两天学会DirectX 3D之第二天

提要

前几天很简单地跑了一个DirectX 9 程序，以为DirectX就那么绘制，事实证明有点Naive了。

之前的那个程序最多也就是个固定流水线的东西。但是今天要用DirectX11来写一个小的框架。

龙书就不要看了，看Introduction to 3D GAME PROGRAMMING WITH DIRECTX®11

几个重要的类

ID3D11Device : 一个虚拟适配器；它被用于运行渲染和创建资源。

ID3D11DeviceContext:  represents a device context which generates rendering commands.

ID3D11RenderTargetView:  identifies the render-target subresources that can be accessed during rendering.

ID3D11InputLayout: An input-layout interface holds a definition of how to feed vertex data that is laid out in memory into the input-assembler stage of the graphics pipeline.

渲染流水线（翻译自微软文档）

DirectX编程流水线是为了实时游戏应用设计的，上图显示了由输入到输出的各个阶段的数据流向。相对于DirectX10 的图形流水线，DirectX11添加了一些额外的Stage来支持一些新的特性。

你可以使用DirectX 11API来配置所有的Stage，通过HLSL语言来设置就可以了，这样整个流水线就拥有非常大的可扩展性和适应性了。下面列出每个阶段所做的事情.

Input-Assembler Stage : 提供渲染时的数据（三角形，线，点）；

Vertex-Shader Stage：处理顶点，通常的操作有：Transformmation，蒙皮，光照计算。通常一个VertexShader输入是一组顶点，输出也是一组顶点。

Geometry-Shader Statge：这个阶段会处理所有的图元，输入是完整的图元（三角形就是三个顶点，线段就是两个顶点，还有就是单个的点）。另外，每个图元可以包含邻接图元的信息。另外这个阶段还可以对图元进行一定的简化和精细化。给定一个图元，geometry shader可以丢弃这个图元，或者可以生成新的一个或者多个的图元。

Stream-Output Stage: 从上一个阶段流下来的数据，可以将图元信息从流水线放入到存储中，或者放到Rasterizer阶段。被放到内存中的数据可以再次放到流水线中，或者被CPU读取。

Rasterizer Stage：裁剪图元，为pixel shader准备图元，并准备怎样调用pixel shader.

Pixel-Shader Stage: 收到经过插值的结果，生成最终的图像。

Output-Merger Stage ：合并各种类型的输出信息(pixel shader 值，深度信息，Stencil值)，并和当前render target的深度/Stencil 缓存，得到最后的流水线结果。

Tessellation stage：这个阶段由Hull-shader, tessellator还有domain-shader组成，它主要是将高阶表面转换成一系列的三角行，然后放到流水线中。

Direct3D 11 可编程流水线也可以用高速的计算任务，一个compute shader可以将Direct3D11扩展用于通用GPU计算。

用Shader绘制一个三角形

Direct3D，我们需要完成以下几个步骤：

1.定义我们需要检查的设备类型（device types）和特征级别（feature levels）

2.创建Direct3D设备，渲染设备（context）和交换链（swap chain）。

3.创建渲染目标（render target）。

4.设置视口（viewport）

5.开始渲染

6.渲染模型

7.清屏幕

代码清单

// include the basic windows header files and the Direct3D header files
#include 
#include 
#include 
#include 
#include 
#include "assimpmodel.h"

// include the Direct3D Library file
#pragma comment (lib, "d3d11.lib")
#pragma comment (lib, "d3dx11.lib")
#pragma comment (lib, "d3dx10.lib")

// define the screen resolution
#define SCREEN_WIDTH  800
#define SCREEN_HEIGHT 600

// global declarations
IDXGISwapChain *swapchain;             // the pointer to the swap chain interface
ID3D11Device *dev;                     // the pointer to our Direct3D device interface
ID3D11DeviceContext *devcon;           // the pointer to our Direct3D device context
ID3D11RenderTargetView *backbuffer;    // the pointer to our back buffer
ID3D11InputLayout *pLayout;            // the pointer to the input layout
ID3D11VertexShader *pVS;               // the pointer to the vertex shader
ID3D11PixelShader *pPS;                // the pointer to the pixel shader
ID3D11Buffer *pVBuffer;                // the pointer to the vertex buffer

// a struct to define a single vertex
struct VERTEX{ D3DXVECTOR3 position; D3DXCOLOR Color; };

// function prototypes
void InitD3D(HWND hWnd);    // sets up and initializes Direct3D
void RenderFrame(void);     // renders a single frame
void CleanD3D(void);        // closes Direct3D and releases memory
void InitGraphics(void);    // creates the shape to render
void InitPipeline(void);    // loads and prepares the shaders

// the WindowProc function prototype
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);


// the entry point for any Windows program
int WINAPI WinMain(HINSTANCE hInstance,
	HINSTANCE hPrevInstance,
	LPSTR lpCmdLine,
	int nCmdShow)
{
	HWND hWnd;
	WNDCLASSEX wc;

	ZeroMemory(&wc, sizeof(WNDCLASSEX));

	wc.cbSize = sizeof(WNDCLASSEX);
	wc.style = CS_HREDRAW | CS_VREDRAW;
	wc.lpfnWndProc = WindowProc;
	wc.hInstance = hInstance;
	wc.hCursor = LoadCursor(NULL, IDC_ARROW);
	wc.lpszClassName = "WindowClass";

	RegisterClassEx(&wc);

	RECT wr = { 0, 0, SCREEN_WIDTH, SCREEN_HEIGHT };
	AdjustWindowRect(&wr, WS_OVERLAPPEDWINDOW, FALSE);

	hWnd = CreateWindowEx(NULL,
		"WindowClass",
		"Triangle",
		WS_OVERLAPPEDWINDOW,
		300,
		300,
		wr.right - wr.left,
		wr.bottom - wr.top,
		NULL,
		NULL,
		hInstance,
		NULL);

	ShowWindow(hWnd, nCmdShow);

	// set up and initialize Direct3D
	InitD3D(hWnd);

	// enter the main loop:

	MSG msg;

	while (TRUE)
	{
		if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
		{
			TranslateMessage(&msg);
			DispatchMessage(&msg);

			if (msg.message == WM_QUIT)
				break;
		}

		RenderFrame();
	}

	// clean up DirectX and COM
	CleanD3D();

	return msg.wParam;
}


// this is the main message handler for the program
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	switch (message)
	{
	case WM_DESTROY:
	{
					   PostQuitMessage(0);
					   return 0;
	} break;
	}

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


// this function initializes and prepares Direct3D for use
void InitD3D(HWND hWnd)
{
	// create a struct to hold information about the swap chain
	DXGI_SWAP_CHAIN_DESC scd;

	// clear out the struct for use
	ZeroMemory(&scd, sizeof(DXGI_SWAP_CHAIN_DESC));

	// fill the swap chain description struct
	scd.BufferCount = 1;                                   // one back buffer
	scd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;    // use 32-bit color
	scd.BufferDesc.Width = SCREEN_WIDTH;                   // set the back buffer width
	scd.BufferDesc.Height = SCREEN_HEIGHT;                 // set the back buffer height
	scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;     // how swap chain is to be used
	scd.OutputWindow = hWnd;                               // the window to be used
	scd.SampleDesc.Count = 4;                              // how many multisamples
	scd.Windowed = TRUE;                                   // windowed/full-screen mode
	scd.Flags = DXGI_SWAP_CHAIN_FLAG_ALLOW_MODE_SWITCH;    // allow full-screen switching

	// create a device, device context and swap chain using the information in the scd struct
	D3D11CreateDeviceAndSwapChain(NULL,
		D3D_DRIVER_TYPE_HARDWARE,
		NULL,
		NULL,
		NULL,
		NULL,
		D3D11_SDK_VERSION,
		&scd,
		&swapchain,
		&dev,
		NULL,
		&devcon);


	// get the address of the back buffer
	ID3D11Texture2D *pBackBuffer;
	swapchain->GetBuffer(0, __uuidof(ID3D11Texture2D), (LPVOID*)&pBackBuffer);

	// use the back buffer address to create the render target
	dev->CreateRenderTargetView(pBackBuffer, NULL, &backbuffer);
	pBackBuffer->Release();

	// set the render target as the back buffer
	devcon->OMSetRenderTargets(1, &backbuffer, NULL);


	// Set the viewport
	D3D11_VIEWPORT viewport;
	ZeroMemory(&viewport, sizeof(D3D11_VIEWPORT));

	viewport.TopLeftX = 0;
	viewport.TopLeftY = 0;
	viewport.Width = SCREEN_WIDTH;
	viewport.Height = SCREEN_HEIGHT;

	devcon->RSSetViewports(1, &viewport);

	InitPipeline();
	InitGraphics();
}


// this is the function used to render a single frame
void RenderFrame(void)
{
	// clear the back buffer to a deep blue
	devcon->ClearRenderTargetView(backbuffer, D3DXCOLOR(0.0f, 0.2f, 0.4f, 1.0f));

	// select which vertex buffer to display
	UINT stride = sizeof(VERTEX);
	UINT offset = 0;
	devcon->IASetVertexBuffers(0, 1, &pVBuffer, &stride, &offset);

	// select which primtive type we are using
	devcon->IASetPrimitiveTopology(D3D10_PRIMITIVE_TOPOLOGY_TRIANGLELIST);

	// draw the vertex buffer to the back buffer
	devcon->Draw(3, 0);

	// switch the back buffer and the front buffer
	swapchain->Present(0, 0);
}


// this is the function that cleans up Direct3D and COM
void CleanD3D(void)
{
	swapchain->SetFullscreenState(FALSE, NULL);    // switch to windowed mode

	// close and release all existing COM objects
	pLayout->Release();
	pVS->Release();
	pPS->Release();
	pVBuffer->Release();
	swapchain->Release();
	backbuffer->Release();
	dev->Release();
	devcon->Release();
}


// this is the function that creates the shape to render
void InitGraphics()
{
	//Assimpmodel *model = new Assimpmodel();
	//model->Initialize(dev);
	// create a triangle using the VERTEX struct
	VERTEX OurVertices[] =
	{
		{ D3DXVECTOR3(0.0f, 0.5f, 0.0f), D3DXCOLOR(1.0f, 0.0f, 0.0f, 1.0f) },
		{ D3DXVECTOR3(0.45f, -0.5, 0.0f), D3DXCOLOR(0.0f, 1.0f, 0.0f, 1.0f) },
		{ D3DXVECTOR3(-0.45f, -0.5f, 0.0f), D3DXCOLOR(0.0f, 0.0f, 1.0f, 1.0f) }
	};


	// create the vertex buffer
	D3D11_BUFFER_DESC bd;
	ZeroMemory(&bd, sizeof(bd));

	bd.Usage = D3D11_USAGE_DYNAMIC;                // write access access by CPU and GPU
	bd.ByteWidth = sizeof(VERTEX)* 3;             // size is the VERTEX struct * 3
	bd.BindFlags = D3D11_BIND_VERTEX_BUFFER;       // use as a vertex buffer
	bd.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;    // allow CPU to write in buffer

	dev->CreateBuffer(&bd, NULL, &pVBuffer);       // create the buffer


	// copy the vertices into the buffer
	D3D11_MAPPED_SUBRESOURCE ms;
	devcon->Map(pVBuffer, NULL, D3D11_MAP_WRITE_DISCARD, NULL, &ms);    // map the buffer
	memcpy(ms.pData, OurVertices, sizeof(OurVertices));                 // copy the data
	devcon->Unmap(pVBuffer, NULL);                                      // unmap the buffer
}


// this function loads and prepares the shaders
void InitPipeline()
{
	// load and compile the two shaders
	ID3D10Blob *VS, *PS;
	D3DX11CompileFromFile("shaders.shader", 0, 0, "VShader", "vs_5_0", 0, 0, 0, &VS, 0, 0);
	D3DX11CompileFromFile("shaders.shader", 0, 0, "PShader", "ps_5_0", 0, 0, 0, &PS, 0, 0);

	// encapsulate both shaders into shader objects
	dev->CreateVertexShader(VS->GetBufferPointer(), VS->GetBufferSize(), NULL, &pVS);
	dev->CreatePixelShader(PS->GetBufferPointer(), PS->GetBufferSize(), NULL, &pPS);

	// set the shader objects
	devcon->VSSetShader(pVS, 0, 0);
	devcon->PSSetShader(pPS, 0, 0);

	// create the input layout object
	D3D11_INPUT_ELEMENT_DESC ied[] =
	{
		{ "POSITION", 0, DXGI_FORMAT_R32G32B32_FLOAT, 0, 0, D3D11_INPUT_PER_VERTEX_DATA, 0 },
		{ "COLOR", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, 12, D3D11_INPUT_PER_VERTEX_DATA, 0 },
	};

	dev->CreateInputLayout(ied, 2, VS->GetBufferPointer(), VS->GetBufferSize(), &pLayout);
	devcon->IASetInputLayout(pLayout);
}

shader.shader

struct VOut
{
    float4 position : SV_POSITION;
    float4 color : COLOR;
};

VOut VShader(float4 position : POSITION, float4 color : COLOR)
{
    VOut output;

    output.position = position;
    output.color = color;

    return output;
}


float4 PShader(float4 position : SV_POSITION, float4 color : COLOR) : SV_TARGET
{
    return color;
}

代码就不详细说了，具体可以看参考的链接。

结果如下

封装出一个简单的框架

将所有的代码都写在main.cpp里肯定不是太好，最好按功能抽象出各种类型。下面是参照教程写的一个框架。

简单的一个框架，还是渲染一个小小的三角形，但是是抽了很多个类出来，比如相机，输入之类的，方面后面扩展。

当然还是一个比较槽的框架哈。

代码直接看github吧。

参考

Graphics Pipeline - https://msdn.microsoft.com/en-us/library/windows/desktop/ff476882(v=vs.85).aspx

《Introduction to 3D GAME PROGRAMMING WITH DIRECTX®11》

DirectX 11 Tutorials - http://www.rastertek.com/tutdx11.html

http://www.directxtutorial.com/default.aspx