Shader与固定管线
顶点着色（Vertex Shader）是一段执行在GPU上的程序（一般用HLSL来编写），用来取代fixed pipeline中的transformation和lighting，Vertex Shader主要操作顶点。
有图则一目了然。
Vertex Shader做了什么工作
由上图知，Vertex Shader对输入顶点完成了从local space到homogeneous clip space的变换过程，homogeneous clip space即projection space的下一个space。在这其间共有world transformation, view transformation和projection transformation及lighting几个过程。
优点（与fixed pipeline比较）
由于Vertex Shader是用户自定义程序，所以有很大的灵活性，不必再局限于D3D固定的算法，可以应用许多其他算法，比如可以操作顶点位置模拟衣服效果，操作顶点大小模拟例子系统及顶点混合，变形等，此外，顶点的数据结构也更加灵活。
Shader代码文件
Shader代码可以用纯文本文件来保存，比如记事本文件。我们来看一个最简单的Shader文件，该文件完成的功能是，将顶点由Local Space变换到Homogeneous Space，编辑Shader文件可以用DirectX的Effect Edit，不过新版SDK中没有这个工具了，另外显卡厂商也有自己的编辑器，NVIDIA 有FX Composer，ATI有Render Monkey。
代码
// World, View and Projection Matrix
uniform extern float4x4 gWVP;
// Output Vertex structure
struct OutputVS
{
float4 posH : POSITION0;
};
OutputVS Main(float3 posL : POSITION0)
{
// Zero out our output.
OutputVS outVS = (OutputVS)0;
// Transform to homogeneous clip space.
outVS.posH = mul(float4(posL, 1.0f), gWVP);
// Done--return the output.
return outVS;
}
简单解释一下上述代码
第一行定义了一个全局变量gWVP，这个变量的命名是有规则的，g表示global，即全局变量，W表示World，V表示View，P表示Projection，也就是说这是World，View和Projection矩阵的乘积。但是在程序中我们并没有用到World矩阵，所以实际上就是View矩阵和Projection矩阵的乘积。uniform表示这是个常量，也就是在Shader执行的过程中这个量是不能改变的，extern表示这是一个外部输入量，全局变量默认就是uniform extern的。
接下来的Struct定义了顶点的输出格式，所谓输出就是有VertexShader操作完以后，顶点以何种方式呈现给下一级处理器（一般是Pixel Shader）。这里的输出格式很简单，只包含一个信息，就是顶点的位置。
最后的Main函数就是主要的处理过程，需要注意的是这个函数的名字要和程序中指定的名字保持一致，否则编译会失败。首先定义一个输出结构并清零，然后就是顶点变换，使用mul函数将顶点从Local Space变换到 Homogeneous Space。注意输入顶点是三维的，而齐次坐标是四维的，所以需要转换一下。
如何使用Shader
有了上面的Shader文件，我们就可以在程序中使用它了，下面将以逐步添加代码的方式讲述如何使用Shader文件，为了简化程序，我们将着重讲述有关Shader的代码，其他代码简单带过。
1.定义一个VertexShader指针，该指针可以用来用来保存编译后的Shader
IDirect3DVertexShader9* g_pVertexShader = NULL ; // vertex shader
2. 定义一个常量表指针，常量表用来保存Shader文件中的变量，这些变量是Shader文件与C++ code通讯的媒介，比如我们要设置某些渲染状态，那么首先要通过程序修改这些变量，然后Shader文件读取这些变量就可以得到修改后的值。
ID3DXConstantTable* g_pConstantTable = NULL ; // shader constant table
3. 定义一个函数PrepareVertexShader，该函数用来编译Shader文件并做一些必要的设置，这个函数主要做两件事，一是从编译Shader文件，二是在编译完成后创建相应的Shader，每个步骤后面都有对应的错误处理，如果编译有错误，则输出错误信息，如果创建Shader失败也通知用户。当创建完Shader以后，就释放codeBuffer和errorBuffer。
代码
bool PrepareShader()
{
// Buffer to hold the compiled code
ID3DXBuffer *codeBuffer = NULL;
// Buffer to hold the error message if complile failed
ID3DXBuffer *errorBuffer = NULL;
// Compile shader from file
HRESULT hr = D3DXCompileShaderFromFileA("vertexshader.txt", 0, 0, "Main", "vs_1_1",
D3DXSHADER_ENABLE_BACKWARDS_COMPATIBILITY, &codeBuffer, &errorBuffer, &g_pConstantTable) ;
// output any error messages
if( errorBuffer )
{
MessageBoxA(0, (char*)errorBuffer->GetBufferPointer(), 0, 0);
errorBuffer->Release() ;
return false ;
}
if(FAILED(hr))
{
MessageBox(0, L"D3DXCompileShaderFromFile() - FAILED", 0, 0);
return false;
}
// Create vertex shader
hr = g_pd3dDevice->CreateVertexShader((DWORD*)codeBuffer->GetBufferPointer(), &g_pVertexShader) ;
// handling error
if(FAILED(hr))
{
MessageBox(0, L"CreateVertexShader - FAILED", 0, 0);
return false;
}
// Release code buffer
if (codeBuffer != NULL)
{
codeBuffer->Release() ;
codeBuffer = NULL ;
}
// Release DX buffer
if (errorBuffer != NULL)
{
errorBuffer->Release() ;
errorBuffer = NULL ;
}
// Set handle
ViewProjMatrixHanle = g_pConstantTable->GetConstantByName(0, "gWVP") ;
return true ;
}
4. 设置View Matrix和Projection Matrix。
单独定义一个函数用来设置矩阵，然后对View Matrix和Projection Matrix做乘积，最后通过常量表将乘积矩阵传递给Shader。Shader中通过这个矩阵来变换顶点，这就是本文的核心了。
代码
void SetupMatrix()
{
D3DXVECTOR3 eyePt(0.0f, 0.0f, -10.0f) ;
D3DXVECTOR3 upVec(0.0f, 1.0f, 0.0f) ;
D3DXVECTOR3 lookCenter(0.0f, 0.0f, 0.0f) ;
// Set view matrix
D3DXMATRIX view ;
D3DXMatrixLookAtLH(&view, &eyePt, &lookCenter, &upVec) ;
// Set projection matrix
D3DXMATRIX proj ;
D3DXMatrixPerspectiveFovLH(&proj, D3DX_PI / 4, 1.0f, 1.0f, 1000.0f) ;
D3DXMATRIX viewproj = view * proj ;
g_pConstantTable->SetMatrix(g_pd3dDevice, ViewProjMatrixHanle, &viewproj) ;
// this line is mandatory if you have used Constant table in your code
g_pConstantTable->SetDefaults(g_pd3dDevice);
}
5 渲染，在Render函数中设置VertexShader，然后就可以渲染了。
代码
VOID Render()
{
// Clear the back-buffer to a red color
g_pd3dDevice->Clear( 0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0,0,0), 1.0f, 0 );
// Begin the scene
if( SUCCEEDED( g_pd3dDevice->BeginScene() ) )
{
// Set Vertex Shader
g_pd3dDevice->SetVertexShader(g_pVertexShader) ;
// Render teapot
g_pMesh->DrawSubset(0) ;
// End the scene
g_pd3dDevice->EndScene();
}
// Present the back-buffer contents to the display
g_pd3dDevice->Present( NULL, NULL, NULL, NULL );
}
下面是完整的代码
代码
/*
This is a simple vertex shader program which illustrate how to use vertex shader instead of fixed pipeline
to perform world, view and projection transform
*/
#include <d3dx9.h>
#include <MMSystem.h>
LPDIRECT3D9 g_pD3D = NULL ; // Used to create the D3DDevice
LPDIRECT3DDEVICE9 g_pd3dDevice = NULL ; // Our rendering device
ID3DXMesh* g_pMesh = NULL ; // Hold the sphere
IDirect3DVertexShader9* g_pVertexShader = NULL ; // vertex shader
ID3DXConstantTable* g_pConstantTable = NULL ; // shader constant table
// Handle for world, view and projection matrix
// We use this variable to communicate between the effect file Shader.txt and the C++ code
D3DXHANDLE ViewProjMatrixHanle = 0 ;
void SetupMatrix() ;
bool PrepareShader() ;
HRESULT InitD3D( HWND hWnd )
{
// Create the D3D object, which is needed to create the D3DDevice.
if( NULL == ( g_pD3D = Direct3DCreate9( D3D_SDK_VERSION ) ) )
return E_FAIL;
D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory( &d3dpp, sizeof(d3dpp) );
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.BackBufferFormat = D3DFMT_UNKNOWN;
// Create device
if( FAILED( g_pD3D->CreateDevice( D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd,
D3DCREATE_SOFTWARE_VERTEXPROCESSING,
&d3dpp, &g_pd3dDevice ) ) )
{
return E_FAIL;
}
// Turn off culling, so we see the front and back of the triangle
g_pd3dDevice->SetRenderState( D3DRS_CULLMODE, D3DCULL_NONE );
//g_pd3dDevice->SetRenderState(D3DRS_FILLMODE, D3DFILL_WIREFRAME);
g_pd3dDevice->SetRenderState( D3DRS_LIGHTING , FALSE );
// Create a teapot
D3DXCreateTeapot(g_pd3dDevice, &g_pMesh, NULL) ;
// Prepare Shader
PrepareShader() ;
// Setup matrix
SetupMatrix() ;
return S_OK;
}
VOID Cleanup()
{
if( g_pd3dDevice != NULL)
g_pd3dDevice->Release();
if( g_pD3D != NULL)
g_pD3D->Release();
if(g_pMesh != NULL)
g_pMesh->Release() ;
}
bool PrepareShader()
{
// Buffer to hold the compiled code
ID3DXBuffer *codeBuffer = NULL;
// Buffer to hold the error message if complile failed
ID3DXBuffer *errorBuffer = NULL;
// Compile shader from file
HRESULT hr = D3DXCompileShaderFromFileA("vertexshader.txt", 0, 0, "Main", "vs_1_1",
D3DXSHADER_ENABLE_BACKWARDS_COMPATIBILITY, &codeBuffer, &errorBuffer, &g_pConstantTable) ;
// output any error messages
if( errorBuffer )
{
MessageBoxA(0, (char*)errorBuffer->GetBufferPointer(), 0, 0);
errorBuffer->Release() ;
return false ;
}
if(FAILED(hr))
{
MessageBox(0, L"D3DXCompileShaderFromFile() - FAILED", 0, 0);
return false;
}
// Create vertex shader
hr = g_pd3dDevice->CreateVertexShader((DWORD*)codeBuffer->GetBufferPointer(), &g_pVertexShader) ;
// handling error
if(FAILED(hr))
{
MessageBox(0, L"CreateVertexShader - FAILED", 0, 0);
return false;
}
// Release code buffer
if (codeBuffer != NULL)
{
codeBuffer->Release() ;
codeBuffer = NULL ;
}
// Release DX buffer
if (errorBuffer != NULL)
{
errorBuffer->Release() ;
errorBuffer = NULL ;
}
// Set handle
ViewProjMatrixHanle = g_pConstantTable->GetConstantByName(0, "gWVP") ;
return true ;
}
void SetupMatrix()
{
D3DXVECTOR3 eyePt(0.0f, 0.0f, -10.0f) ;
D3DXVECTOR3 upVec(0.0f, 1.0f, 0.0f) ;
D3DXVECTOR3 lookCenter(0.0f, 0.0f, 0.0f) ;
// Set view matrix
D3DXMATRIX view ;
D3DXMatrixLookAtLH(&view, &eyePt, &lookCenter, &upVec) ;
// Set projection matrix
D3DXMATRIX proj ;
D3DXMatrixPerspectiveFovLH(&proj, D3DX_PI / 4, 1.0f, 1.0f, 1000.0f) ;
D3DXMATRIX viewproj = view * proj ;
g_pConstantTable->SetMatrix(g_pd3dDevice, ViewProjMatrixHanle, &viewproj) ;
// this line is mandatory if you have used Constant table in your code
g_pConstantTable->SetDefaults(g_pd3dDevice);
}
VOID Render()
{
// Clear the back-buffer to a red color
g_pd3dDevice->Clear( 0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0,0,0), 1.0f, 0 );
// Begin the scene
if( SUCCEEDED( g_pd3dDevice->BeginScene() ) )
{
