interactive rendering of atmospheric scattering effects using graphics hardware

Atmospheric Effects

Interactive Rendering of Interactive Rendering of Atmospheric Scattering Effects Atmospheric Scattering Effects

Using Graphics HardwareUsing Graphics Hardware

Interactive Rendering of Interactive Rendering of Atmospheric Scattering Effects Atmospheric Scattering Effects

Using Graphics HardwareUsing Graphics Hardware

Tsuyoshi YamamotoTsuyoshi Yamamoto

Tomoyuki NishitaTomoyuki Nishita Tokyo UniversityTokyo University

Yoshinori DobashiYoshinori Dobashi Hokkaido UniversityHokkaido University

Hokkaido UniversityHokkaido University

Atmospheric Effects

OverviewOverview• Introduction

• Rendering Light Beams

• Rendering the Earth’s Atmosphere

- motivation- previous work

- basic Idea- problems- high quality rendering

- rendering skyrendering the earth viewed from space

• Results

• Conclusion

Atmospheric Effects







• Results

• Conclusion

• Introduction- motivation- previous work

• Rendering Light Beams- basic Idea- problems- high quality rendering

• Rendering the Earth’s Atmosphere- rendering skyrendering the earth viewed from space

• Results

• Conclusion

Atmospheric Effects







• Results

• Conclusion

Atmospheric Effects

• Real-time rendering of realistic imagesReal-time rendering of realistic images

• Atmospheric Scattering Effects

MotivationMotivation

- spotlights- sunlight through windows- earth’s atmosphere

Real-time rendering of atmospheric effectsReal-time rendering of atmospheric effects Real-time rendering of atmospheric effectsReal-time rendering of atmospheric effects

• Our Goal:

requires long computation time

- scattering and absorption of light due to small particles

Atmospheric Effects

Previous Work

- use of voxels to store the intensity of light

• Volume rendering [e.g. Behrens98, Westermann98]

- consuming texture memory for volume data

- difficult to capture the edges of shafts of light

edges ofspotlight

edges ofshadows

Atmospheric Effects

Previous Work

• Interleaved sampling [Keller01]

- a general and efficient solution to the sampling

problem- not optimal for rendering atmospheric scattering

• 2D texture based approach [Dobashi01, Everitt99]

• Earth’s atmosphere

- no methods for real-time rendering of realistic images

- use of shadow and projective texture mapping

- artifacts due to sampling errors

Atmospheric Effects

Proposed Method

• Rendering light beams- point/infinite light sources

- uniform density of atmospheric particles

• Rendering earth’s atmosphere- sky

- density decreases exponentially according to

the height from the ground

- the earth viewed from space

• Precise and efficient rendering of atmospheric effects

Atmospheric Effects







• Results

• Conclusion

Atmospheric Effects

point source

Ieye

viewpoint scattered light

T

ls dttgtHtII0

),()(),()(

Intensity at viewpointIntensity at viewpoint

Shading Model for Light Beams

Atmospheric Effects

Is

t

point light

viewpoint

P

Il

tH )( ： visibility function

Shading Model for Light Beams

T

ls dttgtHtII0

),()(),()(

： intensity of lightl tI ),(

： attenuation functiontg ),(


Atmospheric Effects

Basic IdeaBasic IdeaIntensity at viewpointIntensity at viewpoint

[Dobashi00]

T

ls dttgtHtII0

),()(),()(

n

k 1l tI ),( tg ),( tH )(

screensampling planeviewpoint

point light

computed at lattices

Atmospheric Effects

n

k 1

Basic IdeaBasic Idea

l tI ),( tg ),(


T

ls dttgtHtII0

),()(),()( tH )(

light map

texture mapping

light map

viewpoint

point light

[Dobashi00]

Atmospheric Effects

n

k 1


l tI ),( tg ),(


T

ls dttgtHtII0

),()(),()( tH )(

viewpoint

point light

[Dobashi00]

object

shadowmapping

Atmospheric Effects

n

k 1


l tI ),( tg ),(


T

ls dttgtHtII0

),()(),()( tH )(

viewpoint

point light

render sampling planeswith additive blending

[Dobashi00]

