Canvas DrawImage() 质量差
Canvas DrawImage() poor quality
我有问题 Html5 canvas
我画了一个图像,但它的质量变得很差
用canvas画出来后就变成了这个
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);
}
您可以逐步缩小图像以获得更好的效果。
由于您的最终尺寸是原始尺寸的 1/4,您可以:
将 1000x669 图像缩放一半到 500x334 到临时 canvas
将 500x335 canvas 缩小一半到 250x167 到主 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://ictcluster.ge/wp-content/uploads/2018/09/wandio-logo-1-1024x724.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>
我有问题 Html5 canvas
我画了一个图像,但它的质量变得很差
用canvas画出来后就变成了这个
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);
}
您可以逐步缩小图像以获得更好的效果。
由于您的最终尺寸是原始尺寸的 1/4,您可以:
将 1000x669 图像缩放一半到 500x334 到临时 canvas
将 500x335 canvas 缩小一半到 250x167 到主 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://ictcluster.ge/wp-content/uploads/2018/09/wandio-logo-1-1024x724.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>