用javascript实现画板的代码

        { 
            var dx=start[0]-end[0]; 
            var dy=start[1]-end[1]; 
            var x,y; 

            if( Math.abs(dx) > Math.abs(dy) ) 
            { 
                for(var x=start[0];x!=end[0]+(end[0]-start[0])/Math.abs(end[0]-start[0]);x+=(end[0]-start[0])/Math.abs(end[0]-start[0]) ) 
                { 
                    y=Math.round((x-start[0])/dx*dy+start[1]); 
                    this.container.childNodes[this.trans([x,y])].style.backgroundColor=color; 
                } 
            } 
            else 
            { 
                for(var y=start[1];y!=end[1]+(end[1]-start[1])/Math.abs(end[1]-start[1]);y+=(end[1]-start[1])/Math.abs(end[1]-start[1]) ) 
                { 
                    x=Math.round((y-start[1])/dy*dx+start[0]); 
                    this.container.childNodes[this.trans([x,y])].style.backgroundColor=color; 
                } 
            } 
        } 
        this.drawCircle=function(m,R,color) 
        { 

            for(var r=0;r<=Math.floor(Math.sqrt(R*R-r*r));r++) 
            { 

                x=m[0]+r;y=m[1]+Math.floor(Math.sqrt(R*R-r*r));