/* SPDX-License-Identifier: LGPL-2.1-or-later */ /* * Copyright (C) 2019, Google Inc. * * utils.cpp - Miscellaneous utility functions */ #include "utils.h" #include #include #include #include #include #include #include #include /** * \file utils.h * \brief Miscellaneous utility functions */ /* musl doesn't declare _DYNAMIC in link.h, declare it manually. */ extern ElfW(Dyn) _DYNAMIC[]; namespace libcamera { namespace utils { /** * \def ARRAY_SIZE(array) * \brief Determine the number of elements in the static array. */ /** * \brief Strip the directory prefix from the path * \param[in] path The path to process * * basename is implemented differently across different C libraries. This * implementation matches the one provided by the GNU libc, and does not * modify its input parameter. * * \return A pointer within the given path without any leading directory * components. */ const char *basename(const char *path) { const char *base = strrchr(path, '/'); return base ? base + 1 : path; } /** * \brief Get an environment variable * \param[in] name The name of the variable to return * * The environment list is searched to find the variable 'name', and the * corresponding string is returned. * * If 'secure execution' is required then this function always returns NULL to * avoid vulnerabilities that could occur if set-user-ID or set-group-ID * programs accidentally trust the environment. * * \return A pointer to the value in the environment or NULL if the requested * environment variable doesn't exist or if secure execution is required. */ char *secure_getenv(const char *name) { #if HAVE_SECURE_GETENV return ::secure_getenv(name); #else if (issetugid()) return NULL; return getenv(name); #endif } /** * \brief Identify the dirname portion of a path * \param[in] path The full path to parse * * This function conforms with the behaviour of the %dirname() function as * defined by POSIX. * * \return A string of the directory component of the path */ std::string dirname(const std::string &path) { if (path.empty()) return "."; /* * Skip all trailing slashes. If the path is only made of slashes, * return "/". */ size_t pos = path.size() - 1; while (path[pos] == '/') { if (!pos) return "/"; pos--; } /* * Find the previous slash. If the path contains no non-trailing slash, * return ".". */ while (path[pos] != '/') { if (!pos) return "."; pos--; } /* * Return the directory name up to (but not including) any trailing * slash. If this would result in an empty string, return "/". */ while (path[pos] == '/') { if (!pos) return "/"; pos--; } return path.substr(0, pos + 1); } /** * \fn libcamera::utils::set_overlap(InputIt1 first1, InputIt1 last1, * InputIt2 first2, InputIt2 last2) * \brief Count the number of elements in the intersection of two ranges * * Count the number of elements in the intersection of the sorted ranges [\a * first1, \a last1) and [\a first1, \a last2). Elements are compared using * operator< and the ranges must be sorted with respect to the same. * * \return The number of elements in the intersection of the two ranges */ /** * \fn libcamera::utils::clamp(const T& v, const T& lo, const T& hi) * \param[in] v The value to clamp * \param[in] lo The lower boundary to clamp v to * \param[in] hi The higher boundary to clamp v to * \return lo if v is less than lo, hi if v is greater than hi, otherwise v */ /** * \typedef clock * \brief The libcamera clock (monotonic) */ /** * \typedef duration * \brief The libcamera duration related to libcamera::utils::clock */ /** * \typedef time_point * \brief The libcamera time point related to libcamera::utils::clock */ /** * \brief Convert a duration to a timespec * \param[in] value The duration * \return A timespec expressing the duration */ struct timespec duration_to_timespec(const duration &value) { uint64_t nsecs = std::chrono::duration_cast(value).count(); struct timespec ts; ts.tv_sec = nsecs / 1000000000ULL; ts.tv_nsec = nsecs % 1000000000ULL; return ts; } /** * \brief Convert a time point to a string representation * \param[in] time The time point * \return A string representing the time point in hh:mm:ss.nanoseconds format */ std::string time_point_to_string(const time_point &time) { uint64_t nsecs = std::chrono::duration_cast(time.time_since_epoch()).count(); unsigned int secs = nsecs / 1000000000ULL; std::ostringstream ossTimestamp; ossTimestamp.fill('0'); ossTimestamp << secs / (60 * 60) << ":" << std::setw(2) << (secs / 60) % 60 << ":" << std::setw(2) << secs % 60 << "." << std::setw(9) << nsecs % 1000000000ULL; return ossTimestamp.str(); } std::basic_ostream> & operator<<(std::basic_ostream> &stream, const _hex &h) { stream << "0x"; std::ostream::fmtflags flags = stream.setf(std::ios_base::hex, std::ios_base::basefield); std::streamsize width = stream.width(h.w); char fill = stream.fill('0'); stream << h.v; stream.flags(flags); stream.width(width); stream.fill(fill); return stream; } /** * \fn hex(T value, unsigned int width) * \brief Write an hexadecimal value to an output string * \param value The value * \param width The width * * Return an object of unspecified type such that, if \a os is the name of an * output stream of type std::ostream, and T is an integer type, then the * expression * * \code{.cpp} * os << utils::hex(value) * \endcode * * will output the \a value to the stream in hexadecimal form with the base * prefix and the filling character set to '0'. The field width is set to \a * width if specified to a non-zero value, or to the native width of type T * otherwise. The \a os stream configuration is not modified. */ /** * \brief Copy a string with a size limit * \param[in] dst The destination string * \param[in] src The source string * \param[in] size The size of the destination string * * This function copies the null-terminated string \a src to \a dst with a limit * of \a size - 1 characters, and null-terminates the result if \a size is * larger than 0. If \a src is larger than \a size - 1, \a dst is truncated. * * \return The size of \a src */ size_t strlcpy(char *dst, const char *src, size_t size) { if (size) { strncpy(dst, src, size); dst[size - 1] = '\0'; } return strlen(src); } details::StringSplitter::StringSplitter(const std::string &str, const std::string &delim) : str_(str), delim_(delim) { } details::StringSplitter::iterator::iterator(const details::StringSplitter *ss, std::string::size_type pos) : ss_(ss), pos_(pos) { next_ = ss_->str_.find(ss_->delim_, pos_); } details::StringSplitter::iterator &details::StringSplitter::iterator::operator++() { pos_ = next_; if (pos_ != std::string::npos) { pos_ += ss_->delim_.length(); next_ = ss_->str_.find(ss_->delim_, pos_); } return *this; } std::string details::StringSplitter::iterator::operator*() const { std::string::size_type count; count = next_ != std::string::npos ? next_ - pos_ : next_; return ss_->str_.substr(pos_, count); } bool details::StringSplitter::iterator::operator!=(const details::StringSplitter::iterator &other) const { return pos_ != other.pos_; } details::StringSplitter::iterator details::StringSplitter::begin() const { return iterator(this, 0); } details::StringSplitter::iterator details::StringSplitter::end() const { return iterator(this, std::string::npos); } /** * \fn split(const std::string &str, const std::string &delim) * \brief Split a string based on a delimiter * \param[in] str The string to split * \param[in] delim The delimiter string * * This function splits the string \a str into substrings based on the * delimiter \a delim. It returns an object of unspecified type that can be * used in a range-based for loop and yields the substrings in sequence. * * \return An object that can be used in a range-based for loop to iterate over * the substrings */ details::StringSplitter split(const std::string &str, const std::string &delim) { /** \todo Try to avoid copies of str and delim */ return details::StringSplitter(str, delim); } /** * \brief Check if libcamera is installed or not * * Utilise the build_rpath dynamic tag which is stripped out by meson at * install time to determine at runtime if the library currently executing * has been installed or not. * * \return True if libcamera is installed, false otherwise */ bool isLibcameraInstalled() { /* * DT_RUNPATH (DT_RPATH when the linker uses old dtags) is removed on * install. */ for (const ElfW(Dyn) *dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn) { if (dyn->d_tag == DT_RUNPATH || dyn->d_tag == DT_RPATH) return false; } return true; } /** * \brief Identify the libcamera.so path * * This function locates the running libcamera.so and returns its full path, * including the file name. * * \return A string stating the path */ std::string libcameraPath() { Dl_info info; /* Look up our own symbol. */ int ret = dladdr(reinterpret_cast(libcameraPath), &info); if (ret == 0) return nullptr; return info.dli_fname; } } /* namespace utils */ } /* namespace libcamera */ 178'>178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655

