Overriding drawFrameOnCanvas and drawImageOnCanvas does not have dimensions and context defined

[Rasmus Melchior Jacobsen]

Describe the bug
Since version 0.19, the parameters for drawFrameOnCanvas and drawImageOnCanvas have changed, but when overriding, the dimensions and context parameters are always undefined.

To Reproduce

this.reader.drawFrameOnCanvas = (srcElement, dimensions, context) => {
// dimensions and context are undefined
}

Expected behavior
The two parameters should be defined when overriding the two functions.