D3D中的網(wǎng)格模型（2）

10.4 優(yōu)化

Mesh的頂點(diǎn)和索引能夠被重組以便能更有效的渲染mesh。當(dāng)我們這樣做時(shí)，我們說我們優(yōu)化了一個(gè)mesh。我們可以使用下面的方法來進(jìn)行優(yōu)化：

HRESULT ID3DXMesh::OptimizeInplace(

DWORD Flags,

CONST DWORD* pAdjacencyIn,

DWORD* pAdjacencyOut,

DWORD* pFaceRemap,

LPD3DXBUFFER* ppVertexRemap

);

Flags — 表示執(zhí)行什么類型的優(yōu)化方法。它可以是下面的一個(gè)或幾個(gè)的組合：

D3DXMESHOPT_COMPACT — 從mesh中移除沒有用的頂點(diǎn)和索引項(xiàng)。

D3DXMESHOPT_ATTRSORT — 根據(jù)屬性給三角形排序并調(diào)整屬性表，這將使DrawSubset執(zhí)行更有效。

D3DXMESHOPT_VERTEXCACHE — 增加頂點(diǎn)緩存的命中率。

D3DXMESHOPT_STRIPREORDER — 重組頂點(diǎn)索引使三角帶盡可能的長。

D3DXMESHOPT_IGNOREVERTS — 只優(yōu)化索引信息，忽略頂點(diǎn)信息。

注意：D3DXMESHOPT_VERTEXCACHE和D3DXMESHOPT_STRIPREORDER不能同時(shí)使用。

pAdjacencyIn — 指向沒有優(yōu)化的mesh的鄰接數(shù)組。

pAdjacencyOut — 指向一個(gè)DWORD數(shù)組，它被用來填充優(yōu)化好了的mesh鄰接信息。該數(shù)組必須有ID3DXMesh::GetNumFaces() * 3個(gè)元素。如果不需要該信息，可以將其設(shè)置為0。

pFaceRemap —指向一個(gè)DWORD數(shù)組，它被用來填充面重影射信息。該數(shù)組必須不小于ID3DXMesh::GetNumFaces()。當(dāng)一個(gè)mesh被優(yōu)化時(shí)，由索引緩存定義的面可能被移動；也就是說，在pFaceRemap中的第i項(xiàng)表示第i個(gè)原始面被移動到的面索引值。如果不需要該信息，可以將其設(shè)置為0。

ppVertexRemap — 指向ID3DXBuffer指針的地址，它被用來填充頂點(diǎn)重影射信息。這個(gè)緩存應(yīng)該包含ID3DXMesh::GetNumVertices()個(gè)頂點(diǎn)。當(dāng)一個(gè)mesh被優(yōu)化后，頂點(diǎn)可能被移動。頂點(diǎn)重影射信息用來說明原來的頂點(diǎn)被移動到新位置；也就是說，在ppVertexRemap中的第i項(xiàng)表示原來的第i個(gè)頂點(diǎn)的新位置。如果不需要該信息，可以將其設(shè)置為0。

例子：

// Get the adjacency info of the non-optimized mesh.

DWORD adjacencyInfo[Mesh->GetNumFaces() * 3];

Mesh->GenerateAdjacency(0.0f, adjacencyInfo);

// Array to hold optimized adjacency info.

DWORD optimizedAdjacencyInfo[Mesh->GetNumFaces() * 3];

Mesh->OptimizeInplace(D3DXMESHOPT_ATTRSORT | D3DXMESHOPT_COMPACT | D3DXMESHOPT_VERTEXCACHE,

adjacencyInfo, optimizedAdjacencyInfo, 0, 0);

一個(gè)更簡單的方法是Optimize方法，它輸出一個(gè)優(yōu)化的mesh，而不是在原來mesh的基礎(chǔ)上進(jìn)行優(yōu)化：

Generates a new mesh with reordered faces and vertices to optimize drawing performance.

