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V-Ray 2.0 for Maya Essential Training
Illustration by Richard Downs

How light cache works


From:

V-Ray 2.0 for Maya Essential Training

with Brian Bradley

Video: How light cache works

If irradiance mapping comes top of the list as the most widely used of V-Ray's GI engines in the primary bounce slot, it is probably safe to say that Light cache can make the same claim when it comes to being used as a secondary bounce engine. Now, just so you are certain where the Light cache controls can be found, let's go and open up our Render Settings window. Let's go into the Indirect Illumination tab, and with Light cache set as our Secondary bounce engine, let's go and open up the Light cache rollout, and you can see, we have all of these options, all of these controls that we can work with to create our GI solution from a secondary bounce engine perspective.
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  1. 4m 28s
    1. Welcome
      59s
    2. What you should know before watching this course
      51s
    3. Exercise files
      40s
    4. Workflow recommendation
      1m 58s
  2. 11m 32s
    1. Installing V-Ray
      4m 25s
    2. Setting up V-Ray
      3m 14s
    3. Locating V-Ray's tools and features
      3m 53s
  3. 24m 41s
    1. Image sampling explained
      3m 19s
    2. Understanding subdivs
      3m 49s
    3. Using the DMC Sampler
      6m 54s
    4. Overview of color mapping
      4m 45s
    5. Understanding the color-mapping modes
      5m 54s
  4. 27m 55s
    1. Dealing with lighting problems
      9m 26s
    2. Adding a spherical fill light
      8m 50s
    3. Creating a mesh light
      2m 43s
    4. Creating a skylight effect
      3m 18s
    5. Working with the dome light
      3m 38s
  5. 44m 25s
    1. Global illumination (GI) explained
      3m 55s
    2. Understanding primary and secondary bounces
      3m 34s
    3. How irradiance mapping works
      5m 30s
    4. Using irradiance mapping, part 1
      4m 35s
    5. Using irradiance mapping, part 2
      5m 44s
    6. How light cache works
      3m 48s
    7. Using light cache
      7m 58s
    8. Understanding brute force GI
      2m 18s
    9. Using brute force GI
      7m 3s
  6. 40m 3s
    1. Introduction to V-Ray-specific materials
      2m 22s
    2. Creating diffuse color
      8m 31s
    3. Making reflective materials
      5m 40s
    4. Blurring reflections
      8m 31s
    5. Making clear and colored glass
      8m 49s
    6. Creating a translucency effect
      6m 10s
  7. 24m 15s
    1. Introduction to image sampling
      2m 56s
    2. Using the Fixed-Rate sampler
      5m 57s
    3. How to use the Adaptive DMC sampler
      5m 21s
    4. Working with the Adaptive Subdivision sampler
      7m 7s
    5. Comparing image-sampling renders
      2m 54s
  8. 17m 23s
    1. The physical workflow explained
      2m 37s
    2. Working with VRaySun and VRaySky
      7m 39s
    3. Controlling the VRayPhysicalCamera
      7m 7s
  9. 45m 0s
    1. Depth of field: VRayPhysicalCamera
      5m 45s
    2. Depth of field: perspective viewport
      5m 49s
    3. Creating a motion blur effect
      9m 30s
    4. Generating caustic effects
      7m 51s
    5. Using VRayFur
      6m 2s
    6. Setting up render-time displacement effects
      10m 3s
  10. 34m 17s
    1. Render elements workflow
      6m 47s
    2. Preparing to composite
      2m 22s
    3. Compositing V-Ray elements
      7m 8s
    4. Putting extra elements to work
      6m 20s
    5. Post-lighting a scene
      11m 40s
  11. 11m 47s
    1. Overview of V-Ray RT
      5m 27s
    2. Demonstrating the RT workflow
      6m 20s
  12. 1m 8s
    1. What's next?
      1m 8s

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V-Ray 2.0 for Maya Essential Training
4h 46m Beginner Mar 08, 2012

Viewers: in countries Watching now:

This course introduces the features of the V-Ray 2.0 rendering engine and demonstrates how to extend the range of Maya with its state-of-the-art tools, such as irradiance mapping, fur and hair textures and shaders, and stereoscopic 3D rendering. The course covers critical concepts such as creating basic materials, image sampling, color mapping, subdivs, and lighting, as well as the Render Elements, RT, and physical rendering workflows in V-Ray. Exercise files are included with the course.

