libcamera: bayer_format: Add the fromV4L2PixelFormat function

Add a static member function to get the corresponding BayerFormat from a
given V4L2PixelFormat. The motivation behind this patch is to align the
overall structure of the BayerFormat class with other parts of the code
base, such as the V4L2PixelFormat class.

The downside of this change is a slightly worse time complexity, but
the upside is a smaller codebase and lower memory consumption. As the
function is probably not used very frequently, I tend to favor the
mentioned upsides.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sebastian Fricke <sebastian.fricke@posteo.net>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/bayer_format.h

@@ -49,6 +49,7 @@ public:
 	std::string toString() const;
 
 	V4L2PixelFormat toV4L2PixelFormat() const;
+	static BayerFormat fromV4L2PixelFormat(V4L2PixelFormat v4l2Format);
 	BayerFormat transform(Transform t) const;
 
 	Order order;

src/libcamera/bayer_format.cpp

@@ -7,6 +7,7 @@
 
 #include "libcamera/internal/bayer_format.h"
 
+#include <algorithm>
 #include <map>
 #include <unordered_map>
 
@@ -272,6 +273,23 @@ V4L2PixelFormat BayerFormat::toV4L2PixelFormat() const
 	return V4L2PixelFormat();
 }
 
+/**
+ * \brief Convert \a v4l2Format to the corresponding BayerFormat
+ * \param[in] v4l2Format The raw format to convert into a BayerFormat
+ * \return The BayerFormat corresponding to \a v4l2Format
+ */
+BayerFormat BayerFormat::fromV4L2PixelFormat(V4L2PixelFormat v4l2Format)
+{
+	auto it = std::find_if(bayerToV4l2.begin(), bayerToV4l2.end(),
+			       [v4l2Format](const auto &i) {
+				       return i.second == v4l2Format;
+			       });
+	if (it != bayerToV4l2.end())
+		return it->first;
+
+	return BayerFormat();
+}
+
 /**
  * \brief Apply a transform to this BayerFormat
  * \param[in] t The transform to apply

src/libcamera/pipeline/raspberrypi/raspberrypi.cpp

@@ -357,7 +357,7 @@ CameraConfiguration::Status RPiCameraConfiguration::validate()
 			 */
 			V4L2PixelFormat fourcc = sensorFormat.fourcc;
 			if (data_->flipsAlterBayerOrder_) {
-				BayerFormat bayer(fourcc);
+				BayerFormat bayer = BayerFormat::fromV4L2PixelFormat(fourcc);
 				bayer.order = data_->nativeBayerOrder_;
 				bayer = bayer.transform(combined);
 				fourcc = bayer.toV4L2PixelFormat();
@@ -1001,7 +1001,7 @@ bool PipelineHandlerRPi::match(DeviceEnumerator *enumerator)
 	BayerFormat bayerFormat;
 	for (const auto &iter : dev->formats()) {
 		V4L2PixelFormat v4l2Format = iter.first;
-		bayerFormat = BayerFormat(v4l2Format);
+		bayerFormat = BayerFormat::fromV4L2PixelFormat(v4l2Format);
 		if (bayerFormat.isValid())
 			break;
 	}