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I have seen this game
Fancy Pants 2 . And the thing I noticed apart from the physics and beautiful animations is that the character is moving along slopes , even curved slopes. I have little experience in Box2d, but this concept of curved slopes is new to me. It would be a great help to me If somebody enlightened me on this concept and its implementation. Even If the implementation is not in box2d, it is welcome.
How do you get curves in Box2D?
In the unreleased version of Box2D, there are two new shape types, b2LoopShape and b2EdgeShape, which let you build curves out of a sequence of line segments.
In the released version, you can use multiple small boxes set at angles to get a similar effect, but bodies have a tendency to do unstable and unexpected things near connection points. So I'd recommend using the unreleased version.
How can a character fall down the curve?
Make the character a wheel! My question about platformer physics has some discussion on this, but the basic idea is to mount your character's body on a rotating wheel, and move by applying rotational force to the wheel. Even though (actually, because) the wheel has friction, the downward force from gravity will cause it to rotate down slopes - like a real wheel. By changing the revolute joint's motor parameters, you can make it resist rotation as much as is necessary to avoid it rolling down small inclines.
Fancy Pants was made in Flash, and Flash has a specific method called 'hitTest' which allows you to test a pixel (in this case, he probably does 2-3 pixel hitTests along the bottom of the Fancy Pants character) against whatever is drawn within a designated movieclip object. It can be a bit tricky to get it feeling right, but this built-in function is why so many Flash games have collisions with curved slopes. The process is much more complicated for most other engines, and usually has to be done manually, but there are a few different methods.
The method I'm most familiar with is if your engine is tile-based (think Sonic the Hedgehog), the tiles designated as curved could each have a formula which determines the 'Y' collision position based on the character's current 'X' position on that tile. You would have to determine the formula based on how steep of a slope and how curved you're looking for. You could use a graphing calculator or graphing program to experiment with the formulas. You can have multiple tiles with different curves and formulas associated with them this way.