HRESULT Optimize(
  DWORD Flags,
  CONST DWORD * pAdjacencyIn,
  DWORD * pAdjacencyOut,
  DWORD * pFaceRemap,
  LPD3DXBUFFER * ppVertexRemap,
  LPD3DXMESH * ppOptMesh
);

Parameters

Flags: [in] Specifies the type of optimization to perform. This parameter can be set to a combination of one or more flags from D3DXMESHOPT and D3DXMESH (except D3DXMESH_32BIT, D3DXMESH_IB_WRITEONLY, and D3DXMESH_WRITEONLY).
pAdjacencyIn: [in] Pointer to an array of three DWORDs per face that specifies the three neighbors for each face in the source mesh. If the edge has no adjacent faces, the value is 0xffffffff. See Remarks.
pAdjacencyOut: [in, out] Pointer to an array of three DWORDs per face that specifies the three neighbors for each face in the optimized mesh. If the edge has no adjacent faces, the value is 0xffffffff.
pFaceRemap: [in, out] An array of DWORDs, one per face, that identifies the original mesh face that corresponds to each face in the optimized mesh. If the value supplied for this argument is NULL, face remap data is not returned.
ppVertexRemap: [out] Address of a pointer to an ID3DXBuffer interface, which contains a DWORD for each vertex that specifies how the new vertices map to the old vertices. This remap is useful if you need to alter external data based on the new vertex mapping.
ppOptMesh: [out] Address of a pointer to an ID3DXMesh interface, representing the optimized mesh.

Return Values

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

Remarks

This method generates a new mesh. Before running Optimize, an application must generate an adjacency buffer by calling ID3DXBaseMesh::GenerateAdjacency. The adjacency buffer contains adjacency data, such as a list of edges and the faces that are adjacent to each other.

This method is very similar to the ID3DXBaseMesh::CloneMesh method, except that it can perform optimization while generating the new clone of the mesh. The output mesh inherits all of the creation parameters of the input mesh.

D3DXMESHOPT

Specifies the type of mesh optimization to be performed.

typedef enum D3DXMESHOPT
{
    D3DXMESHOPT_COMPACT = 0x01000000,
    D3DXMESHOPT_ATTRSORT = 0x02000000,
    D3DXMESHOPT_VERTEXCACHE = 0x04000000,
    D3DXMESHOPT_STRIPREORDER = 0x08000000,
    D3DXMESHOPT_IGNOREVERTS = 0x10000000,
    D3DXMESHOPT_DONOTSPLIT = 0x20000000,
    D3DXMESHOPT_DEVICEINDEPENDENT = 0x40000000,
} D3DXMESHOPT, *LPD3DXMESHOPT;

Constants

D3DXMESHOPT_COMPACT: Reorders faces to remove unused vertices and faces.
D3DXMESHOPT_ATTRSORT: Reorders faces to optimize for fewer attribute bundle state changes and enhanced ID3DXBaseMesh::DrawSubset performance.
D3DXMESHOPT_VERTEXCACHE: Reorders faces to increase the cache hit rate of vertex caches.
D3DXMESHOPT_STRIPREORDER: Reorders faces to maximize length of adjacent triangles.
D3DXMESHOPT_IGNOREVERTS: Optimize the faces only; do not optimize the vertices.
D3DXMESHOPT_DONOTSPLIT: While attribute sorting, do not split vertices that are shared between attribute groups.
D3DXMESHOPT_DEVICEINDEPENDENT: Affects the vertex cache size. Using this flag specifies a default vertex cache size that works well on legacy hardware.

Remarks

The D3DXMESHOPT_STRIPREORDER and D3DXMESHOPT_VERTEXCACHE optimization flags are mutually exclusive.

The D3DXMESHOPT_SHAREVB flag has been removed from this enumeration. Use D3DXMESH_VB_SHARE instead, in D3DXMESH.

