(本文为了方便起见,把DirectX Graphics称为D3D)
D3D中的流
在D3D中,要渲染的顶点数据是放在Vertex Buffer中的,一般的做法是把顶点坐标、颜色等按照自定义的顶点格式放在同一个Vertex Buffer中,代表一个流,然后通过FVF来告诉D3D要渲染的顶点的格式。但是在某些情况下,放在一起并不是最佳选择。比如在动画中,每一帧的顶点坐标都在变化,但是纹理坐标却都不变(md3格式就是如此)。如果只用一个流,每画一帧就得把所有数据都拷贝到一个临时Vertex Buffer中再渲染,开销巨大。如果能把不同的数据放在不同的流中,就可以只更新顶点坐标的流,而纹理坐标的流就可以保持不变了。而且,只用一个Vertex Buffer时要管理FVF和数据结构体之间的关系,万一弄错了,是很难发现的。
多流
如果使用多流,麻烦就能少些。下面就让我们看看如何在D3D中实现多流。这个例子很简单,显示一个三角形,三个顶点的颜色分别是红、绿、蓝。因为本例的数据只有顶点坐标和颜色两种数据,所以只有两个Vertex Buffer。同时,由于D3D8在使用多流时必须使用Shader来声明顶点格式,所以声明一个g_Shader变量。整个程序是这样的:
#include <d3d8.h> #include <d3dx8.h>
#pragma comment(lib, "d3d8.lib") #pragma comment(lib, "d3dx8.lib")
template <typename T> inline void SAFE_RELEASE(T& p) { if (p != 0) { p->Release(); p = 0; } }
IDirect3D8* g_pD3D = NULL; IDirect3DDevice8* g_pd3dDevice = NULL; IDirect3DVertexBuffer8* g_pVBPos = NULL; IDirect3DVertexBuffer8* g_pVBCol = NULL; DWORD g_Shader = 0xFFFFFFFF;
void InitD3D(HWND hWnd) { g_pD3D = Direct3DCreate8(D3D_SDK_VERSION);
D3DDISPLAYMODE d3ddm; g_pD3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT, &d3ddm);
D3DPRESENT_PARAMETERS d3dpp; ZeroMemory(&d3dpp, sizeof(d3dpp)); d3dpp.Windowed = TRUE; d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD; d3dpp.BackBufferFormat = d3ddm.Format;
g_pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &g_pd3dDevice);
g_pd3dDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
D3DXMATRIX matWorld; D3DXMatrixIdentity(&matWorld); g_pd3dDevice->SetTransform(D3DTS_WORLD, &matWorld);
D3DXMATRIX matView; D3DXMatrixLookAtLH(&matView, &D3DXVECTOR3(0, 0, -3), &D3DXVECTOR3(0, 0, 0), &D3DXVECTOR3(0, 1, 0)); g_pd3dDevice->SetTransform(D3DTS_VIEW, &matView);
D3DXMATRIX matProj; D3DXMatrixPerspectiveFovLH(&matProj, D3DX_PI / 4, 1, 0.1f, 10); g_pd3dDevice->SetTransform(D3DTS_PROJECTION, &matProj); }
void InitVB() { // 多个流的格式 DWORD shaderDecl[] = { D3DVSD_STREAM(0), D3DVSD_REG(D3DVSDE_POSITION, D3DVSDT_FLOAT3),
D3DVSD_STREAM(1), D3DVSD_REG(D3DVSDE_DIFFUSE, D3DVSDT_D3DCOLOR),
D3DVSD_END(), };
// 位置数据 D3DVECTOR Positions[] = { { -1, -1, 1 }, { 0, 1, 1 }, { 1, -1, 1 }, };
// 颜色数据 D3DCOLOR Colors[] = { D3DCOLOR_XRGB(0xFF, 0, 0), D3DCOLOR_XRGB(0, 0xFF, 0), D3DCOLOR_XRGB(0, 0, 0xFF), };
// 建立两个VB g_pd3dDevice->CreateVertexBuffer(3 * sizeof(D3DVECTOR), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, 0, D3DPOOL_DEFAULT, &g_pVBPos); g_pd3dDevice->CreateVertexBuffer(3 * sizeof(D3DCOLOR), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, 0, D3DPOOL_DEFAULT, &g_pVBCol);
// 建立VS g_pd3dDevice->CreateVertexShader(shaderDecl, NULL, &g_Shader, 0);
// 填充数据 void* pPositions; g_pVBPos->Lock(0, 0, reinterpret_cast<BYTE**>(&pPositions), 0); memcpy(pPositions, Positions, sizeof(Positions)); g_pVBPos->Unlock();
void* pColor; g_pVBCol->Lock(0, 0, reinterpret_cast<BYTE**>(&pColor), 0); memcpy(pColor, Colors, sizeof(Colors)); g_pVBCol->Unlock(); }
void Cleanup() { // 释放两个流 g_pd3dDevice->SetStreamSource(0, NULL, sizeof(D3DVECTOR)); g_pd3dDevice->SetStreamSource(1, NULL, sizeof(D3DCOLOR));
// 删除VS g_pd3dDevice->DeleteVertexShader(g_Shader);
SAFE_RELEASE(g_pVBPos); SAFE_RELEASE(g_pVBCol);
SAFE_RELEASE(g_pd3dDevice); SAFE_RELEASE(g_pD3D); }
void Render() { g_pd3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0x33, 0x66, 0x99), 1.0f, 0);
g_pd3dDevice->BeginScene();
