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

3 files changed, 13 insertions, 11 deletions

diff --git a/source/blender/editors/animation/drivers.c b/source/blender/editors/animation/drivers.c
index 43ee1133ea0..97a600f1301 100644
--- a/source/blender/editors/animation/drivers.c
+++ b/source/blender/editors/animation/drivers.c
@@ -745,11 +745,8 @@ bool ANIM_driver_vars_paste(ReportList *reports, FCurve *fcu, bool replace)
 		driver->variables.last = tmp_list.last;
 	}
 
-#ifdef WITH_PYTHON
 	/* since driver variables are cached, the expression needs re-compiling too */
-	if (driver->type == DRIVER_TYPE_PYTHON)
-		driver->flag |= DRIVER_FLAG_RENAMEVAR;
-#endif
+	BKE_driver_invalidate_expression(driver, false, true);
 
 	return true;
 }
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;
diff --git a/source/blender/editors/space_graph/graph_buttons.c b/source/blender/editors/space_graph/graph_buttons.c
index 642e8e074fa..1dc57a0da7d 100644
--- a/source/blender/editors/space_graph/graph_buttons.c
+++ b/source/blender/editors/space_graph/graph_buttons.c
@@ -817,13 +817,18 @@ static void graph_draw_driver_settings_panel(uiLayout *layout, ID *id, FCurve *f
 		col = uiLayoutColumn(layout, true);
 		block = uiLayoutGetBlock(col);
 
-		if ((G.f & G_SCRIPT_AUTOEXEC) == 0) {
-			/* TODO: Add button to enable? */
-			uiItemL(col, IFACE_("WARNING: Python expressions limited for security"), ICON_ERROR);
-		}
-		else if (driver->flag & DRIVER_FLAG_INVALID) {
+		if (driver->flag & DRIVER_FLAG_INVALID) {
 			uiItemL(col, IFACE_("ERROR: Invalid Python expression"), ICON_CANCEL);
 		}
+		else if (!BKE_driver_has_simple_expression(driver)) {
+			if ((G.f & G_SCRIPT_AUTOEXEC) == 0) {
+				/* TODO: Add button to enable? */
+				uiItemL(col, IFACE_("WARNING: Python expressions limited for security"), ICON_ERROR);
+			}
+			else {
+				uiItemL(col, IFACE_("Slow Python expression"), ICON_INFO);
+			}
+		}
 
 		/* Explicit bpy-references are evil. Warn about these to prevent errors */
 		/* TODO: put these in a box? */