effector/src/effects/striproll.cpp

#include "effects/striproll.hpp"

#include <algorithm>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>

#include "core/parallel.hpp"

namespace effector {

const std::vector<ParamSpec>& StripRollEffect::params() const {
    static const std::vector<ParamSpec> specs = {
        ParamSpec::makeInt("roll_height", "Strip height", 24, 1, 512,
                           "Height in pixels of each strip."),
        ParamSpec::makeInt("roll_jitter", "Height jitter", 0, 0, 256,
                           "Random +/- variation added to the strip height (0 = uniform)."),
        ParamSpec::makeBool("roll_keep_order", "Cycle images in order", false,
                            "Take strips from the images in order instead of picking randomly."),
        ParamSpec::makeChoice("roll_axis", "Axis", "vertical", {"vertical", "horizontal"},
                              "vertical rolls the picture in each strip up or down through its "
                              "image; horizontal slides it sideways."),
        ParamSpec::makeChoice("roll_direction", "Direction", "alternate",
                              {"alternate", "same", "random"},
                              "alternate rolls every other strip the other way; same rolls them "
                              "all one way; random picks for each strip."),
        ParamSpec::makeInt("roll_speed", "Speed", 120, 0, 8192,
                           "Pixels per second the picture rolls, rounded so that each strip goes "
                           "round its image a whole number of times in the clip; 0 holds still."),
    };
    return specs;
}

namespace {

struct Settings {
    int stripHeight;
    int jitter;
    bool keepOrder;
    bool horizontal;
    std::string direction;
    int speed;

    explicit Settings(const ParamValues& values)
        : stripHeight(static_cast<int>(std::max(1L, paramInt(values, "roll_height", 24)))),
          jitter(static_cast<int>(std::max(0L, paramInt(values, "roll_jitter", 0)))),
          keepOrder(paramBool(values, "roll_keep_order", false)),
          horizontal(paramChoice(values, "roll_axis", "vertical") == "horizontal"),
          direction(paramChoice(values, "roll_direction", "alternate")),
          speed(static_cast<int>(std::max(0L, paramInt(values, "roll_speed", 120)))) {}
};

// One strip of the canvas: where it lies, the image it shows, where in that
// image its picture starts, and which way it rolls.
struct Strip {
    int dstY;
    int height;
    std::size_t sourceIndex;
    int sx;
    int sy;
    int way;  // +1 or -1
};

int wrap(long value, int span) { return static_cast<int>((value % span + span) % span); }

}  // namespace

Image StripRollEffect::compose(const std::vector<Image>& sources, int width, int height,
                               const ParamValues& values, const Moment& at) const {
    const Settings settings(values);

    // What stays put for the whole clip: the strips, drawn as Scanlines draws
    // them, and the way each one rolls.
    Rng steady = at.steady();
    std::vector<Strip> strips;
    strips.reserve(static_cast<std::size_t>(height / settings.stripHeight) + 8);
    for (int y = 0; y < height;) {
        Strip strip{};
        strip.dstY = y;
        strip.sourceIndex = settings.keepOrder ? strips.size() % sources.size()
                                               : steady.below(sources.size() - 1);
        const Image& src = sources[strip.sourceIndex];
        int h = settings.stripHeight;
        if (settings.jitter > 0) {
            h += static_cast<int>(steady.inRange(-settings.jitter, settings.jitter));
        }
        strip.height = std::max(1, std::min(h, height - y));
        strip.sy = static_cast<int>(steady.inRange(0, src.height() - 1));
        strip.sx = static_cast<int>(steady.inRange(0, src.width() - 1));
        if (settings.direction == "random") {
            strip.way = (steady.next() >> 63) != 0 ? 1 : -1;
        } else if (settings.direction == "alternate") {
            strip.way = strips.size() % 2 == 0 ? 1 : -1;
        } else {
            strip.way = 1;
        }
        strips.push_back(strip);
        y += strip.height;
    }

    // Where this frame is in time: how far round its image each strip has
    // rolled, a whole number of rounds in the clip, the nearest to the speed.
    std::vector<long> offsets(strips.size(), 0);
    if (settings.speed > 0) {
        for (std::size_t i = 0; i < strips.size(); ++i) {
            const Image& src = sources[strips[i].sourceIndex];
            const int span = settings.horizontal ? src.width() : src.height();
            const double rounds = std::max(1.0, std::round(settings.speed * at.length() / span));
            const double into = std::fmod(at.seconds() * rounds / at.length(), 1.0);
            offsets[i] = strips[i].way * std::lround(into * span);
        }
    }

    Image canvas(width, height);
    parallelFor(strips.size(), [&](std::size_t begin, std::size_t end) {
        for (std::size_t i = begin; i < end; ++i) {
            const Strip& strip = strips[i];
            const Image& src = sources[strip.sourceIndex];
            const long down = settings.horizontal ? 0 : offsets[i];
            const long across = settings.horizontal ? offsets[i] : 0;
            const int startX = wrap(strip.sx + across, src.width());
            for (int line = 0; line < strip.height; ++line) {
                const std::uint8_t* in = src.row(wrap(strip.sy + line + down, src.height()));
                std::uint8_t* out = canvas.row(strip.dstY + line);
                // Round the image's width as often as the canvas needs.
                int x = 0;
                int from = startX;
                while (x < width) {
                    const int run = std::min(width - x, src.width() - from);
                    std::memcpy(out + static_cast<std::size_t>(x) * 3,
                                in + static_cast<std::size_t>(from) * 3,
                                static_cast<std::size_t>(run) * 3);
                    x += run;
                    from = 0;
                }
            }
        }
    });
    return canvas;
}

}  // namespace effector