mc-mesh/src/main/java/com/aaaaahhhhhhh/bananapuncher714/tess4j/Util.java

package com.aaaaahhhhhhh.bananapuncher714.tess4j;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Optional;

import org.joml.Math;

import com.aaaaahhhhhhh.bananapuncher714.mesh.Point;

public class Util {
    protected static String toString( Object obj ) {
        StringBuilder builder = new StringBuilder();
        
        builder.append( obj.getClass().getSimpleName() );
        builder.append( '{' );
        List< Field > fields = new ArrayList< Field >();
        fields.addAll( Arrays.asList( obj.getClass().getDeclaredFields() ) );
        fields.addAll( Arrays.asList( obj.getClass().getFields() ) );
        
        for ( Iterator< Field > it = fields.iterator(); it.hasNext(); builder.append( "," ) ) {
            Field field = it.next();
            builder.append( field.getName() );
            builder.append( '=' );
            try {
                builder.append( field.get( obj ) );
            } catch ( IllegalArgumentException | IllegalAccessException e ) {
                builder.append( "?" );
            }
        }
        
        builder.append( '}' );
        
        return builder.toString();
    }
    
    public static Optional< Point > intersection( final VertexOld x1, final VertexOld x2, final VertexOld x3, final VertexOld x4 ) {
        Point point = null;
        
        final Vector2dOld p = x1.toVector();
        final Vector2dOld r = x2.subtract( x1 );
        final Vector2dOld q = x3.toVector();
        final Vector2dOld s = x4.subtract( x3 );
        
        final Vector2dOld qp = q.subtract( p );
        final double qpr = qp.cross( r );
        final double rs = r.cross( s );

        // Are the two lines parallel
        if ( rs == 0 ) {
            final Vector2dOld u = x2.toVector();
            final Vector2dOld v = x4.toVector();
            
            // For normalizing against pr
            final double rr = r.dot( r );
            
            // t0 and t1 represent the distance of the second edge endpoints relative to the first edge normalized by r
            // t0 = ( ( q - p ) . r ) / rr;
            double t0 = qp.dot( r ) / rr;
            // t1 = ( ( q + s - p ) . r ) / rr
            double t1 = v.subtract( p ).dot( r ) / rr;

            // If the vectors are pointing in the opposite directions, then swap t0 and t1
            final boolean inverted = s.dot( r ) < 0;
            if ( inverted ) {
                double temp = t0;
                t0 = t1;
                t1 = temp;
            }
            
            if ( qpr == 0 ) {
                if ( t0 < 1 & t1 > 0 ) {
                    final double midt = Math.max( t0, 0 ) + Math.min( t1, 1 ) / 2.0;
                    final Vector2dOld midpoint = r.multiply( midt ).add( p );
                    point = midpoint.toPoint();
                } else {
                    final Vector2dOld pu = t0 > 1 ? u : p;
                    // Same as the first edge but the second edge may be inverted
                    final Vector2dOld qv = ( inverted ^ t0 > 1 ) ? q : v;
                    final Vector2dOld midpoint = pu.add( qv ).divide( 2.0 );
                    point = midpoint.toPoint();
                }
            }
        } else {
            // Calculate t and u
            final double t = qp.cross( s ) / rs;
            final double u = qpr / rs;
            
            // Do the line segments intersect
            if ( t >= 0 && t <= 1 && u >= 0 && u <= 1 ) {
                // Calculate the point of intersection
                final Vector2dOld intersection = r.multiply( t ).add( p );
                point = intersection.toPoint();
            }
        }
        return Optional.ofNullable( point );
    }
    
    // https://stackoverflow.com/questions/563198/how-do-you-detect-where-two-line-segments-intersect
    // Vector based closest intersection method
    public static Point closestPoint( final VertexOld x1, final VertexOld x2, final VertexOld x3, final VertexOld x4 ) {
        Point point = new Point( 0, 0 );
        
        final Vector2dOld p = x1.toVector();
        final Vector2dOld r = x2.subtract( x1 );
        final Vector2dOld q = x3.toVector();
        final Vector2dOld s = x4.subtract( x3 );
        
        final Vector2dOld qp = q.subtract( p );
        final double qpr = qp.cross( r );
        final double rs = r.cross( s );

        // Are the two lines parallel
        if ( rs == 0 ) {
            final Vector2dOld u = x2.toVector();
            final Vector2dOld v = x4.toVector();
            
            // For normalizing against pr
            final double rr = r.dot( r );
            
            // t0 and t1 represent the distance of the second edge endpoints relative to the first edge normalized by r
            // t0 = ( ( q - p ) . r ) / rr;
            double t0 = qp.dot( r ) / rr;
            // t1 = ( ( q + s - p ) . r ) / rr
            double t1 = v.subtract( p ).dot( r ) / rr;

            // If the vectors are pointing in the opposite directions, then swap t0 and t1
            final boolean inverted = s.dot( r ) < 0;
            if ( inverted ) {
                double temp = t0;
                t0 = t1;
                t1 = temp;
            }
            
            // Do the lines overlap
            if ( t0 < 1 && t1 > 0 ) {
                // The midpoint is an arbitrary point that just happens to look good as an intersection
                // Find the midpoint between the overlapping region
                final double midt = Math.max( t0, 0 ) + Math.min( t1, 1 ) / 2.0;
                // If colinear
                if ( qpr == 0 ) {
                    // Do not need to calculate the distance between the two parallel lines since it is 0
                    final Vector2dOld midpoint = r.multiply( midt ).add( p );
                    point.setX( midpoint.x );
                    point.setY( midpoint.y );
                } else {
                    // Calculate the midpoint along pr
                    final Vector2dOld midp = r.multiply( midt ).add( p );
                    // Calculate the perpendicular distance between both lines
                    final Vector2dOld perp = r.perpendicular();
                    final Vector2dOld z = perp.multiply( qp.dot( perp ) / rr );
                    // Sum the components
                    final Vector2dOld midpoint = midp.add( z.divide( 2.0 ) );
                    point.setX( midpoint.x );
                    point.setY( midpoint.y );
                }
            } else {
                // The lines aren't really anywhere close to each other, so just find the midpoint between the 2 closest points
                // If t0 > 1, then the second edge must lie to the right of the first edge
                final Vector2dOld pu = t0 > 1 ? u : p;
                // Same as the first edge but the second edge may be inverted
                final Vector2dOld qv = ( inverted ^ t0 > 1 ) ? q : v;
                final Vector2dOld midpoint = pu.add( qv ).divide( 2.0 );
                point.setX( midpoint.x );
                point.setY( midpoint.y );
            }
        } else {
            // Calculate t and u
            final double t = qp.cross( s ) / rs;
            final double u = qpr / rs;
            
            // Do the line segments intersect
            if ( t >= 0 && t <= 1 && u >= 0 && u <= 1 ) {
                // Calculate the point of intersection
                final Vector2dOld intersection = r.multiply( t ).add( p );
                point.setX( intersection.x );
                point.setY( intersection.y );
            } else {
                // No intersection, so calculate the closest point between the two segments
                // We have t and u, which we can use to find the closest endpoints
                final double nearT = Math.max( Math.min( t, 1 ), 0 );
                final double nearU = Math.max( Math.min( u, 1 ), 0 );
                
                final Vector2dOld nearP = r.multiply( nearT ).add( p );
                final Vector2dOld nearQ = s.multiply( nearU ).add( q );
                
                point.setX( ( nearP.x + nearQ.x ) / 2.0 );
                point.setY( ( nearP.y + nearQ.y ) / 2.0 );
            }
        }
        return point;
    }
}