perlin_s16x16.h

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#pragma once
 
// 2D Perlin noise implementation using s16x16 fixed-point arithmetic
// Extracted from animartrix_detail.hpp for testing and reuse
//
// LUT-accelerated 2D Perlin noise using s16x16 fixed-point.
// Internals use Q8.24 (24 fractional bits) for precision exceeding float.
// The fade LUT replaces the 6t^5-15t^4+10t^3 polynomial with table lookup.
// The z=0 specialization halves work vs full 3D noise.
 
#include "fl/math/fixed_point/s16x16.h"
#include "fl/stl/noexcept.h"
 
 
namespace fl {
 
struct perlin_s16x16 {
    static constexpr int HP_BITS = 24;
    static constexpr fl::i32 HP_ONE = static_cast<fl::i32>(1) << HP_BITS; // 16777216 = 1.0
 
    // Build 257-entry Perlin fade LUT in Q8.24 format.
    static void init_fade_lut(fl::i32 *table) FL_NO_EXCEPT;
 
    // 2D Perlin noise. Input s16x16, output s16x16 approx [-1, 1].
    // perm: 256-byte Perlin permutation table (indexed with & 255).
    static fl::s16x16 pnoise2d(fl::s16x16 fx, fl::s16x16 fy,
                                      const fl::i32 *fade_lut,
                                      const fl::u8 *perm) FL_NO_EXCEPT;
 
    // Raw i32 version: takes s16x16 raw values, returns s16x16 raw value.
    // Avoids from_raw/raw() round-trips when caller already has raw values.
    static fl::i32 pnoise2d_raw(fl::i32 fx_raw, fl::i32 fy_raw,
                                        const fl::i32 *fade_lut,
                                        const fl::u8 *perm) FL_NO_EXCEPT;
 
    static constexpr int FP_BITS = fl::s16x16::FRAC_BITS;
    static constexpr fl::i32 FP_ONE = static_cast<fl::i32>(1) << FP_BITS;
 
    // Decompose s16x16 raw value into integer floor and Q8.24 fractional part.
    static void floor_frac(fl::i32 fp16, int &ifloor,
                                                fl::i32 &frac24) FL_NO_EXCEPT;
 
    // LUT fade: 1 lookup + 1 lerp replaces 5 multiplies.
    static fl::i32 fade(fl::i32 t, const fl::i32 *table) FL_NO_EXCEPT;
 
    static fl::i32 lerp(fl::i32 t, fl::i32 a, fl::i32 b) FL_NO_EXCEPT;
 
    // z=0 gradient via branchless coefficient LUT.
    static fl::i32 grad(int hash, fl::i32 x, fl::i32 y) FL_NO_EXCEPT;
 
    // 3D Perlin noise. Input s16x16, output s16x16 approx [-1, 1].
    static fl::s16x16 pnoise3d(fl::s16x16 fx, fl::s16x16 fy, fl::s16x16 fz,
                                      const fl::i32 *fade_lut,
                                      const fl::u8 *perm) FL_NO_EXCEPT;
 
    // Raw i32 version of 3D Perlin noise.
    static fl::i32 pnoise3d_raw(fl::i32 fx_raw, fl::i32 fy_raw, fl::i32 fz_raw,
                                        const fl::i32 *fade_lut,
                                        const fl::u8 *perm) FL_NO_EXCEPT;
 
    // 3D gradient: 12-direction gradient matching float grad().
    static fl::i32 grad3d(int hash, fl::i32 x, fl::i32 y, fl::i32 z) FL_NO_EXCEPT;
};
 
}  // namespace fl