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Diffstat (limited to 'src/ipa/libipa/pwl.cpp')
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diff --git a/src/ipa/libipa/pwl.cpp b/src/ipa/libipa/pwl.cpp new file mode 100644 index 00000000..901e42ce --- /dev/null +++ b/src/ipa/libipa/pwl.cpp @@ -0,0 +1,447 @@ +/* SPDX-License-Identifier: BSD-2-Clause */ +/* + * Copyright (C) 2019, Raspberry Pi Ltd + * Copyright (C) 2024, Ideas on Board Oy + * + * Piecewise linear functions + */ + +#include "pwl.h" + +#include <assert.h> +#include <cmath> +#include <sstream> +#include <stdexcept> + +/** + * \file pwl.h + * \brief Piecewise linear functions + */ + +namespace libcamera { + +namespace ipa { + +/** + * \class Pwl + * \brief Describe a univariate piecewise linear function in two-dimensional + * real space + * + * A piecewise linear function is a univariate function that maps reals to + * reals, and it is composed of multiple straight-line segments. + * + * While a mathematical piecewise linear function would usually be defined by + * a list of linear functions and for which values of the domain they apply, + * this Pwl class is instead defined by a list of points at which these line + * segments intersect. These intersecting points are known as knots. + * + * https://en.wikipedia.org/wiki/Piecewise_linear_function + * + * A consequence of the Pwl class being defined by knots instead of linear + * functions is that the values of the piecewise linear function past the ends + * of the function are constants as opposed to linear functions. In a + * mathematical piecewise linear function that is defined by multiple linear + * functions, the ends of the function are also linear functions and hence grow + * to infinity (or negative infinity). However, since this Pwl class is defined + * by knots, the y-value of the leftmost and rightmost knots will hold for all + * x values to negative infinity and positive infinity, respectively. + */ + +/** + * \typedef Pwl::Point + * \brief Describe a point in two-dimensional real space + */ + +/** + * \class Pwl::Interval + * \brief Describe an interval in one-dimensional real space + */ + +/** + * \fn Pwl::Interval::Interval(double _start, double _end) + * \brief Construct an interval + * \param _start Start of the interval + * \param _end End of the interval + */ + +/** + * \fn Pwl::Interval::contains + * \brief Check if a given value falls within the interval + * \param value Value to check + * \return True if the value falls within the interval, including its bounds, + * or false otherwise + */ + +/** + * \fn Pwl::Interval::clamp + * \brief Clamp a value such that it is within the interval + * \param value Value to clamp + * \return The clamped value + */ + +/** + * \fn Pwl::Interval::length + * \brief Compute the length of the interval + * \return The length of the interval + */ + +/** + * \var Pwl::Interval::start + * \brief Start of the interval + */ + +/** + * \var Pwl::Interval::end + * \brief End of the interval + */ + +/** + * \brief Construct an empty piecewise linear function + */ +Pwl::Pwl() +{ +} + +/** + * \brief Construct a piecewise linear function from a list of 2D points + * \param points Vector of points from which to construct the piecewise linear function + * + * \a points must be in ascending order of x-value. + */ +Pwl::Pwl(const std::vector<Point> &points) + : points_(points) +{ +} + +/** + * \brief Populate the piecewise linear function from yaml data + * \param params Yaml data to populate the piecewise linear function with + * + * Any existing points in the piecewise linear function *will* be overwritten. + * + * The yaml data is expected to be a list with an even number of numerical + * elements. These will be parsed in pairs into x and y points in the piecewise + * linear function, and added in order. x must be monotonically increasing. + * + * \return 0 on success, negative error code otherwise + */ +int Pwl::readYaml(const libcamera::YamlObject ¶ms) +{ + if (!params.size() || params.size() % 2) + return -EINVAL; + + const auto &list = params.asList(); + + points_.clear(); + + for (auto it = list.begin(); it != list.end(); it++) { + auto x = it->get<double>(); + if (!x) + return -EINVAL; + if (it != list.begin() && *x <= points_.back().x()) + return -EINVAL; + + auto y = (++it)->get<double>(); + if (!y) + return -EINVAL; + + points_.push_back(Point({ *x, *y })); + } + + return 0; +} + +/** + * \brief Append a point to the end of the piecewise linear function + * \param x x-coordinate of the point to add to the piecewise