Directx 11中垂直同步的设置

1、什么是垂直同步？

     垂直同步又称场同步（Vertical Hold），从CRT显示器的显示原理来看，单个象素组成了水平扫描线，水平扫描线在垂直方向的堆积形成了完整的画面。显示器的刷新率受显卡DAC控制，显卡DAC完成一帧的扫描后就会产生一个垂直同步信号。

当我们选择\"等待垂直同步信号"（即打开垂直同步）时，显卡绘制3D图形前会等待垂直同步信号，性能强劲的显卡则会提前完成渲染，并在下个垂直信号之前进行等待。由此可见，当打开垂直同步时，游戏的FPS要受刷新率的制约，对于高端显卡而言，限制了其性能的发挥。

    当我们选择\"不等待垂直同步信号"（即关闭垂直同步）时，3D引擎将全速运行，不再等待垂直同步信号的到来，显卡性能得到了最大的发挥。所以我们测试显卡3D性能时，一定要关闭垂直同步。不少的朋友认为在游戏中关闭垂直同步可以得到更高的帧速，其实不然，这虚高的帧速不仅要受到显示器刷新率的制约，更会对游戏画面产生不良的影响。一般来说，关闭垂直同步会导致游戏画面产生以下两种问题：

（1）画面撕裂
在打cs的时候会碰到这种情况，图像断裂
（2）跳帧
假如显示器设定的刷新率是80Hz，显卡以100FPS循环显示0-9数字，那么，在开始的0.1秒内，显卡显示了10个数字而显示器只刷新了8次。可见，由于显示器刷新率跟不上游戏的FPS，只能舍弃一部分画面，这种现象表现在游戏里就是跳帧。鬼武者3等一些移植到PC上的游戏在关闭垂直同步时通常会出现这种问题。

2、directx 11中设置垂直同步的代码：

bool D3DClass::Initialize(int screenWidth, int screenHeight, bool vsync, HWND hwnd, bool fullscreen, 
                          float screenDepth, float screenNear)
{
    HRESULT result;
    IDXGIFactory* factory;
    IDXGIAdapter* adapter;
    IDXGIOutput* adapterOutput;
    unsigned int numModes, i, numerator, denominator, stringLength;
    DXGI_MODE_DESC* displayModeList;
    DXGI_ADAPTER_DESC adapterDesc;
    int error;
    DXGI_SWAP_CHAIN_DESC swapChainDesc;
    D3D_FEATURE_LEVEL featureLevel;
    ID3D11Texture2D* backBufferPtr;
    D3D11_TEXTURE2D_DESC depthBufferDesc;
    D3D11_DEPTH_STENCIL_DESC depthStencilDesc;
    D3D11_DEPTH_STENCIL_VIEW_DESC depthStencilViewDesc;
    D3D11_RASTERIZER_DESC rasterDesc;
    D3D11_VIEWPORT viewport;
    float fieldOfView, screenAspect;


    // Store the vsync setting.
    m_vsync_enabled = vsync;

    // Create a DirectX graphics interface factory.
    result = CreateDXGIFactory(__uuidof(IDXGIFactory), (void**)&factory);
    if(FAILED(result))
    {
        return false;
    }

    // Use the factory to create an adapter for the primary graphics interface (video card).
    result = factory->EnumAdapters(0, &adapter);
    if(FAILED(result))
    {
        return false;
    }

    // Enumerate the primary adapter output (monitor).
    result = adapter->EnumOutputs(0, &adapterOutput);
    if(FAILED(result))
    {
        return false;
    }

    // Get the number of modes that fit the DXGI_FORMAT_R8G8B8A8_UNORM display format for the adapter output (monitor).
    result = adapterOutput->GetDisplayModeList(DXGI_FORMAT_R8G8B8A8_UNORM, DXGI_ENUM_MODES_INTERLACED, &numModes, NULL);
    if(FAILED(result))
    {
        return false;
    }

    // Create a list to hold all the possible display modes for this monitor/video card combination.
    displayModeList = new DXGI_MODE_DESC[numModes];
    if(!displayModeList)
    {
        return false;
    }

    // Now fill the display mode list structures.
    result = adapterOutput->GetDisplayModeList(DXGI_FORMAT_R8G8B8A8_UNORM, DXGI_ENUM_MODES_INTERLACED, &numModes, displayModeList);
    if(FAILED(result))
    {
        return false;
    }

    // Now go through all the display modes and find the one that matches the screen width and height.
    // When a match is found store the numerator and denominator of the refresh rate for that monitor.
    for(i=0; i<numModes; i++)
    {
        if(displayModeList[i].Width == (unsigned int)screenWidth)
        {
            if(displayModeList[i].Height == (unsigned int)screenHeight)
            {
                numerator = displayModeList[i].RefreshRate.Numerator;
                denominator = displayModeList[i].RefreshRate.Denominator;
            }
        }
    }

    // Get the adapter (video card) description.
    result = adapter->GetDesc(&adapterDesc);
    if(FAILED(result))
    {
        return false;
    }

    // Store the dedicated video card memory in megabytes.
    m_videoCardMemory = (int)(adapterDesc.DedicatedVideoMemory / 1024 / 1024);

    // Convert the name of the video card to a character array and store it.
    error = wcstombs_s(&stringLength, m_videoCardDescription, 128, adapterDesc.Description, 128);
    if(error != 0)
    {
        return false;
    }

    // Release the display mode list.
    delete [] displayModeList;
    displayModeList = 0;

    // Release the adapter output.
    adapterOutput->Release();
    adapterOutput = 0;

    // Release the adapter.
    adapter->Release();
    adapter = 0;

    // Release the factory.
    factory->Release();
    factory = 0;

    // Initialize the swap chain description.
    ZeroMemory(&swapChainDesc, sizeof(swapChainDesc));

    // Set to a single back buffer.
    swapChainDesc.BufferCount = 1;

    // Set the width and height of the back buffer.
    swapChainDesc.BufferDesc.Width = screenWidth;
    swapChainDesc.BufferDesc.Height = screenHeight;

    // Set regular 32-bit surface for the back buffer.
    swapChainDesc.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;

    // Set the refresh rate of the back buffer.
    if(m_vsync_enabled)
    {
        swapChainDesc.BufferDesc.RefreshRate.Numerator = numerator;
        swapChainDesc.BufferDesc.RefreshRate.Denominator = denominator;
    }
    else
    {
        swapChainDesc.BufferDesc.RefreshRate.Numerator = 0;
        swapChainDesc.BufferDesc.RefreshRate.Denominator = 1;
    }

    // Set the usage of the back buffer.
    swapChainDesc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;

    // Set the handle for the window to render to.
    swapChainDesc.OutputWindow = hwnd;

    // Turn multisampling off.
    swapChainDesc.SampleDesc.Count = 1;
    swapChainDesc.SampleDesc.Quality = 0;

    // Set to full screen or windowed mode.
    if(fullscreen)
    {
        swapChainDesc.Windowed = false;
    }
    else
    {
        swapChainDesc.Windowed = true;
    }

    // Set the scan line ordering and scaling to unspecified.
    swapChainDesc.BufferDesc.ScanlineOrdering = DXGI_MODE_SCANLINE_ORDER_UNSPECIFIED;
    swapChainDesc.BufferDesc.Scaling = DXGI_MODE_SCALING_UNSPECIFIED;

    // Discard the back buffer contents after presenting.
    swapChainDesc.SwapEffect = DXGI_SWAP_EFFECT_DISCARD;

    // Don't set the advanced flags.
    swapChainDesc.Flags = 0;

    // Set the feature level to DirectX 11.
    featureLevel = D3D_FEATURE_LEVEL_11_0;

    // Create the swap chain, Direct3D device, and Direct3D device context.
    result = D3D11CreateDeviceAndSwapChain(NULL, D3D_DRIVER_TYPE_HARDWARE, NULL, 0, &featureLevel, 1, 
                                           D3D11_SDK_VERSION, &swapChainDesc, &m_swapChain, &m_device, NULL, &m_deviceContext);
    if(FAILED(result))
    {
        return false;
    }

    // Get the pointer to the back buffer.
    result = m_swapChain->GetBuffer(0, __uuidof(ID3D11Texture2D), (LPVOID*)&backBufferPtr);
    if(FAILED(result))
    {
        return false;
    }

    // Create the render target view with the back buffer pointer.
    result = m_device->CreateRenderTargetView(backBufferPtr, NULL, &m_renderTargetView);
    if(FAILED(result))
    {
        return false;
    }

    // Release pointer to the back buffer as we no longer need it.
    backBufferPtr->Release();
    backBufferPtr = 0;

    // Initialize the description of the depth buffer.
    ZeroMemory(&depthBufferDesc, sizeof(depthBufferDesc));

    // Set up the description of the depth buffer.
    depthBufferDesc.Width = screenWidth;
    depthBufferDesc.Height = screenHeight;
    depthBufferDesc.MipLevels = 1;
    depthBufferDesc.ArraySize = 1;
    depthBufferDesc.Format = DXGI_FORMAT_D24_UNORM_S8_UINT;
    depthBufferDesc.SampleDesc.Count = 1;
    depthBufferDesc.SampleDesc.Quality = 0;
    depthBufferDesc.Usage = D3D11_USAGE_DEFAULT;
    depthBufferDesc.BindFlags = D3D11_BIND_DEPTH_STENCIL;
    depthBufferDesc.CPUAccessFlags = 0;
    depthBufferDesc.MiscFlags = 0;

