gravity/pointer.js

import {
  DISPLAY_CURSOR_INFO,
  MODE_MASS_GENERATION,
  MODE_OBJECT_SELECT,
  MODE_PAN_VIEW,
  POINTER_HISTORY_SIZE,
  POINTER_DOWN_HISTORY_SIZE,
  TOOLBAR_CLASSNAME,
  ZOOM_IN_FACTOR,
  ZOOM_OUT_FACTOR,
} from './config.js';

export class Pointer {
  sim = undefined;

  pointerHistory = [];
  panTouchStart = undefined; // {x: undefined, y: undefined, t: undefined};
  panTouchLatest = undefined; // {x: undefined, y: undefined, t: undefined};
  suppressClick = false;

  constructor(sim) {
    this.sim = sim;

    // Monitor mouse movements
    const el = window;

    el.addEventListener('pointermove', e => {
      if (DISPLAY_CURSOR_INFO) {
        this.sim.info['pointermove'] = [`${e.clientX.toPrecision(6)}, `, `${e.clientY.toPrecision(6)}`];
      }
      this.handlePointerMove({x: e.clientX, y: e.clientY});
    });

    el.addEventListener('pointerdown', e => {
      let target = e.target;
      while (target && !target.classList?.contains(TOOLBAR_CLASSNAME)) {
        target = target.parentNode;
      }
      if (target) {
        return;
      }

      this.handlePointerDown({x: e.clientX, y: e.clientY});
    });

    el.addEventListener('pointerup', e => {
      this.handlePointerUp({x: e.clientX, y: e.clientY});
    });

    el.addEventListener('pointerleave', e => {
      this.handlePointerUp({x: e.clientX, y: e.clientY});
    });

    // Monitor wheel events
    el.addEventListener('wheel', e => {
      const factor = e.deltaY < 0 ? ZOOM_IN_FACTOR : ZOOM_OUT_FACTOR;
      const {x, y} = this.sim.screenToSim(e.clientX, e.clientY);
      this.sim.scheduleZoom({x, y}, factor);
    });
  }

  getPointerVelocity(points = POINTER_HISTORY_SIZE) {
    // Average over pointer history
    if (this.pointerHistory.length < 2) {
      return this.latestPointerVelocity ?? {x: 0, y: 0, dt: 1};
    }
    points = Math.min(points, POINTER_HISTORY_SIZE, this.pointerHistory.length);
    const start = this.pointerHistory[this.pointerHistory.length - points];
    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(keep = 0) {
    this.pointerHistory.splice(0, this.pointerHistory.length - keep)
  }

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

  get latestPointerVelocity() {
    const latestPointer = this.pointerHistory[this.pointerHistory.length - 1];
    return latestPointer?.v;
  }

  handlePointerDown({x: clientX, y: clientY}) {
    this.clearPointerHistory(POINTER_DOWN_HISTORY_SIZE);
    this.updatePointer({x: clientX, y: clientY});

    if (this.sim.isCurrentMode(MODE_MASS_GENERATION)) {
      const {x, y} = this.sim.screenToSim(clientX, clientY)
      this.sim.objects.handlePointerDown({x, y});

    } else if (this.sim.isCurrentMode(MODE_PAN_VIEW)) {
      this.panTouchStart = {
        x: clientX,
        y: clientY,
        t: document.timeline.currentTime,
        viewOrigin: {...this.sim.display.viewOrigin},
      };
      this.panTouchLatest = {...this.panTouchStart};

    } else if (this.sim.isCurrentMode(MODE_OBJECT_SELECT)) {
      // TODO: Start a selection box
    }
  }

  handlePointerUp({x: clientX, y: clientY}) {
    if (this.sim.isCurrentMode(MODE_MASS_GENERATION)) {
      const {x, y} = this.sim.screenToSim(clientX, clientY);
      this.sim.objects.handlePointerUp({x, y});

    } else if (this.sim.isCurrentMode(MODE_PAN_VIEW)) {
      // Set panning velocity
      if (this.panTouchStart && this.panTouchLatest) {
        const dt = (this.panTouchLatest.t - this.panTouchStart.t) / 1000;
        if (!dt) {
          this.sim.panning = undefined;
        } else {
          const v = {...this.latestPointerVelocity};
          // Convert pointer velocity to simulation scale
          v.x /= this.sim.display.scale;
          v.y /= this.sim.display.scale;

          this.sim.panning = {
            velocity: v
          };
        }

        this.panTouchStart = undefined;
      }
    }
  }

  // Handle cursor (mouse or touch) movement
  // TODO: If e.touches.length > 1, user may be engaging pinch to zoom
  handlePointerMove({x: clientX, y: clientY}) {
    this.updatePointer({x: clientX, y: clientY});
    const v = this.latestPointerVelocity;
    // Convert pointer velocity to simulation scale
    v.x /= this.sim.display.scale;
    v.y /= this.sim.display.scale;

    if (this.sim.isCurrentMode(MODE_MASS_GENERATION)) {
      const {x, y} = this.sim.screenToSim(clientX, clientY);
      this.sim.objects.handlePointerMove({x, y, vx: v.x, vy: v.y});

    } else if (this.sim.isCurrentMode(MODE_PAN_VIEW)) {
      if (this.panTouchStart) {
        // Event loop should be able to read
        this.panTouchLatest = {
          x: clientX,
          y: clientY,
          t: document.timeline.currentTime,
        };
      }
    }
  }


}