From 6d3965cf0137fcc6e87fd1cbd3833719a4ac5dbe Mon Sep 17 00:00:00 2001
From: Christian Rauch <Rauch.Christian@gmx.de>
Date: Mon, 5 Aug 2024 19:10:35 +0200
Subject: [PATCH] clarify the value range and meaning of the extracted
 ControlId extent

---
 src/CameraNode.cpp  |  2 +-
 src/type_extent.cpp | 10 ++++++++--
 src/type_extent.hpp |  8 +++++++-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/CameraNode.cpp b/src/CameraNode.cpp
index 0ce9f287..8f83933a 100644
--- a/src/CameraNode.cpp
+++ b/src/CameraNode.cpp
@@ -451,7 +451,7 @@ CameraNode::declareParameters()
     }
 
     // format type description
-    const bool scalar = (extent == 0) || (extent == 1);
+    const bool scalar = (extent == 0);
     const bool dynamic = (extent == libcamera::dynamic_extent);
     const std::string cv_type_descr =
       scalar ? "scalar" : "array[" + (dynamic ? std::string() : std::to_string(extent)) + "]";
diff --git a/src/type_extent.cpp b/src/type_extent.cpp
index d67f28b0..b189cda4 100644
--- a/src/type_extent.cpp
+++ b/src/type_extent.cpp
@@ -19,6 +19,7 @@ template<typename T, std::enable_if_t<!libcamera::details::is_span<T>::value, bo
 std::size_t
 get_extent(const libcamera::Control<T> &)
 {
+  // return an extent of 0 for non-span types
   return 0;
 }
 
@@ -26,7 +27,12 @@ template<typename T, std::enable_if_t<libcamera::details::is_span<T>::value, boo
 std::size_t
 get_extent(const libcamera::Control<T> &)
 {
-  return libcamera::Control<T>::type::extent;
+  // return the span extent, excluding 0
+  // This assumes that libcamera does not define control types
+  // with a fixed size span that does not hold any elements
+  constexpr std::size_t extent = libcamera::Control<T>::type::extent;
+  static_assert(extent != 0);
+  return extent;
 }
 
 #define IF(T)                                  \
@@ -35,7 +41,7 @@ get_extent(const libcamera::Control<T> &)
 
 
 std::size_t
-get_extent(const libcamera::ControlId *id)
+get_extent(const libcamera::ControlId *const id)
 {
 #if LIBCAMERA_VER_GE(0, 1, 0)
   IF(AeEnable)
diff --git a/src/type_extent.hpp b/src/type_extent.hpp
index 40b1efda..ca9b9d19 100644
--- a/src/type_extent.hpp
+++ b/src/type_extent.hpp
@@ -6,5 +6,11 @@ namespace libcamera
 class ControlId;
 }
 
+/**
+ * @brief get the extent of a libcamera::ControlId
+ * @param id
+ * @return the extent of the control: 0 if the control is not a span,
+ *         otherwise [1 ... libcamera::dynamic_extent]
+ */
 std::size_t
-get_extent(const libcamera::ControlId *id);
+get_extent(const libcamera::ControlId *const id);