画布通过鼠标光标绘制线条

Question

这是我通过按/释放鼠标按钮在画布中绘制线条的方式。但它并不完全是我试图得到的结果：通过按下鼠标按钮，直线的起始点被设置，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，就像现在要做的那样。通过释放鼠标按钮，线条完成/固定。

因此，使用该应该能够以任何方向/旋转在画布上的任何位置绘制直线。按下鼠标按钮选择起点并释放直线的终点。

$(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; 
 
    }); 
 
});

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

Answer 1

你需要删除什么是在画布上，一旦它，如果你想修改它
（与ctx.clearRect()）把它漆成;

看看这个：

$(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; 
 
    }); 
 
});

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

Answer 2

你应该做的是这样的。

$(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>