threejs计算两条线段的交点和距离点最近的线段

小咪咪 2022-10-11 12:23 300阅读 0赞

在 `threejs` 创建的三维空间中，可以计算两条线段是否有交点，或者线段的延长线是否有交点，使用其中一条线段创建射线，使用另一条线段创建平面，获取射线和平面的交点就可以了。

还可以在三维空间的某个点上计算最近的线段，分别计算点到线段的距离就可以了。

下面是参考代码：

// 获取两条线的交点
    var getPublicDot = function ( line1Dot, line1Direction, line2Dot, line2Direction ) { 
    
        var dotPublic = new THREE.Vector3('x', 'y', 'z');
    
        function run () { 
            var ray = new THREE.Ray( line1Dot, line1Direction );
            var line2DotPro = line2Dot.clone();
            var line2Vertical = line2Direction.clone();
            line2Vertical.applyAxisAngle(new THREE.Vector3(0, 1, 0), Math.PI/2);
            line2DotPro.projectOnVector(line2Vertical);
            var line2Pos = (line2DotPro.x * line2Vertical.x > 0 ? -1 : 1) * line2DotPro.distanceTo(new THREE.Vector3(0, 0, 0));
            var plane2 = new THREE.Plane( line2Vertical, line2Pos );
            ray.intersectPlane( plane2, dotPublic );
        }
        run();
    
        if ( dotPublic.x !== 'x' ) { 
            return dotPublic;
        } else { 
    
            line1Direction.applyAxisAngle(new THREE.Vector3(0, 1, 0), Math.PI);
            run();
            line1Direction.applyAxisAngle(new THREE.Vector3(0, 1, 0), Math.PI);
    
            if ( dotPublic.x !== 'x' ) { 
                return dotPublic;
            } else { 
                console.log('无法获取交点：', dotPublic);
                return null;
            }
    
        }
    
    }
    
    // 获取最近的线段
    var getCloseLine = function ( dot, lines, refer ) { 
    
        var lineDirection, lineVertical, lenMin, lineMin, dotPro, dotMin,
            dotProDir1, dotProDir2, check = false, dots, axisY = new THREE.Vector3(0, 1, 0);
    
        for (var i = 0, il = lines.length; i < il; i++) { 
    
            dots = refer.getObjDots( lines[i] );
    
            for (var j = 0, jl = dots.length; j < jl-1; j++) { 
    
                lineDirection = dots[j+1].clone();
                lineDirection = lineDirection.sub(dots[j]);
                lineVertical = lineDirection.clone();
                lineVertical.applyAxisAngle(axisY, Math.PI/2);
                lineDirection.normalize();
                lineVertical.normalize();
    
                dotPro = dot.clone();
                dotPro.projectOnPlane(lineVertical);
                dotPro.sub(dot);
                dotPro = refer.getPublicDot(dot, dotPro, dots[j], lineDirection);
                if (!dotPro) return null;
    
                dotProDir1 = dotPro.clone();
                dotProDir2 = dotPro.clone();
                dotProDir1.sub(dots[j]);
                dotProDir2.sub(dots[j+1]);
                dotProDir1.normalize();
                dotProDir2.normalize();
                check = dotProDir1.dot(dotProDir2);
    
                if ( ( !lenMin || lenMin > dotPro.distanceTo(dot) ) && (check.toFixed(4) === '-1.0000') ) { 
                    lenMin = dotPro.distanceTo(dot);
                    lineMin = lines[i];
                    dotMin = dotPro.clone();
                }
    
            }
    
        }
    
        if (lenMin) { 
            return { 
                dot: dotMin,
                line: lineMin
            };
        } else { 
            return null;
        }
    
    }
    
    // 查找模型的端点
    var getObjDots = function ( obj, refer ) { 
    
        var dots = [], dotAll, dotTemp;
    
        if ( obj.geometry.type === 'Geometry' ) { 
            dotAll = obj.geometry.vertices;
            for (var i = 0, il = dotAll.length; i < il; i++) { 
                dotTemp = dotAll[i].clone();
                obj.localToWorld( dotTemp );
    
                if ( !refer ) { 
                    dots.push( dotTemp );
                } else if ( dotTemp[refer.axis] <= refer.max && dotTemp[refer.axis] >= refer.min ) { 
                    dots.push( dotTemp );
                }
            }
        } else if ( obj.geometry.type === 'BufferGeometry' ) { 
            dotAll = obj.geometry.attributes.position;
            dotTemp = new THREE.Vector3();
            for (var i = 0, il = dotAll.count * 3; i < il; i+=3) { 
                dotTemp.set(dotAll.array[i], dotAll.array[i+1], dotAll.array[i+2]);
                obj.localToWorld( dotTemp );
    
                if ( !refer ) { 
                    dots.push( dotTemp.clone() );
                } else if ( dotTemp[refer.axis] <= refer.max && dotTemp[refer.axis] >= refer.min ) { 
                    dots.push( dotTemp.clone() );
                }
            }
        }
    
        return dots;
    
    }