第八章索引緩沖

1、第八章：索引緩沖Introduction （序）這一章我們將學(xué)習(xí)一下關(guān)于索引緩沖的內(nèi)容。首先，我們要改進(jìn)一下CCuboid使它能支持索引緩沖。然后我們會(huì)創(chuàng)建一個(gè)類CTerrain，一個(gè)很簡單的地形發(fā)生器。當(dāng)我們的地形生成后，我們還會(huì)賦予它草的紋理，使它看起來更真實(shí)。What is an Index Buffer? （什么是索引緩沖）索引緩沖就是內(nèi)存中的一塊用于索引頂點(diǎn)的區(qū)域。不明白？接著看。當(dāng)渲染場景時(shí)，DX會(huì)對每個(gè)頂點(diǎn)都進(jìn)行許多計(jì)算，例如燈光、變幻等等，這樣，運(yùn)算量會(huì)很大。但是我們總是希望讓DX做最少的運(yùn)算以增加程序的效率，因此，我們需要把頂點(diǎn)的數(shù)目減到最少。這樣，索引緩沖就派上用場了。舉個(gè)

2、例子能更好地理解：假如我們想要繪制一個(gè)正方形，那末它需要由兩個(gè)三角形來構(gòu)成，總共6個(gè)頂點(diǎn)（用三角列）。但實(shí)際上4頂點(diǎn)就應(yīng)當(dāng)能確定一個(gè)正方形了（每角一個(gè)），用6個(gè)頂點(diǎn)是因?yàn)槠渲杏?個(gè)頂點(diǎn)被重合（相同的值）了。因?yàn)槲覀冇许旤c(diǎn)重合了，所以用索引緩沖是一個(gè)好主意。它是這樣工作的：首先我們在頂點(diǎn)緩沖中只定義4個(gè)頂點(diǎn)（每角一個(gè)），然后在索引緩沖中定義6個(gè)索引，每個(gè)索引都會(huì)映射頂點(diǎn)緩沖中的一個(gè)頂點(diǎn)。然后我們用索引緩沖中的索引來渲染三角形，那末實(shí)際上我們只用了4個(gè)頂點(diǎn)。下圖（8.1）演示了所舉的這個(gè)例子：Fig 8.1在上面的例子中，我們只用了4個(gè)頂點(diǎn)就定義了一個(gè)正方形，實(shí)際節(jié)約了2個(gè)頂點(diǎn)。注意索引緩沖中的順

3、序是順時(shí)針的，這是頂點(diǎn)被渲染的順序。然后我們會(huì)像以前那樣渲染場景，只不過這次除了頂點(diǎn)緩沖之外我們還用了索引緩沖。那末如果我們把這種方法應(yīng)用到我們的立方體上面，我們就會(huì)節(jié)約12個(gè)頂點(diǎn)。不要說那并不多，想象一個(gè)有100個(gè)立方體的場景，我們在每一幀上都會(huì)節(jié)約1200個(gè)頂點(diǎn)呢！Implementing an Index Buffer in DirectX （在DX中實(shí)現(xiàn)索引緩沖）我們需要給CCuboid添加一個(gè)索引緩沖，要實(shí)現(xiàn)這個(gè)，我們需要添加如下代碼：Step 1: Creating the Index Buffer （創(chuàng)建索引緩沖）首先，我們需要兩個(gè)新的成員變量：一個(gè)LPDIRECT3DINDEX

4、BUFFER8型的m_pIndexBuffer，索引緩沖指針；一個(gè)DWORD變量m_dwNumOfIndices，對象（頂點(diǎn)）索引數(shù)目，在此為36（6個(gè)面X每面2個(gè)三角形X每個(gè)三角形3個(gè)頂點(diǎn)），構(gòu)造函數(shù)會(huì)這樣設(shè)置。我們還有一個(gè)新的模塊CreateIndexBuffer，在構(gòu)造函數(shù)中，我們會(huì)在設(shè)置頂點(diǎn)值之前調(diào)用它。使用索引緩沖的方法與使用頂點(diǎn)緩沖是類似的：首先我們創(chuàng)建索引緩沖并且得到它的指針（m_pIndexBuffer），然后我們臨時(shí)地把36個(gè)頂點(diǎn)索引都保存到一個(gè)數(shù)組當(dāng)中，然后鎖定索引緩沖，最后把數(shù)組復(fù)制給它并解鎖。LPDIRECT3DINDEXBUFFER8 m_pIndexBuffer;D

