延迟渲染中的点光源双抛物面VSM

Question

我一直在遵循this tutorial为延迟渲染中的点光源实现我的方差阴影贴图功能。

我用的是GLSL3.3，左手坐标系。这是我一直在做的事情：

我将场景渲染为双抛物面贴图，存储深度和深度*深度。

结果：

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上图包含正面和背面的地图。点光源位于场景的中心，您可以看到它发出的黄色光最多。

然后，我设置了一个全屏着色器过程。我通过将教程代码从FX转换为GLSL来做到这一点。

作者的.fx代码：

    float4 TexturePS(float3 normalW : TEXCOORD0, float2 tex0 : TEXCOORD1, float3 pos : TEXCOORD2) : COLOR
    {
        float4 texColor = tex2D(TexS, tex0 * TexScale);

        pos = mul(float4(pos, 1.0f), LightView);

        float L = length(pos);
        float3 P0 = pos / L;

        float alpha = .5f + pos.z / LightAttenuation;

        P0.z = P0.z + 1;
        P0.x = P0.x / P0.z;
        P0.y = P0.y / P0.z;
        P0.z = L / LightAttenuation;

        P0.x = .5f * P0.x + .5f;
        P0.y = -.5f * P0.y + .5f;

        float3 P1 = pos / L;

        P1.z = 1 - P1.z;
        P1.x = P1.x / P1.z;
        P1.y = P1.y / P1.z;
        P1.z = L / LightAttenuation;

        P1.x = .5f * P1.x + .5f;
        P1.y = -.5f * P1.y + .5f;

        float depth;
        float mydepth;
        float2 moments;
        if(alpha >= 0.5f)
        {
            moments = tex2D(ShadowFrontS, P0.xy).xy;
            depth = moments.x;
            mydepth = P0.z;
        }
        else
        {
            moments = tex2D(ShadowBackS, P1.xy).xy;
            depth = moments.x;
            mydepth = P1.z;
        }

        float lit_factor = (mydepth <= moments[0]);

        float E_x2 = moments.y;
        float Ex_2 = moments.x * moments.x;
        float variance = min(max(E_x2 - Ex_2, 0.0) + SHADOW_EPSILON, 1.0);
        float m_d = (moments.x - mydepth);
        float p = variance / (variance + m_d * m_d); //Chebychev's inequality

        texColor.xyz *= max(lit_factor, p + .2f);

        return texColor;
    }

我翻译的GLSL代码：

    void main() {
        vec3 in_vertex = texture(scenePosTexture, texCoord).xyz; // get 3D vertex from 2D screen coordinate
        vec4 vert = lightViewMat * vec4(in_vertex, 1); // project vertex to point light space (view from light position, look target is -Z)

        float L = length(vert.xyz);

        float distance = length(lightPos - in_vertex);
        float denom = distance / lightRad + 1;
        float attenuation = 1.0 / (denom * denom);

        // to determine which paraboloid map to use
        float alpha = vert.z / attenuation + 0.5f;

        vec3 P0 = vert.xyz / L;

        P0.z = P0.z + 1;
        P0.x = P0.x / P0.z;
        P0.y = P0.y / P0.z;
        P0.z = L / attenuation;

        P0.x = .5f * P0.x + .5f;
        P0.y = -.5f * P0.y + .5f;

        vec3 P1 = vert.xyz / L;

        P1.z = 1 - P1.z;
        P1.x = P1.x / P1.z;
        P1.y = P1.y / P1.z;
        P1.z = L / attenuation;

        P1.x = .5f * P1.x + .5f;
        P1.y = -.5f * P1.y + .5f;

        // Variance shadow mapping
        float depth;
        float mydepth;
        vec2 moments;

        if(alpha >= 0.5f)
        {
            moments = texture(shadowMapFrontTexture, P0.xy).xy;
            depth = moments.x;
            mydepth = P0.z;
        }
        else
        {
            moments = texture(shadowMapBackTexture, P1.xy).xy;
            depth = moments.x;
            mydepth = P1.z;
        }

        // Original .fx code is: float lit_factor = (mydepth <= moments[0]);
        // I'm not sure my translated code belew is correct

        float lit_factor = 0;
        if (mydepth <= moments.x)
            lit_factor = mydepth;
        else
            lit_factor = moments.x;

        float E_x2 = moments.y;
        float Ex_2 = moments.x * moments.x;
        float variance = min(max(E_x2 - Ex_2, 0.0) + SHADOW_EPSILON, 1.0);
        float m_d = (moments.x - mydepth);
        float p = variance / (variance + m_d * m_d); //Chebychev's inequality

        fragColor = texture(sceneTexture, texCoord).rgb; // sample original color
        fragColor.rgb *= max(lit_factor, p + .2f);
    }

渲染结果

​

现在我不知道该在哪里触摸才能正确地渲染阴影。有人能帮我指出一下吗？

Answer 1

我的一些朋友指出，Y分量是反转的，这就是为什么阴影看起来像颠倒的原因。在P0和P1的Y上加上减号后，它开始显示出相当合理的阴影：

​

但另一个问题是阴影的位置是错误的。

​

Answer 2

为什么要重复抛物面投影计算？

你先计算'vert'，然后计算'P0‘和'P1'，难道不应该只计算'P0’和'P1‘吗？(原始代码在“pos”上不做这件事)。

编辑：

您的lit_factor错误，它应该是0.0或1.0。

您可以这样使用step() GLSL内部函数：

float lit_factor = step(mydepth, moments[0]);