旋轉箭頭，即在鼠標移動上繪圖

我想在mousemove上繪製箭頭，代碼波紋管繪製了一個水平箭頭。但是我希望它從開始繪製點旋轉到結束繪製點。我GOOGLE了很多，但我沒有找到解決辦法，也許是因爲我是在畫布上繪畫的新手。旋轉箭頭，即在鼠標移動上繪圖

drawArrowMove: function(e, _self) 
    { 
     var width = e.w ; 
     var height = e.h ; 
     var arrowW = 0.35 * width; 
     var arrowH = 0.75 * height; 
     var p1  = {x: 0,    y: (height-arrowH)/2}; 
     var p2  = {x: (width-arrowW), y: (height-arrowH)/2}; 
     var p3  = {x: (width-arrowW), y: 0}; 
     var p4  = {x: width,   y: height/2}; 
     var p5  = {x: (width-arrowW), y: height}; 
     var p6  = {x: (width-arrowW), y: height-((height-arrowH)/2)}; 
     var p7  = {x: 0,    y: height-((height-arrowH)/2)}; 

     _self.ctxTemp.beginPath(); 
     _self.ctxTemp.moveTo(p1.x, p1.y); 
     _self.ctxTemp.lineTo(p2.x, p2.y); // end of main block 
     _self.ctxTemp.lineTo(p3.x, p3.y); // topmost point 
     _self.ctxTemp.lineTo(p4.x, p4.y); // endpoint 
     _self.ctxTemp.lineTo(p5.x, p5.y); // bottommost point 
     _self.ctxTemp.lineTo(p6.x, p6.y); // end at bottom point 
     _self.ctxTemp.lineTo(p7.x, p7.y); 
     _self.ctxTemp.fillStyle = 'black'; 
     _self.ctxTemp.fill(); 
     _self.ctxTemp.stroke(); 
    }

來源

2013-06-27 user1151563

下面是如何畫一個箭頭在傾斜線

enter image description here

以任意角度繪製箭頭的最簡單方法是使用畫布旋轉能力。

使用Math.atan函數根據線的斜率計算適當的角度。

// calculate the radian angle of the line from [x1,y1] to [x2,y2] 
var radianAngle=Math.atan((y2-y1)/(x2-x1)); 

// adjust the angle based on line slope 
radianAngle+=((x2>x1)?90:-90)*Math.PI/180;

然後，你可以畫線：

// draw the line 
ctx.beginPath(); 
ctx.moveTo(x1,y1); 
ctx.lineTo(x2,y2); 
ctx.stroke();

最後通過旋轉上下文連接箭頭。

// rotate the canvas context to the appropriate angle 
ctx.rotate(radianAngle);

請注意，由於您已旋轉畫布本身，因此您只需將箭頭畫成水平狀態即可。簡單！

// save the un-transformed state of the context 
ctx.save(); 

ctx.beginPath(); 

// translate to the end of the line 
ctx.translate(x2,y2); 

// rotate to the appropriate angle 
ctx.rotate(radianAngle); 

// draw the arrowhead 
ctx.moveTo(0,0); 
ctx.lineTo(8,20); 
ctx.lineTo(-8,20); 
ctx.closePath(); 
ctx.fill(); 

// when done drawing on the rotated context, set it back to its untransformed state 
ctx.restore();

這裏是代碼和一個小提琴：http://jsfiddle.net/m1erickson/CQDww/

<!doctype html> 
<html> 
<head> 
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css --> 
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script> 

<style> 
    body{ background-color: ivory; } 
    canvas{border:1px solid red;} 
</style> 

<script> 
$(function(){ 

    var canvas=document.getElementById("canvas"); 
    var context=canvas.getContext("2d"); 

    function Line(x1,y1,x2,y2){ 
     this.x1=x1; 
     this.y1=y1; 
     this.x2=x2; 
     this.y2=y2; 
    } 
    Line.prototype.drawWithArrowheads=function(ctx){ 

     // arbitrary styling 
     ctx.strokeStyle="blue"; 
     ctx.fillStyle="blue"; 
     ctx.lineWidth=3; 

     // draw the line 
     ctx.beginPath(); 
     ctx.moveTo(this.x1,this.y1); 
     ctx.lineTo(this.x2,this.y2); 
     ctx.stroke(); 

     // draw the starting arrowhead 
     var startRadians=Math.atan((this.y2-this.y1)/(this.x2-this.x1)); 
     startRadians+=((this.x2>this.x1)?-90:90)*Math.PI/180; 
     this.drawArrowhead(ctx,this.x1,this.y1,startRadians); 
     // draw the ending arrowhead 
     var endRadians=Math.atan((this.y2-this.y1)/(this.x2-this.x1)); 
     endRadians+=((this.x2>this.x1)?90:-90)*Math.PI/180; 
     this.drawArrowhead(ctx,this.x2,this.y2,endRadians); 

    } 
    Line.prototype.drawArrowhead=function(ctx,x,y,radians){ 
     ctx.save(); 
     ctx.beginPath(); 
     ctx.translate(x,y); 
     ctx.rotate(radians); 
     ctx.moveTo(0,0); 
     ctx.lineTo(8,20); 
     ctx.lineTo(-8,20); 
     ctx.closePath(); 
     ctx.fill(); 
     ctx.restore(); 
    } 

    // create a new line object 
    var line=new Line(50,50,150,150); 
    // draw the line 
    line.drawWithArrowheads(context); 

}); // end $(function(){}); 
</script> 

</head> 

<body> 
    <canvas id="canvas" width=300 height=300></canvas> 
</body> 
</html>

來源

2013-06-28 05:25:24 markE

非常感謝你解釋這麼詳細的給我，那對我幫助很大！ – user1151563

旋轉箭頭，即在鼠標移動上繪圖

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