An overview of the different ways to make use of PRT

Tutorial Author:Clifton Poli

PRT

http://reality.artificialstudios.com/twiki/bin/view/Main/SphericalHarmonics

• Pros

• • Fully dynamic lighting, shadows, sub-surface scattering, and inter-reflections.

• Cons

• • File size
  • Rendering overhead

Per-Vertex PRT

• File size per vertex: 130 bytes

• Pros

• • Faster than PP-PRT

• Cons

• • File size is dependant on number of verticies of mesh, so If you use PV-PRT on a high resolution mesh, the file size may be larger than if you used PP-PRT, thus it may be beneficial to use PP-PRT instead in these cases.

Per-Pixel PRT

• File size for uncompressed PP-PRT:

• • 32x32: 106 KB
  • 64x64: 394 KB
  • 128x128: 1.50 MB
  • 256x256: 6.00 MB
  • 512x512: 24.00 MB

• File size for compressed PP-PRT:

• • 32x32: 53 KB
  • 64x64: 197 KB
  • 128x128: 750 KB
  • 256x256: 3.00 MB
  • 512x512: 12.00 MB

• Pros

• • Highest Quality

• Cons

• • Resolution limited due to massive file sizes.
  • Requires 2nd uv channel for mesh. Works best with flattened UV cordinates.

Baked PRT

Reality supports per-pixel and per-vertex lightmapping. You can import an external lightmap or convert PRT data to lightmapped data to save memory or performance. To do this go to Modifiers->Bake PRT Lighting. When baking the lighting be sure and do it at a time of day that will look good in all situations, for example you dont want to bake the lighting when the skybox is at nighttime, or it will look out of place during the day lighting.

• Pros

• • Greatly reduced file sizes
  • Improved rendering performance

• Cons

• • Completely static

Baked Per-Vertex PRT

• File size per vertex: 32 bytes

• Pros

• • Smallest file size, even smaller than non prt verts.
  • Best performance

• Cons

• • Static
  • Lowest visual quality

Baked Per-Pixel PRT

• Baked PP-PRT are essentially lightmaps, they are saved in L8 DDS format(8 bit/greyscale).

• • 32x32: 1.45 KB
  • 64x64: 5.45 KB
  • 128x128: 21.4 KB
  • 256x256: 85.4 KB
  • 512x512: 341 KB
  • 1024x1024: 1.33 MB
  • 2048x2048: 5.33 MB

• Pros

• • The high detail of PP-PRT, but in much smaller file sizes and with improved performance.
  • Custamizable, for example the lightmap can be edited in Photoshop, or you can use a 3rd party program to generate the lightmap.

• Cons

• • Static
  • Requires 2nd UV coordinate channel.