用HTML5 实现橡皮擦的涂抹效果的教程

var imgData = ctx.getImageData(0,0,canvas.width,canvas.height); var dd = 0;

for(var x=0;x<imgData.width;x+=30){ for(var y=0;y<imgData.height;y+=30){

var i = (y*imgData.width + x)*4; if(imgData.data[i+3] > 0){

dd++ }

} }

if(dd/(imgData.width*imgData.height/900)<0.4){ canvas.className = "noOp";

} 　　　　　　　},100)

}); function tapmoveHandler(e){

e.preventDefault() x2 = hastouch?e.targetTouches[0].pageX:e.clientX-canvas.offsetLeft;

y2 = hastouch?e.targetTouches[0].pageY:e.clientY-canvas.offsetTop;

ctx.save(); ctx.moveTo(x1,y1);

ctx.lineTo(x2,y2); ctx.stroke();