Comment 5 for bug 2012678

Poppler mostly tries to include changes from xpdfreader but I am not sure if that is still possible as the code bases continue to diverge. The main difference in the behaviour you report is probably that xpdfreader renders directly to the screen instead of into off-screen buffers which can displayed from a cache.

This is also why I am convinced that the redraw-on-focus-change is a cache size issue: The window certainly needs to be redrawn after gaining the focus and the image has come from somewhere. It usually comes from the cache which avoids any rendering. If this operation is slow because the images need to be rendered anew, this hints at a cache that is too small to keep the image data around. (Other options which effectively reduce the available cache size are "Keep obsolete pixmaps" and "Prefetch". Disabling those should also avoid "wasting" any cache capacity.)

If you are convinced that this is a rendering issue, please try to reproduce this using poppler-utils, e.g. pdftoppm, so that this can be reported upstream. Please make sure to use an up-to-date version of Poppler though as the above map renders, if somewhat slowly here taking 1.5 GB of memory at 500 % zoom without tiling and 650 MB with tiling.

As a closing remark, I am willing to help you diagnose this and if anything actionable is found to work on and include changes to qpdfview's code base. But if this stays at the level of "xpdfreader is so much better at this", then my advice is to use xpdfreader and call it a day.