Question

我是JavaScript的新手，并且正在摆弄HTML5元素。

问题是我现在正在使用一个库来帮助简化画布在多种设备上的使用，包括移动设备，但我现在有一个问题就是烦恼我，因为它看起来很简单但我是无法找到解决方案。我相信这可能是一个新手的错误，但这是交易：

我有这两个功能：

function drawLine(sX, sY, eX, eY) {
    ctx.beginPath()
    ctx.moveTo(sX, sY);
    ctx.lineTo(eX, eY);
    ctx.stroke();
    ctx.closePath();
    return { x: eX, y: eY };
}

function canvas() {
    var canvas = new Canvas ('canvas', 0, function () {
        this.clear();
        this.setAutoResize(true);
    });

    canvas.canvasElement.width = window.innerWidth;
    canvas.canvasElement.height = window.innerHeight;

    canvas.onTouchStart = function(start) {
        var sX; var sY;
        return {sX: start.clientX, sY: start.clientY};
    }

    canvas.onTouchEnd = function (end) {
        var eX; var eY;
        return {eX: end.clientX, eY: end.clientY};
    }

    // canvas.onTouchMove = drawLine(sX, sY, eX, eY);
}

没有详细介绍，我如何能够使用onTouchStart（）和onTouchEnd（）返回的值将x，y位置传递给drawLine函数？

我得到的只是未定义的值，我真的迷失了......

更新：

@Juan Mendes，

感谢您的帮助，但这似乎也没有用。

为了更好地理解“背面”代码，以下是touchstart的一个例子：

this.canvasElement.addEventListener('touchstart', function(event) {
    var touchCount = event.changedTouches.length;
    var touches = [];
    var touch = null;

    for (var i = 0; i < touchCount; i++) {
        touch = event.changedTouches[i];

        var touchInfo = {
            pageX : touch.pageX,
            pageY : touch.pageY,
            clientX : touch.clientX,
            clientY : touch.clientY,
            screenX : touch.screenX,
            screenY : touch.screenY,
            target : touch.target,
            identifier : touch.identifier
        };

    self.onTouchStart(touchInfo, i, touchCount, event);

    touches.push(touchInfo);

    self.previousTouchInfo[touch.identifier] = touchInfo;
    }

    if (touchCount == 1) {
        touch = event.changedTouches[0];

        var x = touch.clientX;
        var y = touch.clientY;

        if (self.touchEmulatesMouse) {
            self.mouse.x = x;
            self.mouse.y = y;
            self.mouse.left = true;

            if (self.layerParent != null) {
                self.layerParent.onMouseDown(x, y, 0);
            }

        self.onMouseDown(x, y, 0);
        }
        } else {
            self.onMultiTouchStart(touches, event);
        }
    }, false);

/* A bit more down the library code */
/**
* Called at the start of every touch start (including when multiple touches occured)
*
* The info object contains the folloring info:
* - pageX - X coordinate relative to the full page (includes scrolling)
* - pageY - Y coordinate relative to the full page (includes scrolling)
* - clientX - X coordinate of touch relative to the viewport (excludes scroll offset)
* - clientY - Y coordinate of touch relative to the viewport (excludes scroll offset)
* - screenX - X coordinate relative to the screen
* - screenY - Y coordinate relative to the screen
*
* @param {object} info Touch info
* @param {integer} index Touch index
* @param {integer} count The total number of active touches
* @param {object} event The actual touch event
*/
onTouchStart: function(info, index, count, event) {},

我还更改了我的代码，以反映您的帮助，一些更改，并尝试使用这样的touchInfo参数：

function createCanvas() {
var canvas = new Canvas ('canvas', 0, function () {
    this.clear();
    this.setAutoResize(true);
});

var cWidth = canvas.canvasElement.width = window.innerWidth;
var cHeight = canvas.canvasElement.height = window.innerHeight;

var startPoint = null;

function fill() {
    canvas.fillStyle = "black";
    canvas.fillRect(0, 0, cWidth, cHeight);
    canvas.beginPath();
}

// Draw a line on the canvas from (s)tart to (e)nd
function drawLine(sX, sY, eX, eY) {
    canvas.beginPath()
    canvas.moveTo(sX, sY);
    canvas.lineTo(eX, eY);
    canvas.stroke();
    canvas.closePath();
    //return { x: eX, y: eY };
}

fill();

canvas.onTouchStart = function(start) {
    startPoint = {sX: this.clientX, sY: this.clientY};
}

canvas.onTouchEnd = function (end) {
    drawLine(startPoint.sX, startPoint.sY, this.clientX, this.clientY);
    // return {eX: end.clientX, eY: end.clientY};
}
}

非常感谢任何帮助。提前致谢

Answer 1

很难说出你在问什么，但希望这会有所帮助

我认为您需要的是以下内容

(function() {
// Save the startPoint so we can use it when the touch ends to draw the line
var startPoint;
canvas.onTouchStart = function(e) {
    // set the shared variable 
    startPoint = {x: e.clientX, y: e.clientY};
}

canvas.onTouchEnd = function (e) {
    drawLine(startPoint.x, startPoint.y, e.clientX, e.clientY);
}
})();

我认为活动的名称是ontouchstart，而不是onTouchStart

以下是我认为您的代码应该是什么样的

function drawLine(sX, sY, eX, eY) {
    // Bad use of ctx global, you should pass it into the function so you can support
    // multiple contexts
    ctx.beginPath()
    ctx.moveTo(sX, sY);
    ctx.lineTo(eX, eY);
    ctx.stroke();
    ctx.closePath();
    // Kind of silly to return this object, the caller already passed it in
    // Should be used only if you need some kind of chaining, but
    // makes for a weird API
    return { x: eX, y: eY };
}

// Don't name a function and a variable the same thing, 
// you had canvas as a variable and as a function. 
// They didn't cause a problem, but it's just not pretty to look at
function createCanvas() {    
    var canvas = new Canvas('canvas', 0, function () {
        this.clear();
        this.setAutoResize(true);
    });

    canvas.canvasElement.width = window.innerWidth;
    canvas.canvasElement.height = window.innerHeight;


    // Save the startPoint so we can use it when the touch ends to draw the line
    var startPoint;
    // Correct spelling for ontouchstart
    canvas.ontouchstart = function(start) {
        // set the shared variable that will be used when they finish touching
        startPoint = {x: e.clientX, y: e.clientY};
    }

    // Draw the line
    canvas.ontouchend = function (e) {
        drawLine(startPoint.x, startPoint.y, e.clientX, e.clientY);
    }    
}

}

Answer 2

我终于成功解决了这个问题。原来图书馆没有正确结束（还），我也在没有得到任何论据的情况下滥用这些功能。

JavaScript对象/属性

2 个答案: