So I opened that capx and the only thing I tried to solve in it was a way to slice away chunks of the play area. It was a bit of presumptuous to call it a qix like. I do recall an older capx I made but the forum and a search of my dropbox yielded no results.
The original qix probably did everything pixel based. Things moved a pixel at a time. It knew if the player was on the edge or inside the play area based on the color of the pixel it was on. The filling of areas was done with a pixel flood fill. And finally the filled percentage was done by counting pixels with a certain value.
C3 has the canvas plugin that can be used to set and read pixels so that could be leveraged to do that stuff. The problem is with modern resolutions you deal with more pixels so it may not be as performant.
All my previous attempts tried to do the game in a more modern way such as keeping track of the polygon around the unfilled areas and measuring the distance the player was from the closest edge to those polygons. All which are all slightly involved projects on their own. To top it off some creativity is necessary to utilize constructs available features to achieve that. I typically run out of steam after finding a way to erase chunks of the play area, so most of this is completely unsolved for me.
To make good clone I think the best starting point would be to make a complete list of all the game rules. Like what is happening, what can you do as a player and what happens. Even something complex should be able to be broken down into simpler parts.