From bb0620f3aa466355ac2d76ae2c80f996685a31ad Mon Sep 17 00:00:00 2001
From: Kyle Isom <kyle@imap.cc>
Date: Sat, 16 Feb 2019 16:50:56 -0800
Subject: [PATCH] Add perlin noise implementation.

---
 misc/noise/Makefile |  8 ++++
 misc/noise/noise.cc | 93 +++++++++++++++++++++++++++++++++++++++++++++
 misc/noise/noise.h  | 16 ++++++++
 misc/noise/test.cc  | 15 ++++++++
 misc/noise/util.cc  | 20 ++++++++++
 misc/noise/util.h   | 12 ++++++
 6 files changed, 164 insertions(+)
 create mode 100644 misc/noise/Makefile
 create mode 100644 misc/noise/noise.cc
 create mode 100644 misc/noise/noise.h
 create mode 100644 misc/noise/test.cc
 create mode 100644 misc/noise/util.cc
 create mode 100644 misc/noise/util.h

diff --git a/misc/noise/Makefile b/misc/noise/Makefile
new file mode 100644
index 0000000..cdf21de
--- /dev/null
+++ b/misc/noise/Makefile
@@ -0,0 +1,8 @@
+SOURCES :=	noise.cc test.cc util.cc
+
+noise: $(SOURCES)
+	g++ -o $@ $(SOURCES)
+
+.PHONY: clean
+clean:
+	rm -f noise
diff --git a/misc/noise/noise.cc b/misc/noise/noise.cc
new file mode 100644
index 0000000..2505b04
--- /dev/null
+++ b/misc/noise/noise.cc
@@ -0,0 +1,93 @@
+#include <math.h>
+#include <stdint.h>
+
+#include "noise.h"
+#include "util.h"
+
+
+// C++ conversion of Ken Perlin's improved noise generator from
+// https://mrl.nyu.edu/~perlin/noise/
+
+
+static double
+grad(int hash, double x, double y, double z)
+{
+	int	h = hash & 15;
+	double	u = h < 8 ? x : y;
+	double	v = h < 4 ? y : h == 12 || h == 14 ? x : z;
+
+	return	((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
+}
+
+
+static double
+lerp(double t, double a, double b)
+{
+	return a + t * (b - a);
+}
+
+
+static double
+fade(double t)
+{
+	return t * t * t * (t * (t * 6 - 15) + 10);
+}
+
+
+NoiseGenerator::NoiseGenerator()
+{
+	// Generate a random permutation of 256 values from 0 to 255
+	// inclusive. This is generated by setting each value in the
+	// array to its index value, then putting it through a
+	// Fisher-Yates shuffle.
+	for (int i = 0; i < 256; i++) {
+		perm[i] = i;
+	}
+
+	for (int i = 255; i > 0; i--) {
+		int j = random() % (i + 1);
+		swap_u8(perm[i], perm[j]);
+	}
+
+	for (int i = 0; i < 256; i++) {
+		p[i] = perm[i];
+		p[i+256] = perm[i];
+	}
+}
+
+
+double
+NoiseGenerator::sample(double x, double y, double z)
+{
+	uint16_t	ux = (uint16_t)floor(x) & 255;
+	uint16_t	uy = (uint16_t)floor(y) & 255;
+	uint16_t	uz = (uint16_t)floor(z) & 255;
+	double		u, v, w;
+	uint16_t	a, aa, ab, b, ba, bb;
+
+	x -= floor(x);
+	u = fade(x);
+
+	y -= floor(y);
+	v = fade(y);
+
+	z -= floor(z);
+	w = fade(z);
+
+	a = p[ux] + uy;
+	aa = p[a] + uz;
+	ab = p[a + 1] + uz;
+
+	b = p[ux + 1] + uy;
+	ba = p[b] + uz;
+	bb = p[b + 1] + uz;
+
+	return lerp(w, lerp(v, lerp(u, grad(p[aa], x, y, z),
+					grad(p[ba], x-1, y, z)),
+				lerp(u, grad(p[ab], x, y-1, z),
+					grad(p[bb], x-1, y-1, z))),
+		       lerp(v, lerp(u, grad(p[aa+1], x, y, z-1),
+				       grad(p[ba+1], x-1, y, z-1)),
+			       lerp(u, grad(p[ab+1], x, y-1, z-1),
+				       grad(p[bb+1], x-1, y-1, z-1))));
+}
diff --git a/misc/noise/noise.h b/misc/noise/noise.h
new file mode 100644
index 0000000..f1cb248
--- /dev/null
+++ b/misc/noise/noise.h
@@ -0,0 +1,16 @@
+#ifndef __NOISE_H
+#define __NOISE_H
+
+
+class NoiseGenerator {
+public:
+	NoiseGenerator();
+	double sample(double x, double y, double z);
+	void randomise();
+private:
+	uint8_t	p[512];
+	uint8_t	perm[256];
+};
+
+
+#endif // __NOISE_H
diff --git a/misc/noise/test.cc b/misc/noise/test.cc
new file mode 100644
index 0000000..f83e4b9
--- /dev/null
+++ b/misc/noise/test.cc
@@ -0,0 +1,15 @@
+#include <iostream>
+#include "noise.h"
+
+using namespace std;
+
+
+int
+main(void)
+{
+	NoiseGenerator	noise;
+
+	for (double t = 0; t < 5; t += 0.01) {
+		cout << t << "\t" << noise.sample(t, t, t) << endl;
+	}
+}
diff --git a/misc/noise/util.cc b/misc/noise/util.cc
new file mode 100644
index 0000000..1cf5461
--- /dev/null
+++ b/misc/noise/util.cc
@@ -0,0 +1,20 @@
+#include "util.h"
+#include <stdint.h>
+
+
+void
+swap_u8(uint8_t &a, uint8_t &b)
+{
+	a ^= b;
+	b ^= a;
+	a ^= b;
+}
+
+
+void
+swap_ul(unsigned long &a, unsigned long &b)
+{
+	a ^= b;
+	b ^= a;
+	a ^= b;
+}
diff --git a/misc/noise/util.h b/misc/noise/util.h
new file mode 100644
index 0000000..e134f99
--- /dev/null
+++ b/misc/noise/util.h
@@ -0,0 +1,12 @@
+#ifndef __UTIL_H
+#define __UTIL_H
+
+
+#include <stdint.h>
+
+
+void	swap_u8(uint8_t &a, uint8_t &b);
+void	swap_ul(unsigned long &a, unsigned long &b);
+
+
+#endif // __UTIL_H