javascript - HTML5 - 跟踪 Canvas 上的圆圈数

Question

有没有办法统计 Canvas 上绘制的形状数量我正在使用某种画笔在 Canvas 上绘制一串圆圈，并希望找到一种方法来计算存在的数量

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 fiddle http://jsfiddle.net/A2vyY/

提前致谢

Answer 1

您需要清理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制放在绘图函数中，如下所示

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 (我将计数器移动了一些，以便有更多的空间容纳点)