Use reinterpret when applying solution_variables for visualization (#2388)

* remove todo and try reinterpret

* Revert "remove todo and try reinterpret"

This reverts commit d53b1f8.

* Just add a comment

reinterpret does not work because of Measurements non-bits type

---------

Co-authored-by: Hendrik Ranocha <[email protected]>

Author: benegee

src/visualization/utilities.jl

@@ -465,14 +465,9 @@ function get_unstructured_data(u, solution_variables, mesh, equations, solver, c
         raw_data = u
         n_vars = size(raw_data, 1)
     else
-        # FIXME: Remove this comment once the implementation following it has been verified
-        # Reinterpret the solution array as an array of conservative variables,
-        # compute the solution variables via broadcasting, and reinterpret the
-        # result as a plain array of floating point numbers
-        # raw_data = Array(reinterpret(eltype(u),
-        #        solution_variables.(reinterpret(SVector{nvariables(equations),eltype(u)}, u),
-        #                   Ref(equations))))
-        # n_vars = size(raw_data, 1)
+        # Similar to `save_solution_file` in `callbacks_step/save_solution_dg.jl`.
+        # However, we cannot use `reinterpret` here as `u` might have a non-bits type.
+        # See https://github.com/trixi-framework/Trixi.jl/pull/2388
         n_vars_in = nvariables(equations)
         n_vars = length(solution_variables(get_node_vars(u, equations, solver),
                                            equations))