libcamera: video_device: Convert between ColorSpace class and V4L2 formats

Add functions to the V4L2Device class to convert to and from
libcamera ColorSpace.

These functions are added to the base V4L2Device class so that they can
be shared both by the video device class and subdevices.

With the ColorSpace class, the color space and related other fields
are stored together, corresponding to a number of fields in the
various different V4L2 format structures. Template functions are
therefore a convenient implementation, and we must explicitly
instantiate the templates that will be needed.

Note that unset color spaces are converted to requests for the
device's "default" color space.

Signed-off-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

2 files changed, 218 insertions, 0 deletions

diff --git a/include/libcamera/internal/v4l2_device.h b/include/libcamera/internal/v4l2_device.h
index 8886b750..a52a5f2c 100644
--- a/include/libcamera/internal/v4l2_device.h
+++ b/include/libcamera/internal/v4l2_device.h
@@ -9,6 +9,7 @@
 
 #include <map>
 #include <memory>
+#include <optional>
 #include <vector>
 
 #include <linux/videodev2.h>
@@ -18,6 +19,7 @@
 #include <libcamera/base/span.h>
 #include <libcamera/base/unique_fd.h>
 
+#include <libcamera/color_space.h>
 #include <libcamera/controls.h>
 
 namespace libcamera {
@@ -56,6 +58,12 @@ protected:
 
 	int fd() const { return fd_.get(); }
 
+	template<typename T>
+	static std::optional<ColorSpace> toColorSpace(const T &v4l2Format);
+
+	template<typename T>
+	static int fromColorSpace(const std::optional<ColorSpace> &colorSpace, T &v4l2Format);
+
 private:
 	static ControlType v4l2CtrlType(uint32_t ctrlType);
 	static std::unique_ptr<ControlId> v4l2ControlId(const v4l2_query_ext_ctrl &ctrl);
diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
index 39f36009..62c91779 100644
--- a/src/libcamera/v4l2_device.cpp
+++ b/src/libcamera/v4l2_device.cpp
@@ -10,11 +10,15 @@
 #include <fcntl.h>
 #include <iomanip>
 #include <limits.h>
+#include <map>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/syscall.h>
 #include <unistd.h>
+#include <vector>
+
+#include <linux/v4l2-mediabus.h>
 
 #include <libcamera/base/event_notifier.h>
 #include <libcamera/base/log.h>
@@ -728,4 +732,210 @@ void V4L2Device::eventAvailable()
 	frameStart.emit(event.u.frame_sync.frame_sequence);
 }
 
