domain repetition now offsets correctly for even counts

1 files changed, 23 insertions, 6 deletions

diff --git a/ray_marching.cginc b/ray_marching.cginc
index daba713..7b95972 100644
--- a/ray_marching.cginc
+++ b/ray_marching.cginc
@@ -109,15 +109,32 @@ float domain_repeat(inout float3 p) {
   float d;
 #if defined(_RAY_MARCHING_CART_GRID)
   {
-    const float3 count = float3(_Ray_Marching_Cart_Grid_Count_X, _Ray_Marching_Cart_Grid_Count_Y, _Ray_Marching_Cart_Grid_Count_Z);
-    const float3 span = float3(_Ray_Marching_Cart_Grid_Span_X, _Ray_Marching_Cart_Grid_Span_Y, _Ray_Marching_Cart_Grid_Span_Z);
+    const float3 count = float3(
+        _Ray_Marching_Cart_Grid_Count_X,
+        _Ray_Marching_Cart_Grid_Count_Y,
+        _Ray_Marching_Cart_Grid_Count_Z);
+    const float3 span = float3(
+        _Ray_Marching_Cart_Grid_Span_X,
+        _Ray_Marching_Cart_Grid_Span_Y,
+        _Ray_Marching_Cart_Grid_Span_Z) * 2.0f;
     const float3 period = span / count;
-    float3 half_period = period*0.5f;
-    float3 which = floor((p + half_period) / period);
-    if (any(abs(which) > count/2)) {
+    const float3 half_period = period * 0.5f;
+    // count = 2
+    // which = 0 -> ok
+    // which = 1 -> ok
+    // which = -1 -> not ok
+    const float3 max_allowed = count / 2;
+    const float3 min_allowed = -count / 2 + 0.5;
+    const float3 offset = float3(
+        count.x % 2 == 0 ? half_period.x : 0,
+        count.y % 2 == 0 ? half_period.y : 0,
+        count.z % 2 == 0 ? half_period.z : 0);
+    const float3 shifted = p + offset;
+    float3 which = floor((shifted + half_period) / period);
+    if (any(which > max_allowed || which < min_allowed)) {
       p = 1e6;
     } else {
-      p = glsl_mod(p + half_period, period) - half_period;
+      p = glsl_mod(shifted + half_period, period) - half_period;
     }
     d = map(p);
   }