Add grass shader

See prefab. Given a 10m square of grass, this repeats it in a 4x4 grid
and applies a sway animation to it using a height map.

1 files changed, 90 insertions, 0 deletions

diff --git a/Shaders/grass/motion.cginc b/Shaders/grass/motion.cginc
new file mode 100644
index 0000000..d6458e9
--- /dev/null
+++ b/Shaders/grass/motion.cginc
@@ -0,0 +1,90 @@
+#ifndef MOTION_
+#define MOTION_
+
+// xyz represent quaternion vector, w represents theta.
+typedef float4 Quaternion;
+
+// Math from here:
+//   https://en.wikipedia.org/wiki/Quaternions_and_spatial_rotation
+float3 qrot(in float3 v, in Quaternion q)
+{
+  float a = q.w;
+  float b = q.x;
+  float c = q.y;
+  float d = q.z;
+
+  float a2 = a*a;
+  float b2 = b*b;
+  float c2 = c*c;
+  float d2 = d*d;
+
+  float3x3 rot = float3x3(
+    (a2 + b2 - c2) - d2, 2*b*c - 2*a*d, 2*b*d + 2*a*c,
+    2*b*c + 2*a*d, (a2 - b2) + (c2 - d2), 2*c*d - 2*a*b,
+    2*b*d - 2*a*c, 2*c*d + 2*a*b, ((a2 - b2) - c2) + d2
+  );
+
+  return mul(rot, v);
+}
+
+Quaternion qinv(in Quaternion q)
+{
+  return Quaternion(q.xyz, -q.w);
+}
+
+// Multiply two quaternions.
+// Math from here: https://www.haroldserrano.com/blog/quaternions-in-computer-graphics
+Quaternion qmul(in Quaternion a, in Quaternion b)
+{
+	return Quaternion(a.w * b.xyz + b.w * a.xyz + cross(a.xyz, b.xyz), a.w * b.w - dot(a.xyz, b.xyz));
+}
+
+float4 affine3(in float3 m)
+{
+  return float4(m, 1.0);
+}
+
+float4x4 affine3x3(in float3x3 m)
+{
+  return float4x4(
+    m[0][0], m[0][1], m[0][2], 0,
+    m[1][0], m[1][1], m[1][2], 0,
+    m[2][0], m[2][1], m[2][2], 0,
+    0,       0,       0,       1
+  );
+}
+
+float4x4 eye()
+{
+  return float4x4(
+    1, 0, 0, 0,
+    0, 1, 0, 0,
+    0, 0, 1, 0,
+    0, 0, 0, 1
+  );
+}
+
+// Return affine translation matrix.
+float4x4 translate(in float dx, in float dy, in float dz)
+{
+  return float4x4(
+    1, 0, 0, dx,
+    0, 1, 0, dy,
+    0, 0, 1, dz,
+    0, 0, 0, 1
+  );
+}
+
+// Return affine scaling matrix.
+float4x4 scale(in float sx, in float sy, in float sz)
+{
+  return float4x4(
+    sx, 0,  0,  0,
+    0,  sy, 0,  0,
+    0,  0,  sz, 0,
+    0,  0,  0,  1
+  );
+}
+
+#endif // MOTION_
+