Viewport should support multiple bounding regions

[parasyte]

See: #349 and https://groups.google.com/forum/#!msg/melonjs/T7nOCwaI8vI/VqdsDkp0EhIJ

Multiple bounding regions will allow customized map scrolling mechanics found in games like Megaman, and Legend of Zelda: A Link to the Past. Where a map's scrolling will be "locked" into some region until the followed entity leaves the viewport.

[Warpten]

Another example would be Metroid Zero Mission (which I have been working on a few months ago, until it turned into vapor, but anyway). My idea at the time about this was to add viewport areas to the tmx level info, but I had no idea how to do that with Tiled at the time, and not even how to do it inside MelonJS.

Also, In some games, viewport boundaries cross each other: so I believe that if you enter in a new viewport area, you should not clog the viewport into this boundary if you are already in another viewport boundary. A perfect example for that is metroid zero mission:

(Notice the gray lines; those are the viewport boundaries)

Another interesting technique used in MZM is that destroying some blocks expand the viewport, typically revealing secret areas. That would be interesting to implement as well.

There are also places in games where viewport boundaris do not cross over each other; typically the game will smoothly transition from a viewport to another.

If by april nobody has done it i would be more than glad to work on that (I currently cannot work much; even my chess engine is sporadically programmed)

[parasyte]

I was playing with an idea for this late last night involving collision shapes to define how the viewport is allowed to scroll. For cases where hidden areas of a map may be revealed by the player entity moving into the area, the collision shape can simply be removed, allowing the viewport to continue scrolling into the hidden area.

This is not a high priority feature, but there's an idea that we might use (or not) later.