gravity/pointer.js

import {
  POINTER_HISTORY_SIZE,
  ZOOM_IN_FACTOR,
  ZOOM_OUT_FACTOR,
  DISPLAY_CURSOR_INFO,
  DRAGGABLE_ELEMENT_CLASSNAME,
} from './config.js';

function dispatchEvent(target, eventType, data) {
  const ev = new CustomEvent(eventType, {detail: data});
  target.dispatchEvent(ev);
}

export class Pointer {
  sim = undefined;

  pointerHistory = [];
  draggingElement = undefined;

  constructor(sim) {
    this.sim = sim;

    // Monitor mouse movements
    const el = window;

    el.addEventListener('pointermove', e => {
      if (DISPLAY_CURSOR_INFO) {
        this.sim.info['pointermove'] = [`${e.clientX}, `, `${e.clientY}`];
      }
      if (this.draggingElement) {
        // e.preventDefault();
        this.draggingElement.dragging.pointerEnd = {
          x: e.clientX,
          y: e.clientY,
        };
      } else {
        const {x, y} = this.sim.screenToSim(e.clientX, e.clientY);
        this.handlePointerMove({x, y});
      }
    });
   
    el.addEventListener('pointerdown', e => {
      // e.preventDefault();
      let target = e.target;
      while (target && !target.classList.contains(DRAGGABLE_ELEMENT_CLASSNAME)) {
        target = target.parentElement;
      }
      if (target?.classList.contains(DRAGGABLE_ELEMENT_CLASSNAME)) {
        // e.preventDefault();
        this.draggingElement = target;
        this.draggingElement.dragging = {
          elementStart: {
            x: parseInt(this.draggingElement.style.left),
            y: parseInt(this.draggingElement.style.top),
          },
          pointerStart: {
            x: e.clientX,
            y: e.clientY,
          },
          pointerEnd: {
            x: e.clientX,
            y: e.clientY,
          },
        };
      } else {
        this.handlePointerDown(this.sim.screenToSim(e.clientX, e.clientY));
      }
    });

    el.addEventListener('pointerup', e => {
      // e.preventDefault();
      if (this.draggingElement) {
        this.draggingElement.dragging = undefined;
        this.draggingElement = undefined;
        this.lastPosition = {x: undefined, y: undefined};
      } else {
        this.handlePointerUp(this.sim.screenToSim(e.clientX, e.clientY));
      }
    });

    el.addEventListener('click', e => {
      // e.preventDefault();
    });

    // Monitor wheel events
    el.addEventListener('wheel', e => {
      // e.preventDefault();
      // Wheel scroll down => positive deltaY => ZOOM IN
      const factor = e.deltaY > 0 ? ZOOM_IN_FACTOR : ZOOM_OUT_FACTOR;
      this.sim.scheduleZoom(this.sim.screenToSim(e.clientX, e.clientY), factor);
    });

  }

  getPointerVelocity() {
    // Average over pointer history
    if (this.pointerHistory.length < 2) {
      return {x: 0, y: 0, dt: 1};
    }
    const start = this.pointerHistory[0];
    const end = this.pointerHistory[this.pointerHistory.length - 1];
    const dt = (end.t - start.t) / 1000;
    return {
      x: (end.x - start.x) / dt,
      y: (end.y - start.y) / dt,
      dt
    };
  }

  clearPointerHistory() {
    this.pointerHistory = [];
  }

  updatePointer({x, y}) {
    const t = document.timeline.currentTime;
    this.pointerHistory.push({x, y, t});
    if (this.pointerHistory.length > POINTER_HISTORY_SIZE) {
      this.pointerHistory.shift();
    }
  }

  handlePointerDown({x, y}) {
    this.clearPointerHistory();
    this.updatePointer({x, y});

    this.sim.objects.handlePointerDown({x, y});
  }

  handlePointerUp({x, y}) {
    // TODO: Conditional?
    this.sim.objects.handlePointerUp({x, y});
  }

  // Handle cursor (mouse or touch) movement
  // TODO: If e.touches.length > 1, user may be engaging pinch to zoom
  handlePointerMove({x, y}) {
    this.updatePointer({x, y});
    const {x: vx, y: vy} = this.getPointerVelocity();

    // If the cursor moves while creating an object, or while an object is selected,
    // update the position and velocity of the object
    const obj = this.sim.objects.getSelectedOrCreating();
    if (obj !== undefined) {
      obj.position.x = x;
      obj.position.y = y;
      obj.velocity.x = vx;
      obj.velocity.y = vy;
    }
  }
}