原文：http://msdn.microsoft.com/en-us/library/bb219690%28v=vs.85%29.aspx

是关于在direct3d9中，对于屏幕空间中，将贴图映射到像素的问题

以下是pixel shader源代码（aaa.ps.txt）

texture MyTexture;

sampler2D MySampler = 
sampler_state 
{ 
	Texture = <MyTexture>;
	MinFilter = LINEAR;
	MagFilter = LINEAR;
	AddressU = Clamp;
	AddressV = Clamp;
};

float4 TextureLookupPS(float2 vTexCoord : TEXCOORD0) : COLOR
{
	return tex2D(MySampler, vTexCoord);
} 

以下是主程序代码（main.cpp）

#include <d3d9.h>
#include <d3dx9.h>

#pragma comment(lib, "d3d9.lib")
#pragma comment(lib, "d3dx9.lib")

LPDIRECT3D9 g_pD3D = NULL;
LPDIRECT3DDEVICE9 g_pd3dDevice = NULL;
LPDIRECT3DTEXTURE9 g_pTexture = NULL;
LPDIRECT3DPIXELSHADER9 g_pPS = NULL;
LPD3DXCONSTANTTABLE g_pPSConstantTable;

#define SAFE_RELEASE(p) if(p) {p->Release();}

struct CUSTOMVERTEX
{
	FLOAT x, y, z, rhw;
	FLOAT tu, tv;
};

#define D3DFVF_CUSTOMVERTEX (D3DFVF_XYZRHW|D3DFVF_TEX1)

HRESULT Init(HWND hWnd)
{
	if(NULL == (g_pD3D = Direct3DCreate9(D3D_SDK_VERSION)))
		return E_FAIL;

	D3DPRESENT_PARAMETERS d3dpp = {0};
	d3dpp.Windowed = TRUE;
	d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
	d3dpp.BackBufferFormat = D3DFMT_UNKNOWN;

	if(FAILED(g_pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &g_pd3dDevice)))
		return E_FAIL;

	if(FAILED(D3DXCreateTextureFromFile(g_pd3dDevice, L"aaa.bmp", &g_pTexture)))
		return E_FAIL;

	LPD3DXBUFFER pShader;
	LPD3DXBUFFER pErrorMsgs;
	if(FAILED(D3DXCompileShaderFromFile(L"aaa.ps.txt", NULL, NULL, "TextureLookupPS", "ps_2_0", 0, &pShader, &pErrorMsgs, &g_pPSConstantTable)))
	{
		MessageBoxA(NULL, (LPSTR)pErrorMsgs->GetBufferPointer(), "Error", MB_OK);
		SAFE_RELEASE(pErrorMsgs);
		return E_FAIL;
	}

	if(FAILED(g_pd3dDevice->CreatePixelShader((DWORD *)pShader->GetBufferPointer(), &g_pPS)))
		return E_FAIL;

	SAFE_RELEASE(pShader);
	SAFE_RELEASE(pErrorMsgs);
	return S_OK;
}

VOID Render(void)
{
	HRESULT hres;
	hres = g_pd3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB( 0, 0, 255 ), 1.0f, 0);

	if(SUCCEEDED(hres = g_pd3dDevice->BeginScene()))
	{
		CUSTOMVERTEX vertices[] =
		{
			{0.0f, 0.0f, 0.5f, 1.0f, 0.0f, 0.0f},
			{4.0f, 0.0f, 0.5f, 1.0f, 1.0f, 0.0f},
			{4.0f, 4.0f, 0.5f, 1.0f, 1.0f, 1.0f},
			{0.0f, 0.0f, 0.5f, 1.0f, 0.0f, 0.0f},
			{4.0f, 4.0f, 0.5f, 1.0f, 1.0f, 1.0f},
			{0.0f, 4.0f, 0.5f, 1.0f, 0.0f, 1.0f},
		};

		//for(int i = 0; i < sizeof(vertices) / sizeof(CUSTOMVERTEX); i++)
		//{
		//	vertices[i].x -= 0.5f;
		//	vertices[i].y -= 0.5f;
		//}

		hres = g_pd3dDevice->SetPixelShader(g_pPS);
		UINT TextureSamplerIndex = g_pPSConstantTable->GetSamplerIndex("MySampler");
		hres = g_pd3dDevice->SetTexture(TextureSamplerIndex, g_pTexture);
		hres = g_pd3dDevice->SetSamplerState(TextureSamplerIndex, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
		hres = g_pd3dDevice->SetSamplerState(TextureSamplerIndex, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
        hres = g_pd3dDevice->SetFVF(D3DFVF_CUSTOMVERTEX);
        hres = g_pd3dDevice->DrawPrimitiveUP(D3DPT_TRIANGLELIST, 2, vertices, sizeof(CUSTOMVERTEX));
		hres = g_pd3dDevice->EndScene();
	}

	hres = g_pd3dDevice->Present(NULL, NULL, NULL, NULL);
}

VOID Cleanup(void)
{
	SAFE_RELEASE(g_pPSConstantTable);
	SAFE_RELEASE(g_pPS);
	SAFE_RELEASE(g_pTexture);
	SAFE_RELEASE(g_pd3dDevice);
	SAFE_RELEASE(g_pD3D);
}

LRESULT WINAPI MsgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	switch( msg )
	{
	case WM_DESTROY:
		Cleanup();
		PostQuitMessage( 0 );
		return 0;
	}

	return DefWindowProc(hWnd, msg, wParam, lParam);
}

INT WINAPI wWinMain(HINSTANCE hInst, HINSTANCE, LPWSTR, INT)
{
	WNDCLASSEX wc = {sizeof( WNDCLASSEX ), CS_CLASSDC, MsgProc, 0L, 0L, GetModuleHandle( NULL ), NULL, NULL, NULL, NULL, L"MappingTexels", NULL};
	RegisterClassEx(&wc);

	HWND hWnd = CreateWindow(L"MappingTexels", L"MappingTexels", WS_OVERLAPPEDWINDOW, 100, 100, 300, 300, NULL, NULL, wc.hInstance, NULL);
	if(SUCCEEDED(Init(hWnd)))
	{
		ShowWindow(hWnd, SW_SHOWDEFAULT);
		UpdateWindow(hWnd);

		MSG msg = {0};
		while(msg.message != WM_QUIT)
		{
			if(PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE))
			{
				TranslateMessage(&msg);
				DispatchMessage(&msg);
			}
			else
				Render();
		}
	}

	UnregisterClass(L"MappingTexels", wc.hInstance);
	return 0;
}