Question

有没有办法记住画布上绘制的形状数量我正在使用各种画笔在画布上绘制一串圆圈，并希望找到一种计算存在多少圆圈的方法

var mainCanvas = document.getElementById('draw1');
mainContext = mainCanvas.getContext('2d');

var CircleBrush = {

iPrevX: 0,
iPrevY: 0,

// initialization function
init: function () {
    mainContext.globalCompositeOperation = 'source-over';
    mainContext.lineWidth = 1;
    mainContext.strokeStyle = '#4679BD';
    mainContext.lineWidth = 1;
    mainContext.lineJoin = 'round';

},

startCurve: function (x, y) {
    this.iPrevX = x;
    this.iPrevY = y;
    mainContext.fillStyle = '#4679BD';
},

draw: function (x, y) {
    var iXAbs = Math.abs(x - this.iPrevX);
    var iYAbs = Math.abs(y - this.iPrevY);
    var rad = 6;

    if (iXAbs > 10 || iYAbs > 10) {
        mainContext.beginPath();
        mainContext.arc(this.iPrevX, this.iPrevY, rad, Math.PI * 2, false);
        mainContext.fill();
        mainContext.stroke();
        this.iPrevX = x;
        this.iPrevY = y;

       }
    }
};
var circleCounter = [0];
mainContext.font = '21pt Arial';
mainContext.fillStyle = '#262732';
mainContext.textBaseline = 'top';
mainContext.fillText(circleCounter, 20, 20);
CircleBrush.init();
$('#draw1').mousedown(function (e) { // mouse down handler
cMoeDo = true;
var canvasOffset = $('#draw1').offset();
var canvasX = Math.floor(e.pageX - canvasOffset.left);
var canvasY = Math.floor(e.pageY - canvasOffset.top);
CircleBrush.startCurve(canvasX, canvasY);
circleCounter ++1;
 });

$('#draw1').mouseup(function (e) { // mouse up handler
 cMoeDo = false;
});

 $('#draw1').mousemove(function (e) { // mouse move handler
  if (cMoeDo) {
    var canvasOffset = $('#draw1').offset();
    var canvasX = Math.floor(e.pageX - canvasOffset.left);
    var canvasY = Math.floor(e.pageY - canvasOffset.top);
    CircleBrush.draw(canvasX, canvasY);
    circleCounter ++1;
 }

})

演示小提琴http://jsfiddle.net/A2vyY/

提前致谢

Answer 1

您需要清除计数器的空间并重新绘制计数。为了做到这一点，我将计数器和文本绘图放在绘图函数中，如此

draw: function (x, y) {        
    var iXAbs = Math.abs(x - this.iPrevX);
    var iYAbs = Math.abs(y - this.iPrevY);
    var rad = 6;  

    if (iXAbs > 10 || iYAbs > 10) {
        mainContext.beginPath();
        mainContext.arc(this.iPrevX, this.iPrevY, rad, Math.PI*2, false);
        mainContext.fill();
        mainContext.stroke();
        this.iPrevX = x;
        this.iPrevY = y;
        circleCounter ++;
        mainContext.clearRect(0,0,50,25);
        mainContext.fillText(circleCounter, 5, 5);           
    }
}

Updated jsFiddle（我把柜台搬了一些，以便有更多的空间）

Answer 2

您可以将计数器放在单独的div中，只需更新文本

即可

<div id="content">
    <div id="counter">0</div>
    <canvas id="draw1" height="500" width="500"></canvas>
</div>

绘制圆圈时返回true，否则返回false

draw: function (x, y) {
    /* ... */
    if (iXAbs > 10 || iYAbs > 10) {
        /* ... */
        return true;
    }

    return false;
}

增量并根据需要显示

if (CircleBrush.draw(canvasX, canvasY)) {
    ++circleCounter;
    $('#counter').text(circleCounter);
}

请参见修改后的JSFiddle

HTML5 - 跟踪画布上的圆圈数量

2 个答案: