Implement surface stable fractal dithering

1 files changed, 59 insertions, 0 deletions

diff --git a/tooner_lighting.cginc b/tooner_lighting.cginc
index 3241394..ab885e6 100644
--- a/tooner_lighting.cginc
+++ b/tooner_lighting.cginc
@@ -1069,6 +1069,65 @@ float4 effect(inout v2f i, out float depth)
   const float frame = 0;
 #endif  // _FRAME_COUNTER
 
+#if defined(_SURFACE_STABLE_FRACTAL_DITHERING)
+  {
+    float2 duv = i.uv0;
+
+    //float duv_fw = fwidth(duv.x) + fwidth(duv.y);
+    // Original paper uses SVD instead of fwidth.
+    float2x2 M = float2x2(ddx(duv), ddy(duv));
+    float2x2 MtM = mul(transpose(M), M);
+    float trace = MtM[0][0] + MtM[1][1];
+    float det = determinant(MtM);
+    // Calculate eigenvalues using quadratic formula.
+    float tmp = sqrt(trace * trace - 4 * det);
+    float e1 = (trace + tmp) * 0.5;
+    float e2 = (trace - tmp) * 0.5;
+    float2 singular_values = sqrt(float2(e1, e2));
+    // Logic from original paper: the smaller eigenvalue corresponds to the
+    // largest amount of stretching, so we use it to determine when to
+    // subdivide.
+    float duv_fw = singular_values.y;
+
+    // Suppose Max_Fwidth is 1.
+    // duv_fw is 16. That means UV is changing a lot per pixel. That means we want to shrink the scale of the UV.
+    // Factor is 16.
+    // log_2(factor) is 4.
+    // Divide original by 16.
+    float fw_factor = duv_fw / _Surface_Stable_Fractal_Dithering_Max_Fwidth;
+    float fractal_level = log2(fw_factor);
+    float fractal_level_floor = floor(fractal_level);
+    float fractal_remainder = fractal_level - fractal_level_floor;
+    duv /= pow(2, fractal_level_floor);
+    duv *= _Surface_Stable_Fractal_Dithering_Scale;
+
+    //float subdivisions = 4;
+    //float fractal_remainder_subd = fractal_remainder * subdivisions;
+
+#if 1
+    // Four layers -> coarsest at 0.125, finest at 0.875.
+    uint width, height, depth;
+    _Surface_Stable_Fractal_Dithering_Noise.GetDimensions(width, height, depth);
+    float n_layers = depth;
+    float not_used_lo = 1/(n_layers*2);
+    float not_used_hi = 1 - not_used_lo;
+    float uvw = (not_used_hi - not_used_lo) * (1 - fractal_remainder) + not_used_lo;
+
+    float3 duv_3d = float3(duv, uvw);
+#else
+    float3 duv_3d = float3(duv, 0);
+#endif
+    float noise = _Surface_Stable_Fractal_Dithering_Noise.SampleLevel(bilinear_repeat_s, duv_3d, 0);
+    noise = (noise > 0.5) ? 1 : 0;
+
+    albedo.rgb = noise;
+#if 0
+    float hue = 0;
+    hue += glsl_mod(fractal_level_floor*.1, 1);
+    albedo.rgb *= HSVtoRGB(float3(hue, 1, 1));
+#endif
+  }
+#endif
 
 #if defined(_GIMMICK_GERSTNER_WATER)
 #if defined(_EXPLODE)