关于VSSM

[minisparks]

我在自己试图实现VSSM的时候发现阴影上有很多不自然的条纹，检查glsl代码后发现在计算blocker平均深度Zocc的时候Zocc这一项有时会为负数，请问有人遇到过这种问题吗，怎么规避这一点呢？
关键glsl代码我贴在下边了，恳请大家帮忙指正。

"   vec4 brightFragColor = ambient+diffuse+specular;\n"
"	float lightDepth = texture(depthMap, vec2(LightSpaceCoord.x/2+0.5, LightSpaceCoord.y/2+0.5)).r;\n"
"	float shadingPointDepth = LightSpaceCoord.z/2+0.5;\n"
"	if(lightDepth+0.0005<shadingPointDepth){\n"
"		float lightDepth2 = texture(depth2Map, vec2(LightSpaceCoord.x/2+0.5, LightSpaceCoord.y/2+0.5)).r;\n"
"		float meanSquareErr = lightDepth2-(lightDepth*lightDepth);\n"
"		float RatioZunocc = meanSquareErr/(meanSquareErr+(shadingPointDepth-lightDepth)*(shadingPointDepth-lightDepth));\n"//切比雪夫1
"		float Zocc = (lightDepth-shadingPointDepth*RatioZunocc)/(1-RatioZunocc);\n"
"		float mipLevel = 5.0*shadingPointDepth/Zocc;\n"
"		float vlightDepth = textureLod(depthMap, vec2(LightSpaceCoord.x/2+0.5, LightSpaceCoord.y/2+0.5), mipLevel).r;\n"
"		float vlightDepth2 = textureLod(depth2Map, vec2(LightSpaceCoord.x/2+0.5, LightSpaceCoord.y/2+0.5), mipLevel).r;\n"
"		float vmeanSquareErr = vlightDepth2-(vlightDepth*vlightDepth);\n"
"		float vRatioZunocc = vmeanSquareErr/(vmeanSquareErr+(shadingPointDepth-vlightDepth)*(shadingPointDepth-vlightDepth));\n"//切比雪夫2
"		if(Zocc<0) FragColor = vec4(0.1,0.6,0.3,1.0);\n"
"		else FragColor = brightFragColor*vRatioZunocc*0.8+brightFragColor*0.2;\n"//brightFragColor*vRatioZunocc*0.8+brightFragColor*0.2;
"	}else{\n"
"		FragColor = brightFragColor;\n"//vec4(0.5,0.5,0.5,1.0f)  vec4(vec3(texture(skybox, TexCoord)),1.0f)//深度cubemap测试中
"	}\n"

其中depthMap为深度图，depthMap2为其平方版本。LightSpaceCoord为光照空间下着色点坐标。

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[brendan87]

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