Dear Blender Community,

first of all: I love the grease Pencil in 2.8!

We all know the mighty interpolation feature which allows for smooth blending between frames. Good job!

However, this only works well if you have a duplicate frame, or better: A frame with the exact number of strokes in the same order and same (local) direction ...

What if you were able to quickly and intuitivly mark strokes throughout frames? So that YOU can decide and manipulate the way strokes are interpolated .

You could make complex keyframe drawings and interpolate between them! This would be so much easier :-)

Let me introduce :

Grease Pencil Interpolation Features of the Future!

• hotkey to switch into "interpolation marking mode" (a temporary edit mode?)
• the "interpolation marking tool" lets you mark strokes :

1. mark a start and end (for the direction)
2. autonaming with numbering: Layername_stroke_1a (or custom tags)

Some thoughts on the implementation and the interface:

• The implementation needs to be slim and hassle free.
• You should be able to stay in Draw-Mode. Maybe have a Brush or Tool specifically for marking.
• When in marking mode the view should be split (like quad view) with two timelines so you can view two keyframes simultaniously and mark start and goal side by side. (don't know if this could be realized in Blender)

Some additional features in mind:

• several interpolation marks per stroke. This will result in splitting the line into parts so that they can be targeted at the goal keyframe to several strokes.

This will also allow for e.g. two lines becoming one ...

Some questions:

• If you handle big animations with more than one keyframe, how are marking informations stored?
• should the marking informations even be stored?

Please let me know what you think about this proposal. I have some ideas in mind how this could be looking (UI). Should I post this somewhere else... and do you think this better should be an add-on? I think it is quite basic.

If you think this is a great idea please spread the word and if I could be of help let's get in touch!

Cheers!

Soul Stinger

Examples

Please bare in mind that the following examples are very abstract drawings but imagine two views of a face with many lines ... :-)

Keyframe 1

I forgot indicators that show the direction of the marks. sorry... interpolated: