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Ray-casting%20in%20VolumePro

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Second generation real-time volume rendering accelerator. Ray-casting ... Ray-per-pixel image quality. Translucent & opaque embedded polygons. 8-, 16-, & 32-bit ... – PowerPoint PPT presentation

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Title: Ray-casting%20in%20VolumePro


1
Ray-casting in VolumePro 1000
  • Yin Wu, Vishal Bhatia, Hugh Lauer, Larry Seiler

2
VolumePro 1000 Summary
  • Second generation real-time volume rendering
    accelerator
  • Ray-casting at 109 samples per second
  • Ray-per-pixel image quality
  • Translucent opaque embedded polygons
  • 8-, 16-, 32-bit voxels (up to four fields)
  • Geometry-based space leaping, early ray
    termination

3
The Challenge in Ray-casting Performance vs.
Image Quality
  • Shear-Warp
  • Traverse resample data in memory order.
  • Warp needed for final image.
  • Fast
  • Efficient memory access
  • VolumePro 500
  • Image Quality
  • 2nd resampling
  • No embedded geometry
  • Full Image order
  • Traverse resample data in pixel order
  • Image Quality
  • No 2nd resampling
  • Embedded geometry
  • Performance
  • Memory accesses similar to random access.

4
VolumePro 1000 Ray-casting
  • Rays through pixels on image plane
  • Image quality equiv. to full image order
  • No 2nd resampling

5
VolumePro 1000 Ray-casting
  • Rays through pixels on image plane
  • Samples organized in planes parallel to faces of
    the volume
  • Traverse process data in memory order
  • Maximize memory performance

6
xy-image order 2 parts (aka shear-image order)
  • Voxel processing part
  • Traverse data slice-by-slice in memory order
  • Read voxels for each slice of samples
  • Voxel-oriented processing (e.g., gradient
    estimation)
  • Store in on-chip buffers
  • Sample processing part
  • Define sample points where rays intersect slices
  • Traverse interpolate on-chip buffer in pixel
    order
  • Sample-oriented processing
  • e.g., illumination, filtering, depth testing,
    compositing
  • Output to image

7
VolumePro 1000 ray-casting (Additional
optimizations)
  • Section rays assoc. with tile of image plane
  • Minimize on-chip buffer space
  • All slices of a section processed before next
    section
  • Enables early ray termination
  • Mini-block and stamp organized memory
  • Burst accesses to 2?2?2 voxels or 2?2 pixels
  • From VolumePro 500
  • Skewed across eight memory channels
  • Parallel access to 8 adjacent mini-blocks or
    stamps in any dimension
  • From VolumePro 500, Cube-4 (SUNY Stony Brook)

8
Block Diagram
Pipelines 250 MHz
Voxels (organized as mini-blocks)
PCI bus Interface 33-66 MHz
control
On-chip Slice buffers
Memory Interface eight channels 16-bit DDR
SDRAM (266-333 MHz)
control
Pixels (organized as stamps)
9
Technical summary
  • Four 250 MHz pipelines, 109 samples per second
  • Trilinear interpolations on seven channels
  • Four colors or voxel fields
  • Three gradient components
  • Classification of (up to) four voxel fields
  • Phong illumination calculation
  • 25-30 individual visibility tests
  • Alpha correction, gradient magnitude modulation
  • Perspective rendering (in Shear-Warp)

10
What next?
  • Is 109 samples/second enough?
  • 1 megapixel at 15 fps ? 66 samples/ray (average)
  • Not very many, even with aggressive space leaping
  • Major items yet to be done
  • Content-based space-leaping
  • Faster memory, pipelines, and Sequencer
  • Perspective volume rendering
  • More programmability

11
Pretty Pictures
12
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13
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14
Supplementary Slides
15
Embedding Surfaces in Volumes
  • Allows inserting pointers, medical prostheses, or
    geological data markers into the volume
  • Also supports arbitrary clipping regions, all in
    real time
  • Each ray is cast in multiple segments, between
    surfaces specified by depth buffers
  • Surface rendering performed in 3D graphics chip
    using OpenGL

Front clip bounds
Trans- lucent surface
Opaque background
16
Embedding Surfaces in Volumes
  • Allows inserting pointers, medical prostheses, or
    geological data markers into the volume
  • Also supports arbitrary clipping regions, all in
    real time
  • Each ray is cast in multiple segments, between
    surfaces specified by depth buffers
  • Surface rendering performed in 3D graphics chip
    using OpenGL

17
Embedding Surfaces in Volumes
  • Allows inserting pointers, medical prostheses, or
    geological data markers into the volume
  • Also supports arbitrary clipping regions, all in
    real time
  • Each ray is cast in multiple segments, between
    surfaces specified by depth buffers
  • Surface rendering performed in 3D graphics chip
    using OpenGL

18
Embedding Surfaces in Volumes
  • Allows inserting pointers, medical prostheses, or
    geological data markers into the volume
  • Also supports arbitrary clipping regions, all in
    real time
  • Each ray is cast in multiple segments, between
    surfaces specified by depth buffers
  • Surface rendering performed in 3D graphics chip
    using OpenGL
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