ipa: raspberrypi: First version of autofocus algorithm using PDAF

Provide the first version of the Raspberry Pi autofocus algorithm. This
implementation uses a hybrid of contrast detect autofocus (CDAF) and phase
detect autofocus (PDAF) statistics. PDAF is always preferred over CDAF due to
having less "hunting" behavior.

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

3 files changed, 952 insertions, 0 deletions

diff --git a/src/ipa/raspberrypi/controller/rpi/af.cpp b/src/ipa/raspberrypi/controller/rpi/af.cpp
new file mode 100644
index 00000000..2e72f239
--- /dev/null
+++ b/src/ipa/raspberrypi/controller/rpi/af.cpp
@@ -0,0 +1,795 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2022-2023, Raspberry Pi Ltd
+ *
+ * af.cpp - Autofocus control algorithm
+ */
+
+#include "af.h"
+
+#include <iomanip>
+#include <math.h>
+#include <stdlib.h>
+
+#include <libcamera/base/log.h>
+
+#include <libcamera/control_ids.h>
+
+using namespace RPiController;
+using namespace libcamera;
+
+LOG_DEFINE_CATEGORY(RPiAf)
+
+#define NAME "rpi.af"
+
+/*
+ * Default values for parameters. All may be overridden in the tuning file.
+ * Many of these values are sensor- or module-dependent; the defaults here
+ * assume IMX708 in a Raspberry Pi V3 camera with the standard lens.
+ *
+ * Here all focus values are in dioptres (1/m). They are converted to hardware
+ * units when written to status.lensSetting or returned from setLensPosition().
+ *
+ * Gain and delay values are relative to the update rate, since much (not all)
+ * of the delay is in the sensor and (for CDAF) ISP, not the lens mechanism;
+ * but note that algorithms are updated at no more than 30 Hz.
+ */
+
+Af::RangeDependentParams::RangeDependentParams()
+	: focusMin(0.0),
+	  focusMax(12.0),
+	  focusDefault(1.0)
+{
+}
+
+Af::SpeedDependentParams::SpeedDependentParams()
+	: stepCoarse(1.0),
+	  stepFine(0.25),
+	  contrastRatio(0.75),
+	  pdafGain(-0.02),
+	  pdafSquelch(0.125),
+	  maxSlew(2.0),
+	  pdafFrames(20),
+	  dropoutFrames(6),
+	  stepFrames(4)
+{
+}
+
+Af::CfgParams::CfgParams()
+	: confEpsilon(8),
+	  confThresh(16),
+	  confClip(512),
+	  skipFrames(5),
+	  map()
+{
+}
+
+template<typename T>
+static void readNumber(T &dest, const libcamera::YamlObject &params, char const *name)
+{
+	auto value = params[name].get<T>();
+	if (value)
+		dest = *value;
+	else
+		LOG(RPiAf, Warning) << "Missing parameter \"" << name << "\"";
+}
+
+void Af::RangeDependentParams::read(const libcamera::YamlObject &params)
+{
+
+	readNumber<double>(focusMin, params, "min");
+	readNumber<double>(focusMax, params, "max");
+	readNumber<double>(focusDefault, params, "default");
+}
+
+void Af::SpeedDependentParams::read(const libcamera::YamlObject &params)
+{
+	readNumber<double>(stepCoarse, params, "step_coarse");
+	readNumber<double>(stepFine, params, "step_fine");
+	readNumber<double>(contrastRatio, params, "contrast_ratio");
+	readNumber<double>(pdafGain, params, "pdaf_gain");
+	readNumber<double>(pdafSquelch, params, "pdaf_squelch");
+	readNumber<double>(maxSlew, params, "max_slew");
+	readNumber<uint32_t>(pdafFrames, params, "pdaf_frames");
+	readNumber<uint32_t>(dropoutFrames, params, "dropout_frames");
+	readNumber<uint32_t>(stepFrames, params, "step_frames");
+}
+
+int Af::CfgParams::read(const libcamera::YamlObject &params)
+{
+	if (params.contains("ranges")) {
+		auto &rr = params["ranges"];
+
+		if (rr.contains("normal"))
+			ranges[AfRangeNormal].read(rr["normal"]);
+		else
+			LOG(RPiAf, Warning) << "Missing range \"normal\"";
+
+		ranges[AfRangeMacro] = ranges[AfRangeNormal];
+		if (rr.contains("macro"))
+			ranges[AfRangeMacro].read(rr["macro"]);
+
+		ranges[AfRangeFull].focusMin = std::min(ranges[AfRangeNormal].focusMin,
+							ranges[AfRangeMacro].focusMin);
+		ranges[AfRangeFull].focusMax = std::max(ranges[AfRangeNormal].focusMax,
+							ranges[AfRangeMacro].focusMax);
+		ranges[AfRangeFull].focusDefault = ranges[AfRangeNormal].focusDefault;
+		if (rr.contains("full"))
+			ranges[AfRangeFull].read(rr["full"]);
+	} else
+		LOG(RPiAf, Warning) << "No ranges defined";
+
+	if (params.contains("speeds")) {
+		auto &ss = params["speeds"];
+
+		if (ss.contains("normal"))
+			speeds[AfSpeedNormal].read(ss["normal"]);
+		else
+			LOG(RPiAf, Warning) << "Missing speed \"normal\"";
+
+		speeds[AfSpeedFast] = speeds[AfSpeedNormal];
+		if (ss.contains("fast"))
+			speeds[AfSpeedFast].read(ss["fast"]);
+	} else
+		LOG(RPiAf, Warning) << "No speeds defined";
+
+	readNumber<uint32_t>(confEpsilon, params, "conf_epsilon");
+	readNumber<uint32_t>(confThresh, params, "conf_thresh");
+	readNumber<uint32_t>(confClip, params, "conf_clip");
+	readNumber<uint32_t>(skipFrames, params, "skip_frames");
+
+	if (params.contains("map"))
+		map.read(params["map"]);
+	else
+		LOG(RPiAf, Warning) << "No map defined";
+
+	return 0;
+}
+
+void Af::CfgParams::initialise()
+{
+	if (map.empty()) {
+		/* Default mapping from dioptres to hardware setting */
+		static constexpr double DefaultMapX0 = 0.0;
+		static constexpr double DefaultMapY0 = 445.0;
+		static constexpr double DefaultMapX1 = 15.0;
+		static constexpr double DefaultMapY1 = 925.0;
+
+		map.append(DefaultMapX0, DefaultMapY0);
+		map.append(DefaultMapX1, DefaultMapY1);
+	}
+}
+
+/* Af Algorithm class */
+
+static constexpr unsigned MaxWindows = 10;
+
+Af::Af(Controller *controller)
+	: AfAlgorithm(controller),
+	  cfg_(),
+	  range_(AfRangeNormal),
+	  speed_(AfSpeedNormal),
+	  mode_(AfAlgorithm::AfModeManual),
+	  pauseFlag_(false),
+	  statsRegion_(0, 0, 0, 0),
+	  windows_(),
+	  useWindows_(false),
+	  phaseWeights_{},
+	  contrastWeights_{},
+	  sumWeights_(0),
+	  scanState_(ScanState::Idle),
+	  initted_(false),
+	  ftarget_(-1.0),
+	  fsmooth_(-1.0),
+	  prevContrast_(0.0),
+	  skipCount_(0),
+	  stepCount_(0),
+	  dropCount_(0),
+	  scanMaxContrast_(0.0),
+	  scanMinContrast_(1.0e9),
+	  scanData_(),
+	  reportState_(AfState::Idle)
+{
+	scanData_.reserve(24);
+}
+
+Af::~Af()
+{
+}
+
+char const *Af::name() const
+{
+	return NAME;
+}
+
+int Af::read(const libcamera::YamlObject &params)
+{
+	return cfg_.read(params);
+}
+
+void Af::initialise()
+{
+	cfg_.initialise();
+}
+
+void Af::switchMode(CameraMode const &cameraMode, [[maybe_unused]] Metadata *metadata)
+{
+	(void)metadata;
+
+	/* Assume that PDAF and Focus stats grids cover the visible area */
+	statsRegion_.x = (int)cameraMode.cropX;
+	statsRegion_.y = (int)cameraMode.cropY;
+	statsRegion_.width = (unsigned)(cameraMode.width * cameraMode.scaleX);
+	statsRegion_.height = (unsigned)(cameraMode.height * cameraMode.scaleY);
+	LOG(RPiAf, Debug) << "switchMode: statsRegion: "
+			  << statsRegion_.x << ','
+			  << statsRegion_.y << ','
+			  << statsRegion_.width << ','
+			  << statsRegion_.height;
+	computeWeights();
+
+	if (scanState_ >= ScanState::Coarse && scanState_ < ScanState::Settle) {
+		/*
+		 * If a scan was in progress, re-start it, as CDAF statistics
+		 * may have changed. Though if the application is just about
+		 * to take a still picture, this will not help...
+		 */
+		startProgrammedScan();
+	}
+	skipCount_ = cfg_.skipFrames;
+}
+
+void Af::computeWeights()
+{
+	constexpr int MaxCellWeight = 240 / (int)MaxWindows;
+
+	sumWeights_ = 0;
+	for (int i = 0; i < PDAF_DATA_ROWS; ++i)
+		std::fill(phaseWeights_[i], phaseWeights_[i] + PDAF_DATA_COLS, 0);
+
+	if (useWindows_ &&
+	    statsRegion_.width >= PDAF_DATA_COLS && statsRegion_.height >= PDAF_DATA_ROWS) {
+		/*
+		 * Here we just merge all of the given windows, weighted by area.
+		 * \todo Perhaps a better approach might be to find the phase in each
+		 * window and choose either the closest or the highest-confidence one?
+		 *
+		 * Using mostly "int" arithmetic, because Rectangle has signed x, y
+		 */
+		int cellH = (int)(statsRegion_.height / PDAF_DATA_ROWS);
+		int cellW = (int)(statsRegion_.width / PDAF_DATA_COLS);
+		int cellA = cellH * cellW;
+
+		for (auto &w : windows_) {
+			for (int i = 0; i < PDAF_DATA_ROWS; ++i) {
+				int y0 = std::max(statsRegion_.y + cellH * i, w.y);
+				int y1 = std::min(statsRegion_.y + cellH * (i + 1), w.y + (int)(w.height));
+				if (y0 >= y1)
+					continue;
+				y1 -= y0;
+				for (int j = 0; j < PDAF_DATA_COLS; ++j) {
+					int x0 = std::max(statsRegion_.x + cellW * j, w.x);
+					int x1 = std::min(statsRegion_.x + cellW * (j + 1), w.x + (int)(w.width));
+					if (x0 >= x1)
+						continue;
+					int a = y1 * (x1 - x0);
+					a = (MaxCellWeight * a + cellA - 1) / cellA;
+					phaseWeights_[i][j] += a;
+					sumWeights_ += a;
+				}
+			}
+		}
+	}
+
+	if (sumWeights_ == 0) {
+		/*
+		 * Default AF window is the middle 1/2 width of the middle 1/3 height
+		 * since this maps nicely to both PDAF (16x12) and Focus (4x3) grids.
+		 */
+		for (int i = PDAF_DATA_ROWS / 3; i < 2 * PDAF_DATA_ROWS / 3; ++i) {
+			for (int j = PDAF_DATA_COLS / 4; j < 3 * PDAF_DATA_COLS / 4; ++j) {
+				phaseWeights_[i][j] = MaxCellWeight;
+				sumWeights_ += MaxCellWeight;
+			}
+		}
+	}
+
+	/* Scale from PDAF to Focus Statistics grid (which has fixed size 4x3) */
+	constexpr int FocusStatsRows = 3;
+	constexpr int FocusStatsCols = 4;
+	static_assert(FOCUS_REGIONS == FocusStatsRows * FocusStatsCols);
+	static_assert(PDAF_DATA_ROWS % FocusStatsRows == 0);
+	static_assert(PDAF_DATA_COLS % FocusStatsCols == 0);
+	constexpr int YFactor = PDAF_DATA_ROWS / FocusStatsRows;
+	constexpr int XFactor = PDAF_DATA_COLS / FocusStatsCols;
+
+	LOG(RPiAf, Debug) << "Recomputed weights:";
+	for (int i = 0; i < FocusStatsRows; ++i) {
+		for (int j = 0; j < FocusStatsCols; ++j) {
+			unsigned w = 0;
+			for (int y = 0; y < YFactor; ++y)
+				for (int x = 0; x < XFactor; ++x)
+					w += phaseWeights_[YFactor * i + y][XFactor * j + x];
+			contrastWeights_[FocusStatsCols * i + j] = w;
+		}
+		LOG(RPiAf, Debug) << "   "
+				  << contrastWeights_[FocusStatsCols * i + 0] << " "
+				  << contrastWeights_[FocusStatsCols * i + 1] << " "
+				  << contrastWeights_[FocusStatsCols * i + 2] << " "
+				  << contrastWeights_[FocusStatsCols * i + 3];
+	}
+}
+
+bool Af::getPhase(PdafData const &data, double &phase, double &conf) const
+{
+	uint32_t sumWc = 0;
+	int64_t sumWcp = 0;
+
+	for (unsigned i = 0; i < PDAF_DATA_ROWS; ++i) {
+		for (unsigned j = 0; j < PDAF_DATA_COLS; ++j) {
+			if (phaseWeights_[i][j]) {
+				uint32_t c = data.conf[i][j];
+				if (c >= cfg_.confThresh) {
+					if (c > cfg_.confClip)
+						c = cfg_.confClip;
+					c -= (cfg_.confThresh >> 2);
+					sumWc += phaseWeights_[i][j] * c;
+					c -= (cfg_.confThresh >> 2);
+					sumWcp += phaseWeights_[i][j] * data.phase[i][j] * (int64_t)c;
+				}
+			}
+		}
+	}
+
+	if (0 < sumWeights_ && sumWeights_ <= sumWc) {
+		phase = (double)sumWcp / (double)sumWc;
+		conf = (double)sumWc / (double)sumWeights_;
+		return true;
+	} else {
+		phase = 0.0;
+		conf = 0.0;
+		return false;
+	}
+}
+
+double Af::getContrast(struct bcm2835_isp_stats_focus const focus_stats[FOCUS_REGIONS]) const
+{
+	uint32_t sumWc = 0;
+
+	for (unsigned i = 0; i < FOCUS_REGIONS; ++i) {
+		unsigned w = contrastWeights_[i];
+		sumWc += w * (focus_stats[i].contrast_val[1][1] >> 10);
+	}
+
+	return (sumWeights_ == 0) ? 0.0 : (double)sumWc / (double)sumWeights_;
+}
+
+void Af::doPDAF(double phase, double conf)
+{
+	/* Apply loop gain */
+	phase *= cfg_.speeds[speed_].pdafGain;
+
+	if (mode_ == AfModeContinuous) {
+		/*
+		 * PDAF in Continuous mode. Scale down lens movement when
+		 * delta is small or confidence is low, to suppress wobble.
+		 */
+		phase *= conf / (conf + cfg_.confEpsilon);
+		if (std::abs(phase) < cfg_.speeds[speed_].pdafSquelch) {
+			double a = phase / cfg_.speeds[speed_].pdafSquelch;
+			phase *= a * a;
+		}
+	} else {
+		/*
+		 * PDAF in triggered-auto mode. Allow early termination when
+		 * phase delta is small; scale down lens movements towards
+		 * the end of the sequence, to ensure a stable image.
+		 */
+		if (stepCount_ >= cfg_.speeds[speed_].stepFrames) {
+			if (std::abs(phase) < cfg_.speeds[speed_].pdafSquelch)
+				stepCount_ = cfg_.speeds[speed_].stepFrames;
+		} else
+			phase *= stepCount_ / cfg_.speeds[speed_].stepFrames;
+	}
+
+	/* Apply slew rate limit. Report failure if out of bounds. */
+	if (phase < -cfg_.speeds[speed_].maxSlew) {
+		phase = -cfg_.speeds[speed_].maxSlew;
+		reportState_ = (ftarget_ <= cfg_.ranges[range_].focusMin) ? AfState::Failed
+									  : AfState::Scanning;
+	} else if (phase > cfg_.speeds[speed_].maxSlew) {
+		phase = cfg_.speeds[speed_].maxSlew;
+		reportState_ = (ftarget_ >= cfg_.ranges[range_].focusMax) ? AfState::Failed
+									  : AfState::Scanning;
+	} else
+		reportState_ = AfState::Focused;
+
+	ftarget_ = fsmooth_ + phase;
+}
+
+bool Af::earlyTerminationByPhase(double phase)
+{
+	if (scanData_.size() > 0 &&
+	    scanData_[scanData_.size() - 1].conf >= cfg_.confEpsilon) {
+		double oldFocus = scanData_[scanData_.size() - 1].focus;
+		double oldPhase = scanData_[scanData_.size() - 1].phase;
+
+		/*
+		 * Check that the gradient is finite and has the expected sign;
+		 * Interpolate/extrapolate the lens position for zero phase.
+		 * Check that the extrapolation is well-conditioned.
+		 */
+		if ((ftarget_ - oldFocus) * (phase - oldPhase) > 0.0) {
+			double param = phase / (phase - oldPhase);
+			if (-3.0 <= param && param <= 3.5) {
+				ftarget_ += param * (oldFocus - ftarget_);
+				LOG(RPiAf, Debug) << "ETBP: param=" << param;
+				return true;
+			}
+		}
+	}
+
+	return false;
+}
+
+double Af::findPeak(unsigned i) const
+{
+	double f = scanData_[i].focus;
+
+	if (i > 0 && i + 1 < scanData_.size()) {
+		double dropLo = scanData_[i].contrast - scanData_[i - 1].contrast;
+		double dropHi = scanData_[i].contrast - scanData_[i + 1].contrast;
+		if (0.0 <= dropLo && dropLo < dropHi) {
+			double param = 0.3125 * (1.0 - dropLo / dropHi) * (1.6 - dropLo / dropHi);
+			f += param * (scanData_[i - 1].focus - f);
+		} else if (0.0 <= dropHi && dropHi < dropLo) {
+			double param = 0.3125 * (1.0 - dropHi / dropLo) * (1.6 - dropHi / dropLo);
+			f += param * (scanData_[i + 1].focus - f);
+		}
+	}
+
+	LOG(RPiAf, Debug) << "FindPeak: " << f;
+	return f;
+}
+
+void Af::doScan(double contrast, double phase, double conf)
+{
+	/* Record lens position, contrast and phase values for the current scan */
+	if (scanData_.empty() || contrast > scanMaxContrast_) {
+		scanMaxContrast_ = contrast;
+		scanMaxIndex_ = scanData_.size();
+	}
+	if (contrast < scanMinContrast_)
+		scanMinContrast_ = contrast;
+	scanData_.emplace_back(ScanRecord{ ftarget_, contrast, phase, conf });
+
+	if (scanState_ == ScanState::Coarse) {
+		if (ftarget_ >= cfg_.ranges[range_].focusMax ||
+		    contrast < cfg_.speeds[speed_].contrastRatio * scanMaxContrast_) {
+			/*
+			 * Finished course scan, or termination based on contrast.
+			 * Jump to just after max contrast and start fine scan.
+			 */
+			ftarget_ = std::min(ftarget_, findPeak(scanMaxIndex_) +
+					2.0 * cfg_.speeds[speed_].stepFine);
+			scanState_ = ScanState::Fine;
+			scanData_.clear();
+		} else
+			ftarget_ += cfg_.speeds[speed_].stepCoarse;
+	} else { /* ScanState::Fine */
+		if (ftarget_ <= cfg_.ranges[range_].focusMin || scanData_.size() >= 5 ||
+		    contrast < cfg_.speeds[speed_].contrastRatio * scanMaxContrast_) {
+			/*
+			 * Finished fine scan, or termination based on contrast.
+			 * Use quadratic peak-finding to find best contrast position.
+			 */
+			ftarget_ = findPeak(scanMaxIndex_);
+			scanState_ = ScanState::Settle;
+		} else
+			ftarget_ -= cfg_.speeds[speed_].stepFine;
+	}
+
+	stepCount_ = (ftarget_ == fsmooth_) ? 0 : cfg_.speeds[speed_].stepFrames;
+}
+
+void Af::doAF(double contrast, double phase, double conf)
+{
+	/* Skip frames at startup and after sensor mode change */
+	if (skipCount_ > 0) {
+		LOG(RPiAf, Debug) << "SKIP";
+		skipCount_--;
+		return;
+	}
+
+	if (scanState_ == ScanState::Pdaf) {
+		/*
+		 * Use PDAF closed-loop control whenever available, in both CAF
+		 * mode and (for a limited number of iterations) when triggered.
+		 * If PDAF fails (due to poor contrast, noise or large defocus),
+		 * fall back to a CDAF-based scan. To avoid "nuisance" scans,
+		 * scan only after a number of frames with low PDAF confidence.
+		 */
+		if (conf > (dropCount_ ? 1.0 : 0.25) * cfg_.confEpsilon) {
+			doPDAF(phase, conf);
+			if (stepCount_ > 0)
+				stepCount_--;
+			else if (mode_ != AfModeContinuous)
+				scanState_ = ScanState::Idle;
+			dropCount_ = 0;
+		} else if (++dropCount_ == cfg_.speeds[speed_].dropoutFrames)
+			startProgrammedScan();
+	} else if (scanState_ >= ScanState::Coarse && fsmooth_ == ftarget_) {
+		/*
+		 * Scanning sequence. This means PDAF has become unavailable.
+		 * Allow a delay between steps for CDAF FoM statistics to be
+		 * updated, and a "settling time" at the end of the sequence.
+		 * [A coarse or fine scan can be abandoned if two PDAF samples
+		 * allow direct interpolation of the zero-phase lens position.]
+		 */
+		if (stepCount_ > 0)
+			stepCount_--;
+		else if (scanState_ == ScanState::Settle) {
+			if (prevContrast_ >= cfg_.speeds[speed_].contrastRatio * scanMaxContrast_ &&
+			    scanMinContrast_ <= cfg_.speeds[speed_].contrastRatio * scanMaxContrast_)
+				reportState_ = AfState::Focused;
+			else
+				reportState_ = AfState::Failed;
+			if (mode_ == AfModeContinuous && !pauseFlag_ &&
+			    cfg_.speeds[speed_].dropoutFrames > 0)
+				scanState_ = ScanState::Pdaf;
+			else
+				scanState_ = ScanState::Idle;
+			scanData_.clear();
+		} else if (conf >= cfg_.confEpsilon && earlyTerminationByPhase(phase)) {
+			scanState_ = ScanState::Settle;
+			stepCount_ = (mode_ == AfModeContinuous) ? 0
+								 : cfg_.speeds[speed_].stepFrames;
+		} else
+			doScan(contrast, phase, conf);
+	}
+}
+
+void Af::updateLensPosition()
+{
+	if (scanState_ >= ScanState::Pdaf) {
+		ftarget_ = std::clamp(ftarget_,
+				      cfg_.ranges[range_].focusMin,
+				      cfg_.ranges[range_].focusMax);
+	}
+
+	if (initted_) {
+		/* from a known lens position: apply slew rate limit */
+		fsmooth_ = std::clamp(ftarget_,
+				      fsmooth_ - cfg_.speeds[speed_].maxSlew,
+				      fsmooth_ + cfg_.speeds[speed_].maxSlew);
+	} else {
+		/* from an unknown position: go straight to target, but add delay */
+		fsmooth_ = ftarget_;
+		initted_ = true;
+		skipCount_ = cfg_.skipFrames;
+	}
+}
+
+void Af::startAF()
+{
+	/* Use PDAF if the tuning file allows it; else CDAF. */
+	if (cfg_.speeds[speed_].dropoutFrames > 0 &&
+	    (mode_ == AfModeContinuous || cfg_.speeds[speed_].pdafFrames > 0)) {
+		if (!initted_) {
+			ftarget_ = cfg_.ranges[range_].focusDefault;
+			updateLensPosition();
+		}
+		stepCount_ = (mode_ == AfModeContinuous) ? 0 : cfg_.speeds[speed_].pdafFrames;
+		scanState_ = ScanState::Pdaf;
+		scanData_.clear();
+		dropCount_ = 0;
+		reportState_ = AfState::Scanning;
+	} else
+		startProgrammedScan();
+}
+
+void Af::startProgrammedScan()
+{
+	ftarget_ = cfg_.ranges[range_].focusMin;
+	updateLensPosition();
+	scanState_ = ScanState::Coarse;
+	scanMaxContrast_ = 0.0;
+	scanMinContrast_ = 1.0e9;
+	scanMaxIndex_ = 0;
+	scanData_.clear();
+	stepCount_ = cfg_.speeds[speed_].stepFrames;
+	reportState_ = AfState::Scanning;
+}
+
+void Af::goIdle()
+{
+	scanState_ = ScanState::Idle;
+	reportState_ = AfState::Idle;
+	scanData_.clear();
+}
+
+/*
+ * PDAF phase data are available in prepare(), but CDAF statistics are not
+ * available until process(). We are gambling on the availability of PDAF.
+ * To expedite feedback control using PDAF, issue the V4L2 lens control from
+ * prepare(). Conversely, during scans, we must allow an extra frame delay
+ * between steps, to retrieve CDAF statistics from the previous process()
+ * so we can terminate the scan early without having to change our minds.
+ */
+
+void Af::prepare(Metadata *imageMetadata)
+{
+	/* Initialize for triggered scan or start of CAF mode */
+	if (scanState_ == ScanState::Trigger)
+		startAF();
+
+	if (initted_) {
+		/* Get PDAF from the embedded metadata, and run AF algorithm core */
+		PdafData data;
+		double phase = 0.0, conf = 0.0;
+		double oldFt = ftarget_;
+		double oldFs = fsmooth_;
+		ScanState oldSs = scanState_;
+		uint32_t oldSt = stepCount_;
+		if (imageMetadata->get("pdaf.data", data) == 0)
+			getPhase(data, phase, conf);
+		doAF(prevContrast_, phase, conf);
+		updateLensPosition();
+		LOG(RPiAf, Debug) << std::fixed << std::setprecision(2)
+				  << static_cast<unsigned int>(reportState_)
+				  << " sst" << static_cast<unsigned int>(oldSs)
+				  << "->" << static_cast<unsigned int>(scanState_)
+				  << " stp" << oldSt << "->" << stepCount_
+				  << " ft" << oldFt << "->" << ftarget_
+				  << " fs" << oldFs << "->" << fsmooth_
+				  << " cont=" << (int)prevContrast_
+				  << " phase=" << (int)phase << " conf=" << (int)conf;
+	}
+
+	/* Report status and produce new lens setting */
+	AfStatus status;
+	if (pauseFlag_)
+		status.pauseState = (scanState_ == ScanState::Idle) ? AfPauseState::Paused
+								    : AfPauseState::Pausing;
+	else
+		status.pauseState = AfPauseState::Running;
+
+	if (mode_ == AfModeAuto && scanState_ != ScanState::Idle)
+		status.state = AfState::Scanning;
+	else
+		status.state = reportState_;
+	status.lensSetting = initted_ ? std::optional<int>(cfg_.map.eval(fsmooth_))
+				      : std::nullopt;
+	imageMetadata->set("af.status", status);
+}
+
+void Af::process(StatisticsPtr &stats, [[maybe_unused]] Metadata *imageMetadata)
+{
+	(void)imageMetadata;
+	prevContrast_ = getContrast(stats->focus_stats);
+}
+
+/* Controls */
+
+void Af::setRange(AfRange r)
+{
+	LOG(RPiAf, Debug) << "setRange: " << (unsigned)r;
+	if (r < AfAlgorithm::AfRangeMax)
+		range_ = r;
+}
+
+void Af::setSpeed(AfSpeed s)
+{
+	LOG(RPiAf, Debug) << "setSpeed: " << (unsigned)s;
+	if (s < AfAlgorithm::AfSpeedMax) {
+		if (scanState_ == ScanState::Pdaf &&
+		    cfg_.speeds[s].pdafFrames > cfg_.speeds[speed_].pdafFrames)
+			stepCount_ += cfg_.speeds[s].pdafFrames - cfg_.speeds[speed_].pdafFrames;
+		speed_ = s;
+	}
+}
+
+void Af::setMetering(bool mode)
+{
+	if (useWindows_ != mode) {
+		useWindows_ = mode;
+		computeWeights();
+	}
+}
+
+void Af::setWindows(libcamera::Span<libcamera::Rectangle const> const &wins)
+{
+	windows_.clear();
+	for (auto &w : wins) {
+		LOG(RPiAf, Debug) << "Window: "
+				  << w.x << ", "
+				  << w.y << ", "
+				  << w.width << ", "
+				  << w.height;
+		windows_.push_back(w);
+		if (windows_.size() >= MaxWindows)
+			break;
+	}
+	computeWeights();
+}
+
+bool Af::setLensPosition(double dioptres, int *hwpos)
+{
+	bool changed = false;
+
+	if (mode_ == AfModeManual) {
+		LOG(RPiAf, Debug) << "setLensPosition: " << dioptres;
+		ftarget_ = cfg_.map.domain().clip(dioptres);
+		changed = !(initted_ && fsmooth_ == ftarget_);
+		updateLensPosition();
+	}
+
+	if (hwpos)
+		*hwpos = cfg_.map.eval(fsmooth_);
+
+	return changed;
+}
+
+std::optional<double> Af::getLensPosition() const
+{
+	/*
+	 * \todo We ought to perform some precise timing here to determine
+	 * the current lens position.
