D3D摄像机类和非摄像机类需要进行摄像机操作的思路

1.摄像机类的实现思想

摄像机类的实现，主要是因为D3DXMatrixLookAtLH()求取的是指定摄像机位置和观察坐标系向量的矩阵，但如果摄像机位置和观察坐标系向量是根据用户输入来确定的，那么D3DXMatrixLookAtLH显得力不从心。原因：

D3DXMATRIX* D3DXMatrixLookAtLH(
  _Inout_       D3DXMATRIX  *pOut,
  _In_    const D3DXVECTOR3 *pEye,
  _In_    const D3DXVECTOR3 *pAt,
  _In_    const D3DXVECTOR3 *pUp
);

其中的pAt是观察的朝向，摄像机的z = (pAt - pEye).Normalize(), 摄像机的y = pUp, 摄像机的x= 摄像机z x 摄像机y再规范单位化。但是用户输入时候，很难从改变pAt位置来改变摄像机z。设置也很不直观，所以需要开发自己的摄像机类，特别是在飞行或者第一人称射击游戏中。

开发自己的摄像机类，主要思想是：定义摄像机的位置_pos，方向向量_look, _right, _up；主角可以在这些方向上进行移动摄像机的位置_pos(这些方向向量也是有自己的xyz的)，也可以绕这些方向进行旋转（旋转时候只针对某个轴进行旋转，然后对其它轴乘以该旋转矩阵进行变换)；从而可以简单的得到新的_pos,_look, _right, _up，将整个世界坐标系中的物体变换到观察坐标系中即可。因为模型坐标系转换到世界坐标系要进行RT,所以世界坐标系中旋转到视图坐标系（模型坐标系）中进行V = T-1R-1矩阵变换即可。这个变换也是

D3DXMatrixLookAtLH函数得到视图矩阵的方法， 这里只不过是使得输入移动和旋转更加直观。

2.非摄像机类需要用到摄像机效果的实现思路

如果不是第一人称类型的摄像机操作，而是RPG类型的飞行摄像机，不能输入位置和摄像机旋转，那么可以直接配置pos 位置。2D中通过D3DXMatrixOrthoLH函数的参数，放大传入的w、h可以实现模拟的远离缩小；拉动摄像机的y坐标就可以上升了。3D中设置固定的摄像机位置y值上下移动，z值可以设置近大远小效果，还是通过D3DXMatrixLookAtLH设置变换矩阵即可。

3.摄像机类实现代码及其注释

#ifndef __cameraH__
#define __cameraH__

#include <d3dx9.h>

class Camera
{
public:
	enum CameraType { LANDOBJECT, AIRCRAFT };

	Camera();
	Camera(CameraType cameraType);
	~Camera();

	void strafe(float units); // left/right
	void fly(float units);    // up/down
	void walk(float units);   // forward/backward
	
	void pitch(float angle); // rotate on right vector
	void yaw(float angle);   // rotate on up vector
	void roll(float angle);  // rotate on look vector

	void getViewMatrix(D3DXMATRIX* V); 
	void setCameraType(CameraType cameraType); 
	void getPosition(D3DXVECTOR3* pos); 
	void setPosition(D3DXVECTOR3* pos); 

	void getRight(D3DXVECTOR3* right);
	void getUp(D3DXVECTOR3* up);
	void getLook(D3DXVECTOR3* look);
private:
	CameraType  _cameraType;

	D3DXVECTOR3 _right;
	D3DXVECTOR3 _up;
	D3DXVECTOR3 _look;

	D3DXVECTOR3 _pos;
};
#endif 

#include "camera.h"

Camera::Camera()
{
	_cameraType = AIRCRAFT;

	_pos   = D3DXVECTOR3(0.0f, 0.0f, 0.0f);
	_right = D3DXVECTOR3(1.0f, 0.0f, 0.0f);
	_up    = D3DXVECTOR3(0.0f, 1.0f, 0.0f);
	_look  = D3DXVECTOR3(0.0f, 0.0f, 1.0f);
}

Camera::Camera(CameraType cameraType)
{
	_cameraType = cameraType;

	_pos   = D3DXVECTOR3(0.0f, 0.0f, 0.0f);
	_right = D3DXVECTOR3(1.0f, 0.0f, 0.0f);
	_up    = D3DXVECTOR3(0.0f, 1.0f, 0.0f);
	_look  = D3DXVECTOR3(0.0f, 0.0f, 1.0f);
}

