[libcamera-devel] [PATCH v5 01/12] libcamera: stream: Add stream hints to StreamConfiguration

[Naushir Patuck]

Add a new hints flags field in the StreamConfiguration structure to allow the
application to specify certain intended behavior when driving libcamera.
Pipeline handlers are expected to look at these hint flags and may optimise
internal operations based on them.

Currently, only one flag is listed, OptionalStream, which the application can
set to inform the pipeline handler that a buffer may not be provided on every
Request for a given stream.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 include/libcamera/stream.h |  8 ++++++++
 src/libcamera/stream.cpp   | 24 ++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/libcamera/stream.h b/include/libcamera/stream.h
index 29235ddf0d8a..233ff0450451 100644
--- a/include/libcamera/stream.h
+++ b/include/libcamera/stream.h
@@ -13,6 +13,8 @@
 #include <string>
 #include <vector>
 
+#include <libcamera/base/flags.h>
+
 #include <libcamera/color_space.h>
 #include <libcamera/framebuffer.h>
 #include <libcamera/geometry.h>
@@ -51,6 +53,12 @@ struct StreamConfiguration {
 
 	std::optional<ColorSpace> colorSpace;
 
+	enum class Hint {
+		None = 0,
+		OptionalStream = (1 << 0),
+	};
+	Flags<Hint> hints;
+
 	Stream *stream() const { return stream_; }
 	void setStream(Stream *stream) { stream_ = stream; }
 	const StreamFormats &formats() const { return formats_; }
diff --git a/src/libcamera/stream.cpp b/src/libcamera/stream.cpp
index 67f308157fbf..b7de85f8b9c7 100644
--- a/src/libcamera/stream.cpp
+++ b/src/libcamera/stream.cpp
@@ -349,6 +349,30 @@ StreamConfiguration::StreamConfiguration(const StreamFormats &formats)
  * color spaces can be supported and in what combinations.
  */
 
+/**
+ * \enum StreamConfiguration::Hint
+ * \brief List of available hint flags provided by the application for a stream
+ *
+ * \var StreamConfiguration::Hint::None
+ * No hints for this stream.
+ * \var StreamConfiguration::Hint::OptionalStream
+ * Informs the pipeline handler that the application may not always provide a
+ * buffer for the configured stream in every Request. This may ensure the
+ * pipeline handler allocates additional stream buffers for internal use.
+ */
+
+/**
+ * \var StreamConfiguration::hints
+ * \brief Application provided StreamConfiguration::Hint flags for specific
+ * stream behavior
+ *
+ * Provides hints from the application to the pipeline handlers on how it
+ * intends on handling a given configured stream. These hints may alter the
+ * behavior of the pipeline handlers, for example, by allocating additional
+ * buffers for internal use if an application does not guarantee buffers will be
+ * provided in every Request for a stream.
+ */
+
 /**
  * \fn StreamConfiguration::stream()
  * \brief Retrieve the stream associated with the configuration
-- 
2.25.1