+	 */
+	return initted_ ? std::optional<double>(fsmooth_) : std::nullopt;
+}
+
+void Af::cancelScan()
+{
+	LOG(RPiAf, Debug) << "cancelScan";
+	if (mode_ == AfModeAuto)
+		goIdle();
+}
+
+void Af::triggerScan()
+{
+	LOG(RPiAf, Debug) << "triggerScan";
+	if (mode_ == AfModeAuto && scanState_ == ScanState::Idle)
+		scanState_ = ScanState::Trigger;
+}
+
+void Af::setMode(AfAlgorithm::AfMode mode)
+{
+	LOG(RPiAf, Debug) << "setMode: " << (unsigned)mode;
+	if (mode_ != mode) {
+		mode_ = mode;
+		pauseFlag_ = false;
+		if (mode == AfModeContinuous)
+			scanState_ = ScanState::Trigger;
+		else if (mode != AfModeAuto || scanState_ < ScanState::Coarse)
+			goIdle();
+	}
+}
+
+AfAlgorithm::AfMode Af::getMode() const
+{
+	return mode_;
+}
+
+void Af::pause(AfAlgorithm::AfPause pause)
+{
+	LOG(RPiAf, Debug) << "pause: " << (unsigned)pause;
+	if (mode_ == AfModeContinuous) {
+		if (pause == AfPauseResume && pauseFlag_) {
+			pauseFlag_ = false;
+			if (scanState_ < ScanState::Coarse)
+				scanState_ = ScanState::Trigger;
+		} else if (pause != AfPauseResume && !pauseFlag_) {
+			pauseFlag_ = true;
+			if (pause == AfPauseImmediate || scanState_ < ScanState::Coarse)
+				goIdle();
+		}
+	}
+}
+
+// Register algorithm with the system.
+static Algorithm *create(Controller *controller)
+{
+	return (Algorithm *)new Af(controller);
+}
+static RegisterAlgorithm reg(NAME, &create);
diff --git a/src/ipa/raspberrypi/controller/rpi/af.h b/src/ipa/raspberrypi/controller/rpi/af.h
new file mode 100644
index 00000000..f7baf897
--- /dev/null
+++ b/src/ipa/raspberrypi/controller/rpi/af.h
@@ -0,0 +1,156 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2022-2023, Raspberry Pi Ltd
+ *
+ * af.h - Autofocus control algorithm
+ */
+#pragma once
+
+#include "../af_algorithm.h"
+#include "../af_status.h"
+#include "../pdaf_data.h"
+#include "../pwl.h"
+
+/*
+ * This algorithm implements a hybrid of CDAF and PDAF, favouring PDAF.
+ *
+ * Whenever PDAF is available, it is used in a continuous feedback loop.
+ * When triggered in auto mode, we simply enable AF for a limited number
+ * of frames (it may terminate early if the delta becomes small enough).
+ *
+ * When PDAF confidence is low (due e.g. to low contrast or extreme defocus)
+ * or PDAF data are absent, fall back to CDAF with a programmed scan pattern.
+ * A coarse and fine scan are performed, using ISP's CDAF focus FoM to
+ * estimate the lens position with peak contrast. This is slower due to
+ * extra latency in the ISP, and requires a settling time between steps.
+ *
+ * Some hysteresis is applied to the switch between PDAF and CDAF, to avoid
+ * "nuisance" scans. During each interval where PDAF is not working, only
+ * ONE scan will be performed; CAF cannot track objects using CDAF alone.
+ *
+ * This algorithm is unrelated to "rpi.focus" which merely reports CDAF FoM.