/* SPDX-License-Identifier: BSD-2-Clause */
/*
 * Copyright (C) 2019, Raspberry Pi (Trading) Limited
 *
 * agc.cpp - AGC/AEC control algorithm
 */

#include <map>

#include "linux/bcm2835-isp.h"

#include "../awb_status.h"
#include "../device_status.h"
#include "../histogram.hpp"
#include "../logging.hpp"
#include "../lux_status.h"
#include "../metadata.hpp"

#include "agc.hpp"

using namespace RPiController;

#define NAME "rpi.agc"

#define PIPELINE_BITS 13 // seems to be a 13-bit pipeline

void AgcMeteringMode::Read(boost::property_tree::ptree const &params)
{
	int num = 0;
	for (auto &p : params.get_child("weights")) {
		if (num == AGC_STATS_SIZE)
			throw std::runtime_error("AgcConfig: too many weights");
		weights[num++] = p.second.get_value<double>();
	}
	if (num != AGC_STATS_SIZE)
		throw std::runtime_error("AgcConfig: insufficient weights");
}

static std::string
read_metering_modes(std::map<std::string, AgcMeteringMode> &metering_modes,
		    boost::property_tree::ptree const &params)
{
	std::string first;
	for (auto &p : params) {
		AgcMeteringMode metering_mode;
		metering_mode.Read(p.second);
		metering_modes[p.first] = std::move(metering_mode);
		if (first.empty())
			first = p.first;
	}
	return first;
}

static int read_double_list(std::vector<double> &list,
			    boost::property_tree::ptree const &params)
{
	for (auto &p : params)
		list.push_back(p.second.get_value<double>());
	return list.size();
}

void AgcExposureMode::Read(boost::property_tree::ptree const &params)
{
	int num_shutters =
		read_double_list(shutter, params.get_child("shutter"));
	int num_ags = read_double_list(gain, params.get_child("gain"));
	if (num_shutters < 2 || num_ags < 2)
		throw std::runtime_error(
			"AgcConfig: must have at least two entries in exposure profile");
	if (num_shutters != num_ags)
		throw std::runtime_error(
			"AgcConfig: expect same number of exposure and gain entries in exposure profile");
}

static std::string
read_exposure_modes(std::map<std::string, AgcExposureMode> &exposure_modes,
		    boost::property_tree::ptree const &params)
{
	std::string first;
	for (auto &p : params) {
		AgcExposureMode exposure_mode;
		exposure_mode.Read(p.second);
		exposure_modes[p.first] = std::move(exposure_mode);
		if (first.empty())
			first = p.first;
	}
	return first;
}

void AgcConstraint::Read(boost::property_tree::ptree const &params)
{
	std::string bound_string = params.get<std::string>("bound", "");
	transform(bound_string.begin(), bound_string.end(),
		  bound_string.begin(), ::toupper);
	if (bound_string != "UPPER" && bound_string != "LOWER")
		throw std::runtime_error(
			"AGC constraint type should be UPPER or LOWER");
	bound = bound_string == "UPPER" ? Bound::UPPER : Bound::LOWER;
	q_lo = params.get<double>("q_lo");
	q_hi = params.get<double>("q_hi");
	Y_target.Read(params.get_child("y_target"));
}

static AgcConstraintMode
read_constraint_mode(boost::property_tree::ptree const &params)
{
	AgcConstraintMode mode;
	for (auto &p : params) {
		AgcConstraint constraint;
		constraint.Read(p.second);
		mode.push_back(std::move(constraint));
	}
	return mode;
}

static std::string read_constraint_modes(
	std::map<std::string, AgcConstraintMode> &constraint_modes,
	boost::property_tree::ptree const &params)
{
	std::string first;
	for (auto &p : params) {
		constraint_modes[p.first] = read_constraint_mode(p.second);
		if (first.empty())
			first = p.first;
	}
	return first;
}

void AgcConfig::Read(boost::property_tree::ptree const &params)
{
	RPI_LOG("AgcConfig");
	default_metering_mode = read_metering_modes(
		metering_modes, params.get_child("metering_modes"));
	default_exposure_mode = read_exposure_modes(
		exposure_modes, params.get_child("exposure_modes"));
	default_constraint_mode = read_constraint_modes(
		constraint_modes, params.get_child("constraint_modes"));
	Y_target.Read(params.get_child("y_target"));
	speed = params.get<double>("speed", 0.2);
	startup_frames = params.get<uint16_t>("startup_frames", 10);
	fast_reduce_threshold =
		params.get<double>("fast_reduce_threshold", 0.4);
	base_ev = params.get<double>("base_ev", 1.0);
}

