1 files changed, 87 insertions, 0 deletions
diff --git a/src/procgen.cpp b/src/procgen.cpp
new file mode 100644
index 0000000..09ccae5
--- /dev/null
+++ b/src/procgen.cpp
@@ -0,0 +1,87 @@
+#include "common.hpp"
+#include <cmath>
+
+namespace procgen {
+
+void prng_t::seed(uint32_t seed)
+{
+	state = seed;
+	next();
+	next();
+}
+
+uint32_t prng_t::next(void)
+{
+	// glibc's LCG parameters (with m = 2^32 - 1).
+	state *= 1103515245;
+	state += 12345;
+	return state;
+}
+
+float prng_t::next_float(void)
+{
+	return (float)next() / 4294967295.0f;
+}
+
+void prng_t::unit_vec(float out[2])
+{
+	float t;
+
+	t = next_float() * 2.0f * M_PI;
+	out[0] = cos(t);
+	out[1] = sin(t);
+}
+
+void perlin_noise_t::generate(prng_t *prng, size_t size_)
+{
+	if (table)
+		delete table;
+
+	size = size_;
+	table = new float[size * size][2];
+
+	for (size_t y = 0; y < size; y++)
+	for (size_t x = 0; x < size; x++)
+		prng->unit_vec(table[y * size + x]);
+}
+
+float perlin_noise_t::table_dot(size_t nx, size_t ny, float dx, float dy)
+{
+	return table[ny * size + nx][0] * dx + table[ny * size + nx][1] * dy;
+}
+
+static float smooth_step(float x)
+{
+	return 3 * x * x - 2 * x * x * x;
+}
+
+float perlin_noise_t::get(float x, float y, float scale)
+{
+	size_t nx, ny, nx1, ny1;
+	float s, t, a, b, c, d;
+
+	x /= scale;
+	y /= scale;
+
+	nx = mod<ssize_t>(floor(x), size);
+	ny = mod<ssize_t>(floor(y), size);
+	nx1 = (nx == size - 1 ? 0 : nx + 1);
+	ny1 = (ny == size - 1 ? 0 : ny + 1);
+
+	s = smooth_step(x - floor(x));
+	t = smooth_step(y - floor(y));
+
+	a = table_dot(nx,  ny,  -s,        -t);
+	b = table_dot(nx1, ny,  -s + 1.0f, -t);
+	c = table_dot(nx,  ny1, -s,        -t + 1.0f);
+	d = table_dot(nx1, ny1, -s + 1.0f, -t + 1.0f);
+
+	return bilerp(a, b, c, d, s, t);
+}
+
+perlin_noise_t::~perlin_noise_t()
+{
+	delete table;
+}
+
+} // namespace procgen