clipper库使用的一些心得

标签：c++   多边形处理   clipper 库   

clipper 

sourceforge官网：http://sourceforge.net/projects/polyclipping/

1. 版本差异

之前工程里面使用4.8.6，最近升级到最新版本6.2.1，接口层面有点差别：

老版本使用Polygon概念，最新版本用Path代替了Polygon，对用的Polygons用Paths代替，Clipper::AddPath的时候还需要制定是否封闭。

2. 注意数据类型

一个测试，回字上半部分和下半部分，两半部分进行合并，但是输出结果总是不对：

void transform_array_to_path(int* arr, int size, ClipperLib::Path& path, int scale = 1)
{
	for (int i = 0; i < size; i += 2)
	{
		path.push_back(ClipperLib::IntPoint(arr[i] * scale, arr[i + 1] * scale));
	}
}

void ClipperTest::merge_case()
{
	using namespace ClipperLib;

	Clipper union_worker;
	Paths solution;

	Path positive_path;
	{
		int points[] = { 1, 1, 1, 0, 2, 0, 2, 2, -2, 2, -2, 0, -1, 0, -1, 1 };
		transform_array_to_path(points, sizeof(points) / sizeof(points[0]), positive_path, 10);
	}

	union_worker.AddPath(positive_path, ClipperLib::ptSubject, true);

	Path negative_path;
	{
		int points[] = { 1, -1, 1, 0, 2, 0, 2, -2, -2, -2, -2, 0, -1, 0, -1, -1 };
		transform_array_to_path(points, sizeof(points) / sizeof(points[0]), negative_path, 10);
	}

	union_worker.AddPath(negative_path, ClipperLib::ptClip, true);

	union_worker.Execute(ClipperLib::ctUnion, solution, pftEvenOdd, pftEvenOdd);

	for (int k = 0; k < solution.size(); k++)
	{
		Path& path = solution[k];
		
		printf("[ %dth ] : ", k + 1);

		for (int t = 0; t < path.size(); t++)
		{
			printf("%d,%d  ", path[t].X, path[t].Y);
		} 
		printf("\n");		
	}
}

// [1th] : -10, -1 - 10, -1  10, 0  10, 0
// [2th] : -20, -1 - 20, -1  20, 0  20, 0

不断地跟clipper自带的demo程序比对，终于发现了问题所在：问题出在Clipper内部的IntPoint，如果没有定义宏use_int32，采用的是long long存储顶点XY值，而上面code中printf是%d，使用%lld或者cout 就没问题了。坑啊。。。

2. 带洞多边形和多边形填充规则

void ClipperTest::polygon_with_hole_merge_test()
{
	using namespace ClipperLib;	
	
	Path path1_outer;
	Path path1_inner;
	{
		int outer[] = { -2, -2, 2, -2, 2, 2, -2, 2 };
		int inner[] = { -1, -1, 1, -1, 1, 1, -1, 1 };		
		transform_array_to_path(outer, sizeof(outer)/sizeof(outer[0]), path1_outer);
		transform_array_to_path(inner, sizeof(inner)/sizeof(inner[0]), path1_inner);
	}

	Path path2;
	{
		int outer[] = { 2, 2, 3, 2, 3, -2, 2, -2 };
		transform_array_to_path(outer, sizeof(outer) / sizeof(outer[0]), path2);
	}

	Paths sub_poly;
	sub_poly.push_back(path1_outer);
	sub_poly.push_back(path1_inner);

	Clipper union_worker;
	union_worker.AddPaths(sub_poly, ptSubject, true);
	union_worker.AddPath(path2, ptClip, true);

	Paths solution;
	union_worker.Execute(ClipperLib::ctUnion, solution, pftEvenOdd, pftEvenOdd);

	for (int k = 0; k < solution.size(); k++)
	{
		Path& path = solution[k];

		printf("[ %dth ] : ", k + 1);

		for (int t = 0; t < path.size(); t++)
		{
			// printf("%d,%d  ", path[t].X, path[t].Y);
			cout << path[t].X << "," << path[t].Y << " ";
		} printf("\n");
	}
}

clipper库使用的一些心得

标签：c++   多边形处理   clipper 库   

原文地址：http://blog.csdn.net/ryfdizuo/article/details/40682639