• Non-polygons The system currently allows you to create a polygon of 0, 1, or 2 vertices. The former makes no sense at all, the latter doesn't really form a polygon, but rather a point. Prevent the user from creating a 0 polygon (or simply ignore it, but don't let it be entered into the list of active polygons), display the single point as a point, and the line as a line.

• Vertex moving (shape modification)Currently, only an entire polygon may be moved. Allow the user to drag a single vertex, changing the shape of the polygon. This requires that you be able to distinguish between the user wishing to move an entire polygon or a single vertex. Feel free to choose any scheme you wish-- the one I did that a click near a vertex indicated that the user wished to move only the vertex, while a click more to the middle of the polygon indicated the user wished to move the entire polygon. The actual mechanism to detect proximity to a vertex s again up to you. I mentioned in class having a distance value and checking if the click was within that distance of a vertex. Another approach mentioned by one of you was to introduce bounding boxes for the vertices as well as the polygon itself. Both work, and there may be other techniqes as well.

• Fixing color selection The color selection is currently not very intuitive. Fix it so that if you are not creating a polygon and you are positioned on a polygon, selecting a color from the menu, sets the polygon to that color.

• Predefined shape submenu Add another submenu labelled 'Shapes' that allows the user to select from a triangle, square and hexagon. The selected shape sppears (without the user having to click vertices) on the screen (either at a constant position-- say the middle) or at the position of the mouse. This is easiest done by simply creating the appropriate polygon object (i.e., when the user specifies a shape-- say a square-- you set up the appropriate vertex vector/array and create a new polygon object), which requires ittle change to the system

  A more sophisticated,object-oriented and difficult approach would be to create a Shape base class and use inheritance to create Triangle, Square, Hexagon, and Polygon subclasses. I haven't actually coded this approach so I can't speak to its difficulty or gotchas-- furthermore, I'm not sure how many of you have experience with inheritance in C++, so unless you've done everything else, I wouldn't even attempt to try this approach.

• Send to back You may notice a strange effect when two or more polygons overlap-- it always moves the same polygon (regardless of which one was there first). Add a menu entry to the top-level menu-- Send to back that effectively positions the topmost polygon behind all the other ones it overlaps. (You can achieve this by moving the particular polygon to the front/back of your polygon vector/array).

• Displaying the front in front Now that polygons have selection order, display them properly-- a polygon that is behind another should be displayed as such (i.e., it should be occluded, rather than occlude the others).

Furthermore, it's may be the case that your program will upon occasion crash. That's fine and is to be expected at an early stage of testing. When you submit your code, please indicate as much as possibly, the conditions that cause any failures.

Files for Assignment 3