From BlenderWiki

There are two views of your animation, and thus two ways to define and adjust animation: curves and keys. A curve connects two points. The shape of the curve is adjusted by moving handles for the points. The handles assert the degree of influence that the point has on the curve. A key is a combination of values of points at a particular point in time. Using keys in animation is called Keyframing.

Ipo Curves

The Ipo Curve Editor allows you to edit the 2D curves that define animation in Blender. The curves represent the edited value in the vertical (Y) axis (location, size, rotation, energy, etc.) and time on the horizontal (X) axis. The rate of change of these values over time can be seen in the slope of the curve.

You can turn any window into an Ipo Curve Editor with the Window Type menu, but it is often handy to have both a 3D View and an Ipo editor at the same time. This shows all the Ipo Curves, the channels used and those available. You can zoom in and out the Ipo Window and translate it just as every other Blender Window.

In addition to the standard channels, which can be set via I, you have the delta options, such as dLocX. These channels allow you to assign a relative change. This option is primarily used to control multiple objects with the same Ipo. In addition, it is possible to work in animation 'layers'. To set an Ipo Curve for these channels, select the channel and then create control points via Ctrl LMB clicking in the Ipo Window.

The Ipo curves have an important feature that distinguishes them from normal curves: it is impossible to place more than one curve segment horizontally. Loops and circles in an Ipo are senseless and ambiguous. An Ipo can only have 1 value at a time. This is automatically detected and corrected in the Ipo Editor. Every Ipo channel that has already been keyed is shown in the channel list to the right of the window with a color button by its side.

Curve showing/hiding

You can show an Ipo curve by using LMB on the relative Ipo channel name on the right (one that already possess a color button next to list channel name). By doing this you hide all previously shown Ipo curves. If you want to show many Ipo curves together (for example if you're working with a group of channels such as the LocX, LocY, LocZ) use shift LMB on every channel name you want to be shown (their names appear in white).

Curve Selection

Some of the standard Blender selection methods work in the Ipo Curve editor. RMB click on a curve to select it. You can also use LMB on the color button next to its name. You can select many curves by using Shift RMB on every curve that is shown or by using Shift LMB on every color button. A curve that is selected shows its control points in white and its respective color button appear outlined in black (if it is the last selected when selecting multi curves the other button appear as pushed).

Options

RMB

Select an Ipo curve under the mouse pointer

Select/Deselect All A

Select all visible Ipo curves

Border Select B

Select Ipo curves within an interactively mouse-drawn box

Curve Manipulation

Ipo curves can also be manipulated with many of the standard 2D transformations. The same axis locking options apply here too. Moving curves left and right will move them backwards and forwards in time.

Options

Grab/Move G

Move the selected Ipo curve

Scale S

Scale the selected Ipo curve

Curve Interpolation

The interpolation mode determines how the Ipo values are calculated in between each curve point.

Options

Constant

After each point of the curve, the value remains constant (horizontal). No interpolation takes place.

Linear

Each curve point is connected by a straight line

Bezier

The standard smooth curve interpolation

Curve Extend Mode

The curve extend mode determines how the Ipo values are calculated outside the horizontal limits of the Ipo curve. This can be used to repeat a small section of animation or make animation continue endlessly.

Options

Constant

The ends of selected curves are continuously (horizontally) extrapolated.

Extrapolation

The ends of the selected curves continue in the direction in which they ended

Cyclic

The complete width of the curve is repeated cyclically

Cyclic Extrapolation

The complete width of the curve is extrapolated cyclically

Examples

Editing Curve Points

As well as manipulating the curves themselves as a whole, you can also edit the individual points that define the curve. Curve points are added when a key frame is inserted (usually with the Insert Key I menu), and these points can be manipulated in time (X axis) and value (Y axis). Hit Tab to go in edit mode and be able to select each curve point independently. If you select one or more points with RMB , you can then move (G), scale (S) or rotate (R) them. You can also select and edit handle points that allow to finer control the interpolation curve. you can also set points values numerically by hitting N then entering a value in the "Vertex X" and "Vertex Y" fields inside the Transform properties panel.

Adding Curve Points

Alternatively to adding curve points via inserting keyframes (eg. in the 3D View or buttons window), curve points can also be added manually in the Ipo Curve Editor by using Ctrl LMB . The point will be added to the active curve (the one with its color button next to its channel name outlined in black even one that doesn't have any curve point already set), at the location of the mouse pointer.

Points are added according to the following rules:

• There is no Ipo datablock yet (in this window) and one channel is selected: a new Ipo datablock is created along with the first Ipo Curve with one vertex placed where the mouse was clicked.
• There is already an Ipo datablock, and a channel is selected without an Ipo Curve: a new Ipo Curve with one vertex is added.
• There is already an Ipo datablock, and a channel is selected with an existing Ipo Curve: A new point is added to the selected Ipo Curve linked with the nearest points before and after it. This is not possible if multiple Ipo Curve are selected or in Edit Mode.

