The Unofficial guide for those who are COMPLETELY Lost...

1) Intro to SketchyPhysics

3) Shape Physics

4) Jointing Basics

5) Using the UI for Advanced Jointing

## Shape Physics

The other two right-menu options are SHAPE and DEBUG, and they are used together.

SHAPE: Sets the shape that SP sees the group as.

#### Just because you grouped a Cube doesn't mean SP "sees" it as a Cube!

USE THE SHAPE OPTION ON EVERY OBJECT YOU CREATE FOR SP!!!!

DEBUG: Use this option to check the shape SP "sees". After grouping an object and setting its SP shape, select this option and press RUN. SP will make a black wire diagram of the object AS IT SEES IT.

You may be surprised at what it sees. Also, just because you make a cylinder and set the shape to cylinder, doesn't mean it will be oriented correctly. (See below.)

AN INCORRECTLY SHAPED OBJECT:

This cylinder object was set to "cylinder", but by using the DEBUG option, you can see the black wireframe shows SP thinks it is actually on it's side. If any other object interacts with this cylinder, it will hit the black wireframe, NOT the actual grouped shape!

You can purposely set objects to the wrong shape for fun. For example, if I turned this cylinder on its side, it would "roll" end over end like a quarter being flipped.

So what can you do if the shape gets set wrong? Try another shape. "SPHERE" actually works quite well for a short cylinder. SP will squash a sphere to fit the cylinder shape relatively well. (You can see the original wireframe as the cylinder falls below.)

There are a few more shapes that are provided for you when the normal ones don't work out.

The first one to note is "STATIC MESH". This draws a mesh around your shape to create the outlines. This is beneficial when making a "hill" for something to roll down, or a multi-pitched slope. However, it is STATIC and UN-MOVEABLE. Therefore this option is mostly used when making a "ground plane" for everything else to "ride" on.

This ramp was made as a "STATIC MESH".

It does not move, however the ball will fall and roll down its slope.

The next shape to note is "CONVEX HULL". And it is exactly what the name describes. It takes a shape from end point to end point and makes a closed "hull". (Like a boat.) This has some limitations, as I'll describe next.

Example of a convex hull:

You can see that the convex hull made a shape similar to the gear above, but if you tried to make it "work" with another gear, it wouldn't. So how do you fix it? Let's look at a similar shape that I had a problem with. I encountered this situation when using "CONVEX HULL" to make an upside-down arch:

The arch wobbled back and forth as you would expect, but when I dropped a ball on it from above, the ball did not fall into the arch. It stopped  above it. WTF?!!  After using the DEBUG command, I saw this is what was happening:

You can see that SP "drew" in some lines to make this a "CONVEX HULL". (No support for a CONCAVE hull as of yet.) And it behaved more like a half circle than an arch. So how to fix it? Hmmm. No standard shape will overcome this. So we move onto...

## GROUPING GROUPS: Even more advanced shape physics.

The solution: Instead of one  arch, I built the arch out of a number of groups, (like bricks in a real building) and grouped each sub-group together to make one arch shape.

Now the ball falls into the arch and the arch wobbles back and forth on its axis. To better explain this look at the following picture that shows the "group of groups".

Each of these sub-groups are all part of one large group. They do not seperate, and they behave as one large object.

Grouping groups is also the only way that I know  to make a hole in a moveable object.

#### NOTE: You can make a hole in an object using the Static Mesh shape, but then your object cannot move.

Next we'll get into using joints, and work with more than just gravity.