object

shadowmapping

Atmospheric Effects

• accumulation of errors in proportion to number of sampling planes

• quantization with 8 bit precision in most hardware

- artifacts due to quantization errors

ProblemsProblems

• Many planes/lattices for high quality image

• Accuracy number of planes number of lattice points

- increase in rendering time

• rendering time number of planes number of lattice points

sampling errorspseudo-contours

Atmospheric Effects

High Quality RenderingHigh Quality Rendering

n

k 1s tI ),(

T

ls dttgtHtII0

),()(),()(

tt

tlks

k

k

dttgtHtItI ),()(),(),( Is

t

point light

P

Il

t


Atmospheric Effects


n

k 1s tI ),(

T

ls dttgtHtII0

),()(),()(

tt

tlks

k

k


t

point light

P

Il

t


changes severely changes smoothly

const. in t

Atmospheric Effects


n

k 1s tI ),(

T

ls dttgtHtII0

),()(),()(

tt

tlks

k

k


t

point light

P

Il

t


fh fl

tt

tl

k

k

dttHtI )(),( tt

t

k

k

dttg ),( x

Atmospheric Effects


n

k 1s tI ),(

T

ls dttgtHtII0

),()(),()(

tt

tlks

k

k


point light

Il


fh fl

tt

tl

k

k

dttHtI )(),( tt

t

k

k

dttg ),( x

= 1.0

scattered light

scattering component

Atmospheric Effects


n

k 1s tI ),(

T

ls dttgtHtII0

),()(),()(

tt

tlks

k

k


point light

Il


fh fl

tt

tl

k

k

dttHtI )(),( tt

t

k

k

dttg ),( x

scattering component

ratio of reached light

object

Illumination component

Atmospheric Effects

sub-planes for accurate sampling

use of texture to store pre-integrated values


• Illumination component fh: tt

tl

k

k

dttHtI )(),(

• Scattering component fl: tt

t

k

k

dttg ),(

- changes smoothly- can be sampled at a large interval

- includes visibility H and intensity distribution Il

- must be sampled at a short interval

Atmospheric Effects








tl

k

k

dttHtI )(),(


t

k

k

dttg ),(

Atmospheric Effects

Textures for Scattering ComponentTextures for Scattering Component

tt

t

cckl

k

k

dts

tsFtf

2

))(exp(),(),(

(point light)

tk

viewpoint

point light

s

t

P’

tP

： phase function)(, F

c： density： attenuation ratio

： phase angle

s： distance between light and P’

t： distance between viewpoint and P’

tk： distance between viewpoint and P sampling

plane k

samplingplane k+1

Atmospheric Effects

P’P

tt

t

cckl

k

k

dts

tsFtf

2

))(exp(),(),(

s

point light

(point light)

samplingplane k

samplingplane k+1

tk

viewpoint

t

t

- local coordinate UV

P(u, v)

Q

P’(u’, v)

U

V

ktuut '

su /'cos 222 ' vus


Atmospheric Effects

s

point light

P’(u’, v)

samplingplane k

samplingplane k+1

tk

viewpoint

t

tP(u, v)

),,(),,( vuqcvuf kl

)exp( kck tc

''

))''(exp(

)),'/'((cos),,(

22

22

221

duvu

uuvu

vuuFvuq

c

tu

uc

x

kc : constant for each sampling plane

vuq ),,( : 2D texture

fl is evaluated precisely since texture stores integrated values

fl is evaluated precisely since texture stores integrated values

Q

U

Vreducing quantization errorsreducing quantization errors


Atmospheric Effects








tl

k

k

dttHtI )(),(


t

k

k

dttg ),(

Atmospheric Effects

light

Computation of Illumination ComponentComputation of Illumination Component

tt

tlkh

k

k

dttHtItf )(),(),(

viewpoint

sampling plane

sub-plane

- mk sub-planes between

sampling planes k and k+1

- mk is determined adaptively

strong intensity many sub-planes

1

0

)(),(1

),(km

jjjl

kkh rHrI

mtf

rj : distance between viewpoint and

sub-plane j

Atmospheric Effects

light

viewpoint

sampling plane

sub-plane

• Determining number of sub-planes, Determining number of sub-planes, mmkk

1. shoot a ray

2. compute intensity of scattered light

3. generate sub-planes in proportion to intensity

use textures forscattering component

Intensity of scattered light

mk

:user-specified threshold

same contribution same contribution of each sub-plane of each sub-plane to pixel intensityto pixel intensity

same contribution same contribution of each sub-plane of each sub-plane to pixel intensityto pixel intensity

Computation of Illumination ComponentComputation of Illumination Component

Atmospheric Effects







• Results

• Conclusion

Atmospheric Effects

Rendering Earth’s AtmosphereRendering Earth’s Atmosphere• No shadows of objects• Rendering Sky

