Fix for [#30495] Framerate goes crazy after changing Sync mode from "Frame Dropping" to "no Sync" while playing anim

2 files changed, 4 insertions, 2 deletions

diff --git a/source/blender/editors/include/ED_screen_types.h b/source/blender/editors/include/ED_screen_types.h
index 51699d095ae..6f7d0c55b9a 100644
--- a/source/blender/editors/include/ED_screen_types.h
+++ b/source/blender/editors/include/ED_screen_types.h
@@ -41,6 +41,7 @@ typedef struct ScreenAnimData {
 	short flag;			/* flags for playback */
 	int sfra;			/* frame that playback was started from */
 	int nextfra;		/* next frame to go to (when ANIMPLAY_FLAG_USE_NEXT_FRAME is set) */
+	double last_duration;	/* used for frame dropping */
 } ScreenAnimData;
 
 /* for animplayer */
diff --git a/source/blender/editors/screen/screen_ops.c b/source/blender/editors/screen/screen_ops.c
index b1d718f08b5..697f40a507a 100644
--- a/source/blender/editors/screen/screen_ops.c
+++ b/source/blender/editors/screen/screen_ops.c
@@ -2915,13 +2915,12 @@ static int screen_animation_step(bContext *C, wmOperator *UNUSED(op), wmEvent *e
 		}
 		else {
 			if (sync) {
-				int step = floor(wt->duration * FPS);
+				int step = floor((wt->duration - sad->last_duration) * FPS);
 				/* skip frames */
 				if (sad->flag & ANIMPLAY_FLAG_REVERSE)
 					scene->r.cfra -= step;
 				else
 					scene->r.cfra += step;
-				wt->duration -= ((double)step)/FPS;
 			}
 			else {
 				/* one frame +/- */
@@ -2932,6 +2931,8 @@ static int screen_animation_step(bContext *C, wmOperator *UNUSED(op), wmEvent *e
 			}
 		}
 		
+		sad->last_duration = wt->duration;
+
 		/* reset 'jumped' flag before checking if we need to jump... */
 		sad->flag &= ~ANIMPLAY_FLAG_JUMPED;