shaderlab-13chapter

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13.1原理：

• 深度纹理，存储的不是颜色值，而是一个高精度的深度值[0,1] - 归一化的设备坐标（Normalized Device Coordinates，NDC） 精度（24or16位）

• 1）使用延迟渲染时，G-buffer中直接可得。2）否则通过单独的pass，unity使用ShaderReplacement技术选择那些RenderType为Opaque的物体，判断他们的渲染队列是否小于等于2500. 如果满足，就渲染到深度和法线纹理中。

• 获取深度纹理的方式： camera.depthTextureMode = DepthTextrueMode.DepthNormals

13.2再谈运动模糊

SAMPLE_DEPTH_TEXTURE \ SAMPLE_DEPTH_TEXTURE_PROJ \ SAMPLE_DEPTH_TEXTURE_LOD

纹理采样得到的深度值是非线性的，需要转换到视角空间的深度值。

• Unity封装了转换过程--LinearEyeDepth和Linear01Depth --Zview,Z01
• Unity函数DecodeDepthNormal --得到深度值和法线方向。

1 采样深度纹理得 深度值
2 映射到NDC坐标
3 VP矩阵逆转换，再除以w。得到世界坐标
4 上一帧和当前帧算出速度

// Get the depth buffer value at this pixel.
float d = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, i.uv_depth);
// H is the viewport position at this pixel in the range -1 to 1.
float4 H = float4(i.uv.x * 2 - 1, i.uv.y * 2 - 1, d * 2 - 1, 1);
// Transform by the view-projection inverse.
float4 D = mul(_CurrentViewProjectionInverseMatrix, H);
// Divide by w to get the world position. 
float4 worldPos = D / D.w;  //为什么不是  D * D.w

// Current viewport position 
float4 currentPos = H;
// Use the world position, and transform by the previous view-projection matrix.  
float4 previousPos = mul(_PreviousViewProjectionMatrix, worldPos);
// Convert to nonhomogeneous points [-1,1] by dividing by w.
previousPos /= previousPos.w;

// Use this frame‘s position and last frame‘s to compute the pixel velocity.
float2 velocity = (currentPos.xy - previousPos.xy)/2.0f;

float2 uv = i.uv;
float4 c = tex2D(_MainTex, uv);
uv += velocity * _BlurSize;
for (int it = 1; it < 3; it++, uv += velocity * _BlurSize) {
	float4 currentColor = tex2D(_MainTex, uv);
	c += currentColor;
}
c /= 3;

return fixed4(c.rgb, 1.0);

第二个pass—后处理的标配。zwrite off。OnRenderImage
是在不透明pass执行后调用，如果不关闭 影响后面透明pass

ZTest Always Cull Off
ZWrite Off

interpolateRay 有像素到相机的方向和距离信息

13.4再谈边缘检测

1原理

1）相机的深度纹理模式设置为，深度法线模式
2）边缘检测卷积公式用Roberts，如下图Image1-1。
3）计算法线和深度是否足够相似。关键代码如下Code1-1：
问题：CheckSame函数里 diffDepth < 0.1 * centerDepth的centerDepth是必须要乘的吗？为什么？
Image1-1

Code1-1：

v2f vert(appdata_img v) {
      o.uv[1] = uv + _MainTex_TexelSize.xy * half2(1,1) * _SampleDistance;
      o.uv[2] = uv + _MainTex_TexelSize.xy * half2(-1,-1) * _SampleDistance;
      o.uv[3] = uv + _MainTex_TexelSize.xy * half2(-1,1) * _SampleDistance;
      o.uv[4] = uv + _MainTex_TexelSize.xy * half2(1,-1) * _SampleDistance;
      ...
}
half CheckSame(half4 center, half4 sample) {
	half2 centerNormal = center.xy;
	float centerDepth = DecodeFloatRG(center.zw);
	half2 sampleNormal = sample.xy;
	float sampleDepth = DecodeFloatRG(sample.zw);
	// difference in normals
	// do not bother decoding normals - there‘s no need here
	half2 diffNormal = abs(centerNormal - sampleNormal) * _Sensitivity.x;
	int isSameNormal = (diffNormal.x + diffNormal.y) < 0.1;
	// difference in depth
	float diffDepth = abs(centerDepth - sampleDepth) * _Sensitivity.y;
	// scale the required threshold by the distance
	int isSameDepth = diffDepth < 0.1 * centerDepth;
	// return:
	// 1 - if normals and depth are similar enough
	// 0 - otherwise
	return isSameNormal * isSameDepth ? 1.0 : 0.0;
}
fixed4 fragRobertsCrossDepthAndNormal(v2f i) : SV_Target {
	half4 sample1 = tex2D(_CameraDepthNormalsTexture, i.uv[1]);
	half4 sample2 = tex2D(_CameraDepthNormalsTexture, i.uv[2]);
	half4 sample3 = tex2D(_CameraDepthNormalsTexture, i.uv[3]);
	half4 sample4 = tex2D(_CameraDepthNormalsTexture, i.uv[4]);
	half edge = 1.0;
	edge *= CheckSame(sample1, sample2);
	edge *= CheckSame(sample3, sample4);
}

shaderlab-13chapter

标签：影响   mode   方式   mamicode   return   获取   设置   abs   require   

原文地址：https://www.cnblogs.com/Jaysonhome/p/13036954.html