5、WORD m_dwNumOfIndices; bool CCuboid:CreateIndexBuffer() VOID* pBufferIndices; /Create the index buffer from our device if(FAILED(m_pD3DDevice->CreateIndexBuffer(m_dwNumOfIndices * sizeof(WORD), 0, D3DFMT_INDEX16, D3DPOOL_MANAGED, &m_pIndexBuffer) return false; /Set values for the index buffer

6、 WORD pIndices = 0, 1, 2, 3, 2, 1, /Top 4, 5, 6, 7, 6, 5, /Face 1 8, 9,10,11,10, 9, /Face 2 12,13,14,15,14,13, /Face 3 16,17,18,19,18,17, /Face 4 20,21,22,23,22,21; /Bottom /Get a pointer to the index buffer indices and lock the index buffer m_pIndexBuffer->Lock(0, m_dwNumOfIndices * sizeof(WORD)

7、, (BYTE*)&pBufferIndices, 0); /Copy our stored indices values into the index buffer memcpy(pBufferIndices, pIndices, m_dwNumOfIndices * sizeof(WORD); /Unlock the index buffer m_pIndexBuffer->Unlock(); return true; Step 2: Modify the Vertex Buffer （修改頂點(diǎn)緩沖）我們需要修改一下UpdateVertices模塊。首先也是最主要的就是這回我

8、們只需要24個(gè)頂點(diǎn)，而不是36個(gè)。然后我們會(huì)像上一章那樣初始化法線向量為0。此章的另一點(diǎn)不同就是我們將計(jì)算出三角形的共享頂點(diǎn)的均分法線（上一章我們只是把三角形的法線簡單地相加，而沒有均分），實(shí)際上我們并不真的需要對這個(gè)立方體這樣做，目的只是想充當(dāng)一個(gè)例子。在UpdateVertices中我們增添了兩個(gè)新的指針pNumOfSharedPolygons和pSumVertexNormal，它們分別指向兩個(gè)數(shù)組：一個(gè)WORD型的用于描述所有頂點(diǎn)周圍的三角形數(shù)目（也就是幾個(gè)三角形共享那個(gè)頂點(diǎn)）；另一個(gè)D3DVECTOR型的用于保存所有頂點(diǎn)的均分法線向量。接下來我們將計(jì)算出每個(gè)頂點(diǎn)的均分法線向量。在Upd

9、ateVertices中當(dāng)我們初始化所有頂點(diǎn)之后，我們會(huì)有一個(gè)循環(huán)，索引緩沖中的所有的頂點(diǎn)索引都會(huì)通過它。循環(huán)將計(jì)算出每個(gè)三角形的法線、累加被引用的頂點(diǎn)的計(jì)數(shù)（保存在pNumOfSharedPolygons中，被引用的次數(shù)也就是周圍的三角形數(shù)），還把得出的三角形法線向量加到它周圍的三個(gè)頂點(diǎn)的法線向量上（由pSumVertexNormal保存，這樣整個(gè)循環(huán)結(jié)束后就能得出所有頂點(diǎn)的法線向量了，只不過還沒有均分）。然后，我們會(huì)根據(jù)每個(gè)頂點(diǎn)的引用計(jì)數(shù)（也就是幾個(gè)三角形共享那個(gè)頂點(diǎn)）來計(jì)算出所有頂點(diǎn)的均分法線向量，接著我們會(huì)將它規(guī)格化，確保向量的x、y和z都能在0和1之間。最后，我們還得把得出的每個(gè)頂點(diǎn)

10、均分法線向量應(yīng)用到對應(yīng)的頂點(diǎn)上，然后像以往一樣復(fù)制到頂點(diǎn)緩沖中。bool CCuboid:UpdateVertices() DWORD i; VOID* pVertices; WORD* pBufferIndices; D3DXVECTOR3 vNormal; DWORD dwVertex1; DWORD dwVertex2; DWORD dwVertex3; /Array holds how many times this vertex is shared WORD* pNumOfSharedPolygons = new WORDm_dwNumOfVertices; /Array holds

11、 sum of all face normals for shared vertex D3DVECTOR* pSumVertexNormal = new D3DVECTORm_dwNumOfVertices; /Clear memory for(i = 0; i < m_dwNumOfVertices; i+) pNumOfSharedPolygonsi = 0; pSumVertexNormali = D3DXVECTOR3(0,0,0); CUBOID_CUSTOMVERTEX cvVertices = /Top Face m_rX - (m_rWidth / 2), m_rY +

12、(m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 0 m_rX - (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 1 m_rX + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 2

13、m_rX + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 3 /Face 1 m_rX - (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 4 m_rX - (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.

14、0f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 5 m_rX + (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 6 m_rX + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 7 /Face 2 m_rX + (m_rWidth / 2), m_rY - (m_r

15、Height / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 8 m_rX + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 9 m_rX + (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 10 m_r

16、X + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 11 /Face 3 m_rX + (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 12 m_rX + (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0

17、f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 13 m_rX - (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 14 m_rX - (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 15 /Face 4 m_rX - (m_rWidth / 2), m_rY - (m

18、_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 16 m_rX - (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 17 m_rX - (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 18

19、 m_rX - (m_rWidth / 2), m_rY + (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 19 /Bottom Face m_rX + (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, /Vertex 20 m_rX + (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ + (m_rDepth

20、/ 2), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, /Vertex 21 m_rX - (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ - (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, /Vertex 22 m_rX - (m_rWidth / 2), m_rY - (m_rHeight / 2), m_rZ + (m_rDepth / 2), 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, /Vertex 23 ; /Get a pointer to the index b

21、uffer indices and lock the index buffer m_pIndexBuffer->Lock(0, m_dwNumOfIndices * sizeof(WORD), (BYTE*)&pBufferIndices, D3DLOCK_READONLY); /For each triangle, count the number of times each vertex is used and /add together the normals of faces that share a vertex for(i = 0; i < m_dwNumOfI

22、ndices; i += 3) dwVertex1 = pBufferIndicesi; dwVertex2 = pBufferIndicesi + 1; dwVertex3 = pBufferIndicesi + 2; vNormal = GetTriangeNormal(&D3DXVECTOR3(cvVerticesdwVertex1.x, cvVerticesdwVertex1.y, cvVerticesdwVertex1.z), &D3DXVECTOR3(cvVerticesdwVertex2.x, cvVerticesdwVertex2.y, cvVerticesdw

23、Vertex2.z), &D3DXVECTOR3(cvVerticesdwVertex3.x, cvVerticesdwVertex3.y, cvVerticesdwVertex3.z); pNumOfSharedPolygonsdwVertex1+; pNumOfSharedPolygonsdwVertex2+; pNumOfSharedPolygonsdwVertex3+; pSumVertexNormaldwVertex1.x += vNormal.x; pSumVertexNormaldwVertex1.y += vNormal.y; pSumVertexNormaldwVer

24、tex1.z += vNormal.z; pSumVertexNormaldwVertex2.x += vNormal.x; pSumVertexNormaldwVertex2.y += vNormal.y; pSumVertexNormaldwVertex2.z += vNormal.z; pSumVertexNormaldwVertex3.x += vNormal.x; pSumVertexNormaldwVertex3.y += vNormal.y; pSumVertexNormaldwVertex3.z += vNormal.z; /Unlock the index buffer m_

25、pIndexBuffer->Unlock(); /For each vertex, calculate and set the average normal for(i = 0; i < m_dwNumOfVertices; i+) vNormal.x = pSumVertexNormali.x / pNumOfSharedPolygonsi; vNormal.y = pSumVertexNormali.y / pNumOfSharedPolygonsi; vNormal.z = pSumVertexNormali.z / pNumOfSharedPolygonsi; D3DXVe

26、c3Normalize(&vNormal, &vNormal); cvVerticesi.nx = vNormal.x; cvVerticesi.ny = vNormal.y; cvVerticesi.nz = vNormal.z; /Get a pointer to the vertex buffer vertices and lock the vertex buffer if(FAILED(m_pVertexBuffer->Lock(0, sizeof(cvVertices), (BYTE*)&pVertices, 0) return false; /Copy

27、 our stored vertices values into the vertex buffer memcpy(pVertices, cvVertices, sizeof(cvVertices); /Unlock the vertex buffer m_pVertexBuffer->Unlock(); /Clean up delete pNumOfSharedPolygons; delete pSumVertexNormal; pNumOfSharedPolygons = NULL; pSumVertexNormal = NULL; return true;Step 3: Render （渲染）Render模塊也相應(yīng)地做了改動(dòng)：首先，我們要通知DX我們要用索引緩沖來渲染三角形，所以我們得調(diào)用SetIndices并且把索引緩沖的指針給它；其次，我們要用DrawIndexedPrimitive代替原來的DrawPrimitive以支持用索引緩沖渲染三角形。/Select index bufferm_pD3DDevice->SetIndices(m_pIndexBuffer, 0);/Render polygon