Depsgraph: fix false positive time dependencies for simple drivers.

The dependency graph has to know whether a driver must be re-evaluated
every frame due to a dependency on the current frame number. For python
drivers it was using a heuristic based on searching for certain sub-
strings in the expression, notably including '('.

When the expression is actually evaluated using Python, this can't be
easily improved; however if the Simple Expression evaluator is used,
this check can be done precisely by accessing the parsed data.

Differential Revision: https://developer.blender.org/D6624

2 files changed, 19 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_expr_pylike_eval.h b/source/blender/blenlib/BLI_expr_pylike_eval.h
index b8bf88dd85b..1db91ea4205 100644
--- a/source/blender/blenlib/BLI_expr_pylike_eval.h
+++ b/source/blender/blenlib/BLI_expr_pylike_eval.h
@@ -45,6 +45,7 @@ typedef enum eExprPyLike_EvalStatus {
 void BLI_expr_pylike_free(struct ExprPyLike_Parsed *expr);
 bool BLI_expr_pylike_is_valid(struct ExprPyLike_Parsed *expr);
 bool BLI_expr_pylike_is_constant(struct ExprPyLike_Parsed *expr);
+bool BLI_expr_pylike_is_using_param(struct ExprPyLike_Parsed *expr, int index);
 ExprPyLike_Parsed *BLI_expr_pylike_parse(const char *expression,
                                          const char **param_names,
                                          int param_names_len);
diff --git a/source/blender/blenlib/intern/expr_pylike_eval.c b/source/blender/blenlib/intern/expr_pylike_eval.c
index 43923ce8c98..6020dc41a62 100644
--- a/source/blender/blenlib/intern/expr_pylike_eval.c
+++ b/source/blender/blenlib/intern/expr_pylike_eval.c
@@ -140,6 +140,24 @@ bool BLI_expr_pylike_is_constant(ExprPyLike_Parsed *expr)
   return expr != NULL && expr->ops_count == 1 && expr->ops[0].opcode == OPCODE_CONST;
 }
 
+/** Check if the parsed expression uses the parameter with the given index. */
+bool BLI_expr_pylike_is_using_param(ExprPyLike_Parsed *expr, int index)
+{
+  int i;
+
+  if (expr == NULL) {
+    return false;
+  }
+
+  for (i = 0; i < expr->ops_count; i++) {
+    if (expr->ops[i].opcode == OPCODE_PARAMETER && expr->ops[i].arg.ival == index) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 /** \} */
 
 /* -------------------------------------------------------------------- */