Begin work on Burley's per-pixel histogram preserving blending

1 files changed, 32 insertions, 0 deletions

diff --git a/pbr.cginc b/pbr.cginc
index 2ddcdbf..d59001f 100755
--- a/pbr.cginc
+++ b/pbr.cginc
@@ -181,6 +181,37 @@ void apply_letter_grid(v2f i, inout Pbr pbr) {
 #endif
 }
 
+void apply_burley_tiling(v2f i, inout Pbr pbr) {
+#if defined(_BURLEY_TILING)
+  float2 uv = i.uv01.xy - 0.5;
+  uv *= TWO_OVER_SQRT_3;
+  uv /= _Burley_Tiling_Output_Scale;
+  float3 hex_coord = cart_to_hex(uv);
+  float3 cell = round_hex(hex_coord);
+  float3 cube_id = float3(cell.y, cell.z, -cell.y - cell.z);
+  float3 local_hex = hex_coord - cell;
+  // Get UVs on [-1/2,1/2] for the current cell.
+  // This is the tightest square fit that preserves the hex aspect ratio.
+  float2 local_uv = hex_to_cart(local_hex) * SQRT_3_OVER_2;
+  float3 tile_rand3 = hash33_fast(cube_id);
+  // Apply input scaling.
+  float input_scale = saturate(_Burley_Tiling_Input_Scale);
+  local_uv *= input_scale;
+  // Rotate.
+  float theta = hash31_ff(tile_rand3) * TAU;
+  float2x2 rot = float2x2(cos(theta), -sin(theta), sin(theta), cos(theta));
+  local_uv = mul(rot, local_uv);
+  // Apply randomized offset, staying within bounds.
+  // The scaled-and-rotated footprint is bounded by [-Input_Scale / 2, Input_Scale / 2],
+  // so we can offset by [(1 - Input_Scale) / 2].
+  float2 random_offset = (tile_rand3.yz * 2.0 - 1.0) * (0.5 * (1.0 - input_scale));
+  local_uv += random_offset;
+  // Finally, remap onto [0, 1].
+  local_uv += 0.5;
+  pbr.albedo.xy = local_uv.xy;
+#endif  // _BURLEY_TILING
+}
+
 Pbr getPbr(v2f i) {
   Pbr pbr = (Pbr) 0;
 
@@ -227,6 +258,7 @@ Pbr getPbr(v2f i) {
   apply_marble(i.worldPos, pbr.albedo.xyz);
   apply_kintsugi(i.worldPos, pbr.albedo.xyz, pbr.smoothness, pbr.metallic);
   apply_letter_grid(i, pbr);
+  apply_burley_tiling(i, pbr);
 
   applyDecals(i, pbr, normal_tangent);