capybara/frontend/src/Touchpad.js

const HOLDING_THRESHOLD_MS = 300;
const SCROLL_X_DAMPENING = 0.03;
const SCROLL_Y_DAMPENING = 0.09;

class TouchpadController {
    constructor(connection) {
        this.currentMoveX = 0;
        this.currentMoveY = 0;
        this.lastMoveX = 0;
        this.lastMoveY = 0;
        this.shouldResetLastMove = false;
        this.isInHoldingMode = false;
        this.ongoingTouches = {};
        this.holdModeTimeout = null;
        this.touchpadDiv = null;

        this.connection = connection;
    }

    getButtonCode(button) {
        let buttonCode = 0;
        if (button === "right") buttonCode = 1;
        return buttonCode;
    }

    // takes a gesture name and a touch list
    // adds the gesture name to the touch and returns false if that touch already had that gesture
    _gesture(gestureName, touchList) {
        for (let i = 0; i < touchList.length; i++) {
            const touch = this.ongoingTouches[touchList[i].identifier];
            if (touch.gestured.includes(gestureName)) return false;
            touch.gestured.push(gestureName);   
        }
        return true;
    }

    _sendRelativeMouseMovement(dx, dy) {
        if (dx === 0 && dy === 0)
            return false;
        this.connection.sendMessage("r", [dx, dy]);
        return true;
    }

    _sendRelativeMouseScroll(dx, dy) {
        if (dx === 0 && dy === 0)
            return false;
        this.connection.sendMessage("s", [dx, dy]);
        return true;
    }

    _sendMouseButtonDown(button="left") {
        this.connection.sendMessage("d", [this.getButtonCode(button)]);
    }

    _sendMouseButtonUp(button="left") {
        this.connection.sendMessage("u", [this.getButtonCode(button)]);
    }

    _sendSingleClick(button="left") {
        this.connection.sendMessage("c", [this.getButtonCode(button)]);
    }

    mountOn(element) {
        if (this.touchpadDiv)
            return; // Already mounted

        this.touchpadDiv = document.createElement("div");
        this.touchpadDiv.classList.add("touchpad");
        element.appendChild(this.touchpadDiv);

        this.touchpadDiv.addEventListener("touchmove", this.onTouchMove.bind(this));
        this.touchpadDiv.addEventListener("touchend", this.onTouchEnd.bind(this));
        this.touchpadDiv.addEventListener("touchstart", this.onTouchStart.bind(this));
    }

    unmount() {
        if (!this.touchpadDiv)
            return; // Not mounted - don't do anything

        this.touchpadDiv.parentElement.removeChild(this.touchpadDiv);
        this.touchpadDiv = null;
    }

    onTouchMove(event) {
        const touches = event.changedTouches;
        event.preventDefault();

        const targetTouch = touches[0];

        this.currentMoveX = targetTouch.pageX;
        this.currentMoveY = targetTouch.pageY;
        // When ending a touch and starting a new one in another part of the touchpad,
        // the cursor "rubber bands" to that position.
        // To solve this, the "last move" parameters are reset when a touch is ended
        // (see onTouchEnd())
        if (this.shouldResetLastMove) {
            this.shouldResetLastMove = false;
            this.lastMoveX = this.currentMoveX;
            this.lastMoveY = this.currentMoveY;
        }
        const deltaX = this.currentMoveX - this.lastMoveX;
        const deltaY = this.currentMoveY - this.lastMoveY;
        this.lastMoveX = this.currentMoveX;
        this.lastMoveY = this.currentMoveY;
        // if two touches moved at the same time, assume scrolling intent

        // if _sendRelativeMouseScroll or _sendRelativeMouseMovement return true, it means that the delta values are non-zero and a packet has been sent to the server
        // in that case, the touches will be marked as moved
        let shouldMarkTouchesAsMoved = false;
        if (touches.length === 2) {
            if (
                this._sendRelativeMouseScroll(deltaX * SCROLL_X_DAMPENING, deltaY * SCROLL_Y_DAMPENING)
            ) {
                shouldMarkTouchesAsMoved = true;
            }
        } else if (touches.length === 3 && this._gesture("GESTURE_RIGHT_CLICK", touches)) {
            shouldMarkTouchesAsMoved = true;
            this._sendSingleClick("right");
        } else {
            if (
                this._sendRelativeMouseMovement(deltaX, deltaY)
            ) {
                shouldMarkTouchesAsMoved = true;
            }
        }
        if (shouldMarkTouchesAsMoved) {
            for (let i = 0; i < touches.length; i++) {
                this.ongoingTouches[touches[i].identifier].hasMoved = true;
            }
        }
    }

    onTouchEnd(event) {
        const changedTouches = event.changedTouches;
        this.shouldResetLastMove = true;

        if (changedTouches.length === 1) {
            // This is a single tap - left click
            if (!this.ongoingTouches[changedTouches[0].identifier].hasMoved) {
                this._sendSingleClick("left");

                // We were in "holding mode" and now that touch event has ended,
                // thus we have to stop holding the left click button
            } else if (this.isInHoldingMode) {
                this._sendMouseButtonUp("left");
                this.isInHoldingMode = false;
            }
        }

        // remove all ended touches
        for (let i = 0; i < changedTouches.length; i++) {
            const touch = changedTouches[i];
            this.ongoingTouches[touch.identifier] = null;
            delete this.ongoingTouches[touch.identifier];
        }
    }

    onTouchStart(event) {
        const changedTouches = event.changedTouches;

        // Clear the hold mode time out if another touch begins
        if (this.holdModeTimeout)
            clearTimeout(this.holdModeTimeout);

        // If the touch is still unmoved and held for a certain amount of time,
        // we will enter "holding mode" which keeps the mouse button held while dragging
        // allowing you to, for example, select text or drag a scrollbar
        if (changedTouches.length === 1) {
            const targetTouch = changedTouches[0];
            this.holdModeTimeout = setTimeout(() => {
                if (this.ongoingTouches[targetTouch.identifier] && !this.ongoingTouches[targetTouch.identifier].hasMoved) {
                    this.isInHoldingMode = true;
                    this._sendMouseButtonDown("left");
                }
            }, HOLDING_THRESHOLD_MS);
        }

        for (let i = 0; i < changedTouches.length; i++) {
            const touch = changedTouches[i];
            this.ongoingTouches[touch.identifier] = {
                identifier: touch.identifier,
                clientX: touch.clientX,
                clientY: touch.clientY,
                hasMoved: false,
                gestured: []
            };
        }
    }
}

export default TouchpadController;