g_pd3dDevice->SetVertexShader(g_Shader); g_pd3dDevice->SetStreamSource(0, g_pVBPos, sizeof(D3DVECTOR)); g_pd3dDevice->SetStreamSource(1, g_pVBCol, sizeof(D3DCOLOR)); g_pd3dDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);
g_pd3dDevice->EndScene();
g_pd3dDevice->Present(NULL, NULL, NULL, NULL); }
LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) { switch (msg) { case WM_DESTROY: PostQuitMessage(0); return 0; }
return DefWindowProc(hWnd, msg, wParam, lParam); }
LPCTSTR wcName(TEXT("Multistream"));
INT WINAPI WinMain(HINSTANCE hInst, HINSTANCE, LPSTR, INT) { WNDCLASS wc; wc.style = CS_HREDRAW | CS_VREDRAW; wc.lpfnWndProc = MsgProc; wc.cbClsExtra = 0; wc.cbWndExtra = 0; wc.hInstance = hInst; wc.hIcon = NULL; wc.hCursor = LoadCursor(NULL, IDC_ARROW); wc.hbrBackground = static_cast<HBRUSH>(GetStockObject(BLACK_BRUSH)); wc.lpszMenuName = NULL; wc.lpszClassName = wcName; RegisterClass(&wc);
HWND hWnd(CreateWindow(wcName, wcName, WS_OVERLAPPEDWINDOW, 100, 100, 300, 300, GetDesktopWindow(), NULL, wc.hInstance, NULL));
InitD3D(hWnd); InitVB();
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); } else { Render(); } }
Cleanup(); UnregisterClass(wcName, wc.hInstance);
return 0; }
这里把顶点坐标放在一个VB中,而把颜色放在另一个VB中,也终于看到了SetStreamSource的第一个参数不是0的情况:-)。由于使用了两个流,所以设置了0号和1号流,分别为前面填充的顶点坐标流和颜色流。然后建立Vertex Shaer。由于这里只使用固定的pipeline,所以CreateVertexShader的第二参数为NULL。要注意的是,SetVertexShader的参数是Verter Shader的句柄,而不是FVF。如果没有CreateVertexShader,而想当然地直接把FVF的值作为参数传给SetVertexShader,则会出现结果未定义的情况。
DX9的情况
D3D9对流的部分作了不少改进,所以,我们要写的代码也得做一些更改。全局变量改为:
IDirect3D9* g_pD3D = NULL; IDirect3DDevice9* g_pd3dDevice = NULL; IDirect3DVertexBuffer9* g_pVBPos = NULL; IDirect3DVertexBuffer9* g_pVBCol = NULL; IDirect3DVertexDeclaration9* g_pVertexDeclaration = NULL;
前四个变量不用说了,只是把8变成9。而IDirect3DVertexDeclaration9是D3D9新增的,专门用于声明流的格式,相当于一个功能更强大的FVF。这回不用声明Vertex Shader了。
InitD3D中只需把
g_pD3D = Direct3DCreate8(D3D_SDK_VERSION); 改为
g_pD3D = Direct3DCreate9(D3D_SDK_VERSION); 就行了。
InitVB改为:
void InitVB() { D3DVERTEXELEMENT9 shaderDecl[] = { { 0, 0, D3DDECLTYPE_FLOAT3, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_POSITION, 0 }, { 1, 0, D3DDECLTYPE_D3DCOLOR, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_COLOR, 0 }, { 0xFF, 0, D3DDECLTYPE_UNUSED, 0, 0, 0 }, };
D3DVECTOR Positions[] = { { -1, -1, 1 }, { 0, 1, 1 }, { 1, -1, 1 }, };
D3DCOLOR Colors[] = { D3DCOLOR_XRGB(0xFF, 0, 0), D3DCOLOR_XRGB(0, 0xFF, 0), D3DCOLOR_XRGB(0, 0, 0xFF), };
g_pd3dDevice->CreateVertexBuffer(3 * sizeof(D3DVECTOR), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, 0, D3DPOOL_DEFAULT, &g_pVBPos, NULL); g_pd3dDevice->CreateVertexBuffer(3 * sizeof(D3DCOLOR), D3DUSAGE_DYNAMIC | D3DUSAGE_WRITEONLY, 0, D3DPOOL_DEFAULT, &g_pVBCol, NULL);
g_pd3dDevice->CreateVertexDeclaration(shaderDecl, &g_pVertexDeclaration);
void* pPositions; g_pVBPos->Lock(0, 0, &pPositions, 0); memcpy(pPositions, Positions, sizeof(Positions)); g_pVBPos->Unlock();
void* pColor; g_pVBCol->Lock(0, 0, &pColor, 0); memcpy(pColor, Colors, sizeof(Colors)); g_pVBCol->Unlock(); }
在DX9中应该通过D3DVERTEXELEMENT9来声明数据格式,所以shaderDecl部分做了变化,并用CreateVertexDeclaration建立了一个VertexDeclaration。
最后在Render中把
g_pd3dDevice->SetVertexShader(g_Shader); 换成
g_pd3dDevice->SetVertexDeclaration(g_pVertexDeclaration); 这就是多流的DX9版本。
总结
灵活运用多流,能提高渲染效率,减少出错的可能性。如果要做跨API的渲染系统,应该优先考虑使用多流。
参考 DX SDK OGRE
附带源码 |