- extending method for light beams

• Rendering the earth viewed from space

earth

viewpoint

atmosphere

Atmospheric Effects




atmosphere

viewpoint

earth- atmosphere is very thin layer covering the earth

Atmospheric Effects




atmosphere

viewpoint

earth

sampling spheres

- use of sampling spheres instead of sampling plane

- atmosphere is very thin layer covering the earth

Atmospheric Effects




- atmosphere is very thin layer covering the earth

- use of sampling spheres instead of sampling plane

atmosphere

viewpoint

earth

sampling spheres

Atmospheric Effects

• Intensity at viewpointIntensity at viewpoint

Rendering SkyRendering Sky

T

vlsunv dttgsgtFII0

),(),(),(),()()(

sunI )( : intensity of sunlight

l sg ),( : attenuation ratio between Ps and P

v tg ),( : attenuation ratio between P and Pv

F ),( : phase function

: density of particlest ),(

st

P viewpoint

earth

Ps

atmosphere

Pv

sunI

Atmospheric Effects

Rendering SkyRendering Sky• Intensity at viewpointIntensity at viewpoint

T

vlsunv dttgsgtFII0

),(),(),(),()()(

sunI )( : intensity of sunlight

v tg ),( : attenuation ratio between Ps and P

l sg ),( : attenuation ratio between P and Pv


: density of particlest ),(

earth

viewpoint

atmosphere

Pv

Atmospheric Effects

Rendering SkyRendering Sky• Intensity at viewpointIntensity at viewpoint

earth

viewpoint

atmosphere

Pv

n

k

k

jjvlsunv tgsgtFII

1

1

1

),(),()(),()()( R

P

Ps

k

k+1sunI )( : intensity of sunlight

l sg ),( : attenuation ratio between Ps and P


),( kv tg : attenuation between sampling planes k and k+1

t)(R : cumulative density of particles between sampling planes k and k+1

sunI

Atmospheric Effects

earth


• AlgorithmAlgorithm• create textures of gl , gv , R• for k = n to 1, repeat:

- map gl , gv , R textures

onto sampling plane k


n

k

k

jjvlsunv tgsgtFII

1

1

1

),(),()(),()()( R

viewpointPv

Atmospheric Effects

earth






n

k

k

jjvlsunv tgsgtFII

1

1

1

),(),()(),()()( R

- compute IsunF at lattice points

viewpointPv

Atmospheric Effects

earth





- draw plane with blending:FB = FB x gv + F x R x gl (FB: frame buffer)

intensity of scattered lightattenuation


n

k

k

jjvlsunv tgsgtFII

1

1

1

),(),()(),()()( R

viewpointPv

- compute IsunF at lattice points

Atmospheric Effects

Rendering SkyRendering Sky• Textures of Textures of gl, gv , R

sunI

P viewpoint

earth

Ps

satmosphere: extinction coefficient (constant)

: density of particles)exp()( ahh (a: const)

sPPdll

0))()(exp( sl PPg ),(

Pv

h

Atmospheric Effects


sunI

P viewpoint

earth

Ps

atmosphere

h

l

s

• Textures of Textures of gl, gv , R

Pv

: extinction coefficient (constant): density of particles

)exp()( ahh (a: const)

sPPdll

0))()(exp( sl PPg ),(

),,(),( llsl hgPPg

Atmospheric Effects

),,(),( vvvv hgPPg

),,(),( vv hRPPR

),,(),( llsl hgPPg


sunI

P viewpoint

earth

Ps

atmosphere

h

v

• Textures of Textures of gl, gv , R

store as 2D texturesstore as 2D textures

Pv

: extinction coefficient (constant): density of particles

)exp()( ahh (a: const)

sPPdll

0))()(exp( sl PPg ),(

Atmospheric Effects







• Results

• Conclusion

Atmospheric Effects

Experimental ResultsExperimental Results

#planes: 40mesh: 60x60

#planes: 160mesh: 60x60

#planes: 30#sub-planes: 120 (ave.)

mesh: 10x10

previous method previous method proposed method

computer: Athlon 1.7GHz, GeForce3

Atmospheric Effects


Image size: 300x450 computer: Athlon 1.7GHz, GeForce3

# of planes(sub-planes)

time

result

method

40

0.13 [sec.]

previous ray-tracing

29 [sec.]

-

interleaved[Keller01]

0.12 [sec.]

160

mesh 60x90 10x15 -

23 (174)

0.08 [sec.]

proposed

10x15

Atmospheric Effects


# of planes(sub-planes)

time

result

method

40

0.13 [sec.]

previous ray-tracing

29 [sec.]

-

interleaved[Keller01]

0.12 [sec.]

160


mesh 60x90 10x15 -

23 (174)

0.08 [sec.]

proposed

10x15

Atmospheric Effects

ResultsResults

sampling plane: 9sub-plane:309

sampling plane: 30sub-plane:263


time: 0.32 [sec.] time: 0.12 [sec.]

Atmospheric Effects

sampling plane: 100(sky) 30(shaft)sub-plane:135

time: 0.16 [sec.]

ResultsResults


sampling sphere: 10

time: 0.06 [sec.]

Atmospheric Effects

DEMODEMO

• Real-time Animation Using Note PC• Pentium III (1.2 GHz)• Nvidia GeForce 2 Go

Atmospheric Effects

ConclusionConclusion

• Fast rendering of atmospheric effects

- 2D textures to store intensities of scattered light

- sub-planes for precise sampling of shadows

- rendering of sky

• Rendering of light beams

• Extension to rendering earth’s atmosphere

- rendering of earth viewed from space

interactive rendering of atmospheric scattering effects using graphics hardware

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