10.5 屬性表

當(dāng)一個(gè)mesh被使用D3DXMESHOPT_ATTRSORT參數(shù)來優(yōu)化后，mesh的幾何信息將按照屬性進(jìn)行排序，這樣各個(gè)子集的頂點(diǎn)/索引將組成連續(xù)的塊（如圖10.3）。

除了進(jìn)行幾何信息的排序外，D3DXMESHOPT_ATTRSORT優(yōu)化項(xiàng)還將創(chuàng)建一個(gè)屬性表。該表是D3DXATTRIBUTERANGE結(jié)構(gòu)的一個(gè)數(shù)組。在屬性表中的每一項(xiàng)對應(yīng)mesh的一個(gè)子集并指示頂點(diǎn)/索引緩存中的一個(gè)連續(xù)連續(xù)內(nèi)存塊，這個(gè)子集的幾何信息就包含在這個(gè)塊中。D3DXATTRIBUTERANGE結(jié)構(gòu)的定義如下：

typedef struct _D3DXATTRIBUTERANGE {

DWORD AttribId;

DWORD FaceStart;

DWORD FaceCount;

DWORD VertexStart;

DWORD VertexCount;

} D3DXATTRIBUTERANGE;

AttribId — 子集的ID。

FaceStart — 該子集的面的起始值，F(xiàn)aceStart*3就是起始三角形在索引緩存中的序號。

FaceCount — 在子集中的面（三角形）數(shù)。

VertexStart — 該子集的起始頂點(diǎn)在頂點(diǎn)緩存中的序號。

VertexCount — 在子集中的頂點(diǎn)數(shù)。

建立了屬性表以后，渲染一個(gè)子集就很容易了。僅僅查一下屬性表就能找出自己的幾何信息。注意如果沒有屬性表，每渲染一個(gè)子集就需要對屬性緩存進(jìn)行一次線性搜索來找出子集包含的幾何信息。

可以使用下面的方法來訪問mesh的屬性表：

Retrieves either an attribute table for a mesh, or the number of entries stored in an attribute table for a mesh.

HRESULT GetAttributeTable(
  D3DXATTRIBUTERANGE * pAttribTable,
  DWORD * pAttribTableSize
);

Parameters

pAttribTable: [in, out] Pointer to an array of D3DXATTRIBUTERANGE structures, representing the entries in the mesh's attribute table. Specify NULL to retrieve the value for pAttribTableSize.
pAttribTableSize: [in, out] Pointer to either the number of entries stored in pAttribTable or a value to be filled in with the number of entries stored in the attribute table for the mesh.

Return Values

If the method succeeds, the return value is D3D_OK. If the method fails, the return value can be D3DERR_INVALIDCALL.

Remarks

An attribute table is created by ID3DXMesh::Optimize and passing D3DXMESHOPT_ATTRSORT for the Flags parameter.

An attribute table is used to identify areas of the mesh that need to be drawn with different textures, render states, materials, and so on. In addition, the application can use the attribute table to hide portions of a mesh by not drawing a given attribute identifier when drawing the frame.

這個(gè)方法能夠做兩件事情：它可以返回屬性表的屬性數(shù)，也可以用屬性數(shù)據(jù)來填充一個(gè)D3DXATTRIBUTERANGE結(jié)構(gòu)數(shù)組。

要得到屬性表的元素個(gè)數(shù)，可以就將第一個(gè)參數(shù)設(shè)置為0：

DWORD numSubsets = 0;

Mesh->GetAttributeTable(0, &numSubsets);

一旦我們知道了屬性表的元素個(gè)數(shù)，我們就能夠通過寫屬性表來填充一個(gè)D3DXATTRIBUTERANGE結(jié)構(gòu)數(shù)組：

D3DXATTRIBUTERANGE table = new D3DXATTRIBUTERANGE [numSubsets];

Mesh->GetAttributeTable( table, &numSubsets );

我們能夠使用ID3DXMesh::SetAttributeTable方法來直接設(shè)置屬性表。

Sets the attribute table for a mesh and the number of entries stored in the table.

