PointerState.hpp

#pragma once
#include <QPointF>
#include <QSizeF>
 
#include <array>
#include <mutex>
 
namespace score::gfx
{
struct PointerState
{
  static constexpr int slots = 32;
  struct Slot
  {
    float x{}, y{}, pressure{};
  };
 
  static QPointF toClip(QPointF win, QSizeF sz) noexcept
  {
    const double w = sz.width() > 0 ? sz.width() : 1.;
    const double h = sz.height() > 0 ? sz.height() : 1.;
    return {win.x() / w * 2. - 1., win.y() / h * -2. + 1.};
  }
 
  void move(int slot, float x, float y) noexcept
  {
    if(slot < 0 || slot >= slots)
      return;
    std::lock_guard l{m_mtx};
    m_slots[slot].x = x;
    m_slots[slot].y = y;
  }
 
  void press(int slot, float pressure) noexcept
  {
    if(slot < 0 || slot >= slots)
      return;
    std::lock_guard l{m_mtx};
    m_slots[slot].pressure = pressure;
  }
 
  int slotForTouch(int id) noexcept
  {
    std::lock_guard l{m_mtx};
    int free = -1;
    for(int i = 0; i < slots; i++)
    {
      if(m_touchIds[i] == id)
        return i;
      if(free < 0 && m_touchIds[i] == noTouch)
        free = i;
    }
    if(free < 0)
    {
      m_touchIds.fill(noTouch);
      free = 0;
    }
    m_touchIds[free] = id;
    return free;
  }
 
  void releaseTouch(int id) noexcept
  {
    std::lock_guard l{m_mtx};
    for(int i = 0; i < slots; i++)
      if(m_touchIds[i] == id)
      {
        m_touchIds[i] = noTouch;
        m_slots[i].pressure = 0.f;
      }
  }
 
  std::array<Slot, slots> snapshot() const noexcept
  {
    std::lock_guard l{m_mtx};
    return m_slots;
  }
 
private:
  static constexpr int noTouch = -1;
  mutable std::mutex m_mtx;
  std::array<Slot, slots> m_slots{};
  std::array<int, slots> m_touchIds = [] {
    std::array<int, slots> a;
    a.fill(noTouch);
    return a;
  }();
};
}