Motion blur in DX9

1. Pixel Motion Blur
http://ozlael.egloos.com

2. Motion blur
• What is motion blur?
– Rapidly moving objects appear to be blurred in
direction of motion
• What causes motion blur?
– In real cameras, film is exposed to moving scene
while shutter is open
• Why do motion blur?
– Adds realism, cinematic look to games
– 24fps with motion blur can look better than 60fps
without

3. Trails behind objects
● Not the same as real motion blur

4. Radial Blur
● 2D Effect

5. Depth-Base Velocity
depth
● For static mesh
velocity

6. Using Accumulation Buffer
● Large time interval between multiple rend
ering

7. Image space (2.5D) motion blur
● Pixel Process Motion Blur

8. Pixel Motion Blur
● Works as a Post Process
● Blurs an image of the scene based on obj
ect velocities
● Not a physically correct but plausible

9. Better than Accumulation Buffer

10. Algorithm
● 1. Render scene to texture
- At current time
● 2. Calculate velocity at each pixel
- Another Buffer
- Calculate current position – previous po
sition
● 3. Render motion blurred scene

11. Velocity

12. Step 1

13. Step 2

14. Step 3

15. What is the Fault?

16. What is the Fault?

17. What are the fault?
● Without knowledge of object edges
● Velocity outside silhouette of object is zer
o(= no blur)
● Solution : Geometry distortion

18. Stretch object geometry

19. Matthias Wloka's trick

20. Matthias Wloka's trick
● stretch object geometry between previous
and current position
● Compare normal direction with motion ve
ctor using dot product
● If normal is pointing in direction of motio
n, transform vertex by current transform,
else transform it by the previous transfor
m
● Not perfect, but it works

21. Matthias Wloka's trick

22. Original Image

23. Stretched Geometry

24. Velocity Visualization

25. Motion Blurred Image

26. Well... Not Perfect
● Not information to avoid occlusion artifact
s
● Number of samples needed depends on a
mount of motion
- 8 samples is good, 16 is better
- Ironically, more samples will reduce fra
me rate, and therefore increase motion m
agnitude

27. Occlusion fault

28. Resolve occlusion
Color Motion
Depth

29. Iterative sampling
● First pass uses 8 samples
● Ping-pong results
● Second pass uses blurred results, this res
ults in 8 * 8 samples (virtually 64)
● 3rd = 512 samples, 4th = 4096, etc

30. Iterative sampling

31. Skinning limitation in DX9
● 256 vertex shader constant registers limit
● Our characters have an average of 54 Mat
rix per drawcall
● For motion blur we need previous frame b
one(Matrix)s transformations
● If Bone == Quaternion & Tlanslation then
must be Uniform Transform
● Or decrease bone count

32. So....?
● In RS3 for Now
● Using Pixel Motion Blur = Only Object’s Tr
ansform
● Animation’s Proceed = Using Accumulatio
n Buffer
● Any suggestion?

33. Reference
● Stupid OpenGL ShaderTricks -Simon Green
● Pixmotor:A Pixel Motion Integrator - Ivan Neulander
● Interactive Real-Time Motion Blur - Matthias M. Wloka & Robert C.
Zeleznik
● Motion Blur Using Geometry and Shading Distortion - Natalya Tata
rchuk, Chris Brennan, John Isidoro
● Pixel Motion Blur - Direct X SDK
● Motion Blur as a Post-Processing Effect - GPU Gems 3
● CrysisNext Gen Effects -TiagoSousa
● Hardware Accelerated Motion Blur Generation -Clement Shimizu, A
mitShesh, BaoquanChen
● Motionblur - Myia
● http://incrysis.com/forums/
● Capcom presentation on Lost Planet