在画布内检测鼠标点击位置

Question

在画布内检测鼠标点击位置

5

我在定义点击空白区域的函数上遇到了一些问题。目前为止，我已经成功地定义了当我点击对象时的函数 - 共有10个对象 - 但是现在我需要一个单独的函数来处理当我没有点击任何对象时的情况。可以在 http://deciballs.co.uk/experience.html 上找到一般想法。这些对象是指环。我的代码如下... 有什么想法吗？

var shapeObj = function (context, canvas, settingsBox, radius) {
    this.ctx = context;
    this.canvas = canvas;
    this.sBox = settingsBox;

    this.frequencies = new Array(220, 440, 1024, 2048);
    this.cols = new Array(255, 225, 200, 175, 150);
    this.strokes = new Array(1, 1.5, 2);
    this.waves = new Array('sine', 'sawtooth', 'triangle', 'square');

    this.properties = {
        dur: Math.random()*0.5,
        freq: this.frequencies[Math.floor(Math.random() * this.frequencies.length)],
        radius: radius,
        stroke: this.strokes[Math.floor(Math.random() * this.strokes.length)],
        speed: Math.random()*6-3,
        vol: Math.random()*10,
        col1: this.cols[Math.floor(Math.random() * this.cols.length)],
        col2: this.cols[Math.floor(Math.random() * this.cols.length)],
        col3: this.cols[Math.floor(Math.random() * this.cols.length)],
        alpha: 0,
        wave: this.waves[Math.floor(Math.random() * this.waves.length)],
        delay: 0 
    }

    this.x = Math.random()*this.ctx.canvas.width;
    this.y = Math.random()*this.ctx.canvas.height; 
    this.vx = 0.5;
    this.vy = 1;

    this.draw = function () {
        this.ctx.beginPath();
        this.ctx.arc(this.x, this.y, this.properties.radius, 0, Math.PI*2, false);
        this.ctx.closePath();
        this.ctx.stroke();
        this.ctx.fill();
    }

    this.clickTest = function (e) {
        var canvasOffset = this.canvas.offset();
        var canvasX = Math.floor(e.pageX-canvasOffset.left);
        var canvasY = Math.floor(e.pageY-canvasOffset.top);     
            var dX = this.x-canvasX;
            var dY = this.y-canvasY;
            var distance = Math.sqrt((dX*dX)+(dY*dY));
            if (distance < this.properties.radius) {
                this.manageClick();
            } else {
                this.properties.alpha = 0;
            }
    };

    this.manageClick = function () {
        this.sBox.populate(this.properties, this);
        var divs = document.getElementsByTagName('section');
        for(var i = 0, e = divs[0], n = divs.length; i < n; e = divs[++i]){
            e.className='class2';
        }
        this.properties.alpha = 0.5;
    }
}

- Jon_091

这是您要找的吗：在画布中获取鼠标位置？ - Brandon Boone

项目可以在http://deciballs.co.uk/experience.html找到，这样你就能更好地了解它了？ - Jon_091

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Simon Sarris · Accepted Answer

获得完美的鼠标点击有点棘手，我将分享迄今为止我创建的最可靠的鼠标代码。它适用于所有浏览器以及各种填充、边距、边框和插件（例如stumbleupon顶部栏）。

// Creates an object with x and y defined,
// set to the mouse position relative to the state's canvas
// If you wanna be super-correct this can be tricky,
// we have to worry about padding and borders
// takes an event and a reference to the canvas
function getMouse(e, canvas) {
  var element = canvas, offsetX = 0, offsetY = 0, mx, my;

  // Compute the total offset. It's possible to cache this if you want
  if (element.offsetParent !== undefined) {
    do {
      offsetX += element.offsetLeft;
      offsetY += element.offsetTop;
    } while ((element = element.offsetParent));
  }

  // Add padding and border style widths to offset
  // Also add the <html> offsets in case there's a position:fixed bar (like the stumbleupon bar)
  // This part is not strictly necessary, it depends on your styling
  offsetX += stylePaddingLeft + styleBorderLeft + htmlLeft;
  offsetY += stylePaddingTop + styleBorderTop + htmlTop;

  mx = e.pageX - offsetX;
  my = e.pageY - offsetY;

  // We return a simple javascript object with x and y defined
  return {x: mx, y: my};
}

您会注意到我在函数中使用了一些（可选的）未定义变量。它们是：

  stylePaddingLeft = parseInt(document.defaultView.getComputedStyle(canvas, null)['paddingLeft'], 10)      || 0;
  stylePaddingTop  = parseInt(document.defaultView.getComputedStyle(canvas, null)['paddingTop'], 10)       || 0;
  styleBorderLeft  = parseInt(document.defaultView.getComputedStyle(canvas, null)['borderLeftWidth'], 10)  || 0;
  styleBorderTop   = parseInt(document.defaultView.getComputedStyle(canvas, null)['borderTopWidth'], 10)   || 0;
  // Some pages have fixed-position bars (like the stumbleupon bar) at the top or left of the page
  // They will mess up mouse coordinates and this fixes that
  var html = document.body.parentNode;
  htmlTop = html.offsetTop;
  htmlLeft = html.offsetLeft;

我建议只计算一次，这就是为什么它们没有在getMouse函数中的原因。

你应该有一个单独的函数来处理鼠标点击事件，调用getMouse函数一次，然后遍历对象列表，检查每个对象的x和y。伪代码：

function onMouseDown(e) {
  var mouse = getMouse(e, canvas)
  var l = myObjects.length;
  var found = false;

  // Maybe "deselect" them all right here

  for (var i = 0; i < l; i++) {
    if (distance sqrt to myObjects[i]) {
      found = true;
      myObjects[i].ManageClickOrWhateverYouWantHere()
    }
    break;
  }

  // And now we can know if we clicked on empty space or not!
  if (!found) {
    // No objects found at the click, so nothing has been clicked on
    // do some relevant things here because of that
    // I presume from your question this may be part of what you want
  }

}