Camera::~Camera()
{

}

void Camera::getPosition(D3DXVECTOR3* pos)
{
	*pos = _pos;
}

void Camera::setPosition(D3DXVECTOR3* pos)
{
	_pos = *pos;
}

void Camera::getRight(D3DXVECTOR3* right)
{
	*right = _right;
}

void Camera::getUp(D3DXVECTOR3* up)
{
	*up = _up;
}

void Camera::getLook(D3DXVECTOR3* look)
{
	*look = _look;
}

void Camera::walk(float units)
{
	// move only on xz plane for land object
	// 观察摄像机，在方向_look只能沿着xz（ 不一定是(0,0,1) )改变前行
	if( _cameraType == LANDOBJECT )
		_pos += D3DXVECTOR3(_look.x, 0.0f, _look.z) * units;

	if( _cameraType == AIRCRAFT )
		_pos += _look * units;
}

void Camera::strafe(float units)
{
	// move only on xz plane for land object
	// 观察摄像机，在方向_right只能沿着xz（ 不一定是(1,0,0) )改变前行
	if( _cameraType == LANDOBJECT )
		_pos += D3DXVECTOR3(_right.x, 0.0f, _right.z) * units;

	if( _cameraType == AIRCRAFT )
		_pos += _right * units;
}

void Camera::fly(float units)
{
	// move only on y-axis for land object
	// 观察摄像机，在_up方向上只能向上_pos.y移动
	if( _cameraType == LANDOBJECT )
		_pos.y += units;

	if( _cameraType == AIRCRAFT )
		_pos += _up * units;
}

void Camera::pitch(float angle)
{
	// 绕_right轴旋转，地面摄像机和空中摄像机都可以
	D3DXMATRIX T;
	D3DXMatrixRotationAxis(&T, &_right,	angle);

	// rotate _up and _look around _right vector
	// 因为绕_right轴移动，所以_up需要进行T旋转
	D3DXVec3TransformCoord(&_up,&_up, &T);
	// _look轴需要进行T旋转
	D3DXVec3TransformCoord(&_look,&_look, &T);
}

void Camera::yaw(float angle)
{
	D3DXMATRIX T;

	// rotate around world y (0, 1, 0) always for land object
	// 地面摄像机不能做_up旋转,因为_up不一定是世界坐标系的y,所以只能做基于世界坐标系Y轴旋转
	if( _cameraType == LANDOBJECT )
		D3DXMatrixRotationY(&T, angle);

	// rotate around own up vector for aircraft
	if( _cameraType == AIRCRAFT )
		D3DXMatrixRotationAxis(&T, &_up, angle);

	// rotate _right and _look around _up or y-axis
	D3DXVec3TransformCoord(&_right,&_right, &T);
	D3DXVec3TransformCoord(&_look,&_look, &T);
}

void Camera::roll(float angle)
{
	// only roll for aircraft type
	// 地面观察摄像机，不能进行绕_look轴旋转，因为太怪异了
	if( _cameraType == AIRCRAFT )
	{
		D3DXMATRIX T;
		D3DXMatrixRotationAxis(&T, &_look,	angle);

		// rotate _up and _right around _look vector
		D3DXVec3TransformCoord(&_right,&_right, &T);
		D3DXVec3TransformCoord(&_up,&_up, &T);
	}
}

void Camera::getViewMatrix(D3DXMATRIX* V)
{
	// Keep camera's axes orthogonal to eachother
	// 摄像机的视图变换，本来是物体坐标系到世界坐标系中需要进行S*R*T变换（缩放，旋转，平移)
	// 现在是世界坐标系变换到物体坐标系（观察坐标系中）,也就是要进行T-1R-1S-1变换（逆向平移，逆向旋转，逆向缩放）
	// 因为这里没有缩放S所以进行T-1R-1变换就得到在视图坐标系描述世界坐标系中物体的位置。
	// 因为摄像机_look,_right,_up向量由于外部的位置移动和旋转，发生了改变，所以需要先规格化为单位向量，方便旋转
	D3DXVec3Normalize(&_look, &_look);

	// 由于_right,_look求得_up向量,认为
	D3DXVec3Cross(&_up, &_look, &_right);
	D3DXVec3Normalize(&_up, &_up);

	// 如果_right存在精度问题，那么认为_up是正确的，求取_right向量
	D3DXVec3Cross(&_right, &_up, &_look);
	D3DXVec3Normalize(&_right, &_right);

	// Build the view matrix:
	// V = T-1R-1平移部分，进行平移
	float x = -D3DXVec3Dot(&_right, &_pos);
	float y = -D3DXVec3Dot(&_up, &_pos);
	float z = -D3DXVec3Dot(&_look, &_pos);

