libcamera: matrix: Add read-only accessor to internal data

Add a data() function to the Matrix class to access the internal data.
This is useful for code that needs to use the matrix contents as a
linear array, as shown by the RkISP1::Ccm::process() function that needs
to copy the matrix data to a local variable. Simplify that function by
using the new accessor.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>

include/libcamera/internal/matrix.h

@@ -66,6 +66,8 @@ public:
 		return out.str();
 	}
 
+	Span<const T, Rows * Cols> data() const { return data_; }
+
 	Span<const T, Cols> operator[](size_t i) const
 	{
 		return Span<const T, Cols>{ &data_.data()[i * Cols], Cols };

src/ipa/rkisp1/algorithms/ccm.cpp

@@ -120,12 +120,7 @@ void Ccm::process([[maybe_unused]] IPAContext &context,
 		  [[maybe_unused]] const rkisp1_stat_buffer *stats,
 		  ControlList &metadata)
 {
-	float m[9];
-	for (unsigned int i = 0; i < 3; i++) {
-		for (unsigned int j = 0; j < 3; j++)
-			m[i * 3 + j] = frameContext.ccm.ccm[i][j];
-	}
-	metadata.set(controls::ColourCorrectionMatrix, m);
+	metadata.set(controls::ColourCorrectionMatrix, frameContext.ccm.ccm.data());
 }
 
 REGISTER_IPA_ALGORITHM(Ccm, "Ccm")

src/libcamera/matrix.cpp

@@ -52,6 +52,17 @@ LOG_DEFINE_CATEGORY(Matrix)
  * \return A string describing the matrix
  */
 
+/**
+ * \fn Matrix::data()
+ * \brief Access the matrix data as a linear array
+ *
+ * Access the contents of the matrix as a one-dimensional linear array of
+ * values in row-major order. The size of the array is equal to the product of
+ * the number of rows and columns of the matrix (Rows x Cols).
+ *
+ * \return A span referencing the matrix data as a linear array
+ */
+
 /**
  * \fn Span<const T, Cols> Matrix::operator[](size_t i) const
  * \brief Index to a row in the matrix