portapack-mayhem/firmware/application/touch.cpp

/*
 * Copyright (C) 2015 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.
 */

#include "touch.hpp"

#include "portapack_persistent_memory.hpp"
using namespace portapack;

#include "utility.hpp"

namespace touch {

Metrics calculate_metrics(const Frame& frame) {
    /* TODO: Yikes! M0 doesn't have floating point, so this code is
     * expensive! On the other hand, it seems to be working well (and
     * fast *enough*?), so maybe leave it alone at least for now.
     */

    const auto x_max = frame.x.xp;
    const auto x_min = frame.x.xn;
    const auto x_range = x_max - x_min;
    const float x_position = (frame.x.yp + frame.x.yn) * 0.5f;
    const float x_norm = (x_position - x_min) / x_range;

    const auto y_max = frame.y.yn;
    const auto y_min = frame.y.yp;
    const auto y_range = y_max - y_min;
    const float y_position = (frame.y.xp + frame.y.xn) * 0.5f;
    const float y_norm = (y_position - y_min) / y_range;

    const auto z_max = frame.pressure.yp;
    const auto z_min = frame.pressure.xn;
    const auto z_range = z_max - z_min;
    const auto z1_position = frame.pressure.xp;
    const float z1_norm = float(z1_position - z_min) / z_range;
    const auto z2_position = frame.pressure.yn;
    const float z2_norm = float(z2_position - z_min) / z_range;

    const float r_x_plate = 330.0f;
    // const float r_y_plate = 600.0f;
    const float r_touch = r_x_plate * x_norm * (z2_norm / z1_norm - 1.0f);

    return {
        .x = x_norm,
        .y = y_norm,
        .r = r_touch,
    };
}

ui::Point Calibration::translate(const DigitizerPoint& p) const {
    static constexpr range_t<int32_t> x_range{0, 240 - 1};
    static constexpr range_t<int32_t> y_range{0, 320 - 1};

    const int32_t x = (a * p.x + b * p.y + c) / k;
    const int32_t y = (d * p.x + e * p.y + f) / k;
    const auto x_clipped = x_range.clip(x);
    const auto y_clipped = y_range.clip(y);
    return {x_clipped, y_clipped};
}

void Manager::feed(const Frame& frame) {
    // touch_debounce.feed(touch_raw);
    const auto touch_raw = frame.touch;
    // const auto touch_stable = touch_debounce.state();
    const auto touch_stable = frame.touch;
    bool touch_down_pressure = false;
    bool touch_up_pressure = false;

    // Only feed coordinate averaging if there's a touch.
    // TODO: Separate threshold to gate coordinates for filtering?
    if (touch_raw) {
        const auto metrics = calculate_metrics(frame);

        constexpr float r_touch_down_threshold = 3200.0f;
        constexpr float r_touch_up_threshold = r_touch_down_threshold * 2.0f;

        touch_down_pressure = (metrics.r < r_touch_down_threshold);
        touch_up_pressure = (metrics.r < r_touch_up_threshold);

        if (touch_down_pressure) {
            filter_x.feed(metrics.x * 1024);
            filter_y.feed(metrics.y * 1024);
        }
    } else {
        filter_x.reset();
        filter_y.reset();
    }

    switch (state) {
        case State::NoTouch:
            if (touch_stable && touch_down_pressure && !persistent_memory::disable_touchscreen()) {
                if (point_stable()) {
                    state = State::TouchDetected;
                    touch_started();
                }
            }
            break;

        case State::TouchDetected:
            if (touch_stable && touch_up_pressure) {
                touch_moved();
            } else {
                state = State::NoTouch;
                touch_ended();
            }
            break;

        default:
            state = State::NoTouch;
            break;
    }
}

ui::Point Manager::filtered_point() const {
    return persistent_memory::touch_calibration().translate({filter_x.value(), filter_y.value()});
}

} /* namespace touch */