libcamera: controls: Add support for string controls

String controls are stored internally as an array of char, but the
ControlValue constructor, get() and set() functions operate on an
std::string for convenience. Array of strings are thus not supported.

Unlike for other control types, the ControlInfo range reports the
minimum and maximum allowed lengths of the string (the minimum will
usually be 0), not the minimum and maximum value of each element.

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

1 files changed, 24 insertions, 6 deletions

diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
index 9c6cbffb..5cf6280e 100644
--- a/include/libcamera/controls.h
+++ b/include/libcamera/controls.h
@@ -26,6 +26,7 @@ enum ControlType {
 	ControlTypeInteger32,
 	ControlTypeInteger64,
 	ControlTypeFloat,
+	ControlTypeString,
 };
 
 namespace details {
@@ -64,6 +65,11 @@ struct control_type<float> {
 	static constexpr ControlType value = ControlTypeFloat;
 };
 
+template<>
+struct control_type<std::string> {
+	static constexpr ControlType value = ControlTypeString;
+};
+
 template<typename T, std::size_t N>
 struct control_type<Span<T, N>> : public control_type<std::remove_cv_t<T>> {
 };
@@ -76,7 +82,9 @@ public:
 	ControlValue();
 
 #ifndef __DOXYGEN__
-	template<typename T, typename std::enable_if_t<!details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<!details::is_span<T>::value &&
+						       !std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 	ControlValue(const T &value)
 		: type_(ControlTypeNone), numElements_(0)
 	{
@@ -84,7 +92,9 @@ public:
 		    &value, 1, sizeof(T));
 	}
 
-	template<typename T, typename std::enable_if_t<details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<details::is_span<T>::value ||
+						       std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 #else
 	template<typename T>
 #endif
@@ -115,7 +125,9 @@ public:
 	}
 
 #ifndef __DOXYGEN__
-	template<typename T, typename std::enable_if_t<!details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<!details::is_span<T>::value &&
+						       !std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 	T get() const
 	{
 		assert(type_ == details::control_type<std::remove_cv_t<T>>::value);
@@ -124,7 +136,9 @@ public:
 		return *reinterpret_cast<const T *>(data().data());
 	}
 
-	template<typename T, typename std::enable_if_t<details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<details::is_span<T>::value ||
+						       std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 #else
 	template<typename T>
 #endif
@@ -139,14 +153,18 @@ public:
 	}
 
 #ifndef __DOXYGEN__
-	template<typename T, typename std::enable_if_t<!details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<!details::is_span<T>::value &&
+						       !std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 	void set(const T &value)
 	{
 		set(details::control_type<std::remove_cv_t<T>>::value, false,
 		    reinterpret_cast<const void *>(&value), 1, sizeof(T));
 	}
 
-	template<typename T, typename std::enable_if_t<details::is_span<T>::value, std::nullptr_t> = nullptr>
+	template<typename T, typename std::enable_if_t<details::is_span<T>::value ||
+						       std::is_same<std::string, std::remove_cv_t<T>>::value,
+						       std::nullptr_t> = nullptr>
 #else
 	template<typename T>
 #endif