Issue Summary

Hi I've made a video to encompass two of the key features that should be brought back. Even back then (2016) I've been consistently asking for the fill tool to have this option of a layer selection or "target"

Currently the two main regressions or re-implementations, considering the tool has been refactored quite a bit, would be:

• Color Bleed: Bring back the function to automatically color a different layer based on the active layer that is being colored (e.g lineart)
  • Add the option to select up to which layer would the color transpose itself. By default it would always source and target the active layer.
  • Add the option to color multiple layers with the same layer "filter" e.g Source layer can be one or many and Target layers can be one or many.
• Color Spill: Bring back the pixel color expansion when filling the same area
  • Add an option toggle so this is not default behavior
  • Add a pixel expansion slider, or use the color tolerance to determine how much it can "bleed"

I think ideally this should be implemented before the tracing & coloring PR #1178 mainly so David's implementation can support itself on this existing behavior and become further simplified in the coloring part and since we always try to strive for simplicity yet for the tools to work functionally and thoroughly, one of the main issues I've been having with the pipeline process is that the thinning and the blending portion might only be needed for the color separation part, if we had the Color Bleed and Color Spill functionalities back as I explain in the video, of course this is subject to discussion as well, but I can only see it as a powerful asset and one that's been consistently requested by actual artists using Pencil2D consistently for their work.

Let me know what you think.

Video or Image Reference

https://youtu.be/VULg2ONoo9o

System Information

• Pencil2D Version: 0.5.4b

Some of the changes made to modify the original behavior were made in #687 by @candyface but I'll keep looking for other PR's that might have modified this further to help out have a better picture of the required work.