Implementing walkable area for a game engine

[fhgaha]

Hello, let's say I have some random closed plane shape with two holes (as target, yellow area) and a small square shape of a character (as clip, bottom side of the green cube, i.e. a square projected on the yellow area).

How would I implement a system checking if the green square is inside of the yellow area?

If I just do something like the example on the main page I dont get adequate results.
If we take the image above, I expect the green square to be inside of yeallow area, but the output says it's not:

Clipper2Lib::PathD clip = {{-1.3,-0.3},    {-0.7,-0.3},    {-0.7,0.3},     {-1.3,0.3}};
Clipper2Lib::PathD target = {{-0.7,2.8},     {-0.7,5.5},     {-0.7,5.5},     {1.02971,5.50548},      {1.03649,4.96927},      {-0.699297,5.02357},    {1.08519,2.77163},      {1.08519,2.77163},  {1.02292,4.97829},      {1.08519,2.77163},      {1.02292,4.97829},      {0.459555,4.98508},     {0.42743,2.77555},      {0.308085,-0.36081},    {0.253785,1.51457},     {1.18582,1.54701},  {1.29442,-1.00375},     {0.362386,-1.03619},    {1.18582,1.84701},      {-0.223107,1.53228},    {-1.36155,1.59114},     {-1.9,1.85},    {-2.0,5.5},       {-1.36834,-1.00848},        {-0.326501,-0.067525},  {-0.229895,-1.06733},   {-0.337614,-1.03619},   {-0.391915,-0.36081}};

Clipper2Lib::PathsD solution = Clipper2Lib::Difference(
    {target}, 
    {clip}, 
    Clipper2Lib::FillRule::NonZero
);
bool inside = solution.empty();
std::cout << "inside area: " << inside << "\n";
//Expected output: inside area: 1
//Actual output: inside area: 0

So I cant just feed the points into Clipper2 library so it constructs everything by itself? I assume I should separate somehow yellow area into three parts:

1. path which outlines everything
2. another path for one hole
3. one more path for the second hole

How would I do that? I just slapped some shape in Blender and exported it into the thing.

[AngusJohnson]

Here's a briefly tested function that could be added to clipper.h:

  template <typename T>
  inline bool Path2ContainsPath1(const Path<T>& path1, const Path<T>& path2)
  {
    // precondition: paths must not intersect, except for
    // transient (and presumed 'micro') path intersections 
    PointInPolygonResult pip = PointInPolygonResult::IsOn;
    for (const Point<T>& pt : path1)
    {
      switch (PointInPolygon(pt, path2))
      {
      case PointInPolygonResult::IsOutside: 
        if (pip == PointInPolygonResult::IsOutside) return false; 
        pip = PointInPolygonResult::IsOutside; 
        break;
      case PointInPolygonResult::IsInside:
        if (pip == PointInPolygonResult::IsInside) return true;
        pip = PointInPolygonResult::IsInside;
        break;
      }
    }
    if (pip != PointInPolygonResult::IsInside) return false;
    // result is likely true but check midpoint
    Point<T> mp1 = GetBounds(path1).MidPoint();
    return PointInPolygon(mp1, path2) == PointInPolygonResult::IsInside;
  }

[fhgaha]

Hmm looking at the code, it will check the first point of path1 and return after that immediately, leaving the rest three points unchecked. Still unclear how path2 will be constructed though.

Btw I have tested it for the simple one yellow square area by just checking if all the green squared points are inside of big yellow square and it works. Maybe I just should only use rectangles for constructing the yellow area.

[AngusJohnson]

Hmm looking at the code, it will check the first point of path1 and return after that immediately, leaving the rest three points unchecked.

I will always check at least 2 points in path1 against all the points in path2.

[fhgaha]

Ok, I managed to make it to work without using clipper2, just by checking if every of the small square points is inside of at least one triangle of the walking area. Sorry for bothering.