Blender 3D: Noob to Pro/Advanced Tutorials/Advanced Animation/Guided tour/NLA/intro

NLA (Non-Linear Animation)
''WARNING-This page assumes the reader to understand the IPO window and the Action Editor window, as well as rigging a character with an armature object. This tutorial will make little sense without this previous knowledge.''

Imagine this--yourself, sitting at your computer late at night, beating away at a huge blender animation. You didn't think it would take as long as it did, but you lost your composure staring into the jungle of colorful IPO lines, little white and yellow Action diamonds, and that annoying green current frame line. You know that the NLA window would help you make sense of it all, but you are afraid of opening that Pandora's Box because of the problems that will follow it. Never fear, for this tutorial will clean up all those problems and revolutionize the way you blend for the rest of your life.

Setting up the Scene
It will be easier for you if you start with a small demo file than if you go straight for the big prize. Give a character or other armature-rigged object a few SEPARATE actions (remember to name them something distinct, like "Walk" or "Run" as you always should with everything). For your own sanity, you will want to have a path or an IPO that correlates with the actions in question. All of the blender screenshots I will be using come from a file with a very basic stick person, rigged with an armature skeleton. He has two actions; a normal walk cycle, and then another, hunched over one, as if to pass beneath a low ceiling. If you use this idea in your own test file (and I thoroughly recommend it) do yourself a favor and give them both the same stride length! Give this guy an IPO or a path to follow that keeps his feet from slipping, and make sure that it has a linear interpolation mode. The rest of the scene consists of a floor-plane and an arch too small for him to walk under (hence the crouching walk). Place this arch exactly one walkcycle away for now, we will move it around later. Complete the scene before going on to the next step.

Adding Action Strips
Now, he moves forwards as you scroll through the frames, but how do we get him to walk forward, duck, and walk under the arch, too? First of all, you need to select the armature object and create a link to the normal walk. By pressing the up or right arrows, or pressing "alt+a", you should be able to see him walk up to the arch, stop walking, but keep sliding through, with his head sticking out the top. As ridiculous as this seems, right now, however, you are on the right track. Split your window now and open the NLA window with.

At first glance, this window looks almost identical to the action window we all know and love. This is not totally off of the mark. The NLA window is, in essence, an abbreviated version of the action and IPO windows. This is what you should see in the NLA window. You see a space with the name of your armature (named "Armature" in my demo) and in that row you see a few key diamonds. These show the ipo you have put on the person. I made it so the IPO extended on forever, using the first ten frames as a guide. In a subset beneath the armature object, you see the name of an action. The bullet next to it means that the armature is currently linked to that object. In that row, you see key diamonds, and those correlate with the keys you put into the action in question. If you switch actions in the action window, you see that the NLA window also changes. But how do you get it to keep the first and play the second later?

Go to the first frame you want him to walk in (most likely number one) and place your cursor in the NLA window. Press "shift+a" to see a dropdown menu. Pick the name of the first walk cycle. You should see a new subset space appear, with the name of the first walk in it. This space should be occupied by an action strip. Two colors of action strips are yellow and pink, yellow meaning selected and pink meaning deselected, just like IPO vertices. This strip takes up the amount of frames the walk did. The NLA window has now saved your first action. Now to toggle to the next action, move the frame line to the end of the first strip, then press "shift+a" again, this time clicking the other action on the dropdown menu. The result.

Getting the Strips to Play
Now, as cool as this seems so far, if you press "alt+a", you will be disappointed and confused. The animation will only play one of the actions. This is a simple problem to fix. If you look carefully, you will see that the armature is still linked to the action it played. This data is overriding any other data from the NLA window. Press the "X" in the action window right next to the name of the action. Press "alt+a" again. It works!

This is, however, a jerky and instantaneous switch from one action to the other. Making it less weird is easy. Press the "N" key with your cursor in the NLA window. You will see a small box with a bunch of functions in it (this will be explained in detail on later pages).

The Properties window. This little box is the lifeblood of the NLA in blender. It contains all the tools you will need to be able to run this feature smoothly. I will illustrate a few of them right know, but most others will be shown in the section on this window.

Make sure you have highlighted the second action strip, and look at the space where it says "Blendin". The number there is the number of frames blender will use to smooth the transitions in to the highlighted action. Depending on how fast your character is walking, you may need to change the number a bit, but I set my "blendin" for seven. Whatever number you used, however, move the second strip back that same amount of frames. The wedge on the end of the action strip should end as the other strip ends.

The NLA solution.

Conclusion
You now have the necessary skills to complete much more involved and complex animations. You can, however, increase this even more by continuing to read the other NLA tutorials in this wikibook.

Good Luck!