PowerPoint Presentation

							Rendering Forest Scenes in Real-Time
     Philippe Decaudin      Fabrice Neyret
       GRAVIR/IMAG-INRIA, Grenoble, France




                                         EGSR 2004
Rendering Forest Scenes in Real-Time:
Previous work
 Billboards
      Textured quad facing camera,
       or cross
      Widely used by applications
           Flight simulators, Games, …
     + efficiency
     - no parallax, popping



 Simplified textured trees
     + parallax, 3D consistency
     - more expensive



 2                Rendering Forest Scenes in Real-Time   EGSR 2004
Rendering Forest Scenes in Real-Time:
Previous work
 Points
     Objects = distribution of discs
        [Levoy, Whitted - 85]
        [Pfister et al - SIG’00] [Rusinkiewicz et al - SIG’00]
        [Stamminger, Drettakis - EWR’01] [Dachsbacher et al - SIG’03]
        …
     + adaptive
     - aliasing
    (-) cost = 1 transformed vertex / point




                                                                        [Stamminger Drettakis 01]


3                   Rendering Forest Scenes in Real-Time                    EGSR 2004
Rendering Forest Scenes in Real-Time:
Previous work
 Volumetric textures
     Volumetric densities to represent fuzzy material
        [Kajiya, Kay - SIG’89]
        [Neyret - GI’95TVCG’98]
        [Meyer, Neyret - EWR’98]
        [Lengyel et al - EWR’01]
        …
                                                          pattern
    + few polygons, more textures
    + easy to filter
    - repetitive tiling
    - slicing might be visible




4                  Rendering Forest Scenes in Real-Time             EGSR 2004
Our approach

 Goal:
     Render dense forests
     In real-time
     With good visual quality
     Smooth during a flyover

    Assumption: forests are viewed from a distance


 Approach: improved real-time volumetric textures
    1. Avoid pattern mapping repetition
    2. Avoid view dependant artifacts
    3. Adapted to the distance


5              Rendering Forest Scenes in Real-Time   EGSR 2004
1. Making volumetric texture aperiodic

 Aperiodic mapping
     Avoids repetitivity
     Requires a set of edge-compatible patterns
       [Stam - 97]      [Neyret, Cani - SIG’99]   [Cohen et al - SIG’03]




6                    Rendering Forest Scenes in Real-Time                  EGSR 2004
1. Making volumetric texture aperiodic
 Storing the patterns
                      v




                                      u




                                                    Hardware friendly

                                                    + one texture
                                                    + wrap
                                                    + compliant with
                                                      min and mag filtering
7            Rendering Forest Scenes in Real-Time                EGSR 2004
1. Making volumetric texture aperiodic

 Shape of a forest pattern: a prism

     We build a set of edge-compatible prisms,
      that we call Texcells




8              Rendering Forest Scenes in Real-Time   EGSR 2004
2. Our slicing scheme

 Volumetric data cannot be rendered directly by GPU
 Rendered using textured slices
 The simplest slicing scheme:
     Slices parallel to the terrain




                                                       Texcell
                 Slices
                                            Terrain



     But suffer from artifacts…
9               Rendering Forest Scenes in Real-Time             EGSR 2004
 2. Our slicing scheme
       Slices parallel to the terrain : artifacts



    Slicing is
    visible at
 grazing angles
 Silhouette
  texcells                                                 LOD




                                                           Too blurred

       Too                                                   Anisotropic
   transparent                                                filtering
    Opacity
   adjustment


 10                Rendering Forest Scenes in Real-Time   EGSR 2004
2. Our slicing scheme
 2 kinds of texcells




  Regular texcells                        Silhouette texcells
     Sliced parallel to the ground           Sliced "parallel" to the screen




      Setof 2D textures                        3D texture
      Good quality and efficiency              More expensive used
       except at the silhouette                  near the landscape silhouette
11               Rendering Forest Scenes in Real-Time             EGSR 2004
2. Our slicing scheme: silhouette texcells
 Tilting the slices
      Vertices are moved vertically, no new vertices are created
      Can be done by a vertex program




12              Rendering Forest Scenes in Real-Time       EGSR 2004
3. LOD scheme

 For silhouette texcells
      We fit the slicing rate to the MIP-map level of the 3D texture



 For regular texcells
      Texture set: 2D textures + MIP-map




13               Rendering Forest Scenes in Real-Time        EGSR 2004
Results
 Texcells:
      128 slices of 256x256 textures
        12 Mb of compressed texture
      20 trees / texture
      Aperiodically mapped
 Shading
      precomputed and stored in the textures
      + pseudo-shading corresponding to the lighting of the terrain




14              Rendering Forest Scenes in Real-Time        EGSR 2004
Results

                                                  Seq #1
                                                   ~2300 trees
                                                   570 texcells
                                                    with 4 trees/texcell
                                                   ~30 fps 640x480
                                                    (P4 1.7GHz,
                                                    GeForceFX 5800)

                                                  Seq #2
                                                  ~37000 trees
                                                  9200 texcells
                                                   with 4 trees/texcell
                                                  ~20 fps 640x480
                                                   (P4 1.7GHz,
                                                   GeForceFX 5800)



15        Rendering Forest Scenes in Real-Time           EGSR 2004
Conclusion & future work
 A scheme for quality real-time volumetric textures
 Coupled with an aperiodic mapping scheme
 Correct filtering of the volumetric data
 Full parallax effects
 Well suited to represent and render dense forests
 Texcells can be mixed with other representations

Future work
 Better culling
 Dynamic lighting and shadowing
     [Poster at Siggraph 2004]
 Maximize the use of the GPU

16              Rendering Forest Scenes in Real-Time   EGSR 2004