Question

这就是我通过按下/释放鼠标按钮在画布中绘制线条的方法。但这并不是我想要得到的：通过按下鼠标按钮，直线的起点将被设置，终点将跟随鼠标光标。但是这条线应该总是一条直线 - 而不是绘制一些曲线，就像现在这样做。通过释放鼠标按钮，线条完成/固定。

使用它应该能够在任何方向/旋转的画布上的任何地方绘制直线。按下鼠标按钮作为起点并释放直线终点。

＆＃13;

$(function() {
  var letsdraw = false;

  var theCanvas = document.getElementById('paint');
  var ctx = theCanvas.getContext('2d');
  theCanvas.width = 420;
  theCanvas.height = 300;

  var canvasOffset = $('#paint').offset();

  $('#paint').mousemove(function(e) {
    if (letsdraw === true) {
      ctx.lineTo(e.pageX - canvasOffset.left, e.pageY - canvasOffset.top);
      ctx.stroke();
    }
  });

  $('#paint').mousedown(function() {
    letsdraw = true;
    ctx.strokeStyle = 'blue';
    ctx.lineWidth = 1;
    ctx.beginPath();
    ctx.moveTo(e.pageX - canvasOffset.left, e.pageY - canvasOffset.top);
  });

  $(window).mouseup(function() {
    letsdraw = false;
  });
});

＆＃13;

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<canvas id="paint"></canvas>

＆＃13;

Answer 1

如果你想要修改画布，你需要删除画布上的内容（使用ctx.clearRect()）;

看看这个：

＆＃13;

$(function() {
  var letsdraw ;

  var theCanvas = document.getElementById('paint');
  var ctx = theCanvas.getContext('2d');
  theCanvas.width = 420;
  theCanvas.height = 300;

  var canvasOffset = $('#paint').offset();

  $('#paint').mousemove(function(e) {
    if (letsdraw) {
      ctx.clearRect(0,0,theCanvas.width,theCanvas.height);
      ctx.strokeStyle = 'blue';
      ctx.lineWidth = 1;
      ctx.beginPath();
    
      ctx.moveTo(letsdraw.x, letsdraw.y);
      ctx.lineTo(e.pageX - canvasOffset.left, e.pageY - canvasOffset.top);
      ctx.stroke();
    }
  });

  $('#paint').mousedown(function(e) {
    letsdraw = {
      x:e.pageX - canvasOffset.left,
      y:e.pageY - canvasOffset.top
      }
    
  });

  $(window).mouseup(function() {
    letsdraw = null;
  });
});

＆＃13;

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<canvas id="paint"></canvas>

＆＃13;

Answer 2

你应该这样做。

$(function() {
  var letsdraw = false;
  var theCanvas = document.getElementById('paint');
  var ctx = theCanvas.getContext('2d');
  theCanvas.width = 420;
  theCanvas.height = 300;
  var canvasOffset = $('#paint').offset();
  var lastpoints = {
    "x": 0,
    "y": 0
  };

  $('#paint').mousemove(function(e) {
    if (letsdraw === true) {
      lastpoints.x = e.pageX;
      lastpoints.y = e.pageY;
    }
  });

  $('#paint').mousedown(function(e) {
    letsdraw = true;
    ctx.strokeStyle = 'blue';
    ctx.lineWidth = 1;
    ctx.beginPath();
    ctx.moveTo(e.pageX - canvasOffset.left, e.pageY - canvasOffset.top);
  });

  $('#paint').mouseup(function(e) {
    ctx.lineTo(lastpoints.x - canvasOffset.left, lastpoints.y - canvasOffset.top);
    ctx.stroke();
    letsdraw = false;
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<canvas id="paint"></canvas>

画布通过鼠标光标绘制线条

2 个答案: