Polygon Filling | Scan Line Algorithm

Question

I'm developing a Game like paper.io in C++ with Win32 API. My Game data is stored in an array like:

1 = Player's Head

2 = Player's base

3 = Player's tail

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1. 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,


2. 0, 0, 3, 3, 3, 3, 3, 3, 3, 3, 3, 0, 0, 0, 3, 3, 3, 3, 0, 0, 0, 0,


3. 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 3, 0, 0, 3, 0, 0, 0, 0,


4. 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 3, 3, 3, 3, 3, 0, 0, 3, 0, 0, 0, 0,


5. 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0,


6. 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0, 0, 3, 3, 3, 3, 0,


7. 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0,


8. 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 3, 3, 3, 3, 3, 3, 3, 3, 3, 0,


9. 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,


10. 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,


11. 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

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Now I want to fill the polygon (Player's tail) with the Number 2 (Player's base).

Scan Line Algorithm:

What works:

1. If I scan the 5. line The first 3 trigger the algorithm and toggle the painting function. The next 3 toggles it again it stops the painting function again

Problems:

1. If I scan the 2. line After Every 3 the painting function will be toggled and after the line, it will paint further, because it's an odd amount of numbers.

Solutions:

1. Toggle on the transition from zero to non-zero (and non-zero to zero)

Boundary Fill Algorithm:

Problems:

1. I need to find the middle/spot to begin, that's in the polygon

Answer 1

There are a lot of special cases that make it tricky to determine which areas are inside the new base vs. outside, but this one is simple and reliable:

1. Do a flood fill starting at the outer edges to find the area that is not in the base. This fill can cover any color except 1, 2, and 3
2. Fill everything else with color 2 to make the new base.