Selected curve points can also be duplicated. Note that this will not duplicate the curve segments, but the points themselves, connected to the original curve.

Hints

Repeated Ctrl LMB clicking along a curve can be a good way to add randomness and unpredictability to an animation

Point Handle Types

Similarly to 3D Curve objects, Ipo curve points possess two handle points by each side of it. Those handle points can have a variety of types, that can be used to specifically control the interpolation of segments between points.

Options

Free Handle H (black)

The point handles are unlinked and can be manipulated in any way. (H toggles between Free and Aligned)

Aligned Handle H

The point handles are linked in a straight line. (H toggles between Free and Aligned)

Vector V

Both ends of a handle always point to the previous or next handle

Auto Shift H (yellow)

This handle has a completely automatic length and direction, based on the points' proximity to each other

As soon as handles are rotated, by moving one of the point's handles, the type is changed automatically:

• Auto Handle becomes Aligned.
• Vector Handle becomes Free.

Ipo Keys

As easy as it is to work with animation curves, some people find it even easier to manipulate the keys. Changing the Ipo Editor to keys display makes two things happen:

• The Ipo Curve Editor now draws vertical lines through all the points of all the visible curves (curves are now show in black). Points with the same 'frame' value are linked through the vertical lines. The vertical lines (the "Ipo Keys") can be selected, moved or duplicated, just like the points. You can translate the keys only horizontally.
• The object is not only shown in the 3D View in its current position but 'ghost' objects are also shown at all the key positions. On some video displays, you may have to press K in the 3D View window. In addition to now being able to visualize the key positions of the object, you can also modify them in the 3D View. For example, you can move the selected Ipo Keys.

Onion Skinning and Ghosting

It is possible to see the keyed positions of an object in the 3D View. With the IPO editor in Keyframe mode, press K in the 3D View window. The location of the object will be drawn as ghostly outlines. The ghost location of the selected key will be drawn in a highlight color. Using this feature, you can physcially see the location, or path, that your object will take in 3D space.

Hints

• Use keyframe mode to change where an object is in time. For example if you currently have an object in a certain position in frame 100, but find that it gets there too early, go into key mode, select that key at frame 100, and Ggrab it and move it to the right. Click to drop it into position.
• Holding Control down while dragging keyframes makes them snap to even frames.
• The I "Insert Key" always affects all selected objects. The IPOKeys for multiple objects can also be transformed simultaneously in the 3D View. Use the Shift K command: Timeline → Show and Select Keyframes to transform complete animations of a group of objects all at once.
• Use Page Up and Page Down commands to select subsequent keys in the 3D View.
• You can create Ipo Keys with each arrangement of channels. By consciously excluding certain channels, you can force a situation in which changes to key positions in the 3DWindow can only be made to the values specified by the visible channels. For example, with only the channel LocX selected, the keys can only be moved in the X direction.
• Each Ipo Key consists of the vertices that have exactly the same frame value. If vertices are moved manually, this can result in large numbers of keys, each having only one curve. In this case, use the J ("Join") command to combine selected IPOKeys. It is also possible to assign selected IPOKeys vertices for all the visible curves: use I in the IPOWindow and choose "Selected keys".
• The DrawKey option and the IPOKey mode can be switched on and off independently. Use the button EditButtons->DrawKey to switch off this option or object. You can switch IPOKey mode on and off yourself with K in the IPOWindow. Only K in the 3DWindow turns on/off both the DrawKey and IPOKey mode.

Examples

Special Notes on the Time Curve

With the Time curve you can manipulate the animation time of objects without changing the animation or the other Ipos. In fact, it changes the mapping of animation time to global animation time (Linear time IPO). The Time curve is a channel in the Object Ipo.

In frames where the slope of the Time curve is positive, your object will advance in its animation. The speed depends on the value of the slope. A slope bigger than 1 will animate faster than the base animation. A slope smaller than 1 will animate slower. A slope of 1 means no change in the animation, negative power slopes allow you to reverse the animation. The Time curve is especially interesting for particle systems, allowing you to "freeze" the particles or to animate particles absorbed by an object instead of emitted. Other possibilities are to make a time lapse or slow motion animation.

Examples

To grasp this concept, make a simple keyframe-animation of a moving object, from a position to another in, say, 50 frames. Then select the Time channel and create a TimeIpo in the IpoWindow going from point (1,1) to point (50,50). It is easy to set the start and end point of an IPO by using N and entering the values numerically.

Multiple Time IPOs You need to copy the TimeIpo for every animation system to get a full slow motion. But by stopping only some animations, and continue to animate, for example, the camera you can achieve some very nice effects (like those used in the movie "The Matrix")

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