linear function + * \param y y-coordinate of the point to add to the piecewise linear function + * \param eps Epsilon for the minimum x distance between points (optional) + * + * The point's x-coordinate must be greater than the x-coordinate of the last + * (= greatest) point already in the piecewise linear function. + */ +void Pwl::append(double x, double y, const double eps) +{ + if (points_.empty() || points_.back().x() + eps < x) + points_.push_back(Point({ x, y })); +} + +/** + * \brief Prepend a point to the beginning of the piecewise linear function + * \param x x-coordinate of the point to add to the piecewise linear function + * \param y y-coordinate of the point to add to the piecewise linear function + * \param eps Epsilon for the minimum x distance between points (optional) + * + * The point's x-coordinate must be less than the x-coordinate of the first + * (= smallest) point already in the piecewise linear function. + */ +void Pwl::prepend(double x, double y, const double eps) +{ + if (points_.empty() || points_.front().x() - eps > x) + points_.insert(points_.begin(), Point({ x, y })); +} + +/** + * \brief Get the domain of the piecewise linear function + * \return An interval representing the domain + */ +Pwl::Interval Pwl::domain() const +{ + return Interval(points_[0].x(), points_[points_.size() - 1].x()); +} + +/** + * \brief Get the range of the piecewise linear function + * \return An interval representing the range + */ +Pwl::Interval Pwl::range() const +{ + double lo = points_[0].y(), hi = lo; + for (auto &p : points_) + lo = std::min(lo, p.y()), hi = std::max(hi, p.y()); + return Interval(lo, hi); +} + +/** + * \brief Check if the piecewise linear function is empty + * \return True if there are no points in the function, false otherwise + */ +bool Pwl::empty() const +{ + return points_.empty(); +} + +/** + * \brief Evaluate the piecewise linear function + * \param[in] x The x value to input into the function + * \param[inout] span Initial guess for span + * \param[in] updateSpan Set to true to update span + * + * Evaluate Pwl, optionally supplying an initial guess for the + * "span". The "span" may be optionally be updated. If you want to know + * the "span" value but don't have an initial guess you can set it to + * -1. + * + * \return The result of evaluating the piecewise linear function at position \a x + */ +double Pwl::eval(double x, int *span, bool updateSpan) const +{ + int index = findSpan(x, span && *span != -1 + ? *span + : points_.size() / 2 - 1); + if (span && updateSpan) + *span = index; + return points_[index].y() + + (x - points_[index].x()) * (points_[index + 1].y() - points_[index].y()) / + (points_[index + 1].x() - points_[index].x()); +} + +int Pwl::findSpan(double x, int span) const +{ + /* + * Pwls are generally small, so linear search may well be faster than + * binary, though could review this if large Pwls start turning up. + */ + int lastSpan = points_.size() - 2; + /* + * some algorithms may call us with span pointing directly at the last + * control point + */ + span = std::max(0, std::min(lastSpan, span)); + while (span < lastSpan && x >= points_[span + 1].x()) + span++; + while (span && x < points_[span].x()) + span--; + return span; +} + +/** + * \brief Compute the inverse function + * \param[in] eps Epsilon for the minimum x distance between points (optional) + * + * The output includes whether the resulting inverse function is a proper + * (true) inverse, or only a best effort (e.g. input was non-monotonic). + * + * \return A pair of the inverse piecewise linear function, and whether or not + * the result is a proper/true inverse + */ +std::pair<Pwl, bool> Pwl::inverse(const double eps) const +{ + bool appended = false, prepended = false, neither = false; + Pwl inverse; + + for (Point const &p : points_) { + if (inverse.empty()) { + inverse.append(p.y(), p.x(), eps); + } else if (std::abs(inverse.points_.back().x() - p.y()) <= eps || + std::abs(inverse.points_.front().x() - p.y()) <= eps) { + /* do nothing */; + } else if (p.y() > inverse.points_.back().x()) { + inverse.append(p.y(), p.x(), eps); + appended = true; + } else if (p.y() < inverse.points_.front().x()) { + inverse.prepend(p.y(), p.x(), eps); + prepended = true; + } else { + neither = true; + } + } + + /* + * This is not a proper inverse if we found ourselves putting points + * onto both ends of the inverse, or if there were points that couldn't + * go on either. + */ + bool trueInverse = !