some ray marching

1 files changed, 89 insertions, 0 deletions

diff --git a/ray_marching_maps.slang b/ray_marching_maps.slang
new file mode 100644
index 0000000..d98248b
--- /dev/null
+++ b/ray_marching_maps.slang
@@ -0,0 +1,89 @@
+#ifndef __RAY_MARCHING_MAPS_INC
+#define __RAY_MARCHING_MAPS_INC
+
+#include "math.cginc"
+#include "pema99.cginc"
+
+// Macros for transforming normal and tangent using autodiff.
+// r3r1 refers to "r3 to r1 transform", aka a mapping from a 3d real-valued
+// space to a 1d space. This is intended for use with a ray marcher.
+#define R3R1_DECLARE_BASIS_VECTORS(xyz) \
+  DifferentialPair<float3> dp_x = diffPair(xyz, float3(1, 0, 0)); \
+  DifferentialPair<float3> dp_y = diffPair(xyz, float3(0, 1, 0)); \
+  DifferentialPair<float3> dp_z = diffPair(xyz, float3(0, 0, 1))
+
+#define R3R1_AUTODIFF_BASIS_VECTORS(fun, ...) \
+  DifferentialPair<float> dp_x_out = fwd_diff(fun)(dp_x, ##__VA_ARGS__); \
+  DifferentialPair<float> dp_y_out = fwd_diff(fun)(dp_y, ##__VA_ARGS__); \
+  DifferentialPair<float> dp_z_out = fwd_diff(fun)(dp_z, ##__VA_ARGS__)
+
+#define R3R1_DEFORM_NORMAL_AND_TANGENT(normal, tangent) \
+  { \
+    float3 gradient = float3(dp_x_out.d, dp_y_out.d, dp_z_out.d); \
+    normal = normalize(gradient); \
+    float3 helper = abs(normal.z) < 0.999 ? float3(0, 0, 1) : float3(0, 1, 0); \
+    tangent = normalize(cross(helper, normal)); \
+  }
+
+// Syntactic sugar - wraps the previous three macros.
+#define R3R1_RAY_MARCH_NORMALS(xyz, normal, tangent, fun, ...)  \
+  R3R1_DECLARE_BASIS_VECTORS(xyz);                              \
+  R3R1_AUTODIFF_BASIS_VECTORS(fun, ##__VA_ARGS__);              \
+  R3R1_DEFORM_NORMAL_AND_TANGENT(normal, tangent)
+
+float distance_from_hex_comb(
+    float3 p,
+    float3 period,
+    float count) {
+  float3 p_hex = cart_to_hex(p.yz);
+
+  float3 half_period = period * 0.5;
+  float3 which = abs(floor((p_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)
+  p_hex = p_hex - period * round(p_hex / period);
+
+  p.yz = hex_to_cart(p_hex);
+
+  float hex_d = length(p) - 0.15;
+  return hex_d;
+}
+
+// Just trace a sphere of radius 0.1 for now.
+[Differentiable]
+public float map(float3 p) {
+  float period = 0.2f;
+  float3 count = float3(6,5,1);
+  float half_period = period * 0.5f;
+  float3 which = abs(floor((p + half_period) / period));
+  if (any(abs(which) >= count)) {
+    p = 1e6;
+  } else {
+    p = glsl_mod(p + half_period, period) - half_period;
+  }
+  p.z += 0.1f;
+  return length(p) - 0.1f;
+}
+
+public void map_normal(inout float3 xyz, inout float3 normal,
+    inout float3 tangent) {
+  R3R1_RAY_MARCH_NORMALS(xyz, normal, tangent, map);
+}
+
+#endif  // __RAY_MARCHING_MAPS_INC
+