Agc::Agc(Controller *controller)
	: AgcAlgorithm(controller), metering_mode_(nullptr),
	  exposure_mode_(nullptr), constraint_mode_(nullptr),
	  frame_count_(0), lock_count_(0)
{
	ev_ = status_.ev = 1.0;
	flicker_period_ = status_.flicker_period = 0.0;
	fixed_shutter_ = status_.fixed_shutter = 0;
	fixed_analogue_gain_ = status_.fixed_analogue_gain = 0.0;
	// set to zero initially, so we can tell it's not been calculated
	status_.total_exposure_value = 0.0;
	status_.target_exposure_value = 0.0;
	status_.locked = false;
	output_status_ = status_;
}

char const *Agc::Name() const
{
	return NAME;
}

void Agc::Read(boost::property_tree::ptree const &params)
{
	RPI_LOG("Agc");
	config_.Read(params);
	// Set the config's defaults (which are the first ones it read) as our
	// current modes, until someone changes them.  (they're all known to
	// exist at this point)
	metering_mode_name_ = config_.default_metering_mode;
	metering_mode_ = &config_.metering_modes[metering_mode_name_];
	exposure_mode_name_ = config_.default_exposure_mode;
	exposure_mode_ = &config_.exposure_modes[exposure_mode_name_];
	constraint_mode_name_ = config_.default_constraint_mode;
	constraint_mode_ = &config_.constraint_modes[constraint_mode_name_];
}

void Agc::SetEv(double ev)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	ev_ = ev;
}

void Agc::SetFlickerPeriod(double flicker_period)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	flicker_period_ = flicker_period;
}

void Agc::SetFixedShutter(double fixed_shutter)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	fixed_shutter_ = fixed_shutter;
}

void Agc::SetFixedAnalogueGain(double fixed_analogue_gain)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	fixed_analogue_gain_ = fixed_analogue_gain;
}

void Agc::SetMeteringMode(std::string const &metering_mode_name)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	metering_mode_name_ = metering_mode_name;
}

void Agc::SetExposureMode(std::string const &exposure_mode_name)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	exposure_mode_name_ = exposure_mode_name;
}

void Agc::SetConstraintMode(std::string const &constraint_mode_name)
{
	std::unique_lock<std::mutex> lock(settings_mutex_);
	constraint_mode_name_ = constraint_mode_name;
}

void Agc::SwitchMode([[maybe_unused]] CameraMode const &camera_mode,
		     Metadata *metadata)
{
	// On a mode switch, it's possible the exposure profile could change,
	// so we run through the dividing up of exposure/gain again and
	// write the results into the metadata we've been given.
	if (status_.total_exposure_value) {
		housekeepConfig();
		divvyupExposure();
		writeAndFinish(metadata, false);
	}
}

void Agc::Prepare(Metadata *image_metadata)
{
	AgcStatus status;
	{
		std::unique_lock<std::mutex> lock(output_mutex_);
		status = output_status_;
	}
	int lock_count = lock_count_;
	lock_count_ = 0;
	status.digital_gain = 1.0;
	if (status_.total_exposure_value) {
		// Process has run, so we have meaningful values.
		DeviceStatus device_status;
		if (image_metadata->Get("device.status", device_status) == 0) {
			double actual_exposure = device_status.shutter_speed *
						 device_status.analogue_gain;
			if (actual_exposure) {
				status.digital_gain =
					status_.total_exposure_value /
					actual_exposure;
				RPI_LOG("Want total exposure " << status_.total_exposure_value);
				// Never ask for a gain < 1.0, and also impose
				// some upper limit. Make it customisable?
				status.digital_gain = std::max(
					1.0,
					std::min(status.digital_gain, 4.0));
				RPI_LOG("Actual exposure " << actual_exposure);
				RPI_LOG("Use digital_gain " << status.digital_gain);
				RPI_LOG("Effective exposure " << actual_exposure * status.digital_gain);
				// Decide whether AEC/AGC has converged.
				// Insist AGC is steady for MAX_LOCK_COUNT
				// frames before we say we are "locked".
				// (The hard-coded constants may need to
				// become customisable.)
				if (status.target_exposure_value) {
#define MAX_LOCK_COUNT 3
					double err = 0.10 * status.target_exposure_value + 200;
					if (actual_exposure <
					    status.target_exposure_value + err
					    && actual_exposure >
					    status.target_exposure_value - err)
						lock_count_ =
							std::min(lock_count + 1,
							       MAX_LOCK_COUNT);
					else if (actual_exposure <
						 status.target_exposure_value
						 + 1.5 * err &&
						 actual_exposure >
						 status.target_exposure_value
						 - 1.5 * err)
						lock_count_ = lock_count;
					RPI_LOG("Lock count: " << lock_count_);
				}
			}
		} else
			RPI_LOG(Name() << ": no device metadata");
		status.locked = lock_count_ >= MAX_LOCK_COUNT;
		//printf("%s\n", status.locked ? "+++++++++" : "-");
		image_metadata->Set("agc.status", status);
	}
}

