Merge pull request #14518 from SSteve:intersectConvexConvex-example

modules/imgproc/include/opencv2/imgproc.hpp

@@ -4149,7 +4149,23 @@ without self-intersections. Otherwise, the function output is undefined.
  */
 CV_EXPORTS_W bool isContourConvex( InputArray contour );
 
-//! finds intersection of two convex polygons
+/** @example samples/cpp/intersectExample.cpp
+Examples of how intersectConvexConvex works
+*/
+
+/** @brief Finds intersection of two convex polygons
+
+@param _p1 First polygon
+@param _p2 Second polygon
+@param _p12 Output polygon describing the intersecting area
+@param handleNested When true, an intersection is found if one of the polygons is fully enclosed in the other.
+When false, no intersection is found. If the polygons share a side or the vertex of one polygon lies on an edge
+of the other, they are not considered nested and an intersection will be found regardless of the value of handleNested.
+
+@returns Absolute value of area of intersecting polygon
+
+@note intersectConvexConvex doesn't confirm that both polygons are convex and will return invalid results if they aren't.
+ */
 CV_EXPORTS_W float intersectConvexConvex( InputArray _p1, InputArray _p2,
                                           OutputArray _p12, bool handleNested = true );
 

samples/cpp/intersectExample.cpp

+/*
+ * Author: Steve Nicholson
+ *
+ * A program that illustrates intersectConvexConvex in various scenarios
+ */
+
+#include "opencv2/imgproc.hpp"
+#include "opencv2/highgui.hpp"
+
+using namespace cv;
+using namespace std;
+
+// Create a vector of points describing a rectangle with the given corners
+static vector<Point> makeRectangle(Point topLeft, Point bottomRight)
+{
+    vector<Point> rectangle;
+    rectangle.push_back(topLeft);
+    rectangle.push_back(Point(bottomRight.x, topLeft.y));
+    rectangle.push_back(bottomRight);
+    rectangle.push_back(Point(topLeft.x, bottomRight.y));
+    return rectangle;
+}
+
+static vector<Point> makeTriangle(Point point1, Point point2, Point point3)
+{
+    vector<Point> triangle;
+    triangle.push_back(point1);
+    triangle.push_back(point2);
+    triangle.push_back(point3);
+    return triangle;
+}
+
+// Run intersectConvexConvex on two polygons then draw the polygons and their intersection (if there is one)
+// Return the area of the intersection
+static float drawIntersection(Mat &image, vector<Point> polygon1, vector<Point> polygon2, bool handleNested = true)
+{
+    vector<Point> intersectionPolygon;
+
+    vector<vector<Point> > polygons;
+    polygons.push_back(polygon1);
+    polygons.push_back(polygon2);
+
+    float intersectArea = intersectConvexConvex(polygon1, polygon2, intersectionPolygon, handleNested);
+
+    if (intersectArea > 0)
+    {
+        Scalar fillColor(200, 200, 200);
+        // If the input is invalid, draw the intersection in red
+        if (!isContourConvex(polygon1) || !isContourConvex(polygon2))
+        {
+            fillColor = Scalar(0, 0, 255);
+        }
+        vector<vector<Point> > pp;
+        pp.push_back(intersectionPolygon);
+        fillPoly(image, pp, fillColor);
+    }
+    polylines(image, polygons, true, Scalar(0, 0, 0));
+
+    return intersectArea;
+}
+
+static void drawDescription(Mat &image, int intersectionArea, string description, Point origin)
+{
+    const size_t bufSize=1024;
+    char caption[bufSize];
+    snprintf(caption, bufSize, "Intersection area: %d%s", intersectionArea, description.c_str());
+    putText(image, caption, origin, FONT_HERSHEY_SIMPLEX, 0.6, Scalar(0, 0, 0));
+}
+
+static void intersectConvexExample()
+{
+    Mat image(610, 550, CV_8UC3, Scalar(255, 255, 255));
+    float intersectionArea;
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 10), Point(50, 50)),
+        makeRectangle(Point(20, 20), Point(60, 60)));
+
+    drawDescription(image, (int)intersectionArea, "", Point(70, 40));
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 70), Point(35, 95)),
+        makeRectangle(Point(35, 95), Point(60, 120)));
+
+    drawDescription(image, (int)intersectionArea, "", Point(70, 100));
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 130), Point(60, 180)),
+        makeRectangle(Point(20, 140), Point(50, 170)),
+        true);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested true)", Point(70, 160));
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 190), Point(60, 240)),
+        makeRectangle(Point(20, 200), Point(50, 230)),
+        false);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 220));
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 250), Point(60, 300)),
+        makeRectangle(Point(20, 250), Point(50, 290)),
+        true);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested true)", Point(70, 280));
+
+    // These rectangles share an edge so handleNested can be false and an intersection is still found
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 310), Point(60, 360)),
+        makeRectangle(Point(20, 310), Point(50, 350)),
+        false);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 340));
+
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 370), Point(60, 420)),
+        makeRectangle(Point(20, 371), Point(50, 410)),
+        false);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 400));
+
+    // A vertex of the triangle lies on an edge of the rectangle so handleNested can be false and an intersection is still found
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 430), Point(60, 480)),
+        makeTriangle(Point(35, 430), Point(20, 470), Point(50, 470)),
+        false);
+
+    drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 460));
+
+    // Show intersection of overlapping rectangle and triangle
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 490), Point(40, 540)),
+        makeTriangle(Point(25, 500), Point(25, 530), Point(60, 515)),
+        false);
+
+    drawDescription(image, (int)intersectionArea, "", Point(70, 520));
+
+    // This concave polygon is invalid input to intersectConvexConvex so it returns an invalid intersection
+    vector<Point> notConvex;
+    notConvex.push_back(Point(25, 560));
+    notConvex.push_back(Point(25, 590));
+    notConvex.push_back(Point(45, 580));
+    notConvex.push_back(Point(60, 600));
+    notConvex.push_back(Point(60, 550));
+    notConvex.push_back(Point(45, 570));
+    intersectionArea = drawIntersection(image,
+        makeRectangle(Point(10, 550), Point(50, 600)),
+        notConvex,
+        false);
+
+    drawDescription(image, (int)intersectionArea, " (invalid input: not convex)", Point(70, 580));
+
+    imshow("Intersections", image);
+    waitKey(0);
+}
+
+int main()
+{
+    intersectConvexExample();
+}