修复屏幕空间反射中的伪影

如何解决修复屏幕空间反射中的伪影

我正在尝试实现 SSR（屏幕空间反射）。我设法获得了基本效果，但您可以从下面的图像和视频中看到一些伪影。首先我想解决这些视觉问题，然后如果可能的话，我想尝试提高算法的性能。

SSR 工件：https://youtu.be/LFBAJHa_mFM

我的 SSR 实现基于此 tutorial。

您可以在下面找到生成反射贴图（或反射 UV 贴图）的像素着色器的代码，在这里您可以找到 full implementation。如您所见，除了少量更改外，它与教程 (screen-space-reflection.frag) 的代码实际上相同：

• 我不将每个像素的 3D 位置存储在离屏纹理中，而是根据函数 GetFullViewPosition 中的视图空间深度重建 3D 位置。
• 当我将片段 NDC 转换为纹理坐标时，我乘以 float2(+0.5f,-0.5f) 而不是 float2(+0.5f,+0.5f)。
• 我添加了一个检查，如果当前位置超出屏幕空间，则会停止光线追踪。

SSRReflectionsMapComputePS.hlsl

cbuffer ConstantBuffer : register(b0)
{
    float4   gFrustumFarCorner[4];
    float4x4 gProj;
};

struct VertexOut
{
    float4 PositionH  : SV_POSITION;
    float3 ToFarPlane : TEXCOORD0;
    float2 TexCoord   : TEXCOORD1;
};

Texture2D gnormalDepthMap : register(t0);
SamplerState gnormalDepthSamplerState : register(s2);

float3 GetFullViewPosition(float2 uv,float z)
{
    // bilinear interpolation
    float4 p0 = lerp(gFrustumFarCorner[0],gFrustumFarCorner[3],uv.x);
    float4 p1 = lerp(gFrustumFarCorner[1],gFrustumFarCorner[2],uv.x);
    float3 ToFarPlane = lerp(p0.xyz,p1.xyz,1 - uv.y);

    // reconstruct full view space position (x,y,z)
    // find t such that p = t*pin.tofarplane
    // p.z = t*pin.tofarplane.z ==> t = p.z / pin.tofarplane.z
    return (z / ToFarPlane.z) * ToFarPlane;
}

float3 GetFullViewPosition(float2 uv)
{
    float4 normalDepth = gnormalDepthMap.SampleLevel(gnormalDepthSamplerState,uv,0);
    return GetFullViewPosition(uv,normalDepth.w);
}

// https://lettier.github.io/3d-game-shaders-for-beginners/screen-space-reflection.html
// https://github.com/lettier/3d-game-shaders-for-beginners/blob/master/demonstration/shaders/fragment/screen-space-reflection.frag

float4 main(VertexOut pin) : sv_target
{
    // view space normal and depth (z-coord) of this pixel
    float4 normaldepth = gnormalDepthMap.SampleLevel(gnormalDepthSamplerState,pin.TexCoord,0);

    float3 n = normaldepth.xyz;
    float pz = normaldepth.w;

    //float3 p = (pz / pin.tofarplane.z) * pin.tofarplane;
    float3 p = GetFullViewPosition(pin.TexCoord,pz);

    float maxdistance = 100;
    float resolution = 1;
    int   steps = 10;
    float thickness = 0.5f;

    float2 texsize;
    gnormalDepthMap.GetDimensions(texsize.x,texsize.y);
    float2 texcoord = pin.PositionH.xy / texsize;

    float3 positionfrom = p;
    float3 positionfromunit = normalize(positionfrom);
    float3 normal = normalize(n);
    float3 pivot = normalize(reflect(positionfromunit,normal));

    float3 positionto = positionfrom;
    float4 uv = 0;

    float3 viewstart = positionfrom + pivot * 0;
    float3 viewend = positionfrom + pivot * maxdistance;

    float4 fragstart = float4(viewstart,1);
    fragstart = mul(gProj,fragstart);
    fragstart.xy /= fragstart.w;
    fragstart.xy = fragstart.xy * float2(+0.5f,-0.5f) + 0.5f;
    fragstart.xy *= texsize;

    float4 fragend = float4(viewend,1);
    fragend = mul(gProj,fragend);
    fragend.xy /= fragend.w;
    fragend.xy = fragend.xy * float2(+0.5f,-0.5f) + 0.5f;
    fragend.xy *= texsize;

    float2 frag = fragstart.xy;
    uv.xy = frag / texsize;

    float deltax = fragend.x - fragstart.x;
    float deltay = fragend.y - fragstart.y;
    float usex = abs(deltax) >= abs(deltay) ? 1 : 0;
    float delta = lerp(abs(deltay),abs(deltax),usex) * clamp(resolution,1);
    float2 increment = float2(deltax,deltay) / max(delta,0.001f);

    float search0 = 0;
    float search1 = 0;

    int hit0 = 0;
    int hit1 = 0;

    float viewdistance = viewstart.z;
    float depth = thickness;

    for (int i = 0; i < int(delta); ++i)
    {
        frag += increment;
        uv.xy = frag / texsize;

        // do not sample outside the screen space
        if (any(uv.xy < float2(0,0)) || any(uv.xy > float2(1,1))) break;

        positionto = GetFullViewPosition(uv.xy);

        search1 = lerp((frag.y - fragstart.y) / deltay,(frag.x - fragstart.x) / deltax,usex);
        search1 = clamp(search1,1);

        viewdistance = (viewstart.z * viewend.z) / lerp(viewend.z,viewstart.z,search1);
        depth = viewdistance - positionto.z;

        if (depth > 0 && depth < thickness)
        {
            hit0 = 1;
            break;
        }
        else
        {
            search0 = search1;
        }
    }

    search1 = search0 + ((search1 - search0) / 2);

    steps *= hit0;

    for (int i = 0; i < steps; ++i)
    {
        frag = lerp(fragstart.xy,fragend.xy,search1);
        uv.xy = frag / texsize;

        // do not sample outside the screen space
        if (any(uv.xy < float2(0,1))) break;

        positionto = GetFullViewPosition(uv.xy);

        viewdistance = (viewstart.z * viewend.z) / lerp(viewend.z,search1);
        depth = viewdistance - positionto.z;

        if (depth > 0 && depth < thickness)
        {
            hit1 = 1;
            search1 = search0 + ((search1 - search0) / 2);
        }
        else
        {
            float temp = search1;
            search1 = search1 + ((search1 - search0) / 2);
            search0 = temp;
        }
    }

    float visibility = hit1 *
        (1 - max(dot(-positionfromunit,pivot),0)) *
        (1 - clamp(depth / thickness,1)) *
        (1 - clamp(length(positionto - positionfrom) / maxdistance,1)) *
        (uv.x < 0 || uv.x > 1 ? 0 : 1) *
        (uv.y < 0 || uv.y > 1 ? 0 : 1);

    return float4(uv.xy,saturate(visibility));
}