Keyframe

This is just a draft. Please before edit it, consider that this is an important wiki page and it should be as good as possible.

What is a keyframe?

A keyframe is a basically a "mark" in the timeline. This mark allows the user to make Synfig remember the state of the animation at that point (frame). It means that the keyframe is like a label that tell Synfig that this frame should be taken into account when creating waypoints. It also indicates that the marked frame is a special frame where the information of every parameter in the animation is stored in order to be reused later.

Each keyframe is associated with a particular frame and a frame can only have one keyframe.

What does a keyframe looks like?

A keyframe looks like a light brown vertical dashed line in the timetrack dialog placed at the corresponding frame. You can distinguish it from the time cursor by its color (the time cursor is blue).

Keyframes also appear as entries in a list in the Keyframes Dialog (fix keyframe dialog to explain better the columns of the dialog)

Keyframes and waypoints

A keyframe doesn't necessarily imply a waypoint, and a waypoint doesn't necessarily imply a keyframe.

A keyframe could live all the time without any waypoint but it stores the information of the values of the parameters on that specific frame. If there is a waypoint there then the waypoint information is stored too. If there is no waypoint in the keyframe then its "stored" value is the result of the surrounding waypoints, its parameter values and the interpolation values the waypoints have. This means that a keyframe remembers the values of the parameters at that frame but does not keep them static at that frame. To maintain a parameter's value static in a certain frame you must use a waypoint.

The creation of a waypoint can cause the creation of new waypoints on the neighboring keyframes depending on the current value of the Lock Keyframes state. So, maybe, the creation of a waypoint (modifying a parameter or pasting or moving a waypoint or even duplicating a keyframe) can lead to the creation of a waypoint in the the keyframes that are immediately before and after the inserted waypoint's frame. The waypoints created in the neighboring keyframes are created according to the default interpolation value in the toolbox window.

See the examples to understand how this works.

Adding, duplicating and removing keyframes

Add a keyframe

Place the time cursor at a frame where there isn't currently any keyframe. Then press the Add new Keyframe button. If you place the time cursor at a frame where there is currently an existing keyframe then the Add Keyframe button is disabled. Once you press the button then a new entry is added to the list of keyframes and a vertical dashed line is added in the time line. No waypoint is created.

Duplicate a keyframe

Select a keyframe in the keyframe list of the Keyframes Dialog and place the cursor at a frame where there isn't currently any keyframe. Then press the Duplicate keyframe button. This would have two separated effects:

1. If there is a waypoint at the original keyframe then the waypoint is duplicated. Its duplication include the parameter value and its interpolation values.
2. If there is no waypoint in the original keyframe for any particular parameter then it could happen two things:
   • There is no waypoint for that parameter at ANY frame in the time line: Then NONE waypoint is created.
   • If there is a waypoint in the time line for that parameter, but not in the keyframe that is going to be duplicated, then in the duplicated keyframe is created a new waypoint with a value for the parameter of the result of the current value at the original keyframe and a TBC Smooth interpolation type for both "In" and "Out".

Remove a keyframe

Just select a keyframe from the keyframe list and press the Remove keyframe button. It will remove the keyframe and all the waypoints for all parameters for all layers that are currently there.

Editing keyframes: time & description

WIP

Editing keyframes: Properties dialog

The Keyframe properties dialog allows change the interpolation method for all the existing waypoints of all the layers on the canvas at the same time. The dialog have the following parameters:

• In: Checking this value you can change the interpolation method of the left part of the waypoints of the current selected keyframe of all the layers of the canvas to the selected interpolation method in the drop down menu.
• Out: Same but for the right part of the waypoint.
• Tension: See TCB
• Bias: See TCB
• Continuity: See TCB
• Temporal Tension: See TCB

You can check only one of both "In" or "Out" check boxes to only affect the change to the left or right part of the waypoints. The non checked part would not be modified. Same comment applies for the Manual interpolation method parameters (Tension, Bias, Continuity and Temporal Tension)

This dialog would not affect what's the interpolation method for a new waypoint created by the user or automatically, created by the keyframe duplication or by the lock keyframe state. That interpolation methods for new waypoints will be both the same (In and Out or Left and Right) and depend only on the Default interpolation method of the Tool Box window.

(TODO: The effects on the parameters that haven't a waypoint on the keyframes but yes in other frames...)

See the examples to understand better how it works.

Examples

Duplicate a keyframe with no waypoint on it

For example, imagine that you have following set of keyframes and waypoints and the corresponding parameter of the radius of a circle:

Before duplicate keyframe at 6s

Frame	Keyframe	Waypoint	Radius	Interpolation
0s	yes	yes	20.0	TCB Smooth
2s	yes	no	25.0	n/a
4s	yes	no	30.0	n/a
8s	no	yes	40.0	TCB Smooth

notice that although the interpolation between 0s and 8s is TCB Smooth the real result 
is linear due that they are the only two waypoints of the animation for that parameter.

If you select the keyframe at 2s, place the time cursor at 6s (where there isn't a keyframe), set the default interpolation to TCB Smooth, and have the lock keyframe status to All keyframes locked and press the duplicate keyframe button, then the result is the following:

After duplicate keyframe at 6s

Frame	Keyframe	Waypoint	Radius	Interpolation
0s	yes	yes	20.0	TCB Smooth
2s	yes	no	25,78125	n/a
4s	yes	yes	30.0	TCB Smooth
6s	yes	yes	25.0	TCB Smooth
8s	no	yes	40.0	TCB Smooth

You can see that:

1. At 0s none has changed. Not affected by the insertion of the keyframe. It is two keyframes away from 6s and also have a waypoint.
2. At 2s there was a keyframe and stills there. But previous to the creation of the keyframe at 6s the current interpolated value of the radius was 25.0. After the creation of the keyframe at 6s the radius is the result of the interpolation between 0s and 4s frames waypoints with its radius values and its interpolation methods. That is 25.78125. This keyframe is one keyframe away the new 6s keyframe so no waypoint is created.
3. At 4s there was a keyframe and still being there. But in this case the 4s keyframe is a neighbor of the new 6s keyframe. As well as the lock keyframe state was set to All keyframes locked then the keyframe at 4s has been locked adding a waypoint on it. The radius value hasn't changed (still being 30.0) because it was locked adding a waypoint with its current value). The Interpolation mode of the waypoint was set to TCB Smooth as stated by its default value.
4. At 6s there is a new keyframe with a new waypoint with the old value of the interpolated value of the keyframe at 2s. That is a radius of 25.0.
5. At 8s nothing has changed. There wasn't any keyframe and there was a waypoint so nothing is expected to change.

Imagine now that you repeat the same operations but you choose the default interpolation set to Constant. Then the result is the following:

After duplicate keyframe at 6s (constant interpolation)

Frame	Keyframe	Waypoint	Radius	Interpolation
0s	yes	yes	20.0	TCB Smooth
2s	yes	no	20.0	n/a
4s	yes	yes	30.0	Constant
6s	yes	yes	25.0	TCB Smooth
8s	no	yes	40.0	TCB Smooth

Now you can see that the keyframe at 2s doesn't hold the value of the parameter by itself. It only remember the value if a waypoint is created on it by the result of the insertion of a neighbor waypoint or keyframe, or if a keyframe is duplicated. In this case the value at 2s has changed drastically due to the different interpolation method for the created waypoint on 4s.

Advanced uses of keyframes

WIP