+ */
+
+namespace RPiController {
+
+class Af : public AfAlgorithm
+{
+public:
+	Af(Controller *controller = NULL);
+	~Af();
+	char const *name() const override;
+	int read(const libcamera::YamlObject &params) override;
+	void initialise() override;
+
+	/* IPA calls */
+	void switchMode(CameraMode const &cameraMode, Metadata *metadata) override;
+	void prepare(Metadata *imageMetadata) override;
+	void process(StatisticsPtr &stats, Metadata *imageMetadata) override;
+
+	/* controls */
+	void setRange(AfRange range) override;
+	void setSpeed(AfSpeed speed) override;
+	void setMetering(bool use_windows) override;
+	void setWindows(libcamera::Span<libcamera::Rectangle const> const &wins) override;
+	void setMode(AfMode mode) override;
+	AfMode getMode() const override;
+	bool setLensPosition(double dioptres, int32_t *hwpos) override;
+	std::optional<double> getLensPosition() const override;
+	void triggerScan() override;
+	void cancelScan() override;
+	void pause(AfPause pause) override;
+
+private:
+	enum class ScanState {
+		Idle = 0,
+		Trigger,
+		Pdaf,
+		Coarse,
+		Fine,
+		Settle
+	};
+
+	struct RangeDependentParams {
+		double focusMin;       		/* lower (far) limit in dipotres */
+		double focusMax;	       	/* upper (near) limit in dioptres */
+		double focusDefault;		/* default setting ("hyperfocal") */
+
+		RangeDependentParams();
+		void read(const libcamera::YamlObject &params);
+	};
+
+	struct SpeedDependentParams {
+		double stepCoarse;		/* used for scans */
+		double stepFine;		/* used for scans */
+		double contrastRatio;		/* used for scan termination and reporting */
+		double pdafGain;		/* coefficient for PDAF feedback loop */
+		double pdafSquelch;		/* PDAF stability parameter (device-specific) */
+		double maxSlew;			/* limit for lens movement per frame */
+		uint32_t pdafFrames;		/* number of iterations when triggered */
+		uint32_t dropoutFrames;		/* number of non-PDAF frames to switch to CDAF */
+		uint32_t stepFrames;		/* frames to skip in between steps of a scan */
+
+		SpeedDependentParams();
+		void read(const libcamera::YamlObject &params);
+	};
+
+	struct CfgParams {
+		RangeDependentParams ranges[AfRangeMax];
+		SpeedDependentParams speeds[AfSpeedMax];
+		uint32_t confEpsilon;	       	/* PDAF hysteresis threshold (sensor-specific) */
+		uint32_t confThresh;	       	/* PDAF confidence cell min (sensor-specific) */
+		uint32_t confClip;	       	/* PDAF confidence cell max (sensor-specific) */
+		uint32_t skipFrames;	       	/* frames to skip at start or modeswitch */
+		Pwl map;		       	/* converts dioptres -> lens driver position */
+
+		CfgParams();
+		int read(const libcamera::YamlObject &params);
+		void initialise();
+	};
+
+	struct ScanRecord {
+		double focus;
+		double contrast;
+		double phase;
+		double conf;
+	};
+
+	void computeWeights();
+	bool getPhase(PdafData const &data, double &phase, double &conf) const;
+	double getContrast(struct bcm2835_isp_stats_focus const focus_stats[FOCUS_REGIONS]) const;
+	void doPDAF(double phase, double conf);
+	bool earlyTerminationByPhase(double phase);
+	double findPeak(unsigned index) const;
+	void doScan(double contrast, double phase, double conf);
+	void doAF(double contrast, double phase, double conf);
+	void updateLensPosition();
+	void startAF();
+	void startProgrammedScan();
+	void goIdle();
+
+	/* Configuration and settings */
+	CfgParams cfg_;
+	AfRange range_;
+	AfSpeed speed_;
+	AfMode mode_;
+	bool pauseFlag_;
+	libcamera::Rectangle statsRegion_;
+	std::vector<libcamera::Rectangle> windows_;
+	bool useWindows_;
+	uint8_t phaseWeights_[PDAF_DATA_ROWS][PDAF_DATA_COLS];
+	uint16_t contrastWeights_[FOCUS_REGIONS];
+	uint32_t sumWeights_;
+
+	/* Working state. */
+	ScanState scanState_;
+	bool initted_;
+	double ftarget_, fsmooth_;
+	double prevContrast_;
+	unsigned skipCount_, stepCount_, dropCount_;
+	unsigned scanMaxIndex_;
+	double scanMaxContrast_, scanMinContrast_;
+	std::vector<ScanRecord> scanData_;
+	AfState reportState_;
+};
+
+} // namespace RPiController
diff --git a/src/ipa/raspberrypi/meson.build b/src/ipa/raspberrypi/meson.build
index 517d815b..4e268953 100644
--- a/src/ipa/raspberrypi/meson.build
+++ b/src/ipa/raspberrypi/meson.build
@@ -27,6 +27,7 @@ rpi_ipa_sources = files([
     'controller/controller.cpp',
     'controller/histogram.cpp',
     'controller/algorithm.cpp',
+    'controller/rpi/af.cpp',
     'controller/rpi/alsc.cpp',
     'controller/rpi/awb.cpp',
     'controller/rpi/sharpen.cpp',