[PATCH v6 1/4] ipa: libipa: Add Vector class

[Kieran Bingham]

Quoting Paul Elder (2024-06-07 09:42:58)
> Add a vector class to libipa. The original purpose of this is to replace
> the floating-point Point class that Raspberry Pi used in their Pwl, as
> that implementation of Point seemed more akin to a Vector than a Point.
> 
> This is added to libipa instead of to geometry.h to avoid public API
> issues, plus this is not expected to be needed by applications.
> 
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> 
> ---
> No change in v6
> 
> New in v5
> ---
>  src/ipa/libipa/vector.cpp | 162 ++++++++++++++++++++++++++++++
>  src/ipa/libipa/vector.h   | 206 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 368 insertions(+)
>  create mode 100644 src/ipa/libipa/vector.cpp
>  create mode 100644 src/ipa/libipa/vector.h
> 
> diff --git a/src/ipa/libipa/vector.cpp b/src/ipa/libipa/vector.cpp
> new file mode 100644
> index 000000000..bdc3c447c
> --- /dev/null
> +++ b/src/ipa/libipa/vector.cpp
> @@ -0,0 +1,162 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2019, Raspberry Pi Ltd
> + * Copyright (C) 2024, Paul Elder <paul.elder at ideasonboard.com>
> + *
> + * Vector and related operations
> + */
> +
> +#include "vector.h"
> +
> +#include <libcamera/base/log.h>
> +
> +/**
> + * \file vector.h
> + * \brief Vector class
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(Vector)
> +
> +namespace ipa {
> +
> +/**
> + * \class Vector
> + * \brief Vector class
> + * \tparam T Type of numerical values to be stored in the vector
> + * \tparam R Number of rows in the vector
> + */
> +
> +/**
> + * \fn Vector::Vector()
> + * \brief Construct an identity vector
> + */
> +
> +/**
> + * \fn Vector::Vector(const std::array<T, R> &data)
> + * \brief Construct vector from supplied data
> + * \param data Data from which to construct a vector
> + *
> + * \a data is a one-dimensional vector and will be turned into a vector in
> + * row-major order. The size of \a data must be equal to the product of the
> + * number of rows and columns of the vector (RxC).

Rows and columns of a vector?

> + */
> +
> +/**
> + * \fn Vector::readYaml
> + * \brief Populate the vector with yaml data
> + * \param yaml Yaml data to populate the vector with
> + *
> + * Any existing data in the vector will be overwritten. The size of the data
> + * read from \a yaml must be equal to the product of the number of rows and
> + * columns of the vector (RxC).
> + *
> + * The yaml data is expected to be a list with elements of type T.
> + *
> + * \return 0 on success, negative error code otherwise
> + */
> +
> +/**
> + * \fn Vector::toString
> + * \brief Assemble and return a string describing the vector
> + * \return A string describing the vector
> + */
> +
> +/**
> + * \fn T Vector::operator[](size_t i) const
> + * \brief Index to a row in the vector
> + * \param i Index of row to retrieve
> + *
> + * This operator[] returns a Span, which can then be indexed into again with
> + * another operator[], allowing a convenient m[i][j] to access elements of the
> + * vector. Note that the lifetime of the Span returned by this first-level
> + * operator[] is bound to that of the Vector itself, so it is not recommended
> + * to save the Span that is the result of this operator[].
> + *
> + * \return Row \a i from the vector, as a Span

Are these needed for a vector? I don't understand the indexing of a
vector? I could understand on a matrix - but isn't a vector just a set
of coordinates that represent direction/magnitude?

I don't understand what m[i][j] is used for ? (or represents?)

Perhaps the hint 'm' means this is a left over and needs to be removed?

