Functions: support optional outputs in multi-function

Sometimes not all outputs of a multi-function are required by the
caller. In those cases it would be a waste of compute resources
to calculate the unused values anyway. Now, the caller of a
multi-function can specify when a specific output is not used.
The called function can check if an output is unused and may
ignore it. Multi-functions can still computed unused outputs as
before if they don't want to check if a specific output is unused.

The multi-function procedure system has been updated to support
ignored outputs in call instructions. An ignored output just has no
variable assigned to it.

The field system has been updated to generate a multi-function
procedure where unused outputs are ignored.

1 files changed, 23 insertions, 8 deletions

diff --git a/source/blender/functions/intern/multi_function_procedure_executor.cc b/source/blender/functions/intern/multi_function_procedure_executor.cc
index 38b26415779..b97282accdd 100644
--- a/source/blender/functions/intern/multi_function_procedure_executor.cc
+++ b/source/blender/functions/intern/multi_function_procedure_executor.cc
@@ -978,7 +978,7 @@ static bool evaluate_as_one(const MultiFunction &fn,
     return false;
   }
   for (VariableState *state : param_variable_states) {
-    if (!state->is_one()) {
+    if (state != nullptr && !state->is_one()) {
       return false;
     }
   }
@@ -997,8 +997,13 @@ static void execute_call_instruction(const MFCallInstruction &instruction,
 
   for (const int param_index : fn.param_indices()) {
     const MFVariable *variable = instruction.params()[param_index];
-    VariableState &variable_state = variable_states.get_variable_state(*variable);
-    param_variable_states[param_index] = &variable_state;
+    if (variable == nullptr) {
+      param_variable_states[param_index] = nullptr;
+    }
+    else {
+      VariableState &variable_state = variable_states.get_variable_state(*variable);
+      param_variable_states[param_index] = &variable_state;
+    }
   }
 
   /* If all inputs to the function are constant, it's enough to call the function only once instead
@@ -1008,19 +1013,29 @@ static void execute_call_instruction(const MFCallInstruction &instruction,
 
     for (const int param_index : fn.param_indices()) {
       const MFParamType param_type = fn.param_type(param_index);
-      VariableState &variable_state = *param_variable_states[param_index];
-      variable_states.add_as_param__one(variable_state, params, param_type, mask);
+      VariableState *variable_state = param_variable_states[param_index];
+      if (variable_state == nullptr) {
+        params.add_ignored_single_output();
+      }
+      else {
+        variable_states.add_as_param__one(*variable_state, params, param_type, mask);
+      }
     }
 
     fn.call(IndexRange(1), params, context);
   }
   else {
-    MFParamsBuilder params(fn, mask.min_array_size());
+    MFParamsBuilder params(fn, &mask);
 
     for (const int param_index : fn.param_indices()) {
       const MFParamType param_type = fn.param_type(param_index);
-      VariableState &variable_state = *param_variable_states[param_index];
-      variable_states.add_as_param(variable_state, params, param_type, mask);
+      VariableState *variable_state = param_variable_states[param_index];
+      if (variable_state == nullptr) {
+        params.add_ignored_single_output();
+      }
+      else {
+        variable_states.add_as_param(*variable_state, params, param_type, mask);
+      }
     }
 
     fn.call(mask, params, context);