What is EnvelopeEdit
Envelope is a new visual tool to help you rig your characters faster and easier. It can often save you a lot of time. Each bone has a special area around it, allowing you to tell Blender what part of the geometry will follow each bone. This zone is customizable so you can move, scale and blend them together.
You can edit this white zone in Editmode or posemode by going in Envelope display mode (Buttons Window → Armature → Display Options → Envelope), selecting bones and using SKEY or CTRL-ALT-SKEY.
In Editmode: you can select the Tip, the Body or the Root and scale using SKEY. This area in the middle will assign a weight of 1 to all vertices contained in here. All vertices with a weight of 1 will completely follow this bone. The white transparent area around the center is a zone of influence which loses power as you go away from the center. This area is scaled when selecting the body of a bone and doing CTRL-ALT-SKEY. In Posemode: You can only scale the zone of influence with ALT-SKEY when in Envelope display mode. It's real time, and lets you tweak the influence while you animate. So if you notice there is a vertex not following in the new pose you just did: Just select the bone it should follow, and scale the zone a bit until the vertex goes back with his friends. Example:
It's possible to enable/disable the use of Envelope in the Modifier stack using the "Envelope" toggle.
There are also two important buttons in the Armature Bones panel: Deform and Mult.
Enabling the Deform button will tell Blender to deform geometry with this bone. It's useful because in a more complex rig not all the bones are there to deform, some bones are just there to move other bones.
The Mult option will tell Blender to multiply the weight it gets from envelope (let's say 0.7) with the weight you painted in weight paint (let's say 0.5). The result will be 0.5*0.7=0.35 so in fact you just tweaked the envelope influence to 0.3 when it was at 0.7. If you don't want vertices to be part of the zone, you can always paint it with 0, as 0*(something) will always give 0. This way you can give custom shape to your envelope. More on weight paint on next page.
In this example of a formerly flat surface you can see that all the selected vertices are not following the bone when it is moved upwards. This is because I painted a weight of 0 on them. In weight paint you'll see nothing. But just the fact that they are part of the group with a weight of 0 will make that possible. If Mult is off and you have both a vertex group and envelope, Blender will add value.