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Unity Shader:Blur

时间:2015-11-02 22:40:42      阅读:311      评论:0      收藏:0      [点我收藏+]

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花了一晚上的时间终于看懂Image Effect中的Blur,其实很简单,就是一下子没有理解到。

原理:使用两个一维[1*7]的高斯滤波模板,一个用在x方向,另一个用在y方向。高斯滤波有模糊的效果。

js脚本参数:

Down Sample:OnRenderImage中获取的图像进行降采样,其实就是把要处理的纹理变小。有利于加快shader运行速度。

Blur Size:在使用高斯模板时,相邻像素点的间隔。越大间隔越远,图像越模糊。但过大的值会导致失真。

Blur Iterations:迭代次数,越大模糊效果越好,但消耗越大。

Blur Type:两个不同的shader,后一个是前一个的优化版本,但差别不大。

 

具体代码分析:

function OnRenderImage (source : RenderTexture, destination : RenderTexture) {    
        if(CheckResources() == false) {
            Graphics.Blit (source, destination);
            return;
        }

        var widthMod : float = 1.0f / (1.0f * (1<<downsample)); // 降采样系数的倒数,用于调整降采样后,相邻像素的间隔

        // blurMaterial.SetVector ("_Parameter", Vector4 (blurSize * widthMod, -blurSize * widthMod, 0.0f, 0.0f));
        source.filterMode = FilterMode.Bilinear;

        var rtW : int = source.width >> downsample; // >> 是除法的优化
        var rtH : int = source.height >> downsample;

        // downsample
        var rt : RenderTexture = RenderTexture.GetTemporary (rtW, rtH, 0, source.format);

        rt.filterMode = FilterMode.Bilinear;
      // 对应的shader的Pass 0 Graphics.Blit (source, rt, blurMaterial,
0); //首先对图像进行降采样,同时进行简单的模糊 var passOffs = blurType == BlurType.StandardGauss ? 0 : 2; // 选择不同的blurtype,就调用不同的shader pass for(var i : int = 0; i < blurIterations; i++) { var iterationOffs : float = (i*1.0f);
        // _Parameter.x 记录的是 相邻像素的间隔,随着迭代次数增大 blurMaterial.SetVector (
"_Parameter", Vector4 (blurSize * widthMod + iterationOffs, -blurSize * widthMod - iterationOffs, 0.0f, 0.0f)); // vertical blur 垂直滤波 var rt2 : RenderTexture = RenderTexture.GetTemporary (rtW, rtH, 0, source.format); rt2.filterMode = FilterMode.Bilinear; Graphics.Blit (rt, rt2, blurMaterial, 1 + passOffs); // 对应着shader的pass 1,2 RenderTexture.ReleaseTemporary (rt); rt = rt2; // horizontal blur 水平滤波 rt2 = RenderTexture.GetTemporary (rtW, rtH, 0, source.format); rt2.filterMode = FilterMode.Bilinear; Graphics.Blit (rt, rt2, blurMaterial, 2 + passOffs); // 对应着shader的pass 3,4 RenderTexture.ReleaseTemporary (rt); rt = rt2; } Graphics.Blit (rt, destination); RenderTexture.ReleaseTemporary (rt); }

接着分析shader文件:

先看5个pass,分别是用在上文cs脚本中的Bilt函数中。

SubShader {
      ZTest Off Cull Off ZWrite Off Blend Off
      Fog { Mode off }  

    // 0 
    Pass { 
    
        CGPROGRAM
        
        #pragma vertex vert4Tap 
        #pragma fragment fragDownsample
        #pragma fragmentoption ARB_precision_hint_fastest 
        
        ENDCG
         
        }

    // 1
    Pass {
        ZTest Always
        Cull Off
        
        CGPROGRAM 
        
        #pragma vertex vertBlurVertical
        #pragma fragment fragBlur8
        #pragma fragmentoption ARB_precision_hint_fastest 
        
        ENDCG 
        }    
        
    // 2
    Pass {        
        ZTest Always
        Cull Off
                
        CGPROGRAM
        
        #pragma vertex vertBlurHorizontal
        #pragma fragment fragBlur8
        #pragma fragmentoption ARB_precision_hint_fastest 
        
        ENDCG
        }    

    // alternate blur
    // 3
    Pass {
        ZTest Always
        Cull Off
        
        CGPROGRAM 
        
        #pragma vertex vertBlurVerticalSGX
        #pragma fragment fragBlurSGX
        #pragma fragmentoption ARB_precision_hint_fastest 
        
        ENDCG
        }    
        
    // 4
    Pass {        
        ZTest Always
        Cull Off
                
        CGPROGRAM
        
        #pragma vertex vertBlurHorizontalSGX
        #pragma fragment fragBlurSGX
        #pragma fragmentoption ARB_precision_hint_fastest 
        