	// V = T-1R-1旋转部分，R-1刚好是R的转置
	(*V)(0,0) = _right.x; (*V)(0, 1) = _up.x; (*V)(0, 2) = _look.x; (*V)(0, 3) = 0.0f;
	(*V)(1,0) = _right.y; (*V)(1, 1) = _up.y; (*V)(1, 2) = _look.y; (*V)(1, 3) = 0.0f;
	(*V)(2,0) = _right.z; (*V)(2, 1) = _up.z; (*V)(2, 2) = _look.z; (*V)(2, 3) = 0.0f;
	(*V)(3,0) = x;        (*V)(3, 1) = y;     (*V)(3, 2) = z;       (*V)(3, 3) = 1.0f;
	// 得到V后，就可以通过Device->SetTransform(D3DTS_VIEW, &V);就可以实现视图变换了
}

void Camera::setCameraType(CameraType cameraType)
{
	_cameraType = cameraType;
}

调用：

#include "d3dUtility.h"
#include "camera.h"

//
// Globals
//

IDirect3DDevice9* Device = 0; 

const int Width  = 640;
const int Height = 480;

Camera TheCamera(Camera::AIRCRAFT/*LANDOBJECT*/);

//
// Framework functions
//
bool Setup()
{
	//
	// Setup a basic scene.  The scene will be created the
	// first time this function is called.
	//

	d3d::DrawBasicScene(Device, 0.0f); 

	//
	// Set projection matrix.
	//

	D3DXMATRIX proj;
	D3DXMatrixPerspectiveFovLH(
			&proj,
			D3DX_PI * 0.25f, // 45 - degree
			(float)Width / (float)Height,
			1.0f,
			1000.0f);
	Device->SetTransform(D3DTS_PROJECTION, &proj);

	return true;
}

void Cleanup()
{
	// pass 0 for the first parameter to instruct cleanup.
	d3d::DrawBasicScene(0, 0.0f);
}

bool Display(float timeDelta)
{
	if( Device )
	{
		//
		// Update: Update the camera.
		//

		if( ::GetAsyncKeyState('W') & 0x8000f )
			TheCamera.walk(4.0f * timeDelta);

		if( ::GetAsyncKeyState('S') & 0x8000f )
			TheCamera.walk(-4.0f * timeDelta);

		if( ::GetAsyncKeyState('A') & 0x8000f )
			TheCamera.strafe(-4.0f * timeDelta);

		if( ::GetAsyncKeyState('D') & 0x8000f )
			TheCamera.strafe(4.0f * timeDelta);

		if( ::GetAsyncKeyState('R') & 0x8000f )
			TheCamera.fly(4.0f * timeDelta);

		if( ::GetAsyncKeyState('F') & 0x8000f )
			TheCamera.fly(-4.0f * timeDelta);

		if( ::GetAsyncKeyState(VK_UP) & 0x8000f )
			TheCamera.pitch(1.0f * timeDelta);

		if( ::GetAsyncKeyState(VK_DOWN) & 0x8000f )
			TheCamera.pitch(-1.0f * timeDelta);

		if( ::GetAsyncKeyState(VK_LEFT) & 0x8000f )
			TheCamera.yaw(-1.0f * timeDelta);
			
		if( ::GetAsyncKeyState(VK_RIGHT) & 0x8000f )
			TheCamera.yaw(1.0f * timeDelta);

		if( ::GetAsyncKeyState('N') & 0x8000f )
			TheCamera.roll(1.0f * timeDelta);

		if( ::GetAsyncKeyState('M') & 0x8000f )
			TheCamera.roll(-1.0f * timeDelta);

		// Update the view matrix representing the cameras 
        // new position/orientation.
		D3DXMATRIX V;
		TheCamera.getViewMatrix(&V);
		//D3DXMatrixLookAtLH()
		Device->SetTransform(D3DTS_VIEW, &V);

		//
		// Render
		//

		Device->Clear(0, 0, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, 0x00000000, 1.0f, 0);
		Device->BeginScene();

		d3d::DrawBasicScene(Device, 1.0f);

		Device->EndScene();
		Device->Present(0, 0, 0, 0);
	}
	return true;
}

//
// WndProc
//
LRESULT CALLBACK d3d::WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	switch( msg )
	{
	case WM_DESTROY:
		::PostQuitMessage(0);
		break;
		
	case WM_KEYDOWN:
		if( wParam == VK_ESCAPE )
			::DestroyWindow(hwnd);

		break;
	}
	return ::DefWindowProc(hwnd, msg, wParam, lParam);
}

//
// WinMain
//
int WINAPI WinMain(HINSTANCE hinstance,
				   HINSTANCE prevInstance, 
				   PSTR cmdLine,
				   int showCmd)
{
	if(!d3d::InitD3D(hinstance,
		Width, Height, true, D3DDEVTYPE_HAL, &Device))
	{
		::MessageBox(0, "InitD3D() - FAILED", 0, 0);
		return 0;
	}
		
	if(!Setup())
	{
		::MessageBox(0, "Setup() - FAILED", 0, 0);
		return 0;
	}

	d3d::EnterMsgLoop( Display );

	Cleanup();

	Device->Release();

	return 0;
}