Cg实现景深

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1.渲染深度到纹理。
相关SHADER如下：

//AdaptDepthVS.cg
//取得顶点的深度值，并且插值到PS中去

uniform float4x4 modelViewProj : state.matrix.mvp;
uniform float farclip;  //远裁剪面距离

void main(float4 inPos : POSITION,
     out float4 oPos : POSITION,
     out float oDepth : TEXCOORD0)
{
  float4 OutPos;
  oPos = OutPos = mul(modelViewProj, inPos);
  oDepth = OutPos.w / farclip;
}

//AdaptDepthPs.cg
//将插值的深度转换成颜色
//白色越近，黑色越远。

void main(float4 inDepth : TEXCOORD0,
     out float4 color : COLOR0)
{
  float depthColor = inDepth.r;

  color = float4(depthColor, depthColor, depthColor, 1.0);
}

以上代码讲深度转换成颜色，储存在纹理中，供景深的shader来查询。

2.景深shader

//DepthOfFieldPs.cg
//处理景深效果

uniform sampler2D depthTex;    //深度图
uniform sampler2D sceneTex;    //场景渲染图
uniform float nearclip;      //近裁剪面
uniform float farclip;      //远裁剪面
uniform float focus;      //焦距
uniform float viewPortInvX;    //视口宽度的倒数
uniform float viewPortInvY;    //视口高度的倒数

void main(float2 texCoord : TEXCOORD0,
     out float4 color : COLOR)
{
  float4 DepthValue = tex2D(depthTex, texCoord);
  //计算出真实的深度
  float realDepth = nearclip + DepthValue.r*(farclip - nearclip);
  //计算深度于焦距的差值
  float dfocus = abs(realDepth - focus);
  //计算出模糊因子,距离的平方成正比
  float blurFactor = 1.0-pow(-dfocus/(farclip-nearclip), 2.0);
  blurFactor*=2.5;

  color = float4(0, 0, 0, 0);
  color+=tex2D(sceneTex,texCoord + float2(-1.0*viewPortInvX*blurFactor ,-1.0*viewPortInvY*blurFactor)) * (1.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2(-1.0*viewPortInvX*blurFactor , 1.0*viewPortInvY*blurFactor)) * (1.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 1.0*viewPortInvX*blurFactor ,-1.0*viewPortInvY*blurFactor)) * (1.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 1.0*viewPortInvX*blurFactor , 1.0*viewPortInvY*blurFactor)) * (1.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2(-1.0*viewPortInvX*blurFactor , 0.0*viewPortInvY*blurFactor)) * (2.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 1.0*viewPortInvX*blurFactor , 0.0*viewPortInvY*blurFactor)) * (2.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 0.0*viewPortInvX*blurFactor ,-1.0*viewPortInvY*blurFactor)) * (2.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 0.0*viewPortInvX*blurFactor , 1.0*viewPortInvY*blurFactor)) * (2.0/16.0);
  color+=tex2D(sceneTex,texCoord + float2( 0.0*viewPortInvX*blurFactor , 0.0*viewPortInvY*blurFactor)) * (4.0/16.0);
}

上面代码根据计算出来的blurFactor来做为blur程度的依据，
其算法是，当前像素的深度值与焦距的差值绝对值的平方与模糊程度成正比。

3 blur shader

uniform float gViewportInvX;
uniform float gViewportInvY;
uniform sampler2D gTexture;

float4 main(float2 texCoord : TEXCOORD0) : COLOR
{
float4 col = float4(0,0,0,0);

col+=tex2D(gTexture,texCoord + float2(-1.0*gViewportInvX ,-1.0*gViewportInvY)) * (1.0/16.0);
col+=tex2D(gTexture,texCoord + float2(-1.0*gViewportInvX , 1.0*gViewportInvY)) * (1.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 1.0*gViewportInvX ,-1.0*gViewportInvY)) * (1.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 1.0*gViewportInvX , 1.0*gViewportInvY)) * (1.0/16.0);
col+=tex2D(gTexture,texCoord + float2(-1.0*gViewportInvX , 0.0*gViewportInvY)) * (2.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 1.0*gViewportInvX , 0.0*gViewportInvY)) * (2.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 0.0*gViewportInvX ,-1.0*gViewportInvY)) * (2.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 0.0*gViewportInvX , 1.0*gViewportInvY)) * (2.0/16.0);
col+=tex2D(gTexture,texCoord + float2( 0.0*gViewportInvX , 0.0*gViewportInvY)) * (4.0/16.0);

return col;
}