1. added lines for the light 3 paths for principal rays different colors and arrow heads.
2. added transparent 100 lines to guide visualization
3. added mechanism for lens changing thickness for converge and concave
4. change color scheme to be more like physlets
5. added pictorial and logic for more scaffolds to help people associate the use of the converging lens ;D
6. limited the height of object to height of lens for closer approximation of image possible
7. added 2F F F 2F and the drag-able 4 points
8. redesign the code for the appearance of pictures to follow Boolean logic
9. added the side/opposite of object and image to follow 4 checkbox
10. debug the appearance of strange lines when p = 1.8 instead of 1.8000000000000001 and f also.
11. added marginal rays
12. added all rays that assume the lens is infinitely long because i can't create the logic for bend or don't bend light
13. background color back to grey, darkgrey causes some visual cursor difficulties to visualize
14. added screen but it does do much except allow some ease of noticing non focus light
15. changed to fit typical pen and paper questions < 40 cm instead of 2 cm
16. improved the lens color to grey convex and concave types
17. background to
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