the shape tool needs to be improvised. following are my observation on shape tool limitations and features that require re inventing
1. the resize option actually make the diagram thicker.
2. the line do not perfectly align tangentially to other lines and circles
3. The shapes tools should also have a auto deselect option like eraser.else if someone misses to switch to pen erratic drawing occurs and one needs to undo.
4. the shapetool can occur some mathematical standard shapes like, ellipse, parabola, graph axes, sine and cosine graphs
5. ability to move one vertex of polygon to achieve desired shape