Questions about Sample Framework screens

Topics: User Forum
Jun 20, 2007 at 4:11 PM
Hey Jeff, looks like you're doing some great work on the newest version of the engine.

I just had a few quick questions about how the Bodies and Geometries fit together- more specifically, what's going on in the four sample shots provided in your latest post.

It seems as though there is a pyramid of boxes. It's apparent to me that each box piled up has its own Geometry, but is it also its own body? Another example of this question can be seen in what moves the pyramid of boxes- the 4 yellow circles. They seem to stay together, but I didn't know why. Are the 4 circles seperate Geometries attached together in the same Body? Are they different Bodies and Geometries alltogether, but just constrained to the position of the mouse?

The next question I have is about Geometries in Body objects. I know from what you posted that several Geometry objects can go into a single Body Object. Will these all have a fixed orientation to each other inside the Body object? When I think of a 'Body,' I don't necessarily see a rigid body. I also see a set of Rigid sections connected with joints, able to move freely. Is this the concept behind the Body object, or will everthing inside of it be rigid?

Also, can geometries be freely modified while in the Body? I'm going to use the next Farseer in a game that I'm laying out the structure for now, and would like to have bodies that deform (break apart/lose sections of mass) Will this be possible in one form or another?

Phew, that's a lot of prodding, sorry! I'm eager to get the answers and give the next version a shot. Thanks again!
Jun 21, 2007 at 4:49 PM
A lot of questions and little time to answer:

First things first. It is more accurate to say a geometry is "attached" to a body rather than "in" the body. The body objects know nothing about geometry objects but geometry objects know what body they are attached to.

  • Each sqare in the pyramid is a single body with a single geometry attached.
  • The 4 circles are indeed a single body with 4 geometries attached at offsets to the bodies center.
  • As with most the demos, you can move and spin the yellow bodies using the keyboard or gamepad. The movement is done by applying forces and/or torques.
  • You should be able to do the "deform" thing in some manner using joints and/or multiple geometries. Joints will indeed be "breakable" in the new version. As for modifying the geometries shape on the fly, this might be trickier. There is a computation that has to take place on each geometry when it is created. This sets up the grid that is latter used to detect collisions. It may be possible to modify a geometry and update its grid in real-time if the geometry isn't too complex. I've never tried it though.
Jun 23, 2007 at 2:12 AM
Sounds good, crashlander, thanks for the quick replies.
Hopefully the wait won't be too long!