ipa: libipa: Add generic Interpolator class

The MatrixInterpolator is great for interpolation of matrices for
different color temperatures. It has however one limitation - it can
only handle matrices. For LSC it would be great to interpolate the LSC
tables (or even polynomials) using the same approach. Add a generic
Interpolator class based on the existing MatrixInterpolator. This class
can be adapted to any other type using partial template specialization.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

1 files changed, 157 insertions, 0 deletions

diff --git a/src/ipa/libipa/interpolator.cpp b/src/ipa/libipa/interpolator.cpp
new file mode 100644
index 00000000..73e8d3b7
--- /dev/null
+++ b/src/ipa/libipa/interpolator.cpp
@@ -0,0 +1,157 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Helper class for interpolating objects
+ */
+#include "interpolator.h"
+
+#include <algorithm>
+#include <string>
+
+#include <libcamera/base/log.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+#include "interpolator.h"
+
+/**
+ * \file interpolator.h
+ * \brief Helper class for linear interpolating a set of objects
+ */
+
+namespace libcamera {
+
+LOG_DEFINE_CATEGORY(Interpolator)
+
+namespace ipa {
+
+/**
+ * \class Interpolator
+ * \brief Class for storing, retrieving, and interpolating objects
+ * \tparam T Type of objects stored in the interpolator
+ *
+ * The main use case is to pass a map from color temperatures to corresponding
+ * objects (eg. matrices for color correction), and then requesting a
+ * interpolated object for a specific color temperature. This class will
+ * abstract away the interpolation portion.
+ */
+
+/**
+ * \fn Interpolator::Interpolator()
+ * \brief Construct an empty interpolator
+ */
+
+/**
+ * \fn Interpolator::Interpolator(const std::map<unsigned int, T> &data)
+ * \brief Construct an interpolator from a map of objects
+ * \param data Map from which to construct the interpolator
+ */
+
+/**
+ * \fn Interpolator::Interpolator(std::map<unsigned int, T> &&data)
+ * \brief Construct an interpolator from a map of objects
+ * \param data Map from which to construct the interpolator
+ */
+
+/**
+ * \fn int Interpolator<T>::readYaml(const libcamera::YamlObject &yaml,
+		                     const std::string &key_name,
+		                     const std::string &value_name)
+ * \brief Initialize an Interpolator instance from yaml
+ * \tparam T Type of data stored in the interpolator
+ * \param[in] yaml The yaml object that contains the map of unsigned integers to
+ * objects
+ * \param[in] key_name The name of the key in the yaml object
+ * \param[in] value_name The name of the value in the yaml object
+ *
+ * The yaml object is expected to be a list of maps. Each map has two or more
+ * pairs: one of \a key_name to the key value (usually color temperature), and
+ * one or more of \a value_name to the object. This is a bit difficult to
+ * explain, so here is an example (in python, as it is easier to parse than
+ * yaml):
+ *       [
+ *               {
+ *                   'ct': 2860,
+ *                   'ccm': [ 2.12089, -0.52461, -0.59629,
+ *                           -0.85342,  2.80445, -0.95103,
+ *                           -0.26897, -1.14788,  2.41685 ],
+ *                   'offsets': [ 0, 0, 0 ]
+ *               },
+ *
+ *               {
+ *                   'ct': 2960,
+ *                   'ccm': [ 2.26962, -0.54174, -0.72789,
+ *                           -0.77008,  2.60271, -0.83262,
+ *                           -0.26036, -1.51254,  2.77289 ],
+ *                   'offsets': [ 0, 0, 0 ]
+ *               },
+ *
+ *               {
+ *                   'ct': 3603,
+ *                   'ccm': [ 2.18644, -0.66148, -0.52496,
+ *                           -0.77828,  2.69474, -0.91645,
+ *                           -0.25239, -0.83059,  2.08298 ],
+ *                   'offsets': [ 0, 0, 0 ]
+ *               },
+ *       ]
+ *
+ * In this case, \a key_name would be 'ct', and \a value_name can be either
+ * 'ccm' or 'offsets'. This way multiple interpolators can be defined in
+ * one set of color temperature ranges in the tuning file, and they can be
+ * retrieved separately with the \a value_name parameter.
+ *
+ * \return Zero on success, negative error code otherwise
+ */
+
+/**
+ * \fn void Interpolator<T>::setQuantization(const unsigned int q)
+ * \brief Set the quantization value
+ * \param[in] q The quantization value
+ *
+ * Sets the quantization value. When this is set, 'key' gets quantized to this
+ * size, before doing the interpolation. This can help in reducing the number of
+ * updates pushed to the hardware.
+ *
+ * Note that normally a threshold needs to be combined with quantization.
+ * Otherwise a value that swings around the edge of the quantization step will
+ * lead to constant updates.
+ */
+
+/**
+ * \fn void Interpolator<T>::setData(std::map<unsigned int, T> &&data)
+ * \brief Set the internal map
+ *
+ * Overwrites the internal map using move semantics.
+ */
+
+/**
+ * \fn const T& Interpolator<T>::getInterpolated()
+ * \brief Retrieve an interpolated value for the given key
+ * \param[in] key The unsigned integer key of the object to retrieve
+ * \param[out] quantizedKey If provided, the key value after quantization
+ * \return The object corresponding to the key. The object is cached internally,
+ * so on successive calls with the same key (after quantization) interpolation
+ * is not recalculated.
+ */
+
+/**
+ * \fn void Interpolator<T>::interpolate(const T &a, const T &b, T &dest, double
+ * lambda)
+ * \brief Interpolate between two instances of T
+ * \param a The first value to interpolate
+ * \param b The second value to interpolate
+ * \param dest The destination for the interpolated value
+ * \param lambda The interpolation factor (0..1)
+ *
+ * Interpolates between \a a and \a b according to \a lambda. It calculates
+ * dest = a * (1.0 - lambda) + b * lambda;
+ *
+ * If T supports multiplication with double and addition, this function can be
+ * used as is. For other types this function can be overwritten using partial
+ * template specialization.
+ */
+
+} /* namespace ipa */
+
+} /* namespace libcamera */