var imageWidth = canvas.width / Math.sqrt(scale);
var imageHeight = canvas.height / Math.sqrt(scale);
var sx = (canvas.width-imageWidth)/2;
var sy = (canvas.height-imageHeight)/2;
context.drawImage(image,sx,sy,imageWidth,imageHeight,0,0,canvas.width,canvas.height);
function drawImageByScale(scale){
var imagewidth=600*scale;
var imageheight=400*scale;
var Sx=imagewidth/2-canvas.width/2;
var Sy=imageheight/2-canvas.height/2;
context.drawImage(image,Sx,Sy,image.width,image.height,0,0,imagewidth,imageheight);
}
这样就对了。
