ring_canvas.h

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// ring_canvas.h - ring geometry and additive drawing on a float ring.
//
// Positions are in turns: 0 is the first LED, 1 wraps back to it. Widths
// are also in turns, so a lobe of width 0.05 covers 5% of the ring no
// matter how many LEDs there are.
//
// Everything accumulates in float and is quantised to CRGB exactly once, in
// MoodPainter. Scaling 8-bit values repeatedly is what produced the stair
// steps in the old overlay: a dim pixel at 3 -> 2 -> 1 -> 0 is a visible
// staircase, and a weight quantised to 1/255 steps between frames.
#pragma once
 
#include "FastLED.h"
#include "fl/stl/span.h"
#include "fl/stl/stdint.h"
 
namespace mood_ring {
 
inline float clampf(float v, float lo, float hi) {
    return v < lo ? lo : (v > hi ? hi : v);
}

struct RGBf {
    float r;
    float g;
    float b;
    // Explicit ctors: C++11 forbids brace-init of a struct that has
    // default member initializers.
    RGBf() : r(0.0f), g(0.0f), b(0.0f) {}
    RGBf(float r_, float g_, float b_) : r(r_), g(g_), b(b_) {}
};
 
RGBf toRGBf(CRGB c);
CRGB toCRGB(const RGBf &p);
inline RGBf rgbfWhite() { return RGBf{1.0f, 1.0f, 1.0f}; }

float smoothstepf(float e0, float e1, float x);

float wrapTurns(float t);

float ringOffset(float a, float b);

float ringDistance(float a, float b);

float falloff(float distance, float sigma);

class Xorshift {
  public:
    explicit Xorshift(fl::u32 seed = 0x9E3779B9u) : mState(seed ? seed : 1u) {}
    fl::u32 next();
    float unit();
 
  private:
    fl::u32 mState;
};

class RingCanvas {
  public:
    explicit RingCanvas(fl::span<RGBf> px) : mPx(px) {}
 
    int size() const { return static_cast<int>(mPx.size()); }
 
    void clear();

    void lobe(float pos, float sigma, const RGBf &color, float gain);

    void ring(float origin, float radius, float sigma, const RGBf &color,
              float gain);

    void fill(const RGBf &color, float gain);

    void pixel(int i, const RGBf &color, float gain);

    float posOf(int i) const;
 
  private:
    fl::span<RGBf> mPx;
};
 
} // namespace mood_ring