gistfile1.glsl

vec3 ndc2world(mat4 inv_proj, mat4 inv_view, vec3 ndc_pos)
{
    vec4 v = inv_proj * vec4(ndc_pos, 1.); 
    v.xyz /= v.w; // view space
    vec4 w = inv_view * vec4(v.xyz, 1.); // world space, camera relative (origin = camera position)
    return w.xyz;
    //return v.xyz;
}

// Try reconstructing normal accurately from depth buffer.
// input DepthBuffer: stores linearized depth in range (0, 1).
// 5 taps on each direction: | z | x | * | y | w |, '*' denotes the center sample.
vec3 ReconstructNormal(sampler2D DepthBuffer, vec2 ndc0, vec2 uv0, vec2 texel_size, mat4 inv_proj, mat4 inv_view)
{
    float depth = (textureLod(DepthBuffer, uv0, 0.).x);
    
    vec4 H, H0;
    H0.x = textureLod(DepthBuffer, uv0 - vec2(1. / texel_size.x, 0.), .0).x;
    H0.y = textureLod(DepthBuffer, uv0 + vec2(1. / texel_size.x, 0.), .0).x;
    H0.z = textureLod(DepthBuffer, uv0 - vec2(2. / texel_size.x, 0.), .0).x;
    H0.w = textureLod(DepthBuffer, uv0 + vec2(2. / texel_size.x, 0.), .0).x;
    H.x = (H0.x);
    H.y = (H0.y);
    H.z = (H0.z);
    H.w = (H0.w);
    //vec2 he = abs(H.xy * H.zw / (2. * H.zw - H.xy) - depth);
    vec2 he = vec2(
        abs((2. * H.x - H.z) - depth), // line eq. solutions for (x0 + 2), x0 = x0(z_tap)
        abs((2. * H.y - H.w) - depth) 
    );
    vec3 hDeriv;
    if (he.x > he.y) 
    { // Calculate horizontal derivative of world position from taps | z | x |
        vec3 tap_x_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 - vec2(1. / texel_size.x, 0.) * 2., H0.x));
        vec3 tap_z_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 - vec2(2. / texel_size.x, 0.) * 2., H0.z));
        hDeriv = tap_x_wp - tap_z_wp; // may ignore 1./dx = 2., who cares if we gona normalize anyway
    }
    else 
    {// Calculate horizontal derivative of world position from taps | y | w |
        vec3 tap_y_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 + vec2(0., 1. / texel_size.x) * 2., H0.y));
        vec3 tap_w_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 + vec2(0., 2. / texel_size.x) * 2., H0.w));
        hDeriv = tap_w_wp - tap_y_wp;
    }

    vec4 V, V0;
    V0.x = textureLod(DepthBuffer, uv0 - vec2(0., 1. / texel_size.y), .0).x;
    V0.y = textureLod(DepthBuffer, uv0 + vec2(0., 1. / texel_size.y), .0).x;
    V0.z = textureLod(DepthBuffer, uv0 - vec2(0., 2. / texel_size.y), .0).x;
    V0.w = textureLod(DepthBuffer, uv0 + vec2(0., 2. / texel_size.y), .0).x;
    V.x = (V0.x);
    V.y = (V0.y);
    V.z = (V0.z);
    V.w = (V0.w);
    //vec2 ve = abs(V.xy * V.zw / (2. * V.zw - V.xy) - depth);
    vec2 ve = vec2(  // line eq. solutions for (y0 + 2), y0 = y0(z_tap)
        abs((2. * V.x - V.z) - depth),
        abs((2. * V.y - V.w) - depth)
    );
    vec3 vDeriv;
    if (ve.x > ve.y)
    { // Calculate vertical derivative of world position from taps | z | x |
        vec3 tap_x_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 - vec2(0., 1. / texel_size.y) * 2., V0.x));
        vec3 tap_z_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 - vec2(0., 2. / texel_size.y) * 2., V0.z));
        vDeriv = tap_x_wp - tap_z_wp;
    }
    else 
    { // Calculate vertical derivative of world position from taps | y | w |
        vec3 tap_y_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 + vec2(0., 1. / texel_size.y) * 2., V0.y));
        vec3 tap_w_wp = ndc2world(inv_proj, inv_view, vec3(ndc0 + vec2(0., 2. / texel_size.y) * 2., V0.w));
        vDeriv = tap_w_wp - tap_y_wp;
    }
    return normalize(cross(hDeriv, vDeriv));
}