portapack-mayhem/firmware/application/touch.hpp

/*
 * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
 *
 * This file is part of PortaPack.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifndef __TOUCH_H__
#define __TOUCH_H__

#include <cstdint>
#include <cstddef>

#include <algorithm>
#include <array>
#include <functional>

#include "debounce.hpp"
#include "ui.hpp"

namespace touch {

using sample_t = uint16_t;

constexpr sample_t sample_max = 1023;

// If you have a dead bottom-left corner try to increase the sensitivity,
// but look for flickering touch indicator in the Buttons test screen
// in which case decrease sensitivity to avoid killing backlight timeout
constexpr sample_t touch_sensitivity = 32;
constexpr sample_t touch_threshold = sample_max / touch_sensitivity;

struct Samples {
    sample_t xp;
    sample_t xn;
    sample_t yp;
    sample_t yn;

    constexpr Samples()
        : Samples{0} {
    }

    constexpr Samples(
        uint32_t v)
        : xp{static_cast<sample_t>(v)},
          xn{static_cast<sample_t>(v)},
          yp{static_cast<sample_t>(v)},
          yn{static_cast<sample_t>(v)} {
    }

    constexpr Samples(
        uint32_t xp,
        uint32_t xn,
        uint32_t yp,
        uint32_t yn)
        : xp{static_cast<sample_t>(xp)},
          xn{static_cast<sample_t>(xn)},
          yp{static_cast<sample_t>(yp)},
          yn{static_cast<sample_t>(yn)} {
    }

    Samples& operator+=(const Samples& r) {
        xp += r.xp;
        xn += r.xn;
        yp += r.yp;
        yn += r.yn;
        return *this;
    }

    Samples operator/(const unsigned int r) const {
        return {
            static_cast<sample_t>(xp / r),
            static_cast<sample_t>(xn / r),
            static_cast<sample_t>(yp / r),
            static_cast<sample_t>(yn / r)};
    }

    Samples operator>>(const size_t n) const {
        return {
            static_cast<sample_t>(xp >> n),
            static_cast<sample_t>(xn >> n),
            static_cast<sample_t>(yp >> n),
            static_cast<sample_t>(yn >> n)};
    }
};

struct Frame {
    Samples pressure{};
    Samples x{};
    Samples y{};
    bool touch{false};
};

struct Metrics {
    const float x;
    const float y;
    const float r;
};

Metrics calculate_metrics(const Frame& frame);

struct DigitizerPoint {
    int32_t x;
    int32_t y;
};

struct Calibration {
    /* Touch screen calibration matrix, based on article by Carlos E. Vidales:
     * http://www.embedded.com/design/system-integration/4023968/How-To-Calibrate-Touch-Screens
     */

    constexpr Calibration(
        const std::array<DigitizerPoint, 3>& s,
        const std::array<ui::Point, 3>& d)
        : k{(s[0].x - s[2].x) * (s[1].y - s[2].y) - (s[1].x - s[2].x) * (s[0].y - s[2].y)},
          a{(d[0].x() - d[2].x()) * (s[1].y - s[2].y) - (d[1].x() - d[2].x()) * (s[0].y - s[2].y)},
          b{(s[0].x - s[2].x) * (d[1].x() - d[2].x()) - (d[0].x() - d[2].x()) * (s[1].x - s[2].x)},
          c{s[0].y * (s[2].x * d[1].x() - s[1].x * d[2].x()) + s[1].y * (s[0].x * d[2].x() - s[2].x * d[0].x()) + s[2].y * (s[1].x * d[0].x() - s[0].x * d[1].x())},
          d{(d[0].y() - d[2].y()) * (s[1].y - s[2].y) - (d[1].y() - d[2].y()) * (s[0].y - s[2].y)},
          e{(s[0].x - s[2].x) * (d[1].y() - d[2].y()) - (d[0].y() - d[2].y()) * (s[1].x - s[2].x)},
          f{s[0].y * (s[2].x * d[1].y() - s[1].x * d[2].y()) + s[1].y * (s[0].x * d[2].y() - s[2].x * d[0].y()) + s[2].y * (s[1].x * d[0].y() - s[0].x * d[1].y())} {
    }

    constexpr Calibration()
        : Calibration(
              /* Values derived from one PortaPack H1 unit. */
              {{{256, 731}, {880, 432}, {568, 146}}},
              {{{32, 48}, {208, 168}, {120, 288}}}) {
    }

    ui::Point translate(const DigitizerPoint& p) const;

   private:
    int32_t k;
    int32_t a;
    int32_t b;
    int32_t c;
    int32_t d;
    int32_t e;
    int32_t f;
};

template <size_t N>
class Filter {
   public:
    constexpr Filter() = default;

    void reset() {
        history.fill(0);
        history_history = 0;
        accumulator = 0;
        n = 0;
    }

    void feed(const sample_t value) {
        accumulator = accumulator + value - history[n];
        history[n] = value;
        n = (n + 1) % history.size();

        history_history = (history_history << 1) | 1U;
    }

    int32_t value() const {
        return accumulator / N;
    }

    bool stable(const uint32_t bound) const {
        if (history_valid()) {
            const auto minmax = std::minmax_element(history.cbegin(), history.cend());
            const auto min = *minmax.first;
            const auto max = *minmax.second;
            const uint32_t delta = max - min;
            return (delta < bound);
        } else {
            return false;
        }
    }

   private:
    static constexpr uint32_t history_history_mask{(1U << N) - 1};

    std::array<sample_t, N> history{};
    uint32_t history_history{0};
    int32_t accumulator{0};
    size_t n{0};

    bool history_valid() const {
        return (history_history & history_history_mask) == history_history_mask;
    }
};

class Manager {
   public:
    std::function<void(ui::TouchEvent)> on_event{};

    void feed(const Frame& frame);

   private:
    enum State {
        NoTouch,
        TouchDetected,
    };

    static constexpr size_t touch_count_threshold{3};
    static constexpr uint32_t touch_stable_bound{8};

    // Ensure filter length is equal or less than touch_count_threshold,
    // or coordinates from the last touch will be in the initial averages.
    Filter<touch_count_threshold> filter_x{};
    Filter<touch_count_threshold> filter_y{};

    // Debounce touch_debounce;

    State state{State::NoTouch};

    bool point_stable() const {
        return filter_x.stable(touch_stable_bound) && filter_y.stable(touch_stable_bound);
    }

    ui::Point filtered_point() const;

    void touch_started() {
        fire_event(ui::TouchEvent::Type::Start);
    }

    void touch_moved() {
        fire_event(ui::TouchEvent::Type::Move);
    }

    void touch_ended() {
        fire_event(ui::TouchEvent::Type::End);
    }

    void fire_event(ui::TouchEvent::Type type) {
        if (on_event) {
            on_event({filtered_point(), type});
        }
    }
};

} /* namespace touch */

#endif /*__TOUCH_H__*/