Simple knockout groups should just be rendered with CAIRO_OPERATOR_SOURCE
Submitted by Carl Worth
Assigned to poppler-bugs
Cairo uses knockout groups to put its fallback images into PDF files, and cairo would be happier if poppler would just use SOURCE to draw those groups.
This could probably be done if poppler looked at the knockout group and saw that it just consists of drawing one rectangular image, (so it knows the "shape" is a rectangle and doesn't need to compute the shape and draw with DEST_OUT and ADD to get the shape).
Good luck, Jeff!