effector/src/effects/tracking.cpp

#include "effects/tracking.hpp"

#include <algorithm>
#include <array>
#include <cmath>
#include <numbers>
#include <vector>

#include "core/parallel.hpp"

namespace effector {

const std::vector<ParamSpec>& TrackingEffect::params() const {
    static const std::vector<ParamSpec> specs = {
        ParamSpec::makeInt("tracking_wobble", "Wobble", 4, 0, 256,
                           "How far in pixels the colour planes sway apart and back."),
        ParamSpec::makeDouble("tracking_wobble_speed", "Wobble speed", 0.5, 0.0, 10.0,
                              "Sways per second, rounded so that the clip loops without a jump.",
                              0.1, 1),
        ParamSpec::makeInt("tracking_jitter", "Jitter", 2, 0, 256,
                           "Furthest in pixels a band shakes, anew on every frame."),
        ParamSpec::makeInt("tracking_band_height", "Band height", 24, 1, 2048,
                           "Thickness in pixels of the bands that shake on their own."),
        ParamSpec::makeInt("tracking_bar", "Tracking bar", 16, 0, 512,
                           "How far in pixels the rolling bar tears the rows sideways and the "
                           "colour planes apart; 0 for none."),
        ParamSpec::makeDouble("tracking_bar_time", "Bar pass", 4.0, 0.5, 60.0,
                              "Seconds the tracking bar takes from top to bottom, rounded so "
                              "that the clip loops without a jump.",
                              0.5, 1),
    };
    return specs;
}

namespace {

struct Settings {
    int wobble;
    double wobbleSpeed;
    int jitter;
    int band;
    int bar;
    double barTime;

    explicit Settings(const ParamValues& values)
        : wobble(static_cast<int>(std::max(0L, paramInt(values, "tracking_wobble", 4)))),
          wobbleSpeed(std::max(0.0, paramDouble(values, "tracking_wobble_speed", 0.5))),
          jitter(static_cast<int>(std::max(0L, paramInt(values, "tracking_jitter", 2)))),
          band(static_cast<int>(std::max(1L, paramInt(values, "tracking_band_height", 24)))),
          bar(static_cast<int>(std::max(0L, paramInt(values, "tracking_bar", 16)))),
          barTime(std::max(0.5, paramDouble(values, "tracking_bar_time", 4.0))) {}
};

double unit(Rng& rng) { return static_cast<double>(rng.next() >> 11) * 0x1.0p-53; }

// How far each of the red, green and blue planes is moved on one row.
struct RowShift {
    std::array<int, 3> dx{};
    std::array<int, 3> dy{};
};

}  // namespace

Image TrackingEffect::animate(Image input, const ParamValues& values, const Moment& at) const {
    const Settings settings(values);
    const int width = input.width();
    const int height = input.height();
    constexpr double tau = 2.0 * std::numbers::pi;

    // What stays put for the whole clip: where each plane's sway starts, and
    // the direction it sways in.
    Rng steady = at.steady();
    std::array<double, 3> phase{};
    std::array<double, 3> angle{};
    for (std::size_t c = 0; c < 3; ++c) {
        phase[c] = unit(steady) * tau;
        angle[c] = unit(steady) * tau;
    }

    // Where this frame is in time: the sway of each plane, and the bar -- an
    // eighth of the picture, soft at both edges, entering above the top and
    // leaving below the bottom.
    std::array<double, 3> swayX{};
    std::array<double, 3> swayY{};
    if (settings.wobble > 0 && settings.wobbleSpeed > 0.0) {
        const double turn = at.cycle(settings.wobbleSpeed) * tau;
        for (std::size_t c = 0; c < 3; ++c) {
            const double sway = settings.wobble * std::sin(turn + phase[c]);
            swayX[c] = sway * std::cos(angle[c]);
            swayY[c] = sway * std::sin(angle[c]);
        }
    }
    const double barHeight = std::max(8.0, height / 8.0);
    const double barTop = -barHeight + at.cycle(1.0 / settings.barTime) * (height + barHeight);

    // What changes on every frame: each band's shake, mostly sideways, as a
    // picture losing its horizontal hold. All of it drawn, band by band,
    // before a pixel is touched.
    Rng fresh = at.fresh();
    std::vector<RowShift> rows(static_cast<std::size_t>(height));
    std::vector<int> tear(static_cast<std::size_t>(height), 0);
    for (int top = 0; top < height; top += settings.band) {
        std::array<double, 3> jitterX{};
        std::array<double, 3> jitterY{};
        if (settings.jitter > 0) {
            for (std::size_t c = 0; c < 3; ++c) {
                jitterX[c] = static_cast<double>(fresh.inRange(-settings.jitter, settings.jitter));
                jitterY[c] = static_cast<double>(fresh.inRange(-settings.jitter, settings.jitter)) / 3.0;
            }
        }
        const int end = std::min(height, top + settings.band);
        for (int y = top; y < end; ++y) {
            // The bar pulls red one way and blue the other, and drags the
            // whole row half as far.
            double pull = 0.0;
            if (settings.bar > 0 && y >= barTop && y < barTop + barHeight) {
                pull = settings.bar * std::sin(std::numbers::pi * (y - barTop) / barHeight);
            }
            constexpr std::array<double, 3> apart = {1.0, 0.0, -1.0};
            auto& row = rows[static_cast<std::size_t>(y)];
            for (std::size_t c = 0; c < 3; ++c) {
                row.dx[c] = static_cast<int>(std::lround(swayX[c] + jitterX[c] + pull * apart[c]));
                row.dy[c] = static_cast<int>(std::lround(swayY[c] + jitterY[c]));
            }
            tear[static_cast<std::size_t>(y)] = static_cast<int>(std::lround(pull / 2.0));
        }
    }

    Image frame(width, height);
    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
        for (std::size_t y = begin; y < end; ++y) {
            std::uint8_t* out = frame.row(static_cast<int>(y));
            for (std::size_t c = 0; c < 3; ++c) {
                const int dx = rows[y].dx[c] + tear[y];
                const int sy = std::clamp(static_cast<int>(y) - rows[y].dy[c], 0, height - 1);
                const std::uint8_t* in = input.row(sy);
                for (int x = 0; x < width; ++x) {
                    const int sx = std::clamp(x - dx, 0, width - 1);
                    out[static_cast<std::size_t>(x) * 3 + c] = in[static_cast<std::size_t>(sx) * 3 + c];
                }
            }
        }
    });
    return frame;
}

}  // namespace effector