This document discusses techniques for handling transparency in a deferred rendering system. It proposes using inferred lighting, where lighting and G-buffers are rendered at a lower resolution than the final output. Transparent objects are rendered on alternating lines. Discontinuity sensitive filtering is used to upsample the lighting, grouping pixels with similar normals. Transparent pixels are given special IDs to be lit correctly during the lighting pass. While this allows rendering transparency in deferred lighting, it has limitations such as reduced resolution for transparent objects and increased cost.

1. inferred lighting :
Handling Transparency
in Deferred Render system
OZ
http://ozlael.egloos.com

2. Deferred Render System
result normal depth

3. Deferred Render System
● Transparency is usually solved by splittin
g the Rendering pipeline in two parts
- Render opaque
- Render transparent objects
● Lighting inconsistency problem
● Split pipelines
● Need same pipeline between opaque an
d transparence

4. Deferred Rendering Transparency
in ShaderX7
alpha
G-buffer :
Transparent only every odd
horizontal line is rendered.

5. Deferred Rendering Transparency
in ShaderX7
C0 = CsA + Cd(1-A) or
C0 = Cd + (Cs-Cd)A

6. Inferred lighting
● Extension of Light Pre-pass
●
Mixed resolution rendering :
G-Buffers and Lighting are done at a lower resolut
ion that the final output pass.
● Use DSF filter
●
Same lit approach

7. Inferred lighting
N D DSF
Geometry Pass: 800x450
Light Pass: 800x450
Material Pass: 1280x720, 8x MSAA

8. Discontinuity Sensitive Filtering
(DSF)
Bilinear
DSF

9. DSF Buffer
In 16bit -> Object/Instance ID & Normal Group ID

10. DSF Buffer
Object/Instance ID

11. DSF Buffer
Normal Group ID

12. Up-Sample
High Res.
Low Res.

13. Up-Sample
High Res.
Low Res.

14. Up-Sample
a,b,c :
same DSF ID
X
d: High Res.
other DSF ID
Low Res.

15. Handling Alpha Objects
in Geometry Pass
G-Buffer into
2×2 quads transparency
1 transparent opaque
3 opaques

16. Handling Alpha Objects
in Geometry Pass
G-Buffer into
2×2 quads
3 transparents
1 opaque

17. Handling Alpha Objects
in Geometry Pass
Write stipple pattern

18. Handling Alpha Objects
in Geometry Pass
Alpha samples are lit same as opaque samples

19. Handling Alpha Objects
in Geometry Pass
DSF on opaque objects automatically ignores alpha samples
: different DSF ID

20. Handling Alpha Objects
in Geometry Pass
Alpha object shader knows stipple pattern :
Looks up proper sample locations in L-buffer

21. Inferred lighting
is the perfect one?
● Never!!!

22. Dark side
● Transparents being lit at 1/4 resolution
Forward Render Inferred Render

23. Dark side
● DSF filtering is not cheap
● Incur higher base cost
●
Assign stipple patterns for 3 alpha lightin
g layers
● Complex G-buffer reading at Post image
process
● In the H/W early-Z between G-pass and
M-pass is impossible (back buffer size di
ffer)

24. Dark side
● Assign the appropriate normal ID
Different normal ID Same normal ID
each faces each faces

25. Question?