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>

3 files changed, 290 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 */
diff --git a/src/ipa/libipa/interpolator.h b/src/ipa/libipa/interpolator.h
new file mode 100644
index 00000000..fffce214
--- /dev/null
+++ b/src/ipa/libipa/interpolator.h
@@ -0,0 +1,131 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Paul Elder <paul.elder@ideasonboard.com>
+ *
+ * Helper class for interpolating maps of objects
+ */
+
+#pragma once
+
+#include <algorithm>
+#include <cmath>
+#include <map>
+#include <string>
+#include <tuple>
+
+#include <libcamera/base/log.h>
+
+#include "libcamera/internal/yaml_parser.h"
+
+namespace libcamera {
+
+LOG_DECLARE_CATEGORY(Interpolator)
+
+namespace ipa {
+
+template<typename T>
+class Interpolator
+{
+public:
+	Interpolator() = default;
+	Interpolator(const std::map<unsigned int, T> &data)
+		: data_(data)
+	{
+	}
+	Interpolator(std::map<unsigned int, T> &&data)
+		: data_(std::move(data))
+	{
+	}
+
+	~Interpolator() = default;
+
+	int readYaml(const libcamera::YamlObject &yaml,
+		     const std::string &key_name,
+		     const std::string &value_name)
+	{
+		data_.clear();
+		lastInterpolatedKey_.reset();
+
+		if (!yaml.isList()) {
+			LOG(Interpolator, Error) << "yaml object must be a list";
+			return -EINVAL;
+		}
+
+		for (const auto &value : yaml.asList()) {
+			unsigned int ct = std::stoul(value[key_name].get<std::string>(""));
+			std::optional<T> data =
+				value[value_name].get<T>();
+			if (!data) {
+				return -EINVAL;
+			}
+
+			data_[ct] = *data;
+		}
+
+		if (data_.size() < 1) {
+			LOG(Interpolator, Error) << "Need at least one element";
+			return -EINVAL;
+		}
+
+		return 0;
+	}
+
+	void setQuantization(const unsigned int q)
+	{
+		quantization_ = q;
+	}
+
+	void setData(std::map<unsigned int, T> &&data)
+	{
+		data_ = std::move(data);
+		lastInterpolatedKey_.reset();
+	}
+
+	const T &getInterpolated(unsigned int key, unsigned int *quantizedKey = nullptr)
+	{
+		ASSERT(data_.size() > 0);
+
+		if (quantization_ > 0)
+			key = std::lround(key / static_cast<double>(quantization_)) * quantization_;
+
+		if (quantizedKey)
+			*quantizedKey = key;
+
+		if (lastInterpolatedKey_.has_value() &&
+		    *lastInterpolatedKey_ == key)
+			return lastInterpolatedValue_;
+
+		auto it = data_.lower_bound(key);
+
+		if (it == data_.begin())
+			return it->second;
+
+		if (it == data_.end())
+			return std::prev(it)->second;
+
+		if (it->first == key)
+			return it->second;
+
+		auto it2 = std::prev(it);
+		double lambda = (key - it2->first) / static_cast<double>(it->first - it2->first);
+		interpolate(it2->second, it->second, lastInterpolatedValue_, lambda);
+		lastInterpolatedKey_ = key;
+
+		return lastInterpolatedValue_;
+	}
+
+	void interpolate(const T &a, const T &b, T &dest, double lambda)
+	{
+		dest = a * (1.0 - lambda) + b * lambda;
+	}
+
+private:
+	std::map<unsigned int, T> data_;
+	T lastInterpolatedValue_;
+	std::optional<unsigned int> lastInterpolatedKey_;
+	unsigned int quantization_ = 0;
+};
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
index eff8ce26..2c2712a7 100644
--- a/src/ipa/libipa/meson.build
+++ b/src/ipa/libipa/meson.build
@@ -7,6 +7,7 @@ libipa_headers = files([
     'exposure_mode_helper.h',
     'fc_queue.h',
     'histogram.h',
+    'interpolator.h',
     'matrix.h',
     'matrix_interpolator.h',
     'module.h',
@@ -21,6 +22,7 @@ libipa_sources = files([
     'exposure_mode_helper.cpp',
     'fc_queue.cpp',
     'histogram.cpp',
+    'interpolator.cpp',
     'matrix.cpp',
     'matrix_interpolator.cpp',
     'module.cpp',