HRESULT SetAttributeTable(
  CONST D3DXATTRIBUTERANGE * pAttribTable,
  DWORD cAttribTableSize
);

Parameters

pAttribTable: [in] Pointer to an array of D3DXATTRIBUTERANGE structures, representing the entries in the mesh attribute table.
cAttribTableSize: [in] Number of attributes in the mesh attribute table.

Return Values

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

Remarks

If an application keeps track of the information in an attribute table, and rearranges the table as a result of changes to attributes or faces, this method allows the application to update the attribute tables instead of calling ID3DXMesh::Optimize again.

下面的代碼就是設(shè)置一個(gè)有12個(gè)子集的屬性表：

D3DXATTRIBUTERANGE attributeTable[12];

// ...fill attributeTable array with data

Mesh->SetAttributeTable( attributeTable, 12);

10.6 鄰接信息

對于mesh的某些操作，如優(yōu)化，有必要了解的是三角形之間的鄰接信息。Mesh的鄰接數(shù)組存儲了這些信息。

鄰接數(shù)組是一個(gè)DWORD數(shù)組，其中的每一項(xiàng)對應(yīng)了mesh中的一個(gè)三角形。例如，第i項(xiàng)對應(yīng)的三角形由以下三個(gè)索引值定義：

A = i x3

B = i x3 + 1

C = i x3 + 2

注意，使用ULONG_MAX = 4294967295表示該邊沒有鄰接三角形。我們也可以用-1來表示，因?yàn)?1轉(zhuǎn)換成DWORD就是ULONG_MAX。回想一下，DWORD就是一個(gè)unsigned32-bit整數(shù)。

因?yàn)槊總€(gè)三角形都有三條邊，所以它最多有三個(gè)鄰接三角形（如圖10.4）。

因此，鄰接數(shù)組必須有三項(xiàng)（ID3DXBaseMesh::GetNumFaces()*3）—— 在mesh中每個(gè)三角形都可能有三個(gè)鄰接三角形。

很多D3Dxmesh創(chuàng)造函數(shù)都能輸出鄰接信息，但我們也可以使用下面的方法：

HRESULT ID3DXMesh::GenerateAdjacency(

FLOAT fEpsilon,

DWORD* pAdjacency

);

fEpsilon — 指示當(dāng)兩個(gè)點(diǎn)距離有多近時(shí)，可以認(rèn)為是一個(gè)點(diǎn)。當(dāng)兩點(diǎn)間的距離小于epsilon時(shí)，可認(rèn)為它們是同一個(gè)點(diǎn)。

pAdjacency — 一個(gè)指向填充了鄰接信息的DWORD數(shù)組指針。

例子：

DWORD adjacencyInfo[Mesh->GetNumFaces() * 3];

Mesh->GenerateAdjacency(0.001f, adjacencyInfo);

posted on 2008-03-27 11:32 lovedday 閱讀(1484) 評論(1) 編輯收藏引用

# re: D3D中的網(wǎng)格模型（2） 2008-10-09 23:21 leshy

天行健君子當(dāng)自強(qiáng)而不息

D3D中的網(wǎng)格模型（2）

10.4 優(yōu)化

Parameters

Return Values

Remarks

D3DXMESHOPT

Constants

Remarks

10.5 屬性表

Parameters

Return Values

Remarks

Parameters

Return Values

Remarks

10.6 鄰接信息

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天行健 君子當(dāng)自強(qiáng)而不息

D3D中的網(wǎng)格模型（2）

10.4 優(yōu)化

Parameters

Return Values

Remarks

D3DXMESHOPT

Constants

Remarks

10.5 屬性表

Parameters

Return Values

Remarks

Parameters

Return Values

Remarks

10.6 鄰接信息

評論

# re: D3D中的網(wǎng)格模型（2） 2008-10-09 23:21 leshy

公告

導(dǎo)航

統(tǒng)計(jì)

常用鏈接

隨筆分類(178)

3D游戲編程相關(guān)鏈接

搜索

最新評論

天行健君子當(dāng)自強(qiáng)而不息