画布DrawImage()质量较差 [英] Canvas DrawImage() poor quality

问题描述

我对Html5 canvas有问题

I have a problem with Html5 canvas

我绘制图像，但是图像质量很差

i draw an image but its quality becomes very poor

在我用画布绘制它之后，它就变成了

after i draw it with canvas it becomes this

我的代码在这里

<script type="text/javascript">

$canvasWidth = $('#canvas').width;
$canvasHeight = $('#canvas').height;
var alpha = 0.0;

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');


function draw(){
    var delta = 0.05;
    ctx.clearRect(0,0,$canvasWidth, $canvasHeight);
    ctx.globalAlpha = alpha;

    var logo= new Image();

    WandioLight.onload = function(){
        ctx.drawImage(logo, 0, 0, 250, 167);

    };

    logo.src = "logo.png";

    alpha += delta;
    if(alpha > 1.0){
        return false;
    }
    setTimeout(draw, 50);
}

推荐答案

您可以逐步缩小图像以获得更好的效果.

You can incrementally scale your image down for better results.

由于您的最终尺寸是原始尺寸的1/4，因此您可以:

Since your final size is 1/4 the original size, you could:

• 将1000x669图像的一半缩放到临时画布上的500x334

• scale the 1000x669 image in half to 500x334 onto a temp canvas

将500x335画布的一半缩放到主画布上的250x167

scale the 500x335 canvas in half to 250x167 onto the main canvas

这是示例代码和演示:

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;

var img=new Image();
img.onload=start;
img.src="https://dl.dropboxusercontent.com/u/139992952/multple/wandio.png";
function start(){


  // scale the 1000x669 image in half to 500x334 onto a temp canvas
  var c1=scaleIt(img,0.50);

  // scale the 500x335 canvas in half to 250x167 onto the main canvas
  canvas.width=c1.width/2;
  canvas.height=c1.height/2;
  ctx.drawImage(c1,0,0,250,167);

}

function scaleIt(source,scaleFactor){
  var c=document.createElement('canvas');
  var ctx=c.getContext('2d');
  var w=source.width*scaleFactor;
  var h=source.height*scaleFactor;
  c.width=w;
  c.height=h;
  ctx.drawImage(source,0,0,w,h);
  return(c);
}

body{ background-color: ivory; padding:10px; }
canvas{border:1px solid red;}

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

这篇关于画布DrawImage()质量较差的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！