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 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; }