canvas实现滚动⿏标放⼤缩⼩及拖动
1、canvas实现滚动⿏标放⼤缩⼩
2、实现⿏标拖动
实现⽅式canvas转图⽚
关键代码如下：
<canvas class="canvas"></canvas>
<script type="text/javascript">
  var canvas = ElementsByClassName('canvas');
  var ctx = Context("2d");
  var img = new Image();
$(function(){
trackTransforms(ctx);
var lastX=canvas.width/2, lastY=canvas.height/2;
var dragStart,dragged;
canvas.addEventListener('mousedown',function(evt){
document.UserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
dragStart = ansformedPoint(lastX,lastY);
dragged = false;
},false);
canvas.addEventListener('mousemove',function(evt){
lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
dragged = true;
if (dragStart){
var pt = ansformedPoint(lastX,lastY);
anslate(pt.x-dragStart.x,pt.y-dragStart.y);
redraw();
}
},false);
canvas.addEventListener('mouseup',function(evt){
dragStart = null;
if (!dragged) zoom(evt.shiftKey ? -1 : 1 );
},false);
var scaleFactor = 1.1;
var zoom = function(clicks){
if(clicks==1) return;
var pt = ansformedPoint(lastX,lastY);
var factor = Math.pow(scaleFactor,clicks);
ctx.scale(factor,factor);
redraw();
}
var handleScroll = function(evt){
var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
if (delta) zoom(delta);
return evt.preventDefault() && false;
};
canvas.addEventListener('DOMMouseScroll',handleScroll,false);
canvas.addEventListener('mousewheel',handleScroll,false);
});
img.src = DataURL("image/png");
function redraw(){
/
/ Clear the entire canvas
var p1 = ansformedPoint(0,0);
var p2 = ansformedPoint(canvas.width,canvas.height);
ctx.clearRect(p1.x,p1.y,p2.x-p1.x,p2.y-p1.y);
ctx.save();
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.drawImage(img,0,0);
}
function trackTransforms(ctx){
var svg = ateElementNS("/2000/svg",'svg'); var xform = ateSVGMatrix();
var savedTransforms = [];
var save = ctx.save;
ctx.save = function(){
savedTransforms.anslate(0,0));
return save.call(ctx);
};
var restore = store;
xform = savedTransforms.pop();
return restore.call(ctx);
};
var scale = ctx.scale;
ctx.scale = function(sx,sy){
xform = xform.scaleNonUniform(sx,sy);
return scale.call(ctx,sx,sy);
};
var rotate = ate;
xform = ate(radians*180/Math.PI);
return rotate.call(ctx,radians);
};
var translate = anslate;
xform = anslate(dx,dy);
return translate.call(ctx,dx,dy);
};
var transform = ansform;
var m2 = ateSVGMatrix();
m2.a=a; m2.b=b; m2.c=c; m2.d=d; m2.e=e; m2.f=f;
xform = xform.multiply(m2);
return transform.call(ctx,a,b,c,d,e,f);
};
var setTransform = ctx.setTransform;
ctx.setTransform = function(a,b,c,d,e,f){
xform.a = a;
xform.b = b;
xform.c = c;
xform.d = d;
xform.e = e;
xform.f = f;
return setTransform.call(ctx,a,b,c,d,e,f);
};
var pt  = ateSVGPoint();
pt.x=x; pt.y=y;
return pt.matrixTransform(xform.inverse());
}
}
</script>

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