void Agc::Process(StatisticsPtr &stats, Metadata *image_metadata)
{
	frame_count_++;
	// First a little bit of housekeeping, fetching up-to-date settings and
	// configuration, that kind of thing.
	housekeepConfig();
	// Get the current exposure values for the frame that's just arrived.
	fetchCurrentExposure(image_metadata);
	// Compute the total gain we require relative to the current exposure.
	double gain, target_Y;
	computeGain(stats.get(), image_metadata, gain, target_Y);
	// Now compute the target (final) exposure which we think we want.
	computeTargetExposure(gain);
	// Some of the exposure has to be applied as digital gain, so work out
	// what that is. This function also tells us whether it's decided to
	// "desaturate" the image more quickly.
	bool desaturate = applyDigitalGain(image_metadata, gain, target_Y);
	// The results have to be filtered so as not to change too rapidly.
	filterExposure(desaturate);
	// The last thing is to divvy up the exposure value into a shutter time
	// and analogue_gain, according to the current exposure mode.
	divvyupExposure();
	// Finally advertise what we've done.
	writeAndFinish(image_metadata, desaturate);
}

static void copy_string(std::string const &s, char *d, size_t size)
{
	size_t length = s.copy(d, size - 1);
	d[length] = '\0';
}

void Agc::housekeepConfig()
{
	// First fetch all the up-to-date settings, so no one else has to do it.
	std::string new_exposure_mode_name, new_constraint_mode_name,
		new_metering_mode_name;
	{
		std::unique_lock<std::mutex> lock(settings_mutex_);
		new_metering_mode_name = metering_mode_name_;
		new_exposure_mode_name = exposure_mode_name_;
		new_constraint_mode_name = constraint_mode_name_;
		status_.ev = ev_;
		status_.fixed_shutter = fixed_shutter_;
		status_.fixed_analogue_gain = fixed_analogue_gain_;
		status_.flicker_period = flicker_period_;
	}
	RPI_LOG("ev " << status_.ev << " fixed_shutter "
		      << status_.fixed_shutter << " fixed_analogue_gain "
		      << status_.fixed_analogue_gain);
	// Make sure the "mode" pointers point to the up-to-date things, if
	// they've changed.
	if (strcmp(new_metering_mode_name.c_str(), status_.metering_mode)) {
		auto it = config_.metering_modes.find(new_metering_mode_name);
		if (it == config_.metering_modes.end())
			throw std::runtime_error("Agc: no metering mode " +
						 new_metering_mode_name);
		metering_mode_ = &it->second;
		copy_string(new_metering_mode_name, status_.metering_mode,
			    sizeof(status_.metering_mode));
	}
	if (strcmp(new_exposure_mode_name.c_str(), status_.exposure_mode)) {
		auto it = config_.exposure_modes.find(new_exposure_mode_name);
		if (it == config_.exposure_modes.end())
			throw std::runtime_error("Agc: no exposure profile " +
						 new_exposure_mode_name);
		exposure_mode_ = &it->second;
		copy_string(new_exposure_mode_name, status_.exposure_mode,
			    sizeof(status_.exposure_mode));
	}
	if (strcmp(new_constraint_mode_name.c_str(), status_.constraint_mode)) {
		auto it =
			config_.constraint_modes.find(new_constraint_mode_name);
		if (it == config_.constraint_modes.end())
			throw std::runtime_error("Agc: no constraint list " +
						 new_constraint_mode_name);
		constraint_mode_ = &it->second;
		copy_string(new_constraint_mode_name, status_.constraint_mode,
			    sizeof(status_.constraint_mode));
	}
	RPI_LOG("exposure_mode "
		<< new_exposure_mode_name << " constraint_mode "
		<< new_constraint_mode_name << " metering_mode "
		<< new_metering_mode_name);
}

