_distance += 0.1f;
break;
}
break;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, msg, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE inst, HINSTANCE, LPSTR, INT)
{
WNDCLASSEX wc;
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_CLASSDC;
wc.lpfnWndProc = WinProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = inst;
wc.hIcon = NULL;
wc.hCursor = NULL;
wc.hbrBackground = NULL;
wc.lpszMenuName = NULL;
wc.lpszClassName = CLASS_NAME;
wc.hIconSm = NULL;
if(! RegisterClassEx(&wc))
return -1;
HWND hwnd = CreateWindow(CLASS_NAME, "Direct3D App", WS_OVERLAPPEDWINDOW, 200, 100, 800, 600,
NULL, NULL, wc.hInstance, NULL);
if(hwnd == NULL)
return -1;
if(init_d3d(hwnd))
{
ShowWindow(hwnd, SW_SHOWDEFAULT);
UpdateWindow(hwnd);
MSG msg;
ZeroMemory(&msg, sizeof(msg));
while(msg.message != WM_QUIT)
{
if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
render();
Sleep(10);
}
}
cleanup();
UnregisterClass(CLASS_NAME, wc.hInstance);
return 0;
}