xpt2046.h

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/*
    MIT License

    Copyright (c) 2025, Alexey Dynda

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE.
*/
#ifndef _LCDGFX_TOUCH_XPT2046_H_
#define _LCDGFX_TOUCH_XPT2046_H_

#include "touch.h"

namespace lcdgfx_xpt2046
{
constexpr uint8_t CMD_X  = 0xD3; 
constexpr uint8_t CMD_Y  = 0x93; 
constexpr uint8_t CMD_Z1 = 0xB3; 
constexpr uint8_t CMD_Z2 = 0xC3; 
} // namespace lcdgfx_xpt2046

template <typename SpiT> class LcdGfxXpt2046
{
public:
    explicit LcdGfxXpt2046(SpiT &spi)
        : m_spi(spi)
    {
    }

    void begin()
    {
        m_spi.begin();
    }

    void end()
    {
        m_spi.end();
    }

    void setCalibration(const TouchCalibration &cal)
    {
        m_calibration = cal;
    }

    TouchCalibration &calibration()
    {
        return m_calibration;
    }

    void setPressureThreshold(uint16_t threshold)
    {
        m_pressureThreshold = threshold;
    }

    bool readRaw(int16_t &rawX, int16_t &rawY, int16_t &rawZ)
    {
        m_spi.start();
        uint16_t z1 = sampleChannel(lcdgfx_xpt2046::CMD_Z1);
        uint16_t z2 = sampleChannel(lcdgfx_xpt2046::CMD_Z2);
        rawZ = (int16_t)(z1 + (4095 - z2));

        uint16_t xs[3];
        uint16_t ys[3];
        for ( int i = 0; i < 3; i++ )
        {
            xs[i] = sampleChannel(lcdgfx_xpt2046::CMD_X);
            ys[i] = sampleChannel(lcdgfx_xpt2046::CMD_Y);
        }
        m_spi.stop();

        rawX = (int16_t)median3(xs[0], xs[1], xs[2]);
        rawY = (int16_t)median3(ys[0], ys[1], ys[2]);
        return z1 > m_pressureThreshold;
    }

    bool read(int16_t &x, int16_t &y)
    {
        int16_t rawX, rawY, rawZ;
        bool pressed = readRaw(rawX, rawY, rawZ);
        if ( !pressed )
        {
            return false;
        }
        m_calibration.apply(rawX, rawY, x, y);
        return true;
    }

    bool read(int16_t &x, int16_t &y, int16_t &pressure)
    {
        int16_t rawX, rawY;
        bool pressed = readRaw(rawX, rawY, pressure);
        if ( !pressed )
        {
            return false;
        }
        m_calibration.apply(rawX, rawY, x, y);
        return true;
    }

private:
    SpiT &m_spi;
    TouchCalibration m_calibration{};
    uint16_t m_pressureThreshold = 200;

    uint16_t sampleChannel(uint8_t cmd)
    {
        m_spi.transfer(cmd);
        uint8_t hi = m_spi.transfer(0x00);
        uint8_t lo = m_spi.transfer(0x00);
        // 16 bits clocked out: result is 12-bit, MSB first, with 3 leading
        // status/zero bits and 1 trailing zero bit. Compose the 12-bit value:
        return (uint16_t)(((uint16_t)hi << 5) | (lo >> 3)) & 0x0FFF;
    }

    static uint16_t median3(uint16_t a, uint16_t b, uint16_t c)
    {
        if ( a > b )
        {
            uint16_t t = a;
            a = b;
            b = t;
        }
        if ( b > c )
        {
            uint16_t t = b;
            b = c;
            c = t;
        }
        if ( a > b )
        {
            uint16_t t = a;
            a = b;
            b = t;
        }
        return b;
    }
};

#endif