void Agc::fetchCurrentExposure(Metadata *image_metadata)
{
	std::unique_lock<Metadata> lock(*image_metadata);
	DeviceStatus *device_status =
		image_metadata->GetLocked<DeviceStatus>("device.status");
	if (!device_status)
		throw std::runtime_error("Agc: no device metadata");
	current_.shutter = device_status->shutter_speed;
	current_.analogue_gain = device_status->analogue_gain;
	AgcStatus *agc_status =
		image_metadata->GetLocked<AgcStatus>("agc.status");
	current_.total_exposure = agc_status ? agc_status->total_exposure_value : 0;
	current_.total_exposure_no_dg = current_.shutter * current_.analogue_gain;
}

static double compute_initial_Y(bcm2835_isp_stats *stats, Metadata *image_metadata,
				double weights[])
{
	bcm2835_isp_stats_region *regions = stats->agc_stats;
	struct AwbStatus awb;
	awb.gain_r = awb.gain_g = awb.gain_b = 1.0; // in case no metadata
	if (image_metadata->Get("awb.status", awb) != 0)
		RPI_WARN("Agc: no AWB status found");
	double Y_sum = 0, weight_sum = 0;
	for (int i = 0; i < AGC_STATS_SIZE; i++) {
		if (regions[i].counted == 0)
			continue;
		weight_sum += weights[i];
		double Y = regions[i].r_sum * awb.gain_r * .299 +
			   regions[i].g_sum * awb.gain_g * .587 +
			   regions[i].b_sum * awb.gain_b * .114;
		Y /= regions[i].counted;
		Y_sum += Y * weights[i];
	}
	return Y_sum / weight_sum / (1 << PIPELINE_BITS);
}

// We handle extra gain through EV by adjusting our Y targets. However, you
// simply can't monitor histograms once they get very close to (or beyond!)
// saturation, so we clamp the Y targets to this value. It does mean that EV
// increases don't necessarily do quite what you might expect in certain
// (contrived) cases.

#define EV_GAIN_Y_TARGET_LIMIT 0.9

static double constraint_compute_gain(AgcConstraint &c, Histogram &h,
				      double lux, double ev_gain,
				      double &target_Y)
{
	target_Y = c.Y_target.Eval(c.Y_target.Domain().Clip(lux));
	target_Y = std::min(EV_GAIN_Y_TARGET_LIMIT, target_Y * ev_gain);
	double iqm = h.InterQuantileMean(c.q_lo, c.q_hi);
	return (target_Y * NUM_HISTOGRAM_BINS) / iqm;
}

