Compositor: Allow delayed typing for results

This patch allows result to have their types set after construction but
before allocation.

source/blender/compositor/realtime_compositor/COM_result.hh

@@ -160,6 +160,9 @@ class Result {
   MetaData meta_data;
 
  public:
+  /* Construct a result within the given context. */
+  Result(Context &context);
+
   /* Construct a result of the given type and precision within the given context. */
   Result(Context &context, ResultType type, ResultPrecision precision);
 
@@ -337,6 +340,9 @@ class Result {
   /* Returns the precision of the result. */
   ResultPrecision precision() const;
 
+  /* Sets the type of the result. */
+  void set_type(ResultType type);
+
   /* Sets the precision of the result. */
   void set_precision(ResultPrecision precision);
 

source/blender/compositor/realtime_compositor/intern/result.cc

@@ -19,6 +19,8 @@
 
 namespace blender::realtime_compositor {
 
+Result::Result(Context &context) : context_(&context) {}
+
 Result::Result(Context &context, ResultType type, ResultPrecision precision)
     : context_(&context), type_(type), precision_(precision)
 {
@@ -646,6 +648,13 @@ ResultPrecision Result::precision() const
   return precision_;
 }
 
+void Result::set_type(ResultType type)
+{
+  /* Changing the type can only be done if it wasn't allocated yet. */
+  BLI_assert(!this->is_allocated());
+  type_ = type;
+}
+
 void Result::set_precision(ResultPrecision precision)
 {
   /* Changing the precision can only be done if it wasn't allocated yet. */