显示新图表时清除HTML画布

Question

So I am building an AngularJs chart that utilizes an Angular Library to create the chart on a Canvas tag. However when I drag and drop a new data set onto the canvas to redraw it continues to hold the old data. What I am trying to accomplish is If (there is new data){ clear the canvas}. I know I have to use:

canvasReset.clearRect(0, 0, canvas.width, canvas.height); 

somewhere but what I am really looking for is an event handler to use to assist me in determining if anything is on the canvas, and if so clearing it. However, I am not looking for mouseover mouse-click,etc. But something that is just generally looking to see if the canvas is being utilized.

Answer 1

The short answer, you can't. But you can catch mouseevnets, or you can wrap canvas ctx drawing functions,like

var fill = ctx.fill;
ctx.fill = function(){
    fill.apply(this, arguments);
    setDirty();
};