begin work on corrected hex domain repetition

1 files changed, 67 insertions, 30 deletions

diff --git a/ray_marching.cginc b/ray_marching.cginc
index fe48f2c..bf01eb4 100644
--- a/ray_marching.cginc
+++ b/ray_marching.cginc
@@ -45,6 +45,72 @@ float map(float3 p) {
   return d;
 }
 
+#if defined(_RAY_MARCHING_HEX_GRID)
+void hex_nearest_neighbors(float3 cubeId, float3 neighborDir,
+    out float3 id0, out float3 id1, out float3 id2) {
+  // Standard cube-coordinate neighbour offsets (sum equals zero).
+  const float3 axis0 = float3( 1.0f,  0.0f, -1.0f);
+  const float3 axis1 = float3( 0.0f,  1.0f, -1.0f);
+  const float3 axis2 = float3( 1.0f, -1.0f,  0.0f);
+
+  const float3 cube0 = cubeId + axis0 * neighborDir.xxx;
+  const float3 cube1 = cubeId + axis1 * neighborDir.yyy;
+  const float3 cube2 = cubeId + axis2 * neighborDir.zzz;
+
+  // Convert back to our "x = y + z" coordinate representation.
+  id0 = float3(cube0.x + cube0.y, cube0.x, cube0.y);
+  id1 = float3(cube1.x + cube1.y, cube1.x, cube1.y);
+  id2 = float3(cube2.x + cube2.y, cube2.x, cube2.y);
+}
+
+float domain_repeat_hex_grid(inout float3 p) {
+  float d;
+
+  const float3 count = _Ray_Marching_Hex_Grid_Count * 0.5f;
+  const float3 period = 1.0f / count;
+  const float3 hex = cart_to_hex(p.xy);
+  // Cell ID.
+  const float3 id = round_hex(hex / period);
+  // Coordinates within the current cell.
+  const float3 local = hex - period * id;
+
+  const float3 cubeId = float3(id.y, id.z, -id.y - id.z);
+  const float3 cubeLocal = float3(local.y, local.z, -local.y - local.z);
+  float3 neighborDir = sign(cubeLocal);
+  neighborDir += (1.0f.xxx - abs(neighborDir));
+
+#if defined(_RAY_MARCHING_CORRECT_REPETITION)
+  float3 ids[4];
+  ids[0] = id;
+  hex_nearest_neighbors(cubeId, neighborDir, ids[1], ids[2], ids[3]);
+  const uint kNumCells = 4u;
+#else
+  float3 ids[1];
+  ids[0] = id;
+  const uint kNumCells = 1u;
+#endif
+
+  d = 1e9;
+  float3 bestPos = p;
+  for (uint ii = 0; ii < kNumCells; ++ii) {
+    const float3 rid = ids[ii];
+    if (any(abs(rid) > count * 0.5f)) continue;
+
+    float3 candidate = p;
+    candidate.xy = hex_to_cart(hex - period * rid);
+
+    const float d_cur = map(candidate);
+    if (d_cur < d) {
+      d = d_cur;
+      bestPos = candidate;
+    }
+  }
+
+  p = bestPos;
+  return d;
+}
+#endif  // _RAY_MARCHING_HEX_GRID
+
 float domain_repeat(inout float3 p) {
   float d;
 #if defined(_RAY_MARCHING_CART_GRID)
@@ -62,36 +128,7 @@ float domain_repeat(inout float3 p) {
     d = map(p);
   }
 #elif defined(_RAY_MARCHING_HEX_GRID)
-  {
-    const float3 count = _Ray_Marching_Hex_Grid_Count * 0.5f;
-    const float3 period = 1.0f / count;
-    const float3 hex = cart_to_hex(p.xy);
-
-    float half_period = period * 0.5;
-    float3 which = floor((hex + half_period) / period);
-
-    // The original code here was this:
-    //   p_hex = glsl_mod(p_hex + half_period, period) - half_period;
-    //
-    // But you can simplify it. Given the definition of glsl_mod:
-    //   #define glsl_mod(x,y) (((x)-(y)*floor((x)/(y))))
-    //
-    // You can plug in terms:
-    //  (p_hex + half_period) - (period) * floor((p_hex + half_period) / period)
-    //  = p_hex + half_period - period * floor(p_hex/period + 0.5)
-    //
-    // For all x,
-    //  round(x) = floor(x + 0.5)
-    //
-    // Continuing to simplify:
-    //  (p_hex + half_period - period * round(p_hex/period)) - half_period
-    //  = p_hex - period * round(p_hex / period)
-    const float3 hex_inst = hex - period * round_hex(hex / period);
-
-    p.xy = (any(abs(which) > count/2) ? 1e9 : hex_to_cart(hex_inst));
-
-    d = map(p);
-  }
+  d = domain_repeat_hex_grid(p);
 #else
   d = map(p);
 #endif