gravity/pointer.js

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

export class Pointer {
  sim = undefined;

  pointerHistory = [];
  draggingElement = undefined;
  panning = 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'] = [`${e.clientX}, `, `${e.clientY}`];
      }

      if (this.draggingElement) {
        this.draggingElement.dragging.pointerEnd = {
          x: e.clientX,
          y: e.clientY,
        };
      } else {
        // const {x, y} = this.sim.screenToSim(e.clientX, e.clientY);
        this.handlePointerMove({x: e.clientX, y: e.clientY});
      }
    });

    el.addEventListener('pointerdown', e => {
      // If this is a child of a draggable element, handle dragging
      let target = e.target;
      while (target && !target.classList.contains(DRAGGABLE_ELEMENT_CLASSNAME)) {
        target = target.parentElement;
      }

      if (target?.classList.contains(DRAGGABLE_ELEMENT_CLASSNAME)) {
        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({x: e.clientX, y: e.clientY});
      }
    });

    el.addEventListener('pointerup', e => {
      this.clearPointerHistory();
      if (this.draggingElement) {
        this.draggingElement.dragging = undefined;
        this.draggingElement = undefined;
        this.lastPosition = {x: undefined, y: undefined};
      } else {
        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() {
    // 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;
    // Bonus scale factor for pointer power
    return {
      x: (end.x - start.x) / dt * this.sim.display.scale,
      y: (end.y - start.y) / dt * this.sim.display.scale,
      dt
    };
  }

  getPointerAcceleration() {
    // 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.v.x - start.v.x) / dt,
      y: (end.v.y - start.v.y) / dt,
      dt
    };
  }

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

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

  handlePointerDown({x: clientX, y: clientY}) {
    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.panning = this.panning || {};
      this.panning.gathering = true;
      this.panning.velocity = {x: 0, y: 0};
    }
  }

  handlePointerUp({x: clientX, y: clientY}) {
    this.clearPointerHistory();

    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)) {
      if (this.panning?.gathering) {
        this.panning.gathering = false;
      }
    }
  }

  // Handle cursor (mouse or touch) movement
  // TODO: If e.touches.length > 1, user may be engaging pinch to zoom
  handlePointerMove({x: clientX, y: clientY}) {
    if (this.sim.isCurrentMode(MODE_MASS_GENERATION)) {
      this.updatePointer({x: clientX, y: clientY});
      const {x, y} = this.sim.screenToSim(clientX, clientY);
      const velocity = this.getPointerVelocity();
      // Convert pointer velocity to sim internal scale
      const vx = velocity.x / this.sim.display.scale;
      const vy = velocity.y / this.sim.display.scale;
      this.sim.objects.handlePointerMove({x, y, vx, vy});

    } else if (this.sim.isCurrentMode(MODE_PAN_VIEW)) {
      if (this.panning?.gathering) {
        this.updatePointer({x: clientX, y: clientY});
        const velocity = this.getPointerVelocity();
        const acceleration = this.getPointerAcceleration();
        // Convet to sim coordinates
        // Let's try incorporating pointer acceleration
        this.panning.velocity.x = velocity.x + acceleration.x * velocity.dt;
        this.panning.velocity.y = velocity.y + acceleration.y * velocity.dt;
      }
    }
  }

  computeFrame(elapsedTime) {
    // Add another entry for the current pointer position
    if (this.pointerHistory?.length) {
      const currentPointer = this.pointerHistory[this.pointerHistory.length - 1];
      this.updatePointer(currentPointer);
    }

    // Apply update to viewOrigin based on panning
    if (this.panning && !this.panning.paused) {
      const {velocity} = this.panning;
      // Convert pointer velocity to sim internal scale
      this.sim.display.viewOrigin.x -= velocity.x * elapsedTime;
      this.sim.display.viewOrigin.y -= velocity.y * elapsedTime;
    }
  }
}