I've created a branch at github to begin supporting overlapping shapes.
Currently, shapes in xls and xlsx are cells and do not overlap.
I've converted them to shapes instead so overlapping shapes can be displayed.
However, overlapping shapes are not supported in docx and odt yet.
I, also, haven't supported line as shapes in ods yet so I haven't made a pull request yet because it may degrade for some users. Cheers.
Created a WIP pull request. Added support on ods and odt. Still need to support on docx. I'm currently only tested generated output using LibreOffice. Would appreciate if someone can check against MS Excel.
Tested on MS Office 2007 and were able to open and view xls, xlsx, and pptx generated files without problem. Need to work on docx format.
Probaby better to have property to output in original format for uses who do not want to output shapes.
Added property "net.sf.jasperreports.export.xls.compatibility" in xls export to switch between current cell output and shape output. Will add similar property to other export types.