diff --git a/source/blender/blenkernel/intern/fcurve.c b/source/blender/blenkernel/intern/fcurve.c
index f087727dd9c..90e40dd50fb 100644
--- a/source/blender/blenkernel/intern/fcurve.c
+++ b/source/blender/blenkernel/intern/fcurve.c
@@ -1277,8 +1277,12 @@ static void fcm_generator_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue,
 				value += data->coefficients[i] * powers[i];
 			
 			/* only if something changed, write *cvalue in one go */
-			if (data->poly_order)
-				*cvalue= value;
+			if (data->poly_order) {
+				if (data->flag & FCM_GENERATOR_ADDITIVE)
+					*cvalue += value;
+				else
+					*cvalue= value;
+			}
 				
 			/* cleanup */
 			if (powers) 
@@ -1296,8 +1300,12 @@ static void fcm_generator_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue,
 				value *= (cp[0]*evaltime + cp[1]);
 				
 			/* only if something changed, write *cvalue in one go */
-			if (data->poly_order)
-				*cvalue= value;
+			if (data->poly_order) {
+				if (data->flag & FCM_GENERATOR_ADDITIVE)
+					*cvalue += value;
+				else
+					*cvalue= value;
+			}
 		}
 			break;
 			
@@ -1323,8 +1331,10 @@ static void fcm_generator_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue,
 				case FCM_GENERATOR_FN_TAN: /* tangent wave */
 				{
 					/* check that argument is not on one of the discontinuities (i.e. 90deg, 270 deg, etc) */
-					if IS_EQ(fmod((arg - M_PI_2), M_PI), 0.0)
-						*cvalue= 0.0f; /* no value possible here */
+					if IS_EQ(fmod((arg - M_PI_2), M_PI), 0.0) {
+						if ((data->flag & FCM_GENERATOR_ADDITIVE) == 0)
+							*cvalue = 0.0f; /* no value possible here */
+					}
 					else
 						fn= tan;
 				}
@@ -1332,19 +1342,25 @@ static void fcm_generator_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue,
 				case FCM_GENERATOR_FN_LN: /* natural log */
 				{
 					/* check that value is greater than 1? */
-					if (arg > 1.0f)
+					if (arg > 1.0f) {
 						fn= log;
-					else
-						*cvalue= 0.0f; /* no value possible here */
+					}
+					else {
+						if ((data->flag & FCM_GENERATOR_ADDITIVE) == 0)
+							*cvalue = 0.0f; /* no value possible here */
+					}
 				}
 					break;
 				case FCM_GENERATOR_FN_SQRT: /* square root */
 				{
 					/* no negative numbers */
-					if (arg > 0.0f)
+					if (arg > 0.0f) {
 						fn= sqrt;
-					else
-						*cvalue= 0.0f; /* no vlaue possible here */
+					}
+					else {
+						if ((data->flag & FCM_GENERATOR_ADDITIVE) == 0)
+							*cvalue = 0.0f; /* no value possible here */
+					}
 				}
 					break;
 					
@@ -1353,8 +1369,14 @@ static void fcm_generator_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue,
 			}
 			
 			/* execute function callback to set value if appropriate */
-			if (fn)
-				*cvalue= data->coefficients[0]*fn(arg) + data->coefficients[3];
+			if (fn) {
+				float value= data->coefficients[0]*fn(arg) + data->coefficients[3];
+				
+				if (data->flag & FCM_GENERATOR_ADDITIVE)
+					*cvalue += value;
+				else
+					*cvalue= value;
+			}
 		}
 			break;
 
@@ -1446,6 +1468,7 @@ static void fcm_envelope_evaluate (FCurve *fcu, FModifier *fcm, float *cvalue, f
 	}
 	else {
 		/* evaltime occurs somewhere between segments */
+		// TODO: implement binary search for this to make it faster?
 		for (a=0; prevfed && fed && (a < env->totvert-1); a++, prevfed=fed, fed++) {  
 			/* evaltime occurs within the interval defined by these two envelope points */
 			if ((prevfed->time <= evaltime) && (fed->time >= evaltime)) {
diff --git a/source/blender/editors/space_graph/graph_buttons.c b/source/blender/editors/space_graph/graph_buttons.c
index 7892fe029b6..5207d4843f7 100644
--- a/source/blender/editors/space_graph/graph_buttons.c
+++ b/source/blender/editors/space_graph/graph_buttons.c
@@ -284,7 +284,7 @@ static void draw_modifier__generator(uiBlock *block, FCurve *fcu, FModifier *fcm
 	uiBut *but;
 	
 	/* set the height */
-	(*height) = 70;
+	(*height) = 90;
 	switch (data->mode) {
 		case FCM_GENERATOR_POLYNOMIAL: /* polynomial expression */
 			(*height) += 20*(data->poly_order+1) + 35;
@@ -302,9 +302,14 @@ static void draw_modifier__generator(uiBlock *block, FCurve *fcu, FModifier *fcm
 	
 	/* basic settings (backdrop + mode selector + some padding) */
 	//DRAW_BACKDROP((*height)); // XXX buggy...
-	but= uiDefButS(block, MENU, B_FMODIFIER_REDRAW, gen_mode, 10,cy,width-30,19, &data->mode, 0, 0, 0, 0, "Selects type of generator algorithm.");
-	uiButSetFunc(but, validate_fmodifier_cb, fcu, fcm);
-	cy -= 35;
+	uiBlockBeginAlign(block);
+		but= uiDefButS(block, MENU, B_FMODIFIER_REDRAW, gen_mode, 10,cy,width-30,19, &data->mode, 0, 0, 0, 0, "Selects type of generator algorithm.");
+		uiButSetFunc(but, validate_fmodifier_cb, fcu, fcm);
+		cy -= 20;
+		
+		uiDefButBitS(block, TOG, FCM_GENERATOR_ADDITIVE, B_FMODIFIER_REDRAW, "Additive", 10,cy,width-30,19, &data->flag, 0, 0, 0, 0, "Values generated by this modifier are applied on top of the existing values instead of overwriting them");
+		cy -= 35;
+	uiBlockEndAlign(block);
 	
 	/* now add settings for individual modes */
 	switch (data->mode) {
diff --git a/source/blender/makesdna/DNA_anim_types.h b/source/blender/makesdna/DNA_anim_types.h
index f51300e5f7b..9112a714857 100644
--- a/source/blender/makesdna/DNA_anim_types.h
+++ b/source/blender/makesdna/DNA_anim_types.h
@@ -91,6 +91,12 @@ enum {
 	FCM_GENERATOR_EXPRESSION,
 } eFMod_Generator_Modes;
 
+/* generator flags */
+enum {
+		/* generator works in conjunction with other modifiers (i.e. doesn't replace those before it) */
+	FCM_GENERATOR_ADDITIVE	= (1<<0),
+} eFMod_Generator_Flags;
+
 /* 'function' generator types */
 enum {
 	FCM_GENERATOR_FN_SIN	= 0,
@@ -231,7 +237,7 @@ typedef struct FCurve {
 		/* motion data */
 	BezTriple *bezt;		/* user-editable keyframes (array) */
 	FPoint *fpt;			/* 'baked/imported' motion samples (array) */
-	int totvert;			/* total number of points which define the curve (i.e. size of arrays in FPoints) */
+	unsigned int totvert;	/* total number of points which define the curve (i.e. size of arrays in FPoints) */
 	
 		/* value cache + settings */
 	float curval;			/* value stored from last time curve was evaluated */