esp32-sk6812/src/Animation/SnowfallAnimation.cpp

#include <algorithm>

#include "Animation/SnowfallAnimation.h"

/********* SnowFlake *********/

SnowfallAnimation::SnowFlake::SnowFlake(Fader *fader, int32_t phase, int32_t vertSpeed, int32_t baseStrip)
    : m_fader(fader),
      m_phase(phase),
      m_phaseIncPerFrame(fasttrigon::LUT_SIZE/60),
      m_vertSpeed(vertSpeed),
      m_radius(282), // 1.1 * 256
      m_radiusSq(310),
      m_basePosStrip(baseStrip*256),
      m_posStrip(baseStrip*256),
      m_posLED(fader->modules_per_strip()*256 + m_radius*2)
{}

void SnowfallAnimation::SnowFlake::move(void)
{
    m_phase += m_phaseIncPerFrame;
    if(m_phase > fasttrigon::LUT_SIZE) {
        m_phase -= fasttrigon::LUT_SIZE;
    }

    m_posStrip = m_basePosStrip + FASTTRIGON_8BIT(2*fasttrigon::fastsin(m_phase));
    m_posLED -= m_vertSpeed;
}

bool SnowfallAnimation::SnowFlake::has_fallen(void) const
{
    return m_posLED < -(2*m_radius);
}

int32_t SnowfallAnimation::SnowFlake::cur_strip(void) const
{
    int32_t strip = m_posStrip / 256;

    uint32_t nstrip = m_fader->strips();

    while(strip < 0) {
        strip += nstrip;
    }
    while(strip >= nstrip) {
        strip -= nstrip;
    }

    return strip;
}

void SnowfallAnimation::SnowFlake::render(void) const
{
    int32_t min_strip = (m_posStrip - m_radius) / 256;
    int32_t max_strip = (m_posStrip + m_radius + 256) / 256;
    int32_t min_led = (m_posLED - m_radius) / 256;
    int32_t max_led = (m_posLED + m_radius + 256) / 256;

    for(int32_t strip = min_strip; strip <= max_strip; strip++) {
        int32_t finestrip = strip * 256;

        for(int32_t led = min_led; led <= max_led; led++) {
            if(led < 0 || led >= m_fader->modules_per_strip()) {
                continue;
            }

            int32_t fineled = led * 256;

            int32_t diststrip = finestrip - m_posStrip;
            int32_t distled = fineled - m_posLED;

            int32_t distsq = (diststrip*diststrip + distled*distled) / 256;

            // brightness target range: 0..255
            int32_t brightness = 256 - 256 * distsq / m_radiusSq;

            if(brightness < 0) {
                continue; // this pixel is too far away -> no effect
            }

            int32_t normstrip = strip;
            int32_t nstrips = m_fader->strips();
            while(normstrip < 0) {
                normstrip += nstrips;
            }
            while(normstrip >= nstrips) {
                normstrip -= nstrips;
            }

            m_fader->add_color(normstrip, led,
                Fader::Color{
                    0,
                    0,
                    static_cast<int16_t>(32*brightness/256),
                    static_cast<int16_t>(48*brightness/256)
                });
        }
    }
}

/********* SnowfallAnimation *********/

SnowfallAnimation::SnowfallAnimation(Fader *fader)
    : Animation(fader),
      m_snowLevel(fader->strips(), 0)
{
    reset();
}

void SnowfallAnimation::loop(uint64_t frame)
{
    std::size_t nled = m_fader->modules_per_strip();
    std::size_t nstrip = m_fader->strips();

    // update snow level on ground from fallen snow flakes
    for(auto &flake: m_snowFlakes) {
        if(flake.has_fallen()) {
            m_snowLevel[flake.cur_strip()] += 65536/5;
        }
    }

    // remove fallen snow flakes
    m_snowFlakes.remove_if(
        [](const SnowFlake &flake) { return flake.has_fallen(); });

    if(!m_stopping) {
        // spawn new snowflakes
        std::uniform_int_distribution<uint32_t> spawnRNG(0, 999);
        if(spawnRNG(m_gen) < 50) {
            std::uniform_int_distribution<int32_t> phaseRNG(0, fasttrigon::LUT_SIZE-1);
            std::uniform_int_distribution<int32_t> vertSpeedRNG(13, 38); // 0.05..0.15
            std::uniform_int_distribution<int32_t> baseStripRNG(0, nstrip-1);

            m_snowFlakes.emplace_back(SnowFlake{
                m_fader,
                phaseRNG(m_gen),
                vertSpeedRNG(m_gen),
                baseStripRNG(m_gen)
                });
        }
    }

    // clear the frame buffer
    m_fader->set_color(Fader::Color{0, 0, 0, 0});

    // move snow flakes and render
    for(auto &flake: m_snowFlakes) {
        flake.move();
        flake.render();
    }

    // render snow on the ground and melt it
    for(size_t strip = 0; strip < nstrip; strip++) {
        size_t led = 0;
        size_t level = m_snowLevel[strip];
        size_t brightness;

        while(level > 0 && led < nled) {
            if(level >= 65536) {
                brightness = 65536;
            } else {
                brightness = level;
            }

            m_fader->add_color(strip, led,
                Fader::Color{
                    0,
                    static_cast<int16_t>(8 * brightness / 65535),
                    static_cast<int16_t>(32 * brightness / 65535),
                    static_cast<int16_t>(12 * brightness / 65535)
                });

            level -= brightness;
            led++;
        }

        // "melt" the snow
        m_snowLevel[strip] = m_snowLevel[strip] * 999 / 1000;
    }

    m_fader->update();

    if(m_stopping && m_snowFlakes.empty()) {
        m_running = false;
    }
}

void SnowfallAnimation::reset(void)
{
    m_stopping = false;
    m_running = true;
}