Wrong trail direction with motion blur

[Sylk]

Hi Karba

Is it normal that blur preceeds the object move??

Original for sure but, into the real world, it seems the trail follows the object, not object that follows the trail. Right?

[Karba]

What do you mean by "object" and "blur"? Is should be just blurred object,

[Sylk]

Object : 1 sphere, native 3dsmax primitive geometry.
Blur : a visual trail leaved by a moving object.

"Head" : the sphere itself, as geometry and position.
"Trail" : the blur remanence emitted by the head.
"Tail" : the end of Trail. Opposite to the head.

---

1 FScamera, 1 sphere. The camera doesn't move. Let's say the ball starts from X=0 and goes to X=100.

Expected : with correct motion blur, when the ball is at X=50, the trail tail is between X=0 and X=50.

Happens : with fstorm motion blur, the trail tail is between X=50 and X=100 !! The tail runs before the head, instead of after. The tail reaches the finish line before the head.


It's more a "predictive blur" than a motion blur.

Look at the pictures. The ball comes from blue box. Objects position is the same on both. Only Motion Blur switched [ OFF | ON ].
As you can see, the blur doesn't relie ball to the blue box, the trail seems to be oriented to the same direction of the moving direction (where head goes), instead of the opposite direction (where head comes from) !

---

Other words to describe the behavior :

- Let's say you set the motion blur duration to 10.
- At frame f0 the ball is static, no blur appears on the render. This is normal.
- At f1 the ball starts moving, blur appears on the render. This is ok, BUT the blur (trail) goes from the current position f1 to the future position f11 !

What is the expected behavior? -> The blur should be drawn from the past position f0 to the current position f1.

Note: However it would be nice to leave this issue as a possible setting ; an option to choose if the tail have to preceed or just follow the head as normal.

Hope it is more clear for you.

[Karba]

The behaviour is correct.

If you don't use motion blur, the object position is at frame start.
if you use motion blur with duration 1.0, the object position is blured from frame start, to frame end.

[Sylk]

Hmm ok. You right. My misunderstand of motion blur.

So, please, could you just add a checkbox to generate the blur to the opposite direction (from past to current) ? This will easily allow trail effect.