fredb219 and me have begun to integrate Box2D into Wormux.

Currently, I can't see how to manage collision with the ground!!

"The maximum vertex count is defined by b2_maxPolyVertices which is currently 8" so it's impossible to make the ground acts as one single polygon...

I have read several topics about that in Box2d forum but I'm not convinced by any solution...

Anyway, this one is interested
http://www.box2d.org/forum/viewtopic.php?f=3&t=1180

A good example of 2D physical engine :

Box2D :
http://www.box2d.org/

Very interesting project but no way to compile it with autotools or cmake just VC8 files ...

I'm currently trying to compile it using cmake but actually, it's not working. I have managed to compile the library but no way to link the demo.

So if a cmake guru is interested ...

And Phys2D :
http://www.cokeandcode.com/phys2d/

Written in Java ! try out the demo, it's quite amazing !

Very interesting presentation about the GJK algorithm :

http://realtimecollisiondetection.net/pubs/SIGGRAPH04_Ericson_the_GJK_algorithm.ppt

GJK is used to compute the distance between two polygon.

v 0.2.1

What's new :
- Better stability of stacked object (but still not perfect)
- Higher performance (remove the need of triangle test).

(file #2772)

First some comments about building:
- need to install libtool
- an error : g++ -g -O2 -o physics -R/usr/lib physics.o color.o constraint.o link.o object_generator.o particle.o physical_engine.o physical_polygon.o affine_transform.o error.o random.o -L/usr/lib -lSDL -lSDL_image -lSDL_gfx -lSDL_image -lpng12
g++: unrecognized option '-R/usr/lib'

to fix, remove the unrecognized option ;-) :
cd src/
g++ -g -O2 -o physics physics.o color.o constraint.o link.o object_generator.o particle.o physical_engine.o physical_polygon.o affine_transform.o error.o random.o -L/usr/lib -lSDL -lSDL_image -lSDL_gfx -lSDL_image -lpng12

run:
./physics

Wouw! it's amazing!!! Good work Drayan!
Will it be difficult to integrate into Wormux ?

Todo : push this function in vector2.h :
...
static Vector2<T> Intersection(const Vector2<T> & A, const Vector2<T> & B, const Vector2<T> & C, const Vector2<T> & D) {
double a1, a2, b1, b2, xr, yr;
/*// No intersection possible => compute a fake cross point which is a avg of this four point
if(A.x == B.x && C.x == D.x) {
double x1, y1, x2, y2;
x1 = (C.x - A.x) + A.x;
y1 = (C.y - A.y) + A.y;
x2 = (B.x - D.x) + B.x;
y2 = (B.y - D.y) + B.y;
return Vector2<T>(static_cast<T>((x1 + x2) / 2), static_cast<T>((y1 + y2) / 2));
} else if(A.x == B.x) {
a2 = (C.y - D.y) / (C.x - D.x);
b2 = C.y - a2 * C.x;
return Vector2<T>(static_cast<T>(A.x), static_cast<T>(a2 * A.x + b2));
} else if(C.x == D.x) {
a1 = (C.y - D.y) / (C.x - D.x);
b1 = C.y - a2 * C.x;
return Vector2<T>(static_cast<T>(C.x), static_cast<T>(a1 * A.x + b1));
}
// Youhouh ! A normal situation :)*/
a1 = (A.y - B.y) / (A.x - B.x);
a2 = (C.y - D.y) / (C.x - D.x);
b1 = A.y - a1 * A.x;
b2 = C.y - a2 * C.x;
xr = (b2 - b1) / (a1 - a2);
yr = a1 * xr + b1;
return Vector2<T>(static_cast<T>(xr), static_cast<T>(yr));
}
...

Compute the cross point of 2 lines (A, B) and (C, D).

And here is a new enhanced and clean up version with fully working autotools.

Take the tar physics-0.1.1.tar.bz2 in the bottom of the page then :

tar xfvj physics-0.1.1.tar.bz2
cd physics
./autogen.sh
make

then go in the src directory, run the little program and enjoy it.

cd src
./physics

What is working now :
- ground collision detection.
- wind handling
- gravity
- overlaping detection (but nothing to handle this for the moment)

What need to be done :
- constraints no overlaping shape
- enhance the way we detect overlaping because it's damn slow !

(file #2753)

Interesting paper about physic simulation grab around the net.

Wikipedia reference about collision detection :
http://en.wikipedia.org/wiki/Collision_detection

Minkowski's addition :
http://en.wikipedia.org/wiki/Minkowski_sum

much more funny java applet demonstrating Minkowski's addition :
http://www.cut-the-knot.org/Curriculum/Geometry/PolyAddition.shtml

Gilbert-Johnson-Keerthi distance algorithm :
http://en.wikipedia.org/wiki/Gilbert-Johnson-Keerthi_distance_algorithm

Paper about the nofit polygon algo :
http://www.asap.cs.nott.ac.uk/publications/pdf/gk_wmc99.pdf

What's remain is the need of a colision detection algorithm. A simple way to do it is to sort out every triangle of the polygon by a basic bound test and then to compute a Minkowski's sum for the remaining triangle. If one of the two triangle is fully in the Minkowski polygon, then both triangle overlapse.

A very interesting article about physic simulation :
http://www.teknikus.dk/tj/gdc2001.htm

The author talk about the physical engine used in Hitman: Codename 47.

This engine use the Verlet integration (http://en.wikipedia.org/wiki/Verlet_integration).

Another cool little project of physical engine :

http://people.freedesktop.org/~krh/akamaru.git/