talk gatech imposter 2001
TRANSCRIPT
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Dynamically Generated Imposter
Weidong Shi
Georgia Institute of Technology, 2001
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Dynamically Generated Imposter
Exploit coherence in consecutive frames to speed uprendering
Reduce scene complexity by converting polygonmodels into imposters
Generate imposters on the fly to achieve flexibility
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Frame to Frame Coherence
Frame sequence generated by interactive graphicssystem contains significant amount of coherence.
Relative motion of distant objects on screen is
small.
Close objects often expose the same side to the
viewer when they are moving.
Re-use of rasterized object image to speed uprendering
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Real Time Rendering Techniques
LOD & Progressive Mesh
Static Imposter
object pre-generated and stored as texture, then
mapped to a transparent polygon in real time
huge texture storage space required
limited view direction and navigation space
Hierarchical Z- buffer
works best for highly occluded scene
Dynamic Imposter (Gernot Schaufler)
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Dynamic Imposter
Generate an object image for a certain view
Convert the image into texture
Map the texture to a transparent polygon.
Advantages
fast
more flexible than static imposter
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Dynamic Imposter -cont
Adjust imposter when viewer moves. Rotate aimposter so that its normal always points to theviewer.
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Validity of Old Imposter
Error Angle due to translation
In view V1, B1 = B2
In view V2, B1 and B2 has an angletrans.
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Validity of Old Imposter
Error Angle due to move-in
In view V1, B = B.
In view V2, B and B has an anglesize.
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Algorithm
For each object i
check validity of its old imposterif valid
render object i with imposter
else
if successfully generate a new imposter for object i
render object i with new imposter
else
render object i with its original mesh
endif
endif
endfor
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Real Time Performance of Dynamic
Imposter
View real time rendering not only as graphicsproblem but also a resource management problem.
Real time performance depends on both thecomputational requirement and the availableresources.
Dynamic imposter is beneficial only if leads to betteruse of rendering resources.
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Implementation
Hardware
Dell Inspiron 8000. ATI mobile graphics card withhardware 3D rendering support.
API
Direct X 8.
Imposter Validity Checking
Bounding sphere instead of bounding box used for
computingsize andtrans
CPU converts rendered image into texture with alphachannel.
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Result - cont
Opaque imposters
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Result - cont
Imposters with transparent texture
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Result - cont
Performance becomes worse with dynamic imposter
because of the slow video-system memory bus.
Video-System speed is about 50 times slower thanSystem-Video based on DirectDraw surface copytest.
Possible Solution (RGBA+Stencil buffer)
Render in RGBA format instead of RGB format (16bits). This only worksin full screen mode.
1. Clear rendering target (in Video Memory) with transparent alpha.2. Render and use stencil buffer to record all drawn pixels.3. Write opaque alpha value to all drawn pixels.4. Copy result into a texture buffer (in Video Memory).
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Result
0
50
100
150
200
250
300
1 3 5 7 9 11 13
ReusedImposter
NewImposter& Mesh
13 tigers, viewer uses one as center and
moves along a circle.
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Future Work
Develop adaptive algorithm that chooses how objectsare rendered based on real time performance andavailable resources.
Divide distant objects into groups and generate onlyone imposter for each group.
Combine with LOD. Map imposter texture tosimplified mesh.
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Thanks
?