javascript - 从新的 HTML5 Canvas 开始

Question

以下代码在单击按钮时清除 Canvas

context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears

但是，当我尝试在其上重新绘制时，会出现我不希望出现的旧绘图。我想开始在新的空白 Canvas 上绘画

http://jsfiddle.net/umwc5/

我如何实现这一目标？

如果您想查看完整代码..

  $(function () {
  var c = document.getElementById("canvas");
  var context = c.getContext("2d");
  var clickX = new Array();
  var clickY = new Array();
  var clickDrag = new Array();
  var paint;

  $('#canvas').mousedown(function (e) {
      var mouseX = e.pageX - this.offsetLeft;
      var mouseY = e.pageY - this.offsetTop;

      paint = true;
      addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
      redraw();
  });


  $('#canvas').mousemove(function (e) {
      if (paint) {
          addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop, true);
          redraw();
      }
  });

  $('#canvas').mouseup(function (e) {
      paint = false;
  });

  $('#canvas').mouseleave(function (e) {
      paint = false;
  });

  $('#clear').click(function (e) {
      e.stopPropagation();
      context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears

  });

  function addClick(x, y, dragging) {
      clickX.push(x);
      clickY.push(y);
      clickDrag.push(dragging);
  }

  function redraw() {
      context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears the canvas

      context.strokeStyle = "#000000";
      context.lineJoin = "round";
      context.lineWidth = 2;

      for (var i = 0; i < clickX.length; i++) {
          context.beginPath();
          if (clickDrag[i] && i) {
              context.moveTo(clickX[i - 1], clickY[i - 1]);
          } else {
              context.moveTo(clickX[i] - 1, clickY[i]);
          }
          context.lineTo(clickX[i], clickY[i]);
          context.closePath();
          context.stroke();
      }
  }

  });

Answer 1

您必须清除以下数组clickX、clickY 和clickDrag:

context.clearRect(0, 0, context.canvas.width, context.canvas.height);
clickX = []; // clear mouse "logs"
clickY = [];
clickDrag = [];

<强> Working jsFiddle

当您单击或拖动鼠标时，将调用 addClick 方法，该方法会填充数组 clickX、clickY 和 clickDrag 与鼠标坐标。当调用 redraw 方法时，它会再次在 Canvas 上绘制点。因此清除这些数组将解决您的问题。