    // Create the texture for the depth buffer using the filled out description.
    result = m_device->CreateTexture2D(&depthBufferDesc, NULL, &m_depthStencilBuffer);
    if(FAILED(result))
    {
        return false;
    }

    // Initialize the description of the stencil state.
    ZeroMemory(&depthStencilDesc, sizeof(depthStencilDesc));

    // Set up the description of the stencil state.
    depthStencilDesc.DepthEnable = true;
    depthStencilDesc.DepthWriteMask = D3D11_DEPTH_WRITE_MASK_ALL;
    depthStencilDesc.DepthFunc = D3D11_COMPARISON_LESS;

    depthStencilDesc.StencilEnable = true;
    depthStencilDesc.StencilReadMask = 0xFF;
    depthStencilDesc.StencilWriteMask = 0xFF;

    // Stencil operations if pixel is front-facing.
    depthStencilDesc.FrontFace.StencilFailOp = D3D11_STENCIL_OP_KEEP;
    depthStencilDesc.FrontFace.StencilDepthFailOp = D3D11_STENCIL_OP_INCR;
    depthStencilDesc.FrontFace.StencilPassOp = D3D11_STENCIL_OP_KEEP;
    depthStencilDesc.FrontFace.StencilFunc = D3D11_COMPARISON_ALWAYS;

    // Stencil operations if pixel is back-facing.
    depthStencilDesc.BackFace.StencilFailOp = D3D11_STENCIL_OP_KEEP;
    depthStencilDesc.BackFace.StencilDepthFailOp = D3D11_STENCIL_OP_DECR;
    depthStencilDesc.BackFace.StencilPassOp = D3D11_STENCIL_OP_KEEP;
    depthStencilDesc.BackFace.StencilFunc = D3D11_COMPARISON_ALWAYS;

    // Create the depth stencil state.
    result = m_device->CreateDepthStencilState(&depthStencilDesc, &m_depthStencilState);
    if(FAILED(result))
    {
        return false;
    }

    // Set the depth stencil state.
    m_deviceContext->OMSetDepthStencilState(m_depthStencilState, 1);

    // Initialize the depth stencil view.
    ZeroMemory(&depthStencilViewDesc, sizeof(depthStencilViewDesc));

    // Set up the depth stencil view description.
    depthStencilViewDesc.Format = DXGI_FORMAT_D24_UNORM_S8_UINT;
    depthStencilViewDesc.ViewDimension = D3D11_DSV_DIMENSION_TEXTURE2D;
    depthStencilViewDesc.Texture2D.MipSlice = 0;

    // Create the depth stencil view.
    result = m_device->CreateDepthStencilView(m_depthStencilBuffer, &depthStencilViewDesc, &m_depthStencilView);
    if(FAILED(result))
    {
        return false;
    }

    // Bind the render target view and depth stencil buffer to the output render pipeline.
    m_deviceContext->OMSetRenderTargets(1, &m_renderTargetView, m_depthStencilView);

    // Setup the raster description which will determine how and what polygons will be drawn.
    rasterDesc.AntialiasedLineEnable = false;
    rasterDesc.CullMode = D3D11_CULL_BACK;
    rasterDesc.DepthBias = 0;
    rasterDesc.DepthBiasClamp = 0.0f;
    rasterDesc.DepthClipEnable = true;
    rasterDesc.FillMode = D3D11_FILL_SOLID;
    rasterDesc.FrontCounterClockwise = false;
    rasterDesc.MultisampleEnable = false;
    rasterDesc.ScissorEnable = false;
    rasterDesc.SlopeScaledDepthBias = 0.0f;

    // Create the rasterizer state from the description we just filled out.
    result = m_device->CreateRasterizerState(&rasterDesc, &m_rasterState);
    if(FAILED(result))
    {
        return false;
    }

    // Now set the rasterizer state.
    m_deviceContext->RSSetState(m_rasterState);
    
    // Setup the viewport for rendering.
    viewport.Width = (float)screenWidth;
    viewport.Height = (float)screenHeight;
    viewport.MinDepth = 0.0f;
    viewport.MaxDepth = 1.0f;
    viewport.TopLeftX = 0.0f;
    viewport.TopLeftY = 0.0f;

    // Create the viewport.
    m_deviceContext->RSSetViewports(1, &viewport);

    // Setup the projection matrix.
    fieldOfView = (float)D3DX_PI / 4.0f;
    screenAspect = (float)screenWidth / (float)screenHeight;

    // Create the projection matrix for 3D rendering.
    D3DXMatrixPerspectiveFovLH(&m_projectionMatrix, fieldOfView, screenAspect, screenNear, screenDepth);

    // Initialize the world matrix to the identity matrix.
    D3DXMatrixIdentity(&m_worldMatrix);

    // Create an orthographic projection matrix for 2D rendering.
    D3DXMatrixOrthoLH(&m_orthoMatrix, (float)screenWidth, (float)screenHeight, screenNear, screenDepth);

    return true;
}