add hex grid tiling

1 files changed, 61 insertions, 9 deletions

diff --git a/ray_marching.cginc b/ray_marching.cginc
index b13bee0..57a3dff 100644
--- a/ray_marching.cginc
+++ b/ray_marching.cginc
@@ -42,12 +42,63 @@ void ray_march(inout v2f i) {
   const uint kMaxIter = _Ray_Marching_Max_Iter;
   float d_cur;
   float d_acc = 0;
+  float3 hit_pos;
   for (uint ii = 0; ii < kMaxIter; ++ii) {
     float3 p = ro + rd * d_acc;
     d_cur = 1e9;
-#if defined(_RAY_MARCHING_BALL_GRID)
-    float3 count = float3(_Ray_Marching_Ball_Grid_Count_X, _Ray_Marching_Ball_Grid_Count_Y, _Ray_Marching_Ball_Grid_Count_Z);
-    d_cur = min(d_cur, map_ball_grid(p, count));
+
+    // Coordinate system transformations.
+#if defined(_RAY_MARCHING_CART_GRID)
+    {
+      float3 count = float3(_Ray_Marching_Cart_Grid_Count_X, _Ray_Marching_Cart_Grid_Count_Y, _Ray_Marching_Cart_Grid_Count_Z);
+      float3 period = 1.0f / count;
+      period *= 2;
+      float3 half_period = period*0.5f;
+      float3 which = floor((p + half_period) / period);
+      if (any(abs(which) > count/2)) {
+        p = 1e6;
+      } else {
+        p = glsl_mod(p + half_period, period) - half_period;
+      }
+    }
+#endif
+#if 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));
+    }
+#endif
+
+    // Sdfs.
+#if defined(_RAY_MARCHING_BALL)
+    {
+      float r = _Ray_Marching_Ball_Radius;
+      d_cur = min(d_cur, map_ball(p, _Ray_Marching_Ball_Radius));
+    }
 #endif
 
 #if defined(_RAY_MARCHING_OVERSTEP)
@@ -56,6 +107,7 @@ void ray_march(inout v2f i) {
 
     d_acc += d_cur;
     if (abs(d_cur) < kMinDist) {
+      hit_pos = p;
       break;
     }
     if (d_acc > kMaxDist) {
@@ -67,13 +119,14 @@ void ray_march(inout v2f i) {
     discard;
   }
 
-  // TODO clip / hit detection
-  float3 lclPos = ro + rd * d_acc;
+  float3 lclPos = hit_pos;
   float3 lclNorm;
   float3 lclTan;
-#if defined(_RAY_MARCHING_BALL_GRID)
-  float3 count = float3(_Ray_Marching_Ball_Grid_Count_X, _Ray_Marching_Ball_Grid_Count_Y, _Ray_Marching_Ball_Grid_Count_Z);
-  map_ball_grid_normal(count, lclPos, lclNorm, lclTan);
+#if defined(_RAY_MARCHING_BALL)
+  {
+    float r = _Ray_Marching_Ball_Radius;
+    map_ball_normal(r, lclPos, lclNorm, lclTan);
+  }
 #endif
 
   i.objPos = lclPos;
@@ -83,4 +136,3 @@ void ray_march(inout v2f i) {
 }
 
 #endif  // __RAY_MARCHING_INC
-