I am using clipper for performing a bunch of operations on polygons which represent the outlines of objects in my program. The thing is, I now want to clip a grid of line segments to fill these outlines but I am struggling to do this with Clipper.
At the moment I am converting my lines to rectangles with a thickness of 2 units which I then do an intersection operation with and then finally I need to revert the new polygons back to line segments. This is quite inefficient though and produces quite a few errors.
Can this be done with Clipper, if not is there something else that I can use or do I need to implement my own line segment clipper?
Using Clipper ver 6 ...
using ClipperLib;
using Path = List<IntPoint>;
using Paths = List<List<IntPoint>>;
static Polygon IntsToPolygon(Int64[] ints)
{
int len1 = ints.Length / 2;
Polygon result = new Polygon(len1);
for (int i = 0; i < len1; i++)
result.Add(new IntPoint(ints[i * 2], ints[i * 2 + 1]));
return result;
}
static void Main(string[] args)
{
Paths clip = new Paths(); //clipping polygon(s)
//make a polygon in the shape of a pentagram
//with center (200,200) and radius 100 ...
Int64[][] ints1 = new Int64[][]
{
new Int64[]{222, 169, 295, 169, 236, 212, 259, 281, 200, 238,
141, 281, 164, 212, 105, 169, 178, 169, 200, 100}
};
clip.Add(IntsToPolygon(ints1[0]));
Paths subj = new Paths(); //subject paths, could be open or closed here
int gridWidth = 5;
int loopCnt = 200 / gridWidth;
//now make grid lines and add them to subj ready for clipping ...
//add horizontal grid lines ...
for (int i = 0; i <= loopCnt; i++)
{
Path gridLine = new Path(2);
gridLine.Add(new IntPoint(100, 100 + i * gridWidth));
gridLine.Add(new IntPoint(300, 100 + i * gridWidth));
subj.Add(gridLine);
}
//add vertical grid lines ...
for (int i = 0; i <= loopCnt; i++)
{
Path gridLine = new Path(2);
gridLine.Add(new IntPoint(100 + i * gridWidth, 100));
gridLine.Add(new IntPoint(100 + i * gridWidth, 300));
subj.Add(gridLine);
}
//now clip the gridlines (subj) with the pentagram (clip) ...
Clipper c = new Clipper();
PolyTree solution = new PolyTree();
c.AddPaths(subj, PolyType.ptSubject, false); //ie paths NOT closed
c.AddPaths(clip, PolyType.ptClip, true); //nb: clip paths MUST be closed
c.Execute(ClipType.ctIntersection,
solution, PolyFillType.pftEvenOdd, PolyFillType.pftEvenOdd);
Paths clippedGrids = Clipper.PolyTreeToPaths(solution);
//Display the result (sorry, make your own display function) ...
//Display(Paths p, Color stroke, Color brush, PolyFillType pft, bool IsClosed)
Display(subj, Color.FromArgb(0x18, 0, 0, 0x9c),
Color.Blue, PolyFillType.NonZero, false); //unclipped grid
Display(clippedGrids, FromArgb(0, 0, 0, 0),
Color.Red, false); //clipped grid
}
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