Drop location after drag and drop

Currently developing a drag and drop based on example: https://gojs.net/latest/samples/htmldragdrop.html

I’m trying to understand how the drop location is calculated. is the value of “window.PIXELRATIO” a constant or how is this value calculated?

It’s computed when the diagram is initialized:

window.PIXELRATIO = myDiagram.computePixelRatio(); // constant needed to determine mouse coordinates on the canvas

I see it now. Thanks