This is the patch to Issue 2635032. It adds subtle drop shadows to lines, arrows, ellipses and rectangles.
Two screen shots w/ and w/o drop shadows are attached as well.
The user preference to toggle drop shadows requested in 1844937 is not yet implemented but this should be fairly easy.
The patch is in unified format, the patches to all three changed classes are contained in one patch file. If this is inconvenient for you, please let me know.