(neither || (appended && prepended)); + + return { inverse, trueInverse }; +} + +/** + * \brief Compose two piecewise linear functions together + * \param[in] other The "other" piecewise linear function + * \param[in] eps Epsilon for the minimum x distance between points (optional) + * + * The "this" function is done first, and "other" after. + * + * \return The composed piecewise linear function + */ +Pwl Pwl::compose(Pwl const &other, const double eps) const +{ + double thisX = points_[0].x(), thisY = points_[0].y(); + int thisSpan = 0, otherSpan = other.findSpan(thisY, 0); + Pwl result({ Point({ thisX, other.eval(thisY, &otherSpan, false) }) }); + + while (thisSpan != (int)points_.size() - 1) { + double dx = points_[thisSpan + 1].x() - points_[thisSpan].x(), + dy = points_[thisSpan + 1].y() - points_[thisSpan].y(); + if (std::abs(dy) > eps && + otherSpan + 1 < (int)other.points_.size() && + points_[thisSpan + 1].y() >= other.points_[otherSpan + 1].x() + eps) { + /* + * next control point in result will be where this + * function's y reaches the next span in other + */ + thisX = points_[thisSpan].x() + + (other.points_[otherSpan + 1].x() - + points_[thisSpan].y()) * + dx / dy; + thisY = other.points_[++otherSpan].x(); + } else if (std::abs(dy) > eps && otherSpan > 0 && + points_[thisSpan + 1].y() <= + other.points_[otherSpan - 1].x() - eps) { + /* + * next control point in result will be where this + * function's y reaches the previous span in other + */ + thisX = points_[thisSpan].x() + + (other.points_[otherSpan + 1].x() - + points_[thisSpan].y()) * + dx / dy; + thisY = other.points_[--otherSpan].x(); + } else { + /* we stay in the same span in other */ + thisSpan++; + thisX = points_[thisSpan].x(), + thisY = points_[thisSpan].y(); + } + result.append(thisX, other.eval(thisY, &otherSpan, false), + eps); + } + return result; +} + +/** + * \brief Apply function to (x, y) values at every control point + * \param f Function to be applied + */ +void Pwl::map(std::function<void(double x, double y)> f) const +{ + for (auto &pt : points_) + f(pt.x(), pt.y()); +} + +/** + * \brief Apply function to (x, y0, y1) values wherever either Pwl has a + * control point. + * \param pwl0 First piecewise linear function + * \param pwl1 Second piecewise linear function + * \param f Function to be applied + * + * This applies the function \a f to every parameter (x, y0, y1), where x is + * the combined list of x-values from \a pwl0 and \a pwl1, y0 is the y-value + * for the given x in \a pwl0, and y1 is the y-value for the same x in \a pwl1. + */ +void Pwl::map2(Pwl const &pwl0, Pwl const &pwl1, + std::function<void(double x, double y0, double y1)> f) +{ + int span0 = 0, span1 = 0; + double x = std::min(pwl0.points_[0].x(), pwl1.points_[0].x()); + f(x, pwl0.eval(x, &span0, false), pwl1.eval(x, &span1, false)); + + while (span0 < (int)pwl0.points_.size() - 1 || + span1 < (int)pwl1.points_.size() - 1) { + if (span0 == (int)pwl0.points_.size() - 1) + x = pwl1.points_[++span1].x(); + else if (span1 == (int)pwl1.points_.size() - 1) + x = pwl0.points_[++span0].x(); + else if (pwl0.points_[span0 + 1].x() > pwl1.points_[span1 + 1].x()) + x = pwl1.points_[++span1].x(); + else + x = pwl0.points_[++span0].x(); + f(x, pwl0.eval(x, &span0, false), pwl1.eval(x, &span1, false)); + } +} + +/** + * \brief Combine two Pwls + * \param pwl0 First piecewise linear function + * \param pwl1 Second piecewise linear function + * \param f Function to be applied + * \param[in] eps Epsilon for the minimum x distance between points (optional) + * + * Create a new Pwl where the y values are given by running \a f wherever + * either pwl has a knot. + * + * \return The combined pwl + */ +Pwl Pwl::combine(Pwl const &pwl0, Pwl const &pwl1, + std::function<double(double x, double y0, double y1)> f, + const double eps) +{ + Pwl result; + map2(pwl0, pwl1, [&](double x, double y0, double y1) { + result.append(x, f(x, y0, y1), eps); + }); + return result; +} + +/** + * \brief Multiply the piecewise linear function + * \param d Scalar multiplier to multiply the function by + * \return This function, after it has been multiplied by \a d + */ +Pwl &Pwl::operator*=(double d) +{ + for (auto &pt : points_) + pt[1] *= d; + return *this; +} + +/** + * \brief Assemble and return a string describing the piecewise linear function + * \return A string describing the piecewise linear function + */ +std::string Pwl::toString() const +{ + std::stringstream ss; + ss << "Pwl { "; + for (auto &p : points_) + ss << "(" << p.x() << ", " << p.y() << ") "; + ss << "}"; + return ss.str(); +} + +} /* namespace ipa */ + +} /* namespace libcamera */ |