--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/tesseract/src/ccstruct/detlinefit.h	Mon Sep 15 11:43:07 2025 +0200
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+///////////////////////////////////////////////////////////////////////
+// File:        detlinefit.h
+// Description: Deterministic least upper-quartile squares line fitting.
+// Author:      Ray Smith
+//
+// (C) Copyright 2008, Google Inc.
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+///////////////////////////////////////////////////////////////////////
+
+#ifndef TESSERACT_CCSTRUCT_DETLINEFIT_H_
+#define TESSERACT_CCSTRUCT_DETLINEFIT_H_
+
+#include "kdpair.h"
+#include "points.h"
+
+namespace tesseract {
+
+// This class fits a line to a set of ICOORD points.
+// There is no restriction on the direction of the line, as it
+// uses a vector method, ie no concern over infinite gradients.
+// The fitted line has the least upper quartile of squares of perpendicular
+// distances of all source points from the line, subject to the constraint
+// that the line is made from one of the pairs of [{p1,p2,p3},{pn-2, pn-1, pn}]
+// i.e. the 9 combinations of one of the first 3 and last 3 points.
+// A fundamental assumption of this algorithm is that one of the first 3 and
+// one of the last 3 points are near the best line fit.
+// The points must be Added in line order for the algorithm to work properly.
+// No floating point calculations are needed* to make an accurate fit,
+// and no random numbers are needed** so the algorithm is deterministic,
+// architecture-stable, and compiler-stable as well as stable to minor
+// changes in the input.
+// *A single floating point division is used to compute each line's distance.
+// This is unlikely to result in choice of a different line, but if it does,
+// it would be easy to replace with a 64 bit integer calculation.
+// **Random numbers are used in the nth_item function, but the worst
+// non-determinism that can result is picking a different result among equals,
+// and that wouldn't make any difference to the end-result distance, so the
+// randomness does not affect the determinism of the algorithm. The random
+// numbers are only there to guarantee average linear time.
+// Fitting time is linear, but with a high constant, as it tries 9 different
+// lines and computes the distance of all points each time.
+// This class is aimed at replacing the LLSQ (linear least squares) and
+// LMS (least median of squares) classes that are currently used for most
+// of the line fitting in Tesseract.
+class DetLineFit {
+public:
+  DetLineFit();
+  ~DetLineFit() = default;
+
+  // Delete all Added points.
+  void Clear();
+
+  // Adds a new point. Takes a copy - the pt doesn't need to stay in scope.
+  // Add must be called on points in sequence along the line.
+  void Add(const ICOORD &pt);
+  // Associates a half-width with the given point if a point overlaps the
+  // previous point by more than half the width, and its distance is further
+  // than the previous point, then the more distant point is ignored in the
+  // distance calculation. Useful for ignoring i dots and other diacritics.
+  void Add(const ICOORD &pt, int halfwidth);
+
+  // Fits a line to the points, returning the fitted line as a pair of
+  // points, and the upper quartile error.
+  double Fit(ICOORD *pt1, ICOORD *pt2) {
+    return Fit(0, 0, pt1, pt2);
+  }
+  // Fits a line to the points, ignoring the skip_first initial points and the
+  // skip_last final points, returning the fitted line as a pair of points,
+  // and the upper quartile error.
+  double Fit(int skip_first, int skip_last, ICOORD *pt1, ICOORD *pt2);
+
+  // Constrained fit with a supplied direction vector. Finds the best line_pt,
+  // that is one of the supplied points having the median cross product with
+  // direction, ignoring points that have a cross product outside of the range
+  // [min_dist, max_dist]. Returns the resulting error metric using the same
+  // reduced set of points.
+  // *Makes use of floating point arithmetic*
+  double ConstrainedFit(const FCOORD &direction, double min_dist, double max_dist, bool debug,
+                        ICOORD *line_pt);
+
+  // Returns true if there were enough points at the last call to Fit or
+  // ConstrainedFit for the fitted points to be used on a badly fitted line.
+  bool SufficientPointsForIndependentFit() const;
+
+  // Backwards compatible fit returning a gradient and constant.
+  // Deprecated. Prefer Fit(ICOORD*, ICOORD*) where possible, but use this
+  // function in preference to the LMS class.
+  double Fit(float *m, float *c);
+
+  // Backwards compatible constrained fit with a supplied gradient.
+  // Deprecated. Use ConstrainedFit(const FCOORD& direction) where possible
+  // to avoid potential difficulties with infinite gradients.
+  double ConstrainedFit(double m, float *c);
+
+private:
+  // Simple struct to hold an ICOORD point and a halfwidth representing half
+  // the "width" (supposedly approximately parallel to the direction of the
+  // line) of each point, such that distant points can be discarded when they
+  // overlap nearer points. (Think i dot and other diacritics or noise.)
+  struct PointWidth {
+    PointWidth() : pt(ICOORD(0, 0)), halfwidth(0) {}
+    PointWidth(const ICOORD &pt0, int halfwidth0) : pt(pt0), halfwidth(halfwidth0) {}
+
+    ICOORD pt;
+    int halfwidth;
+  };
+  // Type holds the distance of each point from the fitted line and the point
+  // itself. Use of double allows integer distances from ICOORDs to be stored
+  // exactly, and also the floating point results from ConstrainedFit.
+  using DistPointPair = KDPairInc<double, ICOORD>;
+
+  // Computes and returns the squared evaluation metric for a line fit.
+  double EvaluateLineFit();
+
+  // Computes the absolute values of the precomputed distances_,
+  // and returns the squared upper-quartile error distance.
+  double ComputeUpperQuartileError();
+
+  // Returns the number of sample points that have an error more than threshold.
+  int NumberOfMisfittedPoints(double threshold) const;
+
+  // Computes all the cross product distances of the points from the line,
+  // storing the actual (signed) cross products in distances_.
+  // Ignores distances of points that are further away than the previous point,
+  // and overlaps the previous point by at least half.
+  void ComputeDistances(const ICOORD &start, const ICOORD &end);
+
+  // Computes all the cross product distances of the points perpendicular to
+  // the given direction, ignoring distances outside of the give distance range,
+  // storing the actual (signed) cross products in distances_.
+  void ComputeConstrainedDistances(const FCOORD &direction, double min_dist, double max_dist);
+
+  // Stores all the source points in the order they were given and their
+  // halfwidths, if any.
+  std::vector<PointWidth> pts_;
+  // Stores the computed perpendicular distances of (some of) the pts_ from a
+  // given vector (assuming it goes through the origin, making it a line).
+  // Since the distances may be a subset of the input points, and get
+  // re-ordered by the nth_item function, the original point is stored
+  // along side the distance.
+  std::vector<DistPointPair> distances_; // Distances of points.
+  // The squared length of the vector used to compute distances_.
+  double square_length_;
+};
+
+} // namespace tesseract.
+
+#endif // TESSERACT_CCSTRUCT_DETLINEFIT_H_