metadata_extraction.cpp

A; //< cell A
 
// current iterated node (the one in the middle of the image) smoothness
A.smooth;
 
// It's a cyan node!
assert(!A.connected(D));
assert(!B.connected(C));
 
if ( A.connected(B) ) {
    if ( !C.connected(D) ) {
        bool foreign_is_contour = edge(C, D).contour();
 
        // the number of contour edges
        switch ( edge(A, C).contour()
                 + edge(B, D).contour()
                 + foreign_is_contour ) {
        case 2:
            A.smooth = !foreign_is_contour;
            break;
        default:
            assert(("precondition failed", false));
        // the following cases are only for documentation
        // of possible values (they don't change the algorithm)
        case 3: case 1: case 0:
            // {A, B} is the pair with the angle closest to 180 degrees
            A.smooth = true;
        }
    } else {
        // there might be 2-color, then A.smooth = true
 
        // or it might be 1-color and doesn't matter,
        // because the current node will disappear
        A.smooth = true;
    }
} else if ( A.connected(C) ) {
    // very similar to the previous condition
} else if ( B.connected(D) ) {
    bool foreign_is_contour = edge(C, D).contour();
 
    switch ( edge(A, B).contour()
             + edge(A, C).contour()
             + foreign_is_contour ) {
    case 2:
        A.smooth = !foreign_is_contour;
        break;
    default:
        assert(("precondition failed", false));
    case 3: case 1: case 0:
        // {B, D} is the pair with the angle closest to 180 degrees
        A.smooth = false;
    }
} else if ( C.connected(D) ) {
    // very similar to the previous condition
} else {
    // there is a 4-color pattern, where the current node
    // won't be smooth
    A.smooth = false;
}