Once a chord pro file is rendered, there is just a cached image per page. The images are not re-rendered unless you change the font size or some other property that requires a re-render (pinch zooming changes the font size). So this cost of redrawing the page should be no higher than using a PDF or image file, as the pages of the chord pro file are still just cached in memory as images. One thing I should mention is that, with text/chord pro files, if I processed every small delta with a pinch zoom and re-rendered the file each time, that would overwhelm the cpu, so I instead only process deltas that cross a certain threshold, so that's why there isn't a smooth zoom effect with chord pro files. Also, due to the dynamic nature of chord pro files where the entire layout of every page changes if you change the font size or other text display settings, I can't cache much that would speed up the rendering. PDFs are faster to process in this regard, as all of the page sizes are fixed and they usually just have images stored in the pages, or vector graphics.
Mike
Mike