void Agc::computeGain(bcm2835_isp_stats *statistics, Metadata *image_metadata,
		      double &gain, double &target_Y)
{
	struct LuxStatus lux = {};
	lux.lux = 400; // default lux level to 400 in case no metadata found
	if (image_metadata->Get("lux.status", lux) != 0)
		RPI_WARN("Agc: no lux level found");
	Histogram h(statistics->hist[0].g_hist, NUM_HISTOGRAM_BINS);
	double ev_gain = status_.ev * config_.base_ev;
	// The initial gain and target_Y come from some of the regions. After
	// that we consider the histogram constraints.
	target_Y =
		config_.Y_target.Eval(config_.Y_target.Domain().Clip(lux.lux));
	target_Y = std::min(EV_GAIN_Y_TARGET_LIMIT, target_Y * ev_gain);
	double initial_Y = compute_initial_Y(statistics, image_metadata,
					     metering_mode_->weights);
	gain = std::min(10.0, target_Y / (initial_Y + .001));
	RPI_LOG("Initially Y " << initial_Y << " target " << target_Y
			       << " gives gain " << gain);
	for (auto &c : *constraint_mode_) {
		double new_target_Y;
		double new_gain =
			constraint_compute_gain(c, h, lux.lux, ev_gain,
						new_target_Y);
		RPI_LOG("Constraint has target_Y "
			<< new_target_Y << " giving gain " << new_gain);
		if (c.bound == AgcConstraint::Bound::LOWER &&
		    new_gain > gain) {
			RPI_LOG("Lower bound constraint adopted");
			gain = new_gain, target_Y = new_target_Y;
		} else if (c.bound == AgcConstraint::Bound::UPPER &&
			   new_gain < gain) {
			RPI_LOG("Upper bound constraint adopted");
			gain = new_gain, target_Y = new_target_Y;
		}
	}
	RPI_LOG("Final gain " << gain << " (target_Y " << target_Y << " ev "
			      << status_.ev << " base_ev " << config_.base_ev
			      << ")");
}

void Agc::computeTargetExposure(double gain)
{
	// The statistics reflect the image without digital gain, so the final
	// total exposure we're aiming for is:
	target_.total_exposure = current_.total_exposure_no_dg * gain;
	// The final target exposure is also limited to what the exposure
	// mode allows.
	double max_total_exposure =
		(status_.fixed_shutter != 0.0
			 ? status_.fixed_shutter
			 : exposure_mode_->shutter.back()) *
		(status_.fixed_analogue_gain != 0.0
			 ? status_.fixed_analogue_gain
			 : exposure_mode_->gain.back());
	target_.total_exposure = std::min(target_.total_exposure,
					  max_total_exposure);
	RPI_LOG("Target total_exposure " << target_.total_exposure);
}

bool Agc::applyDigitalGain(Metadata *image_metadata, double gain,
			   double target_Y)
{
	double dg = 1.0;
	// I think this pipeline subtracts black level and rescales before we
	// get the stats, so no need to worry about it.
	struct AwbStatus awb;
	if (image_metadata->Get("awb.status", awb) == 0) {
		double min_gain = std::min(awb.gain_r,
					   std::min(awb.gain_g, awb.gain_b));
		dg *= std::max(1.0, 1.0 / min_gain);
	} else
		RPI_WARN("Agc: no AWB status found");
	RPI_LOG("after AWB, target dg " << dg << " gain " << gain
					<< " target_Y " << target_Y);
	// Finally, if we're trying to reduce exposure but the target_Y is
	// "close" to 1.0, then the gain computed for that constraint will be
	// only slightly less than one, because the measured Y can never be
	// larger than 1.0. When this happens, demand a large digital gain so
	// that the exposure can be reduced, de-saturating the image much more
	// quickly (and we then approach the correct value more quickly from
	// below).
	bool desaturate = target_Y > config_.fast_reduce_threshold &&
			  gain < sqrt(target_Y);
	if (desaturate)
		dg /= config_.fast_reduce_threshold;
	RPI_LOG("Digital gain " << dg << " desaturate? " << desaturate);
	target_.total_exposure_no_dg = target_.total_exposure / dg;
	RPI_LOG("Target total_exposure_no_dg " << target_.total_exposure_no_dg);
	return desaturate;
}

void Agc::filterExposure(bool desaturate)
{
	double speed = frame_count_ <= config_.startup_frames ? 1.0 : config_.speed;
	if (filtered_.total_exposure == 0.0) {
		filtered_.total_exposure = target_.total_exposure;
		filtered_.total_exposure_no_dg = target_.total_exposure_no_dg;
	} else {
		// If close to the result go faster, to save making so many
		// micro-adjustments on the way. (Make this customisable?)
		if (filtered_.total_exposure < 1.2 * target_.total_exposure &&
		    filtered_.total_exposure > 0.8 * target_.total_exposure)
			speed = sqrt(speed);
		filtered_.total_exposure = speed * target_.total_exposure +
					   filtered_.total_exposure * (1.0 - speed);
		// When desaturing, take a big jump down in exposure_no_dg,
		// which we'll hide with digital gain.
		if (desaturate)
			filtered_.total_exposure_no_dg =
				target_.total_exposure_no_dg;
		else
			filtered_.total_exposure_no_dg =
				speed * target_.total_exposure_no_dg +
				filtered_.total_exposure_no_dg * (1.0 - speed);
	}
	// We can't let the no_dg exposure deviate too far below the
	// total exposure, as there might not be enough digital gain available
	// in the ISP to hide it (which will cause nasty oscillation).
	if (filtered_.total_exposure_no_dg <
	    filtered_.total_exposure * config_.fast_reduce_threshold)
		filtered_.total_exposure_no_dg = filtered_.total_exposure *
						 config_.fast_reduce_threshold;
	RPI_LOG("After filtering, total_exposure " << filtered_.total_exposure <<
		" no dg " << filtered_.total_exposure_no_dg);
}