+static const std::map<uint32_t, ColorSpace> v4l2ToColorSpace = {
+	{ V4L2_COLORSPACE_RAW, ColorSpace::Raw },
+	{ V4L2_COLORSPACE_JPEG, ColorSpace::Jpeg },
+	{ V4L2_COLORSPACE_SRGB, ColorSpace::Srgb },
+	{ V4L2_COLORSPACE_SMPTE170M, ColorSpace::Smpte170m },
+	{ V4L2_COLORSPACE_REC709, ColorSpace::Rec709 },
+	{ V4L2_COLORSPACE_BT2020, ColorSpace::Rec2020 },
+};
+
+static const std::map<uint32_t, ColorSpace::TransferFunction> v4l2ToTransferFunction = {
+	{ V4L2_XFER_FUNC_NONE, ColorSpace::TransferFunction::Linear },
+	{ V4L2_XFER_FUNC_SRGB, ColorSpace::TransferFunction::Srgb },
+	{ V4L2_XFER_FUNC_709, ColorSpace::TransferFunction::Rec709 },
+};
+
+static const std::map<uint32_t, ColorSpace::YcbcrEncoding> v4l2ToYcbcrEncoding = {
+	{ V4L2_YCBCR_ENC_601, ColorSpace::YcbcrEncoding::Rec601 },
+	{ V4L2_YCBCR_ENC_709, ColorSpace::YcbcrEncoding::Rec709 },
+	{ V4L2_YCBCR_ENC_BT2020, ColorSpace::YcbcrEncoding::Rec2020 },
+};
+
+static const std::map<uint32_t, ColorSpace::Range> v4l2ToRange = {
+	{ V4L2_QUANTIZATION_FULL_RANGE, ColorSpace::Range::Full },
+	{ V4L2_QUANTIZATION_LIM_RANGE, ColorSpace::Range::Limited },
+};
+
+static const std::vector<std::pair<ColorSpace, v4l2_colorspace>> colorSpaceToV4l2 = {
+	{ ColorSpace::Raw, V4L2_COLORSPACE_RAW },
+	{ ColorSpace::Jpeg, V4L2_COLORSPACE_JPEG },
+	{ ColorSpace::Srgb, V4L2_COLORSPACE_SRGB },
+	{ ColorSpace::Smpte170m, V4L2_COLORSPACE_SMPTE170M },
+	{ ColorSpace::Rec709, V4L2_COLORSPACE_REC709 },
+	{ ColorSpace::Rec2020, V4L2_COLORSPACE_BT2020 },
+};
+
+static const std::map<ColorSpace::Primaries, v4l2_colorspace> primariesToV4l2 = {
+	{ ColorSpace::Primaries::Raw, V4L2_COLORSPACE_RAW },
+	{ ColorSpace::Primaries::Smpte170m, V4L2_COLORSPACE_SMPTE170M },
+	{ ColorSpace::Primaries::Rec709, V4L2_COLORSPACE_REC709 },
+	{ ColorSpace::Primaries::Rec2020, V4L2_COLORSPACE_BT2020 },
+};
+
+static const std::map<ColorSpace::TransferFunction, v4l2_xfer_func> transferFunctionToV4l2 = {
+	{ ColorSpace::TransferFunction::Linear, V4L2_XFER_FUNC_NONE },
+	{ ColorSpace::TransferFunction::Srgb, V4L2_XFER_FUNC_SRGB },
+	{ ColorSpace::TransferFunction::Rec709, V4L2_XFER_FUNC_709 },
+};
+
+static const std::map<ColorSpace::YcbcrEncoding, v4l2_ycbcr_encoding> ycbcrEncodingToV4l2 = {
+	{ ColorSpace::YcbcrEncoding::Rec601, V4L2_YCBCR_ENC_601 },
+	{ ColorSpace::YcbcrEncoding::Rec709, V4L2_YCBCR_ENC_709 },
+	{ ColorSpace::YcbcrEncoding::Rec2020, V4L2_YCBCR_ENC_BT2020 },
+};
+
+static const std::map<ColorSpace::Range, v4l2_quantization> rangeToV4l2 = {
+	{ ColorSpace::Range::Full, V4L2_QUANTIZATION_FULL_RANGE },
+	{ ColorSpace::Range::Limited, V4L2_QUANTIZATION_LIM_RANGE },
+};
+
+/**
+ * \brief Convert the color space fields in a V4L2 format to a ColorSpace
+ * \param[in] v4l2Format A V4L2 format containing color space information
+ *
+ * The colorspace, ycbcr_enc, xfer_func and quantization fields within a
+ * V4L2 format structure are converted to a corresponding ColorSpace.
+ *
+ * If any V4L2 fields are not recognised then we return an "unset"
+ * color space.
+ *
+ * \return The ColorSpace corresponding to the input V4L2 format
+ * \retval std::nullopt One or more V4L2 color space fields were not recognised
+ */
+template<typename T>
+std::optional<ColorSpace> V4L2Device::toColorSpace(const T &v4l2Format)
+{
+	auto itColor = v4l2ToColorSpace.find(v4l2Format.colorspace);
+	if (itColor == v4l2ToColorSpace.end())
+		return std::nullopt;
+
+	/* This sets all the color space fields to the correct "default" values. */
+	ColorSpace colorSpace = itColor->second;
+
+	if (v4l2Format.xfer_func != V4L2_XFER_FUNC_DEFAULT) {
+		auto itTransfer = v4l2ToTransferFunction.find(v4l2Format.xfer_func);
+		if (itTransfer == v4l2ToTransferFunction.end())
+			return std::nullopt;
+
+		colorSpace.transferFunction = itTransfer->second;
+	}
+
+	if (v4l2Format.ycbcr_enc != V4L2_YCBCR_ENC_DEFAULT) {
+		auto itYcbcrEncoding = v4l2ToYcbcrEncoding.find(v4l2Format.ycbcr_enc);
+		if (itYcbcrEncoding == v4l2ToYcbcrEncoding.end())
+			return std::nullopt;
+