> + */
> +
> +/**
> + * \fn T &Vector::operator[](size_t i)
> + * \copydoc Vector::operator[](size_t i) const
> + */
> +
> +/**
> + * \fn Vector::x()
> + * \brief Convenience function to access the first element of the vector
> + */
> +
> +/**
> + * \fn Vector::y()
> + * \brief Convenience function to access the second element of the vector
> + */

These I understand :-)



> +
> +/**
> + * \fn Vector::operator-() const
> + * \brief Negate a Vector by negating both all of its coordinates
> + * \return The negated vector
> + */
> +
> +/**
> + * \fn Vector::operator-(Vector const &other) const
> + * \brief Subtract one vector from another
> + * \param[in] other The other vector
> + * \return The difference of \a other from this vector
> + */
> +
> +/**
> + * \fn Vector::operator+()
> + * \brief Add two vectors together
> + * \param[in] other The other vector
> + * \return The sum of the two vectors
> + */
> +
> +/**
> + * \fn Vector::operator*(const Vector<T, R> &other) const
> + * \brief Compute the dot product
> + * \param[in] other The other vector
> + * \return The dot product of the two vectors
> + */
> +
> +/**
> + * \fn Vector::operator*(T factor) const
> + * \brief Scale up the vector
> + * \param[in] factor The factor
> + * \return The vector scaled up by \a factor
> + */
> +
> +/**
> + * \fn Vector::operator/()
> + * \brief Scale down the vector
> + * \param[in] factor The factor
> + * \return The vector scaled down by \a factor
> + */
> +
> +/**
> + * \fn Vector::len2()
> + * \brief Get the squared length of the vector
> + * \return The squared length of the vector
> + */
> +
> +/**
> + * \fn Vector::len()
> + * \brief Get the length of the vector
> + * \return The length of the vector
> + */

I think all of those probably deserve at least some level of a unit
test. How come we don't seem to have tests for libipa - Seems like the
sort of thing we should have... Particularly as you've got operations on
differing types above.



> +
> +/**
> + * \fn bool operator==(const Vector<T, R> &lhs, const Vector<T, R> &rhs)
> + * \brief Compare vectors for equality
> + * \return True if the two vectors are equal, false otherwise
> + */
> +
> +/**
> + * \fn bool operator!=(const Vector<T, R> &lhs, const Vector<T, R> &rhs)
> + * \brief Compare vectors for inequality
> + * \return True if the two vectors are not equal, false otherwise
> + */
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> diff --git a/src/ipa/libipa/vector.h b/src/ipa/libipa/vector.h
> new file mode 100644
> index 000000000..87aad28b5
> --- /dev/null
> +++ b/src/ipa/libipa/vector.h
> @@ -0,0 +1,206 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2019, Raspberry Pi Ltd
> + * Copyright (C) 2024, Paul Elder <paul.elder at ideasonboard.com>
> + *
> + * Vector and related operations
> + */
> +#pragma once
> +
> +#include <algorithm>
> +#include <array>
> +#include <cmath>
> +#include <sstream>
> +
> +#include <libcamera/base/log.h>
> +#include <libcamera/base/span.h>
> +
> +#include "libcamera/internal/yaml_parser.h"
> +
> +namespace libcamera {
> +
> +LOG_DECLARE_CATEGORY(Vector)
> +
> +namespace ipa {
> +
> +#ifndef __DOXYGEN__
> +template<typename T, unsigned int R,
> +        std::enable_if_t<std::is_arithmetic_v<T> && R >= 2> * = nullptr>
> +#else
> +template<typename T, unsigned int R>

Do we anticipate 3d vectors? (or other dimesions?)

How about defaulting R = 2 so that a 2d vector is the default case?

Then we can use
	Vector<int> v = {x, y};

or such. (Or some how typedef/using to create Vector2d, Vector3d?)

Is R an appropriate name for a vector? Is D for dimensions any better?
Or is it still better to call it Rows?



> +#endif /* __DOXYGEN__ */
> +class Vector
> +{
> +public:
> +       Vector() = default;
> +
> +       Vector(const std::array<T, R> &data)
> +       {
> +               ASSERT(data.size() == R);

Optional, but as we provide direct accessors for x() and y() perhaps:

	ASSERT(R >= 2);

That might stop accidentally creating a vector of one dimesion..


