Support evaluating simple driver expressions without Python interpreter.

Recently @sergey found that hard-coding evaluation of certain very
common driver expressions without calling the Python interpreter
produces a 30-40% performance improvement. Since hard-coding is
obviously not suitable for production, I implemented a proper
parser and interpreter for simple arithmetic expressions in C.

The evaluator supports +, -, *, /, (), ==, !=, <, <=, >, >=,
and, or, not, ternary if; driver variables, frame, pi, True, False,
and a subset of standard math functions that seem most useful.

Booleans are represented as numbers, since within the supported
operation set it seems to be impossible to distinguish True/False
from 1.0/0.0. Boolean operations properly implement lazy evaluation
with jumps, and comparisons support chaining like 'a < b < c...'.

Expressions are parsed into a very simple stack machine program
that can then be safely evaluated in multiple threads.

Reviewers: sergey, campbellbarton

Differential Revision: https://developer.blender.org/D3698

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_fcurve.h b/source/blender/blenkernel/BKE_fcurve.h
index c0bbf146afd..3ae7ebf5d80 100644
--- a/source/blender/blenkernel/BKE_fcurve.h
+++ b/source/blender/blenkernel/BKE_fcurve.h
@@ -108,6 +108,9 @@ bool  driver_get_variable_property(
         struct ChannelDriver *driver, struct DriverTarget *dtar,
         struct PointerRNA *r_ptr, struct PropertyRNA **r_prop, int *r_index);
 
+bool BKE_driver_has_simple_expression(struct ChannelDriver *driver);
+void BKE_driver_invalidate_expression(struct ChannelDriver *driver, bool expr_changed, bool varname_changed);
+
 float evaluate_driver(struct PathResolvedRNA *anim_rna, struct ChannelDriver *driver,
                       struct ChannelDriver *driver_orig, const float evaltime);