+		colorSpace.ycbcrEncoding = itYcbcrEncoding->second;
+	}
+
+	if (v4l2Format.quantization != V4L2_QUANTIZATION_DEFAULT) {
+		auto itRange = v4l2ToRange.find(v4l2Format.quantization);
+		if (itRange == v4l2ToRange.end())
+			return std::nullopt;
+
+		colorSpace.range = itRange->second;
+	}
+
+	return colorSpace;
+}
+
+template std::optional<ColorSpace> V4L2Device::toColorSpace(const struct v4l2_pix_format &);
+template std::optional<ColorSpace> V4L2Device::toColorSpace(const struct v4l2_pix_format_mplane &);
+template std::optional<ColorSpace> V4L2Device::toColorSpace(const struct v4l2_mbus_framefmt &);
+
+/**
+ * \brief Fill in the color space fields of a V4L2 format from a ColorSpace
+ * \param[in] colorSpace The ColorSpace to be converted
+ * \param[out] v4l2Format A V4L2 format containing color space information
+ *
+ * The colorspace, ycbcr_enc, xfer_func and quantization fields within a
+ * V4L2 format structure are filled in from a corresponding ColorSpace.
+ *
+ * An error is returned if any of the V4L2 fields do not support the
+ * value given in the ColorSpace. Such fields are set to the V4L2
+ * "default" values, but all other fields are still filled in where
+ * possible.
+ *
+ * If the color space is completely unset, "default" V4L2 values are used
+ * everywhere, so a driver would then choose its preferred color space.
+ *
+ * \return 0 on success or a negative error code otherwise
+ * \retval -EINVAL The ColorSpace does not have a representation using V4L2 enums
+ */
+template<typename T>
+int V4L2Device::fromColorSpace(const std::optional<ColorSpace> &colorSpace, T &v4l2Format)
+{
+	v4l2Format.colorspace = V4L2_COLORSPACE_DEFAULT;
+	v4l2Format.xfer_func = V4L2_XFER_FUNC_DEFAULT;
+	v4l2Format.ycbcr_enc = V4L2_YCBCR_ENC_DEFAULT;
+	v4l2Format.quantization = V4L2_QUANTIZATION_DEFAULT;
+
+	if (!colorSpace)
+		return 0;
+
+	auto itColor = std::find_if(colorSpaceToV4l2.begin(), colorSpaceToV4l2.end(),
+				    [&colorSpace](const auto &item) {
+					    return colorSpace == item.first;
+				    });
+	if (itColor != colorSpaceToV4l2.end()) {
+		v4l2Format.colorspace = itColor->second;
+		/* Leaving all the other fields as "default" should be fine. */
+		return 0;
+	}
+
+	/*
+	 * If the colorSpace doesn't precisely match a standard color space,
+	 * then we must choose a V4L2 colorspace with matching primaries.
+	 */
+	int ret = 0;
+
+	auto itPrimaries = primariesToV4l2.find(colorSpace->primaries);
+	if (itPrimaries != primariesToV4l2.end()) {
+		v4l2Format.colorspace = itPrimaries->second;
+	} else {
+		libcamera::LOG(V4L2, Warning)
+			<< "Unrecognised primaries in "
+			<< ColorSpace::toString(colorSpace);
+		ret = -EINVAL;
+	}
+
+	auto itTransfer = transferFunctionToV4l2.find(colorSpace->transferFunction);
+	if (itTransfer != transferFunctionToV4l2.end()) {
+		v4l2Format.xfer_func = itTransfer->second;
+	} else {
+		libcamera::LOG(V4L2, Warning)
+			<< "Unrecognised transfer function in "
+			<< ColorSpace::toString(colorSpace);
+		ret = -EINVAL;
+	}
+
+	auto itYcbcrEncoding = ycbcrEncodingToV4l2.find(colorSpace->ycbcrEncoding);
+	if (itYcbcrEncoding != ycbcrEncodingToV4l2.end()) {
+		v4l2Format.ycbcr_enc = itYcbcrEncoding->second;
+	} else {
+		libcamera::LOG(V4L2, Warning)
+			<< "Unrecognised YCbCr encoding in "
+			<< ColorSpace::toString(colorSpace);
+		ret = -EINVAL;
+	}
+
+	auto itRange = rangeToV4l2.find(colorSpace->range);
+	if (itRange != rangeToV4l2.end()) {
+		v4l2Format.quantization = itRange->second;
+	} else {
+		libcamera::LOG(V4L2, Warning)
+			<< "Unrecognised quantization in "
+			<< ColorSpace::toString(colorSpace);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+template int V4L2Device::fromColorSpace(const std::optional<ColorSpace> &, struct v4l2_pix_format &);
+template int V4L2Device::fromColorSpace(const std::optional<ColorSpace> &, struct v4l2_pix_format_mplane &);
+template int V4L2Device::fromColorSpace(const std::optional<ColorSpace> &, struct v4l2_mbus_framefmt &);
+
 } /* namespace libcamera */