Time running forward and reverse with the Time Ipo

There was a question on the Blender Artists forum today regarding how the Time Ipo works. I answered briefly, but figured it would be good to go just a little more in-depth in a post. Here is a brief tutorial on the Time Ipo and how to use it. Keep in mind that the applications of the Time Ipo probably go far beyond what’s presented here, but if you’re unsure about it, this should serve as a good introduction…

Remapping Time with the Time Ipo Curve

The Time Ipo is really a time remapping Ipo, and thinking of it that way will help you to understand how it works. It allows you to remap the time of your object’s animation (including particle effects) to speed up, slow down, or reverse time altogether.

Time remapping works by allowing a key frame of animation to be mapped to another frame on the Timeline. Let’s begin with a simple example.

A simple animation on the Z axis between frames 30 and 60

Above I have diagrammed a basic animation. The cube is animated on the Z axis, between frames 30 and 60. Before frame 30 and after frame 60 there is no motion. In the animation above, the image shows only the key frames. Understand that in Blender the motion is smooth, operating over 30 frames.

Here are some facts about the Time Ipo to review before proceeding:

• The Time Ipo controls the timing of your animation if any of its curve’s keys are set.
• Any part of the curve outside of your actual animation frames will do nothing (more on this later).
• Time can be sped up, slowed down, or reversed by remapping keys on the Time Ipo curve.

One of the things you may want to accomplish with the Time Ipo is to speed up or slow down your animation. An obvious question might be, “Why not just adjust the timing for the individual curve?” Well if your animation is simple, this might be the right way to go; however if you have multiple curves animated on a single object, such as for Location, Rotation, and Scale, then adjusting all of those keys would be a real pain if all you want to accomplish is to speed up or slow down an animation.

Another thing to consider is particles. If you want to reverse the effects of a particle system, often adjusting the Time Ipo is the simplest and most straight forward approach.

Let’s consider again our simple animation.

A simple animation on the Z axis between frames 30 and 60

By default the Time Ipo has no curve. You can add one quickly by selecting the Time item from the right-hand pane of the Ipo editor, and CTRL+LMB twice to create a curve. When you TAB into Edit mode for the curve, you can adjust the keys manually from the Transform Properties window (N). Adjusting values in the properties window for Vertex X and Vertex Y will allow you to key in precise values for the keys.

NOTE: The Vertex Y values are reduced by a factor of ten in the properties window. So if you want to manually enter a value of 30 for the Y axis, enter 3.0 instead.

Time Curve with 2 keys at 0,0 and 20,30 (x,y)

For the Time curve, the Y axis represents the old frame, or the existing frame of your animation. The X axis represents the new frame, or the remapped frame of the animation. In the above curve, we’re remapping frame 0 to frame 0, and frame 30 to frame 20. Since our actual animation doesn’t begin until frame 30, the above curve does nothing.

Look closely. Frame 30 of our original animation, represented by the Y axis of our time curve, is mapped to frame 20 sure enough, so our animation should begin on frame 20 — and indeed it does. However there’s no slope in the curve after frame 20 (X axis). What this shows is that frame 30 (Y axis) of the original animation is mapped to every frame thereafter (X axis). So we’re essentially telling the object not to move at all — and if you press ALT+A in the 3D viewport, that’s exactly what you’ll see.

Let’s get our animation working again by adjusting the keys of the Time curve.

Time curve mapped 1 to 1: 30,30 and 60,60 (x,y)

With the above curve, we’ve restored our animation to pretty much exactly what it was before we started fiddling with the Time Ipo. It has a one to one mapping. If you look at the key positions on X and Y, they’re mapped 30,30 and 60,60. In other words, frame 30 (Y axis) is mapped to frame 30 (X axis) and frame 60 (Y axis) is mapped to frame 60 (X axis).

If you’re not getting this yet, it’s probably because we haven’t done any useful remapping yet. Let’s speed up time, slow it down, and reverse it.

Speeding Up Time

Since our animation begins at frame 30 and lasts until frame 60, we have 30 frames of animation. In order to speed up our animation, we need to reduce the number of frames it takes to finish. We’ll remap frame 60 to frame 50, shortening the total time of our animation by 10 frames.

Time Curve Remapped, frame 60 to 50

Our animation begins at the same time, frame 30, but finishes at frame 50 instead of frame 60. What used to take 30 frames to complete now takes 20, and our animation finishes 10 frames early. According to the above diagram, we’ve remapped our animation’s frame 60 (Y axis) to frame 50 (X axis).

Slowing Down Time

This is no more tricky than speeding up time. All we need to do is extend the Time Ipo so that our original frame 60 finishes later. We’ll remap it to frame 90.

Time Curve Remapped, frame 60 to 90

In the above diagram, our animation’s frame 60 is now extended to frame 90. With the animation requiring another 30 frames to finish, it is slowed down by half.

Reversing Time

For this we’ll plot a curve that proceeds forward in time for the original frames of animation, then reverses time over an additional 30 frames.

Time Curve Remapped, frame 30 to 90

In the above diagram, we have mapped our frame 30 and frame 60 right back to 30 and 60. So for the first 60 frames of the animation, it proceeds just like we originally mapped it. For frames 60 to 90, time moves in reverse. This is because our animation’s frame 30 is mapped again to frame 90. The slope of the Time curve proceeds downwards (backwards) and moves the animation back to it’s starting point.

Conclusion

At first attempt, the Time Ipo might seem unintuitive. However it works very effectively. Start with a simple animation and remap the Time Ipo. Once you’ve experimented a little, it will begin to make sense.

Don’t forget that you can also remap time for a particle system. It works exactly the same way as illustrated above. Give it a try, and you might find that creative possibilities with Blender open up quite a bit.

Sample Blend File: Time Blend

This entry was posted on Saturday, February 9th, 2008 at 7:03 pm and is filed under Tutorials. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.