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, 2 insertions, 2 deletions

diff --git a/source/blender/editors/interface/interface_anim.c b/source/blender/editors/interface/interface_anim.c
index d2a5ab80148..4fe555615c2 100644
--- a/source/blender/editors/interface/interface_anim.c
+++ b/source/blender/editors/interface/interface_anim.c
@@ -168,7 +168,7 @@ bool ui_but_anim_expression_set(uiBut *but, const char *str)
 			BLI_strncpy_utf8(driver->expression, str, sizeof(driver->expression));
 
 			/* tag driver as needing to be recompiled */
-			driver->flag |= DRIVER_FLAG_RECOMPILE;
+			BKE_driver_invalidate_expression(driver, true, false);
 
 			/* clear invalid flags which may prevent this from working */
 			driver->flag &= ~DRIVER_FLAG_INVALID;
@@ -237,7 +237,7 @@ bool ui_but_anim_expression_create(uiBut *but, const char *str)
 			BLI_strncpy_utf8(driver->expression, str, sizeof(driver->expression));
 
 			/* updates */
-			driver->flag |= DRIVER_FLAG_RECOMPILE;
+			BKE_driver_invalidate_expression(driver, true, false);
 			DEG_relations_tag_update(CTX_data_main(C));
 			WM_event_add_notifier(C, NC_ANIMATION | ND_KEYFRAME, NULL);
 			ok = true;