I've posted an example below of a few edits I've made to my own box2d.gpas. After reading the Box2D manual and discovering there were a number of features and behaviours I wanted to make use of but weren't implemented in the wrapper, I had a play around. I'm sure it's all simple stuff to most, but I felt quite accomplished getting them to work, since I don't know anything at all about any flavour of C based languages. Hence coding in BASIC!
I figured I'd post the amendments I made in case they might be of use to others. I've supplied default behaviours, so they should work just fine with your existing code without complaining that you haven't supplied enough parameters and without changing the behaviour of your objects.
The extra parameters:
isSensor... A sensor is a shape that detects collision but does not produce a response. You can flag any shape as being a sensor. Sensors may be static or dynamic. Note it won't collide with anything at all! As the manual says, useful for when you need to know when two shapes overlap yet there should be no collision response.
fixedRotation... stops a physical body from being able to rotate. Can be a useful override for certain objects (say, moving platforms) since the default behaviour of box2d is that objects do rotate on collision etc.
groupIndex... You can have all shapes with the same group index ALWAYS collide by setting a POSITIVE group index, or NEVER collide by setting a NEGATIVE group index. Zero is default behaviour. Very useful, because it allows you to override the default collisions of Box2D while still being able to get and set any of Box2D's physical properties for objects. Using 'isSensor' doesn't cut it for this, because then the object wont collide with anything at all, including groundboxes. I noticed this line was in box2d-extended but commented out. I've personally not found any issues with it.
Incidentally, personally speaking, I've found that ground boxes dont seem to have as good collision detection as actual boxes. I really dont know why, but my objects at even reasonably low velocities will embed themselves into the ground boxes and be unable to move again, even if I use setBullet for supposedly enhanced collision handling. So I now use a static 'ordinary' box (any object is static as long as it has a mass of 0.0) with a positive group index instead of ground boxes, which seems to have eliminated that problem entirely.
FUNCTION b_CreateBox: mass, friction, restitution, lineardamp,angulardamping, x, y, w, h, isSensor = FALSE, fixedRotation = FALSE, groupIndex = 0
INLINE
b2BodyDef def;
def.position.Set(x,y);
def.linearDamping = lineardamp;
def.angularDamping = angulardamping;
def.fixedRotation = fixedRotation; // you would need to add this to other shape functions you want to do the same with
b2Body* pBody = bWorld->CreateBody( &def );
b2PolygonDef poly;
if(mass>0.0) poly.density = mass;
poly.filter.groupIndex = groupIndex; // and add this!
poly.friction = friction;
poly.restitution = restitution;
poly.isSensor = isSensor; // and add this!
poly.SetAsBox(w*.5, h*.5);
pBody->CreateShape( &poly);
if(mass>0.0) pBody->SetMassFromShapes();
return b_NewObject(pBody, bBody);
ENDINLINE
ENDFUNCTION
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