> +
> +               for (unsigned int i = 0; i < R; i++)
> +                       data_[i] = data[i];
> +       }
> +
> +       ~Vector() = default;
> +
> +       int readYaml(const libcamera::YamlObject &yaml)
> +       {
> +               if (yaml.size() != R) {
> +                       LOG(Vector, Error)
> +                               << "Wrong number of values in vector: expected "
> +                               << R << ", got " << yaml.size();
> +                       return -EINVAL;
> +               }
> +
> +               unsigned int i = 0;
> +               for (const auto &x : yaml.asList()) {
> +                       auto value = x.get<T>();
> +                       if (!value) {
> +                               LOG(Vector, Error) << "Failed to read vector value";
> +                               return -EINVAL;
> +                       }
> +
> +                       data_[i++] = *value;
> +               }
> +
> +               return 0;
> +       }
> +
> +       const std::string toString() const
> +       {
> +               std::stringstream out;
> +
> +               out << "Vector { ";
> +               for (unsigned int i = 0; i < R; i++) {
> +                       out << (*this)[i];
> +                       out << ((i + 1 < R) ? ", " : " ");
> +               }
> +               out << " }";
> +
> +               return out.str();
> +       }
> +
> +       const T operator[](size_t i) const
> +       {

ASSERT here if out of bounds?

> +               return data_[i];
> +       }
> +
> +       T &operator[](size_t i)
> +       {
> +               return data_[i];
> +       }
> +
> +       const T x() const
> +       {
> +               return data_[0];
> +       }
> +
> +       const T y() const
> +       {
> +               return data_[1];
> +       }
> +
> +       constexpr Vector<T, R> operator-() const
> +       {
> +               Vector<T, R> ret;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret[i] = -data_[i];
> +               return ret;
> +       }

How would this be used? (differently than below?)

Unit tests would help here I think to confirm and validate intended
purposes.

> +
> +       constexpr Vector<T, R> operator-(const Vector<T, R> &other) const
> +       {
> +               Vector<T, R> ret;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret[i] = data_[i] - other[i];
> +               return ret;
> +       }
> +
> +       constexpr Vector<T, R> operator+(const Vector<T, R> &other) const
> +       {
> +               Vector<T, R> ret;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret[i] = data_[i] + other[i];
> +               return ret;
> +       }
> +
> +       constexpr T operator*(const Vector<T, R> &other) const
> +       {
> +               T ret = 0;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret += data_[i] * other[i];
> +               return ret;
> +       }
> +
> +       constexpr Vector<T, R> operator*(T factor) const
> +       {
> +               Vector<T, R> ret;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret[i] = data_[i] * factor;
> +               return ret;
> +       }
> +
> +       constexpr Vector<T, R> operator/(T factor) const
> +       {
> +               Vector<T, R> ret;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret[i] = data_[i] / factor;
> +               return ret;
> +       }
> +
> +       constexpr T len2() const
> +       {
> +               T ret = 0;
> +               for (unsigned int i = 0; i < R; i++)
> +                       ret += data_[i] * data_[i];
> +               return ret;
> +       }
> +
> +       constexpr double len() const
> +       {
> +               return std::sqrt(len2());
> +       }
> +
> +private:
> +       std::array<T, R> data_;
> +};


> +
> +#ifndef __DOXYGEN__
> +template<typename T, unsigned int R,
> +        std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> +#endif /* __DOXYGEN__ */
> +bool operator==(const Vector<T, R> &lhs, const Vector<T, R> &rhs)
> +{
> +       for (unsigned int i = 0; i < R; i++)
> +               if (lhs[i] != rhs[i])
> +                       return false;
> +
> +       return true;
> +}
> +
> +#ifndef __DOXYGEN__
> +template<typename T, unsigned int R,
> +        std::enable_if_t<std::is_arithmetic_v<T>> * = nullptr>
> +#endif /* __DOXYGEN__ */
> +bool operator!=(const Vector<T, R> &lhs, const Vector<T, R> &rhs)
> +{
> +       for (unsigned int i = 0; i < R; i++)
> +               if (lhs[i] != rhs[i])
> +                       return true;
> +
> +       return false;
> +}
> +
> +} /* namespace ipa */
> +
> +#ifndef __DOXYGEN__
> +template<typename T, unsigned int R>
> +std::ostream &operator<<(std::ostream &out, const ipa::Vector<T, R> &v)
> +{
> +       out << v.toString();
> +       return out;
> +}
> +#endif /* __DOXYGEN__ */
> +
> +} /* namespace libcamera */
> -- 
> 2.39.2
>