DX9下使用
D3DXPLANE plane;
D3DXPlaneFromPointNormal( &plane, &vPoint, &vNormal ); //生成這個平面
D3DXMatrixReflect( &matReflect, &plane ); //取得該平面的反射矩陣
//設置剪切平面，使反射面上的內容被渲染，面下的被丟棄
m_pd3dDevice->SetClipPlane( 0, plane );
m_pd3dDevice->SetRenderState( D3DRS_CLIPPLANEENABLE, 0x01 );
DX10下模擬：
User Clip PlanesUser Clip Planes are emulated by specifying a clip distance output from the Vertex Shader with the SV_ClipDistance[n] flag, where n is either 0 or 1. Each component can hold up to 4 clip distances in x, y, z, and w giving a total of 8 clip distances.
用戶裁減平面通過在VS里設定一個SV_ClipDistance[n]標記，定義一個裁減距離輸出得到,n為0或1。這里一共能存放8個Clip Plane距離，分別使用數(shù)組兩個元素的x,y,z,w通道。
In this scenario, each clip planes is defined by a plane equation of the form:
在這個場景里，每個clip plane被一個平面方程定義：
Ax + By + Cz + D =0;
Where <A,B,C> is the normal of the plane, and D is the distance of the plane from the origin. Plugging in any point <x,y,z> into this equation gives its distance from the plane. Therefore, all points <x,y,z> that satisfy the equation Ax + By + Cz + D = 0 are on the plane. All points that satisfy Ax + By + Cz + D < 0 are below the plane. All points that satisfy Ax + By + Cz + D > 0 are above the plane.
<A,B,C>是平面法向，D是平面到原點的距離。把任意點<x,y,z>代入方程能得到它到平面的距離。所有滿足方程＝0的點在平面上，<0的點在平面下而 >0的點在平面上。
In the Vertex Shader, each vertex is tested against each plane equation to produce a distance to the clip plane. Each of the three clip distances are stored in the first three components of the output component with the semantic SV_ClipDistance0. These clip distances get interpolated over the triangle during rasterization and clipped if the value every goes below 0.
在VS中，每個頂點會帶入平面方程做測試。每個三角形的Clip距離存在SV_ClipDistance0語義輸出的前三個通道中。這個距離在光柵化中被線性插值，所有小于0的像素被剔除。