In DirectX 8, support for rendering to multiple windows is provided through the creation of additional swap chains. However, there are currently no examples of this in the SDK, and the documentation is a bit vague. This article is provided to fill the gaps, and will explain the steps you need to take to write an application that will render multiple views in separate windows.
在DX8中，對多窗口的支持是通過創(chuàng)建更多的Swap Chains來提供的。SDK中沒有相關(guān)的例子而且文檔也只是泛泛而談。這篇文章就是為了解決這個問題，它將向您展示應(yīng)當(dāng)如何一步步地實現(xiàn)在多個分離窗口中渲染多個視圖。
Step 1 - Setting Up The Parent Frame
第一步：設(shè)置父框架窗口
In an application with multiple views, we start with a top level frame that will contain child windows in its client area to display various views. Once the parent frame parent frame has been created, we create our Direct3D device interface, specifying windowed mode and setting the top level window handle as the focus window:
在多視圖的應(yīng)用程序中，我們需要從最高層次的框架——這個框架將包含所有在他用戶區(qū)之內(nèi)的子視圖窗口——開始我們的旅程。當(dāng)父框架創(chuàng)建的時候，我們需要創(chuàng)建Direct3D Device接口，為其指定使用窗口模式，而且設(shè)置這最高層次的窗口句柄作為“焦點窗口”的句柄：
g_pD3D=Direct3DCreate8(D3D_SDK_VERSION);
if (!g_pD3D) return -1;
D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory( &d3dpp, sizeof(d3dpp) );
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_COPY;
// Use the current display mode. 使用當(dāng)前的顯示模式
D3DDISPLAYMODE mode;
if(FAILED(g_pD3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT , &mode))) {
SAFE_RELEASE(g_pD3D);
return -1;
}
d3dpp.BackBufferFormat = mode.Format;
d3dpp.BackBufferWidth = mode.Width;
d3dpp.BackBufferHeight = mode.Height;
d3dpp.EnableAutoDepthStencil=TRUE;
d3dpp.AutoDepthStencilFormat = D3DFMT_D16;
// m_hWnd is handle to top level window m_hWnd是最高層窗口的句柄
if( FAILED( g_pD3D->CreateDevice( D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, m_hWnd,
D3DCREATE_SOFTWARE_VERTEXPROCESSING,
&d3dpp, &g_pd3dDevice) ) ) {
SAFE_RELEASE(g_pD3D);
return -1;
}
Note that for simplicity the above code does not test depth format, instead choosing a fixed format. Your application should determine a compatible depth format for the format of the rendering target.
注意上面代碼處于簡單考慮并沒有去測試深度緩存的格式（？depth format），而只是選擇了一個確定的格式（D3DFMT_D16）。您的程序應(yīng)該為需要渲染的Render Target選擇一個可接受的深度緩存格式。
The device has a frame buffer, which the child views will be rendered into, as well as a depth buffer which will be shared among the views. The frame buffer and depth buffer are sized to the full screen resolution, to allow for the fact that the window may later be resized. Otherwise, window size changes would require resetting the device and re-creating the swap chains.
Device都需要有幀緩存，這樣子視圖才能進(jìn)行渲染，同時，深度緩沖也應(yīng)當(dāng)被不同的視圖進(jìn)行共享。幀緩存和深度緩存都被設(shè)置為全屏幕大小，以考慮到可能窗口會被改變大小的情況。如果不的話，窗口改變大小的時候，就需要Reset Device和重新創(chuàng)建Swap Chain。
Step 2 - Setting Up View Windows
第二步：設(shè)置子視圖窗口
Now we are ready to create our view windows, and associate them with swap chains that can be rendered to the device. Once the windows have been created, the following code generates a swap chain for the child window:
現(xiàn)在我們可以準(zhǔn)備創(chuàng)建我們的子窗口也就是視圖窗口，并把它們與交換鏈關(guān)聯(lián)以使得他們可以被渲染到Device上。當(dāng)窗口創(chuàng)建后，下面的代碼將為子窗口創(chuàng)建一個交換鏈：
D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory( &d3dpp, sizeof(d3dpp) );
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_COPY;
// Use the current display mode. 使用當(dāng)前的顯示模式
D3DDISPLAYMODE mode;
g_pD3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT , &mode);
d3dpp.BackBufferFormat = mode.Format;
// m_hWnd contains child window handle m_hWnd儲存子窗口的句柄
d3dpp.hDeviceWindow=m_hWnd;
// m_pSwapChain is IDirect3DSwapChain * m_pSwapChain是一個IDirect3DSwapChain*對象
g_pd3dDevice->CreateAdditionalSwapChain(&d3dpp, &m_pSwapChain);
After executing this code, the m_pSwapChain variable will contain a pointer to an IDirect3DSwapChain interface, which contains a frame buffer corresponding to the client area of the child window. This process is performed for each view window, so that that there is a swap chain for each view window.
