69 lines
1.8 KiB
C++
69 lines
1.8 KiB
C++
#include "noise_woryley.h"
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namespace fl {
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namespace {
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constexpr i32 Q15_ONE = 32768; // 1.0 in Q15
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// constexpr i32 Q15_HALF = Q15_ONE / 2;
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// Helper: multiply two Q15 numbers (result in Q15)
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// i32 q15_mul(i32 a, i32 b) {
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// return (i32)(((int64_t)a * b) >> 15);
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// }
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// Helper: absolute difference
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i32 q15_abs(i32 a) { return a < 0 ? -a : a; }
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// Pseudo-random hash based on grid coordinates
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u16 hash(i32 x, i32 y) {
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u32 n = (u32)(x * 374761393 + y * 668265263);
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n = (n ^ (n >> 13)) * 1274126177;
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return (u16)((n ^ (n >> 16)) & 0xFFFF);
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}
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// Get fractional feature point inside a grid cell
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void feature_point(i32 gx, i32 gy, i32 &fx, i32 &fy) {
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u16 h = hash(gx, gy);
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fx = (h & 0xFF) * 128; // scale to Q15 (0–32767)
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fy = ((h >> 8) & 0xFF) * 128;
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}
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} // namespace
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// Compute 2D Worley noise at (x, y) in Q15
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i32 worley_noise_2d_q15(i32 x, i32 y) {
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i32 cell_x = x >> 15;
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i32 cell_y = y >> 15;
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i32 min_dist = INT32_MAX;
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// Check surrounding 9 cells
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for (int dy = -1; dy <= 1; ++dy) {
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for (int dx = -1; dx <= 1; ++dx) {
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i32 gx = cell_x + dx;
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i32 gy = cell_y + dy;
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i32 fx, fy;
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feature_point(gx, gy, fx, fy);
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i32 feature_x = (gx << 15) + fx;
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i32 feature_y = (gy << 15) + fy;
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i32 dx_q15 = x - feature_x;
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i32 dy_q15 = y - feature_y;
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// Approximate distance using Manhattan (faster) or Euclidean
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// (costlier)
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i32 dist =
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q15_abs(dx_q15) + q15_abs(dy_q15); // Manhattan distance
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if (dist < min_dist)
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min_dist = dist;
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}
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}
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// Normalize: maximum possible distance is roughly 2*Q15_ONE
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return (min_dist << 15) / (2 * Q15_ONE);
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}
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} // namespace fl
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