// Set Vertex Shader
g_pd3dDevice->SetVertexShader(g_pVertexShader) ;
// Render teapot
g_pMesh->DrawSubset(0) ;
// End the scene
g_pd3dDevice->EndScene();
}
// Present the back-buffer contents to the display
g_pd3dDevice->Present( NULL, NULL, NULL, NULL );
}
LRESULT WINAPI MsgProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
switch( msg )
{
case WM_KEYDOWN:
{
switch( wParam )
{
case VK_ESCAPE:
SendMessage( hWnd, WM_CLOSE, 0, 0 );
break ;
default:
break ;
}
}
break ;
case WM_DESTROY:
Cleanup();
PostQuitMessage( 0 );
return 0;
}
return DefWindowProc( hWnd, msg, wParam, lParam );
}
INT WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPWSTR szCmdLine, int iCmdShow)
{
WNDCLASSEX winClass ;
winClass.lpszClassName = L"Teapot";
winClass.cbSize = sizeof(WNDCLASSEX);
winClass.style = CS_HREDRAW | CS_VREDRAW;
winClass.lpfnWndProc = MsgProc;
winClass.hInstance = hInstance;
winClass.hIcon = NULL ;
winClass.hIconSm = NULL ;
winClass.hCursor = NULL ;
winClass.hbrBackground = NULL ;
winClass.lpszMenuName = NULL ;
winClass.cbClsExtra = 0;
winClass.cbWndExtra = 0;
RegisterClassEx (&winClass) ;
HWND hWnd = CreateWindowEx(NULL,
winClass.lpszClassName, // window class name
L"Teapot", // window caption
WS_OVERLAPPEDWINDOW, // window style
32, // initial x position
32, // initial y position
600, // initial window width
600, // initial window height
NULL, // parent window handle
NULL, // window menu handle
hInstance, // program instance handle
NULL) ; // creation parameters
// Create window failed
if(hWnd == NULL)
{
MessageBoxA(hWnd, "Create Window failed!", "Error", 0) ;
return -1 ;
}
// Initialize Direct3D
if( SUCCEEDED(InitD3D(hWnd)))
{
// Show the window
ShowWindow( hWnd, SW_SHOWDEFAULT );
UpdateWindow( hWnd );
// Enter the message loop
MSG msg ;
ZeroMemory( &msg, sizeof(msg) );
PeekMessage( &msg, NULL, 0U, 0U, PM_NOREMOVE );
// Get last time
static DWORD lastTime = timeGetTime();
while (msg.message != WM_QUIT)
{
if( PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE) != 0)
{
TranslateMessage (&msg) ;
DispatchMessage (&msg) ;
}
else // Render the game if there is no message to process
{
// Get current time
DWORD currTime = timeGetTime();
// Calculate time elapsed
float timeDelta = (currTime - lastTime)*0.001f;
// Render
Render() ;
// Update last time to current time for next loop
lastTime = currTime;
}
}
}
UnregisterClass(winClass.lpszClassName, hInstance) ;
return 0;
}
如何查看显卡所支持的Vertex Shader版本
1 使用DirectX Caps Viewer查看
2 使用下面的代码查看
代码
1 // Check shader version
2 bool CheckShaderVersion(LPDIRECT3DDEVICE9 g_pd3dDevice)
3 {
4 // Get device capabilities
5 D3DCAPS9 caps ;
6 g_pd3dDevice->GetDeviceCaps(&caps);
7
8 // Make sure vertex shader version greater than 2.0
9 if (caps.VertexShaderVersion < D3DVS_VERSION(2, 0))
10 {
11 return false ;
12 }
13
14 // Make sure pixel shader version greater than 2.0
15 if (caps.PixelShaderVersion < D3DPS_VERSION(2, 0))
16 {
17 return false ;
18 }
19
20 return true ;
21 };