        ENDCG
        }    
    }    

pass 0:在降采样的同时,进行简单地模糊处理。

v2f_tap vert4Tap ( appdata_img v )
        {
            v2f_tap o;

            o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
        // 取像素周围的点 o.uv20
= v.texcoord + _MainTex_TexelSize.xy; o.uv21 = v.texcoord + _MainTex_TexelSize.xy * half2(-0.5h,-0.5h); o.uv22 = v.texcoord + _MainTex_TexelSize.xy * half2(0.5h,-0.5h); o.uv23 = v.texcoord + _MainTex_TexelSize.xy * half2(-0.5h,0.5h); return o; } fixed4 fragDownsample ( v2f_tap i ) : SV_Target { fixed4 color = tex2D (_MainTex, i.uv20); color += tex2D (_MainTex, i.uv21); color += tex2D (_MainTex, i.uv22); color += tex2D (_MainTex, i.uv23); return color / 4; }

接下来的pass 1,2 和pass 3, 4,都是分别在x y两个方向进行高斯滤波。

先看看高斯滤波模板:

static const half4 curve4[7] = { half4(0.0205,0.0205,0.0205,0), half4(0.0855,0.0855,0.0855,0), half4(0.232,0.232,0.232,0),
            half4(0.324,0.324,0.324,1), half4(0.232,0.232,0.232,0), half4(0.0855,0.0855,0.0855,0), half4(0.0205,0.0205,0.0205,0) };

这是 [1*7]的模板,对中间点像素的左右两边各3个像素,总共7个像素进行加权求和,得到新的像素值。

pass 1,2的只有vert函数不一样,分别是取水平和垂直方向的偏差值。

v2f_withBlurCoords8 vertBlurHorizontal (appdata_img v)
        {
            v2f_withBlurCoords8 o;
            o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
            
            o.uv = half4(v.texcoord.xy,1,1);
            o.offs = _MainTex_TexelSize.xy * half2(1.0, 0.0) * _Parameter.x; // 水平方向的偏差值

            return o; 
        }
        
        v2f_withBlurCoords8 vertBlurVertical (appdata_img v)
        {
            v2f_withBlurCoords8 o;
            o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
            
            o.uv = half4(v.texcoord.xy,1,1);
            o.offs = _MainTex_TexelSize.xy * half2(0.0, 1.0) * _Parameter.x; // 垂直方向的偏差值
             
            return o; 
        }    

        half4 fragBlur8 ( v2f_withBlurCoords8 i ) : SV_Target
        {
            half2 uv = i.uv.xy; 
            half2 netFilterWidth = i.offs;  
            half2 coords = uv - netFilterWidth * 3.0;  // 这里从中心点偏移3个间隔,从最左边或者是最上边开始进行加权累加
            
            half4 color = 0;
              for( int l = 0; l < 7; l++ )  
              {   
                half4 tap = tex2D(_MainTex, coords);
                color += tap * curve4[l]; // 像素值乘上对应的权值
                coords += netFilterWidth; // 移到下一个像素
              }
            return color;
        }

在pass 1,2中的uv值都是float2向量,然而寄存器可以一次性储存float4,即可以一个float4值存储两个uv值。并且像素着色器函数中,计算相邻像素的步骤,可以放在顶点着色器中。于是就有下面这个版本:

        v2f_withBlurCoordsSGX vertBlurHorizontalSGX (appdata_img v)
        {
            v2f_withBlurCoordsSGX o;
            o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
            
            o.uv = v.texcoord.xy;
            half2 netFilterWidth = _MainTex_TexelSize.xy * half2(1.0, 0.0) * _Parameter.x; 
            half4 coords = -netFilterWidth.xyxy * 3.0;
            // 计算左右相邻各3个像素的坐标
            o.offs[0] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);
            coords += netFilterWidth.xyxy;
            o.offs[1] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);
            coords += netFilterWidth.xyxy;
            o.offs[2] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);

            return o; 
        }        
        
        v2f_withBlurCoordsSGX vertBlurVerticalSGX (appdata_img v)
        {
            v2f_withBlurCoordsSGX o;
            o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
            
            o.uv = half4(v.texcoord.xy,1,1);
            half2 netFilterWidth = _MainTex_TexelSize.xy * half2(0.0, 1.0) * _Parameter.x;
            half4 coords = -netFilterWidth.xyxy * 3.0;
            // 计算上下相邻各3个像素的坐标
            o.offs[0] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);
            coords += netFilterWidth.xyxy;
            o.offs[1] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);
            coords += netFilterWidth.xyxy;
            o.offs[2] = v.texcoord.xyxy + coords * half4(1.0h,1.0h,-1.0h,-1.0h);

            return o; 
        }    

        half4 fragBlurSGX ( v2f_withBlurCoordsSGX i ) : SV_Target
        {
            half2 uv = i.uv.xy;
            
            half4 color = tex2D(_MainTex, i.uv) * curve4[3]; // 中间像素,乘上对应的权值
            
              for( int l = 0; l < 3; l++ )  
              {   
                half4 tapA = tex2D(_MainTex, i.offs[l].xy);
                half4 tapB = tex2D(_MainTex, i.offs[l].zw); 
                color += (tapA + tapB) * curve4[l]; // 由于模板是对称的,可以使用相同的权值
              }

            return color;

        }

结论:

通过调试,发现使用downsampler为1,iteration为2时,调整blursize可以得到较好的效果,并且性能较好。但blursize为0时,还是模糊图像,想做成那种从清晰到模糊的动画,估计还要调整一下代码。

 

Unity Shader:Blur

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原文地址:http://www.cnblogs.com/foxianmo/p/4931507.html

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