HTML5画布绘制椭圆越来越多

Question

我在使用HTML5绘图的白板上书写。 问题是当我试图绘制椭圆时，所以按下并拖动，绘制了许多椭圆。

ctx.moveTo(startX, startY + (y-startY)/2); 
ctx.bezierCurveTo(startX, startY, x, startY, x, startY + (y-startY)/2); 
ctx.bezierCurveTo(x, y, startX, y, startX, startY + (y-startY)/2); 
ctx.stroke(); 

我想每次只显示一个椭圆。 有什么帮助吗？

Answer 1

这可能会有所帮助 - 这是我使用弧和缩放绘制椭圆的版本。

https://jsfiddle.net/richardcwc/wdf9cocz/

//Canvas 
 
var canvas = document.getElementById('canvas'); 
 
var ctx = canvas.getContext('2d'); 
 
//Variables 
 
var scribble_canvasx = $(canvas).offset().left; 
 
var scribble_canvasy = $(canvas).offset().top; 
 
var scribble_last_mousex = scribble_last_mousey = 0; 
 
var scribble_mousex = scribble_mousey = 0; 
 
var scribble_mousedown = false; 
 

 
//Mousedown 
 
$(canvas).on('mousedown', function(e) { 
 
    scribble_last_mousex = parseInt(e.clientX-scribble_canvasx); 
 
\t scribble_last_mousey = parseInt(e.clientY-scribble_canvasy); 
 
    scribble_mousedown = true; 
 
}); 
 

 
//Mouseup 
 
$(canvas).on('mouseup', function(e) { 
 
    scribble_mousedown = false; 
 
}); 
 

 
//Mousemove 
 
$(canvas).on('mousemove', function(e) { 
 
    scribble_mousex = parseInt(e.clientX-scribble_canvasx); 
 
\t scribble_mousey = parseInt(e.clientY-scribble_canvasy); 
 
    if(scribble_mousedown) { 
 
     ctx.clearRect(0,0,canvas.width,canvas.height); //clear canvas 
 
     //Save 
 
     ctx.save(); 
 
     ctx.beginPath(); 
 
     //Dynamic scaling 
 
     var scalex = 1*((scribble_mousex-scribble_last_mousex)/2); 
 
     var scaley = 1*((scribble_mousey-scribble_last_mousey)/2); 
 
     ctx.scale(scalex,scaley); 
 
     //Create ellipse 
 
     var centerx = (scribble_last_mousex/scalex)+1; 
 
     var centery = (scribble_last_mousey/scaley)+1; 
 
     ctx.arc(centerx, centery, 1, 0, 2*Math.PI); 
 
     //Restore and draw 
 
     ctx.restore(); 
 
     ctx.strokeStyle = 'black'; 
 
     ctx.lineWidth = 5; 
 
     ctx.stroke(); 
 
    } 
 
    //Output 
 
    $('#output').html('current: '+scribble_mousex+', '+scribble_mousey+'<br/>last: '+scribble_last_mousex+', '+scribble_last_mousey+'<br/>mousedown: '+scribble_mousedown); 
 
});

canvas { 
 
    cursor: crosshair; 
 
    border: 1px solid #000000; 
 
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
 
<canvas id="canvas" width="800" height="500"></canvas> 
 
<div id="output"></div>