用户裁减平面通过在VS里设定一个SV_ClipDistance[n]标记，定义一个裁减距离输出得到,n为0或1。这里一共能存放8个Clip Plane距离，分别使用数组两个元素的x,y,z,w通道。

In this scenario, each clip planes is defined by a plane equation of the form:

在这个场景里，每个clip plane被一个平面方程定义：

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是平面到原点的距离。把任意点<x,y,z>代入方程能得到它到平面的距离。所有满足方程＝0的点在平面上，<0的点在平面下而 >0的点在平面上。

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，每个顶点会带入平面方程做测试。每个三角形的Clip距离存在SV_ClipDistance0语义输出的前三个通道中。这个距离在光栅化中被线性插值，所有小于0的像素被剔除。

Rendering Shadows

At the top level, the rendering steps look like the following:

• If ambient lighting is enabled, render the entire scene with ambient only.
• For each light in the scene, do the following:
  • Disable depth-buffer and frame-buffer writing.
  • Prepare the stencil buffer render states for rendering the shadow volume.
  • Render the shadow volume mesh with a vertex extruding shader. This sets up the stencil buffer according to whether or not the pixels are in the shadow volume.
  • Prepare the stencil buffer render states for lighting.
  • Prepare the additive blending mode.
  • Render the scene for lighting with only the light being processed.

//
// Calculates fog factor based upon distance
//
// E is defined as the base of the natural logarithm (2.71828)
float CalcFogFactor( float d )
{
         float fogCoeff = 1.0;
        
         if( FOGMODE_LINEAR == g_fogMode )
         {
                 fogCoeff = (g_fogEnd - d)/(g_fogEnd - g_fogStart);
         }
         else if( FOGMODE_EXP == g_fogMode )
         {
                 fogCoeff = 1.0 / pow( E, d*g_fogDensity );
         }
         else if( FOGMODE_EXP2 == g_fogMode )
         {
                 fogCoeff = 1.0 / pow( E, d*d*g_fogDensity*g_fogDensity );
         }
        
         return clamp( fogCoeff, 0, 1 );
}

Finally, the pixel shader uses the fog factor to determine how much of the original color and how much of the fog color to output to the pixel.

最后，PS使用雾化参数确定雾颜色和纹理颜色的混合程度。
return fog * normalColor + (1.0 - fog)*g_fogColor;

    float Dsp = length(pointLightDir);
    float3 L = pointLightDir/Dsp;
    float thetas = acos(dot(N, L));
    float lightIntensity = g_PointLightIntensity * 100;
   
    //spotlight
    float angleToSpotLight = dot(-L, g_SpotLightDir);
    if(g_useSpotLight)
    {    if(angleToSpotLight > g_cosSpotlightAngle)
             lightIntensity *= abs((angleToSpotLight - g_cosSpotlightAngle)/(1-g_cosSpotlightAngle));
         else
             lightIntensity = 0;        
    }  
   
    //diffuse contribution
    float t1 = exp(-g_beta.x*Dsp)*max(cos(thetas),0)/Dsp;
    float4 t2 = g_beta.x*Gtable.SampleLevel(samLinearClamp, float2((g_beta.x*Dsp-g_diffXOffset)*g_diffXScale, (thetas-g_diffYOffset)*g_diffYScale),0)/(2*PI);
    float rCol = (t1+t2.x)*exp(-g_beta.x*Dvp)*Kd*lightIntensity/Dsp;
    float diffusePointLight = float3(rCol,rCol,rCol); 
    return diffusePointLight.xxx;
}
计算高光：
float3 Specular(float lightIntensity, float Ks, float Dsp, float Dvp, float specPow, float3 L, float3 VReflect)
{
    lightIntensity = lightIntensity * 100;
    float LDotVReflect = dot(L,VReflect);
    float thetas = acos(LDotVReflect);

    float t1 = exp(-g_beta*Dsp)*pow(max(LDotVReflect,0),specPow)/Dsp;
    float4 t2 = g_beta.x*G_20table.SampleLevel(samLinearClamp, float2((g_beta.x*Dsp-g_20XOffset)*g_20XScale, (thetas-g_20YOffset)*g_20YScale),0)/(2*PI);
    float specular = (t1+t2.x)*exp(-g_beta.x*Dvp)*Ks*lightIntensity/Dsp;
    return specular.xxx;
}
下一步，考虑如何不通过DX9接口，直接导入X文件。