core: Add aspect ratio control for lores stream

Add a new command line argument "--lores-par" that when set, preserves
the 1:1 aspect ratio of the low res stream. This is only possible on the
PiSP platform. The default behaviour is to have this switch disabled,
allowing for identical behaviour betwen VC4 and PiSP platforms. This
requires the use of the rpi::ScalerCrops vendor control.

This switch can also be triggered via the "rpicam-apps.lores.par" key
in the postprocessing JSON file.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>

core/options.cpp

@@ -270,9 +270,11 @@ Options::Options()
 		("tuning-file", value<std::string>(&tuning_file)->default_value("-"),
 			"Name of camera tuning file to use, omit this option for libcamera default behaviour")
 		("lores-width", value<unsigned int>(&lores_width)->default_value(0),
-			"Width of low resolution frames (use 0 to omit low resolution stream")
+			"Width of low resolution frames (use 0 to omit low resolution stream)")
 		("lores-height", value<unsigned int>(&lores_height)->default_value(0),
-			"Height of low resolution frames (use 0 to omit low resolution stream")
+			"Height of low resolution frames (use 0 to omit low resolution stream)")
+		("lores-par", value<bool>(&lores_par)->default_value(false)->implicit_value(true),
+			"Preserve the 1:1 pixel aspect ratio of the low res image (where possible) by applying a different crop on the stream.")
 		("mode", value<std::string>(&mode_string),
 			"Camera mode as W:H:bit-depth:packing, where packing is P (packed) or U (unpacked)")
 		("viewfinder-mode", value<std::string>(&viewfinder_mode_string),
@@ -695,6 +697,7 @@ void Options::Print() const
 	std::cerr << "    tuning-file: " << (tuning_file == "-" ? "(libcamera)" : tuning_file) << std::endl;
 	std::cerr << "    lores-width: " << lores_width << std::endl;
 	std::cerr << "    lores-height: " << lores_height << std::endl;
+	std::cerr << "    lores-par: " << lores_par << std::endl;
 	if (afMode_index != -1)
 		std::cerr << "    autofocus-mode: " << afMode << std::endl;
 	if (afRange_index != -1)

core/options.hpp

@@ -151,6 +151,7 @@ struct Options
 	bool qt_preview;
 	unsigned int lores_width;
 	unsigned int lores_height;
+	bool lores_par;
 	unsigned int camera;
 	std::string mode_string;
 	Mode mode;

core/post_processor.cpp

@@ -120,6 +120,7 @@ void PostProcessor::Read(std::string const &filename)
 
 				unsigned int lores_width = node.get<unsigned int>("lores.width");
 				unsigned int lores_height = node.get<unsigned int>("lores.height");
+				bool lores_par = node.get<bool>("lores.par", app_->GetOptions()->lores_par);
 				std::string lores_format_str = node.get<std::string>("lores.format", "yuv420");
 
 				libcamera::PixelFormat lores_format = libcamera::formats::YUV420;
@@ -132,6 +133,7 @@ void PostProcessor::Read(std::string const &filename)
 
 				app_->GetOptions()->lores_width = lores_width;
 				app_->GetOptions()->lores_height = lores_height;
+				app_->GetOptions()->lores_par = lores_par;
 				app_->lores_format_ = lores_format;
 
 				LOG(1, "Postprocessing requested lores: " << lores_width << "x" << lores_height << " " << lores_format);

core/rpicam_app.cpp

@@ -635,17 +635,35 @@ void RPiCamApp::StartCamera()
 
 	// Build a list of initial controls that we must set in the camera before starting it.
 	// We don't overwrite anything the application may have set before calling us.
-	if (!controls_.get(controls::ScalerCrop) && options_->roi_width != 0 && options_->roi_height != 0)
+	if (!controls_.get(controls::ScalerCrop) && !controls_.get(controls::rpi::ScalerCrops))
 	{
-		Rectangle sensor_area = camera_->controls().at(&controls::ScalerCrop).max().get<Rectangle>();
-		int x = options_->roi_x * sensor_area.width;
-		int y = options_->roi_y * sensor_area.height;
-		int w = options_->roi_width * sensor_area.width;
-		int h = options_->roi_height * sensor_area.height;
-		Rectangle crop(x, y, w, h);
-		crop.translateBy(sensor_area.topLeft());
-		LOG(2, "Using crop " << crop.toString());
-		controls_.set(controls::ScalerCrop, crop);
+		const Rectangle sensor_area = camera_->controls().at(&controls::ScalerCrop).max().get<Rectangle>();
+		const Rectangle default_crop = camera_->controls().at(&controls::ScalerCrop).def().get<Rectangle>();
+		std::vector<Rectangle> crops;
+
+		if (options_->roi_width != 0 && options_->roi_height != 0)
+		{
+			int x = options_->roi_x * sensor_area.width;
+			int y = options_->roi_y * sensor_area.height;
+			unsigned int w = options_->roi_width * sensor_area.width;
+			unsigned int h = options_->roi_height * sensor_area.height;
+			crops.push_back({ x, y, w, h });
+			crops.back().translateBy(sensor_area.topLeft());
+		}
+		else
+		{
+			crops.push_back(default_crop);
+		}
+
+		LOG(2, "Using crop (main) " << crops.back().toString());
+
+		if (options_->lores_width != 0 && options_->lores_height != 0 && !options_->lores_par)
+		{
+			crops.push_back(crops.back());
+			LOG(2, "Using crop (lores) " << crops.back().toString());
+		}
+
+		controls_.set(controls::rpi::ScalerCrops, libcamera::Span<const Rectangle>(crops.data(), crops.size()));
 	}
 
 	if (!controls_.get(controls::AfWindows) && !controls_.get(controls::AfMetering) && options_->afWindow_width != 0 &&