經(jīng)過這些代碼之后，m_pSwapChain變量就儲存了IDirect3DSwapChain接口的指針，這個接口將儲存子窗口視圖區(qū)所對應(yīng)的幀緩沖。
Step 3 - Rendering a View
第三步：渲染視圖
Prior to rendering each view, we must direct the device to render to the appropriate frame buffer, using the SetRenderTarget() method. We pass the back buffer from the window's swap chain, while using the depth buffer that was originally created with the device:
在渲染每個視圖窗口之前，我們必須使得Device來渲染對應(yīng)的幀緩沖，這我們就需要用到SetRenderTarget方法。我們向其中傳入子窗口SwapChain交換鏈的后備緩沖BackBuffer，以及使用最開始跟著Device一起創(chuàng)建的深度緩沖。
LPDIRECT3DSURFACE8 pBack=NULL,pStencil=NULL;
m_pSwapChain->GetBackBuffer(0,D3DBACKBUFFER_TYPE_MONO,&pBack);
g_pd3dDevice->GetDepthStencilSurface(&pStencil);
g_pd3dDevice->SetRenderTarget(pBack,pStencil);
pBack->Release();
pStencil->Release();
Note that we release the stencil and backbuffer pointers after we use them, because the GetBackBuffer() and GetDepthStencilSurface() functions call AddRef() on these interfaces to increment their reference counters. Failing to release them would lead to a memory leak.
注意我們必須Release掉Stencil和BackBuffer的指針，因為GetBackBuffer和GetDepthStencilSurface這兩個函數(shù)都會調(diào)用COM的AddRef方法，來增加相應(yīng)COM接口的引用計數(shù)，因此如果不刪除它們，將會導(dǎo)致內(nèi)存泄露。
We are now ready to render the view. Rendering is performed within a scene in the normal manner, except that we call Present() on the swap chain interface rather than the device interface:
我們現(xiàn)在已經(jīng)做好準(zhǔn)備渲染視圖窗口了。渲染的方法看起來和我們平常用的方法差不多，只是有一點：我們現(xiàn)在需要調(diào)用Swap Chain的接口，而不是Device的接口。
g_pd3dDevice->Clear(0,NULL,D3DCLEAR_TARGET|D3DCLEAR_ZBUFFER,0x00000000,1.0,0);
if (SUCCEEDED(g_pd3dDevice->BeginScene())) {
// rendering code goes here 渲染代碼寫在這里
g_pd3dDevice->EndScene();
}
m_pSwapChain->Present(NULL,NULL,NULL,NULL);
Step 4 - Handling Resize of Child Views
第四步，子窗口的Resize問題
DirectX will automatically deal with changes in the child view by using a stretch blit to present the swap chain if the dimensions have client area is not the same size as the swap chain's frame buffer. However, this may not be desirable, as it will cause aliasing if the client area is increased in size.
如果窗口的視圖區(qū)大小和SwapChain的大小不一，那么DirectX將通過Stretch Blit來自動處理圖像的伸縮變化。盡管這可能并不令人期待，因為這在視圖區(qū)變大的時候?qū)?dǎo)致圖像的模糊。