cam: kms_sink: Add color space support

KMS defines YCbCr encoding and quantization properties for planes. When
supported by the device, set them to match the color space of the
stream to render colors accurately.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>

src/cam/kms_sink.cpp

@@ -149,6 +149,81 @@ int KMSSink::configure(const libcamera::CameraConfiguration &config)
 	size_ = cfg.size;
 	stride_ = cfg.stride;
 
+	/* Configure color space. */
+	colorEncoding_ = std::nullopt;
+	colorRange_ = std::nullopt;
+
+	if (cfg.colorSpace->ycbcrEncoding == libcamera::ColorSpace::YcbcrEncoding::None)
+		return 0;
+
+	/*
+	 * The encoding and range enums are defined in the kernel but not
+	 * exposed in public headers.
+	 */
+	enum drm_color_encoding {
+		DRM_COLOR_YCBCR_BT601,
+		DRM_COLOR_YCBCR_BT709,
+		DRM_COLOR_YCBCR_BT2020,
+	};
+
+	enum drm_color_range {
+		DRM_COLOR_YCBCR_LIMITED_RANGE,
+		DRM_COLOR_YCBCR_FULL_RANGE,
+	};
+
+	const DRM::Property *colorEncoding = plane_->property("COLOR_ENCODING");
+	const DRM::Property *colorRange = plane_->property("COLOR_RANGE");
+
+	if (colorEncoding) {
+		drm_color_encoding encoding;
+
+		switch (cfg.colorSpace->ycbcrEncoding) {
+		case libcamera::ColorSpace::YcbcrEncoding::Rec601:
+		default:
+			encoding = DRM_COLOR_YCBCR_BT601;
+			break;
+		case libcamera::ColorSpace::YcbcrEncoding::Rec709:
+			encoding = DRM_COLOR_YCBCR_BT709;
+			break;
+		case libcamera::ColorSpace::YcbcrEncoding::Rec2020:
+			encoding = DRM_COLOR_YCBCR_BT2020;
+			break;
+		}
+
+		for (const auto &[id, name] : colorEncoding->enums()) {
+			if (id == encoding) {
+				colorEncoding_ = encoding;
+				break;
+			}
+		}
+	}
+
+	if (colorRange) {
+		drm_color_range range;
+
+		switch (cfg.colorSpace->range) {
+		case libcamera::ColorSpace::Range::Limited:
+		default:
+			range = DRM_COLOR_YCBCR_LIMITED_RANGE;
+			break;
+		case libcamera::ColorSpace::Range::Full:
+			range = DRM_COLOR_YCBCR_FULL_RANGE;
+			break;
+		}
+
+		for (const auto &[id, name] : colorRange->enums()) {
+			if (id == range) {
+				colorRange_ = range;
+				break;
+			}
+		}
+	}
+
+	if (!colorEncoding_ || !colorRange_)
+		std::cerr << "Color space " << cfg.colorSpace->toString()
+			  << " not supported by the display device."
+			  << " Colors may be wrong." << std::endl;
+
 	return 0;
 }
 
@@ -415,6 +490,11 @@ bool KMSSink::processRequest(libcamera::Request *camRequest)
 		drmRequest->addProperty(plane_, "CRTC_W", dst_.width);
 		drmRequest->addProperty(plane_, "CRTC_H", dst_.height);
 
+		if (colorEncoding_)
+			drmRequest->addProperty(plane_, "COLOR_ENCODING", *colorEncoding_);
+		if (colorRange_)
+			drmRequest->addProperty(plane_, "COLOR_RANGE", *colorRange_);
+
 		flags |= DRM::AtomicRequest::FlagAllowModeset;
 	}
 

src/cam/kms_sink.h

@@ -10,6 +10,7 @@
 #include <list>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <string>
 #include <utility>
 
@@ -67,6 +68,8 @@ private:
 	libcamera::PixelFormat format_;
 	libcamera::Size size_;
 	unsigned int stride_;
+	std::optional<unsigned int> colorEncoding_;
+	std::optional<unsigned int> colorRange_;
 
 	libcamera::Rectangle src_;
 	libcamera::Rectangle dst_;