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Volume Clipping via Per-Fragment Operations in Texture-Based Volume Visualization

Volume Clipping via Per-Fragment Operations in Texture-Based Volume Visualization. Visualization and Interactive Systems Group University of Stuttgart Germany. Approach. Currently Primitive clip planes Clip object specified Clip geometry using a polygon mesh

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Volume Clipping via Per-Fragment Operations in Texture-Based Volume Visualization

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  1. Volume Clipping via Per-Fragment Operations in Texture-Based Volume Visualization Visualization and Interactive Systems Group University of Stuttgart Germany

  2. Approach • Currently • Primitive clip planes • Clip object specified • Clip geometry using a polygon mesh • Volumetric 3d textures as a voxel mask

  3. Depth-based clipping • Straightforward approach • 1 boundary • Render clip to depth buffer • Disable writing to depth buffer; • Enable depth test • “Greater” or “less” • - Render textures Depth structure for 1 pixel in the frame buffer

  4. Depth-based volume probing • – Render front faces of geometry to depth buffer to get zfront • Store depth buffer to a texture (gfx-mem) • Fragment shader shifts all depth by –zfront • Render back faces • Render slices with depth shift/test

  5. Volumetric Clip Textures • Voxelise the clip geometry as binary volume • 1: voxel is inside ; 0: voxel is clipped • Per-fragment multiplicaton of vol*clip texture • Disadvantages • Jaggy artifacts due to discretization

  6. Results • Voxel Clipping • Varying alpha for smooth variation • Visible jaggy edges :trilinear interpolation doesn’t give sharp edges • Reuse clip texture – cylinder as many translated 2d circle texture • Clip Geometry • High quality (per pixel) • No aliasing • Change of geometry is trivial • slower (x4) • - Convex geometry (multipass??)

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