aka Tricks and Traps... the making of Gotcha!
SPOILER ALERT
What follows explains in detail the creation of my Gotcha! level.
If you haven't played it yet, you should, and you certainly should before reading on... otherwise it'll spoil the surpises!
Get it here http://goofans.com/download/level/gotcha
First a couple of basic building blocks...
compositegeom objects
Pretty much exclusively in the original levels, compositegeom objects were used to either
i) Produce more complicated movable shapes than just a circle or a rectangle.
(The lifting fingers in Genetic Sorting Machine, the Third Wheel in Third Wheel)
or
ii) To collect together a load of static items (walls, platforms etc) from all over a level, so they could all be tagged and moved together.
It's the third possibility that you can exploit when making traps, and I'm sure it'll have other uses as well.
A compositegeom object is built from a number of child rectangles and circles. Each one is positioned relative to the "center" of the compgeom object, so that when the main object moves or turns all the children move and turn in exactly the same way... as if they were a single solid object.
But... it doesn't mean that any / all of the children have to be close together or even touching. So, you can have multiple objects that move, turn, spin, act together (as if they were a single object).. but that aren't connected together by anything "solid".
This is a VERY useful "feature" of compgeom
The same is true for hinges
When dealing with any non-static (moving/movable) object you need a hinge to fix it to "the world".. otherwise they just free-fall.
The hinge has an "anchor" position and an object it attaches to (the "body")
If you want something to spin about its center (like the Wobbly head in Chain) you position the circle, put the hinge at its center point.. and hey presto.
But there's nothing that means the anchor has to be in the center of the object, or even inside it, or anywhere near it!
Like compositegeom objects, the hinge and the body act as if they are firmly connected together, without having anything solid actually connecting them.
This is also VERY useful
Using Linear Forcefields to throw / move stuff
I spotted this in Product Launcher, it's how they got the gun to rise up at the end.
The gun was just a normal rectangle, non-static with a mass and a material and an the image of the gun applied to it.
Initially it's sitting below the Z, and has a big Forcefield pushing up on it, but it can't move because the blocks that make the Z are in the way.
Once the Z blocks have exploded, the Gun rectangle is pushed up slowly by the forcefield.
Note: There is a very useful property of a linearforcefield.. geomonly
When set to true it means that the force field only acts on geometry objects, and NOT Goos. So you make huge and/or strong force fields wherever you need them, but they don't affect the goos, so the player doesn't know they are there... until it's too late! 