Topics include:
  • Installing and setting up V-Ray
  • Using the DMC Sampler
  • Understanding color mapping modes
  • Adding a spherical fill light
  • Working with the V-Ray Dome Light
  • Using irradiance mapping and the Light cache
  • Creating diffuse color
  • Making reflective materials
  • Creating translucency
  • Ensuring quality with image sampling
  • Controlling the V-Ray physical camera
  • Creating a motion blur effect
  • Compositing V-Ray elements
Subjects:
3D + Animation Rendering Textures Materials Visual Effects
Software:
V-Ray
Author:
Brian Bradley

How light cache works

If irradiance mapping comes top of the list as the most widely used of V-Ray's GI engines in the primary bounce slot, it is probably safe to say that Light cache can make the same claim when it comes to being used as a secondary bounce engine. Now, just so you are certain where the Light cache controls can be found, let's go and open up our Render Settings window. Let's go into the Indirect Illumination tab, and with Light cache set as our Secondary bounce engine, let's go and open up the Light cache rollout, and you can see, we have all of these options, all of these controls that we can work with to create our GI solution from a secondary bounce engine perspective.

Now light cache, like irradiance mapping, is another view-dependant GI technique. This, of course, means that the same limitations apply; the solution is calculated only from the rendering camera's point of view, and so, if we move the camera, we will create holes in the solution that can only be filled by recalculating the light cache. If, again, we need animation in our scene, if we are working with animated cameras, or indeed objects, then there are a couple of options we can use. Again, we have this Use camera path option for cameras that are moving around the scene.

And again, if you come down to the Mode settings, and use the dropdown, you can see we have this Fly-through option. Again, this can help with any animation that is taking place in the scene. To calculate the lighting found in the environment, V-Ray's Light cache engine will trace large amounts of rays from the camera's point of view, and send them out into the scene. These rays are responsible for creating your light cache samples, the number of which will be controlled by your Light cache subdivs primitive. With every hit, or intersection of a ray and a surface, a sample is created.

Unlike the initial rays used in irradiance mapping, light cache rays will bounce, or reflect a number of times, even if they are set in the primary bounce engine slot. Illumination information from each of the subsequent bounces along the ray's path gets recorded, and then stored in a 3D point cloud structure, just, in fact, as a irradiance mapping, and photo maps do. If a bouncing ray hits an already created sample, then any further tracing of that particular ray gets canceled, and the information from the existing sample will be used instead.

This, as you can imagine, really speeds up the process hugely, as no unnecessary tracing of rays takes place in the system. This in turn allows light cache to calculate a lot of light bounces very quickly indeed, making it, of course, an excellent choice for lighting difficult spaces, such as interiors, which are typically much harder than exteriors to light with a global illumination solution. One interesting aspect of light cache is that there is no difference between a light cache computed as either a primary or a secondary bounce engine.

If we've saved a Light cache file to disk when it was computed with Light cache set as the primary bounce engine, we can safely load and use it with Light cache set as a secondary bounce engine. The lighting solution will always be identical. Of course, light cache does have some restrictions, or limitations. Like photo maps, light cache is not adaptive. The illumination is computed at a fixed resolution, which will be determined or set by the user prior to calculating the lighting solution.

Light cache also doesn't work very well with bump maps, so we may need to take special note of how any bump maps we have in our scenes are reacting to the lighting solution we're creating. In fact, light cache is not as good as any of the other GI engines for picking out any kind of fine details that may exist in our scene. So with a basic understanding, now, of how the Light cache system is working, let's again move on to trying it out in our test scene, and see how we can create a GI solution using this particular engine.

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