Animation: from keyposes to keyframes
Keyframe animation is one of the oldest principles of computer graphics creation, drawing its inspiration from traditional 2D animation, itself based on two main concepts:
- Pose to Pose Animation (as opposed to "Straight Ahead Animation")
- Inbetween images, also called "intervals"
Pose to Pose Animation consists in drawing only key positions during a movement, as the extreme positions of an arm during its swing. This allows a better ancitipation of the movement in time, allowing to know the duration and the structure of a movement before defining its details.
Once this rudimentary animation is completed (left), allowing to validate the intension of the movement, intermediate images are drawn (right), to make the animation more fluid.
The same principle applies today in the field of computer animation. The user can define key values for one or more parameters at specific points in time, and the software calculates the intermediate images by interpolating these values.
Keyframes in Autograph
To practice while reading this documentation, you can download the Autograph basketball ball
In order for the keyframes to be visible in Autograph, make sure that the Dopesheet module is used by the timeline, which is the case by default when the software is started. If not, click on the button on the right to select this module.
Keyframes can be added to parameters that can be animated (which is not always the case). They are easily identifiable by the empty square on the right.
This square means that this parameter is animatable, but that it does not contain any animation for the moment. To add a keyframe to the current time defined by the playhead, just click on this square to display a pie menu, composed of 4 parts.
By moving the mouse upwards, we reach a diamond-shaped icon allowing to add a keyframe on the parameter. Once added, the pie menu closes and the square is replaced by a solid diamond, indicating that the parameter is animated, and that a keyframe exists at the current time.
If the playhead remains at the current time and the position values are changed, the keyframe at that location will be updated with these new values. To create a new keyframe, simply move in the timeline to a time that does not have one on this parameter and change the values. A new keyframe will be created automatically. This change can be done either by changing the numerical values of the parameter or, in the case of the position, by moving the layer in the viewer.
The almost universal symbol used by all software to define a keyframe is the diamond you clicked on initially. But historically, this diamond was the only type of interpolation that existed when this concept first appeared, known as Linear IntERPolation, also known as LERP.
You can see that the keyframes drawn in the Dopesheet part are not diamonds, but circles. This is because these keyframes are not of the LERP type by default, but of the "Custom" type.
The default values for the tangents, however, make it a linear motion, similar to what a LERP might produce, as can be seen in the Graph Editor.
These keyframes being in Custom mode, it is however possible to quickly move their tangents to bend the curves.
If the "Linear" interpolation mode is chosen from the almost 50 interpolation modes provided by "Autograph", then the keyframes will be represented by a diamond.
If you want to assign the same interpolation mode to all the keys of an animation curve, a menu containing the most common types of curves can be found in the pie menu, then by clicking on the downward pointing arrow.
Navigating through keyframes
The pie menu that appears when you click the Keyframe icon allows you to perform several actions with a single controller:
- If no keyframe exists at the current time: add a keyframe
- If a keyframe exists at the current time: delete the keyframe
- Move to the nearest keyframe before the current time
- Move to the nearest keyframe after the current time
After clicking one of the buttons, the menu pie will close automatically. To leave it open and click the same button more than once, hold down the Ctrl/Cmd key.
To display the keyframes used by the parameters of the selected layer(s), press the U key.
When moving keyframes, pressing the Shift key enables snapping, based on:
- The playhead
- Other keyframes, including visibility ones.