I am working on a little tool to measure architectural drawings from PDF files. The PDF is rendered by Mozilla pdf.js on to a canvas. Once rendered, I would like to get coordinates all the paths/lines/rects on the canvas. This is to make the tool snap to the endpoints of lines when the mouse cursor is nearby. There don't seem to be an API for retrieving that. As it is not my code that actually renders onto the canvas, I dont path information beforehand.

What I have so far tried is, modify the pdf.js to emit the endpoints' x,y based on moveTo and lineTo, save them in an array. Using this array I can snap correctly in simple drawings. For complex drawings, there seems to be lot of transformations applied and this simple procedure doesnt work.

Any ideas on how to go about it?