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[网页设计]canvas实现刮刮乐

 

canvas实现刮刮乐主要是要注意两个地方:第一个是将绘制的图形设置成背景图片(用到toDataURL属性),这样在擦覆盖层的时候才不会丢失绘制的图案,

第二个是设置在绘制插图的时候,设置透明透明(用到globalCompositeOperation属性)

代码如下:

<script>
var arr=[
{name:"iphone7 磨砂黑",color:"rgba(255,255,0,1)"},
{name:"iphone7 磨砂黑",color:"rgba(0,255,0,.9)"},
{name:"iphone7 磨砂黑",color:"rgba(10,255,255,1)"},
{name:"iphone7 磨砂黑",color:"rgba(10,255,100,1)"}
]
var r=Math.random();
var rIndex= Math.floor(r*arr.length);
var rPrice=arr[rIndex];
var cv=document.getElementsByTagName('canvas')[0];
var isDown=false;
cv.height=400;
cv.width=600;
var ctx=cv.getContext("2d");
function toAngle(radian){
return radian/Math.PI*180;
}
function toRadian(angle){
return angle/180*Math.PI;
}
ctx.textAlign="center";
ctx.textBaseline="middle";
ctx.font="30px consolas";
ctx.fillStyle=rPrice.color;
ctx.fillText(rPrice.name,cv.width/2,cv.height/2); var dataURL=cv.toDataURL("image/jpg",1);
cv.style.background="url("+dataURL+")"; //覆盖层
ctx.beginPath();
ctx.fill;
ctx.fillRect(0,0,cv.width,cv.height); cv.addEventListener("mousedown",function(){
isDown=true;
})
cv.addEventListener("mouseup",function(){
isDown=false;
ctx.globalCompositeOperation="source-out"
})
cv.addEventListener("mousemove",function(e){
if (isDown){
ctx.globalCompositeOperation="destination-out";
ctx.beginPath();
var posObj=cv.getBoundingClientRect(); var left=posObj.left;
var top=posObj.top; var x= e.clientX-left;
var y= e.clientY-top; ctx.arc(x,y,50,0,Math.PI*2);
ctx.fill();
}
})
</script>