void Agc::divvyupExposure()
{
	// Sending the fixed shutter/gain cases through the same code may seem
	// unnecessary, but it will make more sense when extend this to cover
	// variable aperture.
	double exposure_value = filtered_.total_exposure_no_dg;
	double shutter_time, analogue_gain;
	shutter_time = status_.fixed_shutter != 0.0
			       ? status_.fixed_shutter
			       : exposure_mode_->shutter[0];
	analogue_gain = status_.fixed_analogue_gain != 0.0
				? status_.fixed_analogue_gain
				: exposure_mode_->gain[0];
	if (shutter_time * analogue_gain < exposure_value) {
		for (unsigned int stage = 1;
		     stage < exposure_mode_->gain.size(); stage++) {
			if (status_.fixed_shutter == 0.0) {
				if (exposure_mode_->shutter[stage] *
					    analogue_gain >=
				    exposure_value) {
					shutter_time =
						exposure_value / analogue_gain;
					break;
				}
				shutter_time = exposure_mode_->shutter[stage];
			}
			if (status_.fixed_analogue_gain == 0.0) {
				if (exposure_mode_->gain[stage] *
					    shutter_time >=
				    exposure_value) {
					analogue_gain =
						exposure_value / shutter_time;
					break;
				}
				analogue_gain = exposure_mode_->gain[stage];
			}
		}
	}
	RPI_LOG("Divided up shutter and gain are " << shutter_time << " and "
						   << analogue_gain);
	// Finally adjust shutter time for flicker avoidance (require both
	// shutter and gain not to be fixed).
	if (status_.fixed_shutter == 0.0 &&
	    status_.fixed_analogue_gain == 0.0 &&
	    status_.flicker_period != 0.0) {
		int flicker_periods = shutter_time / status_.flicker_period;
		if (flicker_periods > 0) {
			double new_shutter_time = flicker_periods * status_.flicker_period;
			analogue_gain *= shutter_time / new_shutter_time;
			// We should still not allow the ag to go over the
			// largest value in the exposure mode. Note that this
			// may force more of the total exposure into the digital
			// gain as a side-effect.
			analogue_gain = std::min(analogue_gain,
						 exposure_mode_->gain.back());
			shutter_time = new_shutter_time;
		}
		RPI_LOG("After flicker avoidance, shutter "
			<< shutter_time << " gain " << analogue_gain);
	}
	filtered_.shutter = shutter_time;
	filtered_.analogue_gain = analogue_gain;
}

void Agc::writeAndFinish(Metadata *image_metadata, bool desaturate)
{
	status_.total_exposure_value = filtered_.total_exposure;
	status_.target_exposure_value = desaturate ? 0 : target_.total_exposure_no_dg;
	status_.shutter_time = filtered_.shutter;
	status_.analogue_gain = filtered_.analogue_gain;
	{
		std::unique_lock<std::mutex> lock(output_mutex_);
		output_status_ = status_;
	}
	// Write to metadata as well, in case anyone wants to update the camera
	// immediately.
	image_metadata->Set("agc.status", status_);
	RPI_LOG("Output written, total exposure requested is "
		<< filtered_.total_exposure);
	RPI_LOG("Camera exposure update: shutter time " << filtered_.shutter <<
		" analogue gain " << filtered_.analogue_gain);
}

// Register algorithm with the system.
static Algorithm *Create(Controller *controller)
{
	return (Algorithm *)new Agc(controller);
}
static RegisterAlgorithm reg(NAME, &Create);