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// This file is part of the 64k demo project.
// It implements the "Spectral Brush" primitive for procedural audio generation.
// Spectral brushes trace Bezier curves through spectrograms with vertical profiles.
#pragma once
#include <cstdint>
// Profile types for vertical distribution around central Bezier curve
enum ProfileType {
PROFILE_GAUSSIAN = 0, // Smooth harmonic falloff
PROFILE_DECAYING_SINUSOID = 1, // Resonant/metallic texture
PROFILE_NOISE = 2 // Random texture/grit
};
// Evaluate linear Bezier interpolation at given frame
// control_frames: Array of frame positions for control points
// control_values: Array of values at control points (freq_hz or amplitude)
// n_points: Number of control points
// frame: Frame number to evaluate at
// Returns: Interpolated value at frame (linearly interpolated between control points)
float evaluate_bezier_linear(const float* control_frames,
const float* control_values,
int n_points,
float frame);
// Draw a spectral brush stroke onto a spectrogram
// Traces a Bezier curve through time-frequency space with a vertical profile
// spectrogram: Output buffer (dct_size × num_frames), modified in-place
// dct_size: Number of frequency bins (e.g., 512)
// num_frames: Number of time frames
// control_frames: Frame positions of Bezier control points
// control_freqs_hz: Frequency values (Hz) at control points
// control_amps: Amplitude values at control points (0.0-1.0 typical)
// n_control_points: Number of control points (minimum 2 for a curve)
// profile_type: Type of vertical profile to apply
// profile_param1: First parameter (sigma for Gaussian, decay for sinusoid, amplitude for noise)
// profile_param2: Second parameter (unused for Gaussian, frequency for sinusoid, seed for noise)
void draw_bezier_curve(float* spectrogram,
int dct_size,
int num_frames,
const float* control_frames,
const float* control_freqs_hz,
const float* control_amps,
int n_control_points,
ProfileType profile_type,
float profile_param1,
float profile_param2 = 0.0f);
// Additive variant of draw_bezier_curve (adds to existing spectrogram content)
// Use for compositing multiple profiles (e.g., Gaussian + Noise)
// Parameters same as draw_bezier_curve()
void draw_bezier_curve_add(float* spectrogram,
int dct_size,
int num_frames,
const float* control_frames,
const float* control_freqs_hz,
const float* control_amps,
int n_control_points,
ProfileType profile_type,
float profile_param1,
float profile_param2 = 0.0f);
// Evaluate vertical profile at given distance from central curve
// type: Profile type (Gaussian, Decaying Sinusoid, Noise)
// distance: Distance in frequency bins from curve center
// param1: First profile parameter
// param2: Second profile parameter
// Returns: Profile amplitude at given distance (0.0-1.0 range typically)
float evaluate_profile(ProfileType type,
float distance,
float param1,
float param2);
// Home-brew deterministic RNG for noise profile
// Simple linear congruential generator (LCG) for small code size
// seed: Input seed value
// Returns: Pseudo-random uint32_t value
uint32_t spectral_brush_rand(uint32_t seed);
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