cam: Add support for viewfinder through DRM/KMS

Use the KMSSink class to display the viewfinder stream, if any, through
DRM/KMS. The output connector is selected through the new -D/--display
argument.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/camera_session.cpp

@@ -16,6 +16,9 @@
 #include "camera_session.h"
 #include "event_loop.h"
 #include "file_sink.h"
+#ifdef HAVE_KMS
+#include "kms_sink.h"
+#endif
 #include "main.h"
 #include "stream_options.h"
 
@@ -66,6 +69,28 @@ CameraSession::CameraSession(CameraManager *cm,
 
 	bool strictFormats = options_.isSet(OptStrictFormats);
 
+#ifdef HAVE_KMS
+	if (options_.isSet(OptDisplay)) {
+		if (options_.isSet(OptFile)) {
+			std::cerr << "--display and --file options are mutually exclusive"
+				  << std::endl;
+			return;
+		}
+
+		if (roles.size() != 1) {
+			std::cerr << "Display doesn't support multiple streams"
+				  << std::endl;
+			return;
+		}
+
+		if (roles[0] != StreamRole::Viewfinder) {
+			std::cerr << "Display requires a viewfinder stream"
+				  << std::endl;
+			return;
+		}
+	}
+#endif
+
 	switch (config->validate()) {
 	case CameraConfiguration::Valid:
 		break;
@@ -161,6 +186,11 @@ int CameraSession::start()
 
 	camera_->requestCompleted.connect(this, &CameraSession::requestComplete);
 
+#ifdef HAVE_KMS
+	if (options_.isSet(OptDisplay))
+		sink_ = std::make_unique<KMSSink>(options_[OptDisplay].toString());
+#endif
+
 	if (options_.isSet(OptFile)) {
 		if (!options_[OptFile].toString().empty())
 			sink_ = std::make_unique<FileSink>(options_[OptFile]);

src/cam/main.cpp

@@ -132,6 +132,12 @@ int CamApp::parseOptions(int argc, char *argv[])
 			 "Capture until interrupted by user or until <count> frames captured",
 			 "capture", ArgumentOptional, "count", false,
 			 OptCamera);
+#ifdef HAVE_KMS
+	parser.addOption(OptDisplay, OptionString,
+			 "Display viewfinder through DRM/KMS on specified connector",
+			 "display", ArgumentOptional, "connector", false,
+			 OptCamera);
+#endif
 	parser.addOption(OptFile, OptionString,
 			 "Write captured frames to disk\n"
 			 "If the file name ends with a '/', it sets the directory in which\n"

src/cam/main.h

@@ -10,6 +10,7 @@
 enum {
 	OptCamera = 'c',
 	OptCapture = 'C',
+	OptDisplay = 'D',
 	OptFile = 'F',
 	OptHelp = 'h',
 	OptInfo = 'I',