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Saving and reusing shadow maps

From: Lighting and Rendering with mental ray in Maya

Video: Saving and reusing shadow maps

One of the more appealing aspects of using depth map shadows, as opposed to raytrace shadows, is that you can actually save and reuse depth map shadows, and this can help you cut down on rendering time, especially if you're working in a complex scene that has a number of shadow-casting lights. For this example, I'm going to stick to something fairly simple: just three trees and a hill and a single spotlight. So there's my spotlight. I'm going to zoom in here. And in the Attribute Editor for the light, I have Use Depth Map Shadows is turned on, and in the mental ray section, I have Use mental ray shadow map overrides turned on.

Saving and reusing shadow maps

One of the more appealing aspects of using depth map shadows, as opposed to raytrace shadows, is that you can actually save and reuse depth map shadows, and this can help you cut down on rendering time, especially if you're working in a complex scene that has a number of shadow-casting lights. For this example, I'm going to stick to something fairly simple: just three trees and a hill and a single spotlight. So there's my spotlight. I'm going to zoom in here. And in the Attribute Editor for the light, I have Use Depth Map Shadows is turned on, and in the mental ray section, I have Use mental ray shadow map overrides turned on.

My Resolution is set to 1024, and my Samples are set to 64, and I have a little bit of Softness on there. So, the first thing that I want to do is I want to create a name for my shadow map. Generally the process is to create a name for the shadow map, do a test render, and that will save the shadow map to the disk, and then we can turn on Reuse Shadow Maps, so that it will use the same map the next time we render. So, I'm going to call this treeShadows, and I'm going to create just a test render from the Perspective view.

Okay, so here's our render, and we can see the shadow map cast on the surface of the ground. And at this point, we can actually verify that a shadow map has been saved to disk. So I'm going to open up the project, and in the renderData folder, under mentalray, I find shadowMap and here is our treeShadows file. You can see the size of the file and when it's been created.

So, now that I know that that's been saved to disk, I can reopen Maya, and I'm going to go to the Render Settings. In the Render Settings, under the Quality tab, I can scroll down here, and under Shadow Maps, I can turn on Reuse Existing Maps. So this is automatically going to reuse the shadow map that I saved to disk the next time I render. Now, if I open up the Render view, I'm going to save this image and notice that the original render took about 49 seconds and so if I render again, it should take less time.

So the rendering looks identical, but this time it only took 14 seconds. If I scroll between these two images, you can't see any difference whatsoever. So that's the real advantage, especially when you have a very complex scene that uses a lot of shadow-casting lights. So this is one reason why you might choose to use depth map shadows over another method, such as raytracing.

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Image for Lighting and Rendering with mental ray in Maya
Lighting and Rendering with mental ray in Maya

59 video lessons · 7959 viewers

Eric Keller
Author

 
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  1. 3m 46s
    1. Welcome
      1m 32s
    2. Using the exercise files
      2m 14s
  2. 19m 8s
    1. What is a CG light?
      1m 22s
    2. Types of CG lights
      10m 55s
    3. Direct lighting
      4m 48s
    4. Indirect lighting
      2m 3s
  3. 53m 20s
    1. Decay rate
      6m 30s
    2. Previewing lighting and shadows
      2m 37s
    3. Creating depth map shadows
      1m 57s
    4. Troubleshooting depth map shadows
      2m 38s
    5. Shadow map overrides
      5m 30s
    6. Using the shadow map camera
      5m 31s
    7. Saving and reusing shadow maps
      2m 48s
    8. Creating raytraced shadows
      1m 56s
    9. Adding softness to raytraced shadows
      3m 42s
    10. Creating area light shadows
      5m 11s
    11. Sample: mental ray area light
      4m 23s
    12. Setting area light visibility
      8m 7s
    13. Creating soft shadows with spot lights
      2m 30s
  4. 43m 35s
    1. Setting global illumination for interiors
      2m 33s
    2. Tuning global illumination
      5m 56s
    3. Global illumination photons
      1m 12s
    4. Activating caustic light effects
      3m 28s
    5. Tuning caustic settings
      3m 35s
    6. Setting caustic light effects on metal
      2m 35s
    7. Using final gathering for indirect lighting
      2m 9s
    8. Tuning final gathering
      4m 2s
    9. Reusing final gathering maps
      3m 21s
    10. Adding light with shaders
      5m 27s
    11. Creating final gathering maps for animation
      4m 26s
    12. Combining final gathering with global illumination
      4m 51s
  5. 1h 2m
    1. Activating the Physical Sun and Sky network
      2m 33s
    2. Tuning the Physical Sun and Sky settings
      7m 18s
    3. Applying physical light shaders
      8m 54s
    4. Applying image-based lighting
      8m 57s
    5. Tone mapping
      6m 23s
    6. Applying portal light shaders
      7m 45s
    7. Creating light beams with participating media
      10m 9s
    8. Adding depth of field with the Bokeh lens shader
      10m 39s
  6. 48m 21s
    1. Introducing render layers
      6m 13s
    2. Creating render layers
      4m 28s
    3. Splitting a scene into render layers
      15m 36s
    4. Applying render layer presets
      7m 47s
    5. Setting render layer overrides
      7m 7s
    6. Creating render layer composites
      3m 52s
    7. Organizing renders with tokens
      3m 18s
  7. 42m 24s
    1. Introducing render passes
      2m 56s
    2. Comparing render passes and render layers
      6m 44s
    3. Editing render passes
      10m 41s
    4. Using appropriate materials
      5m 51s
    5. Batch-rendering passes
      5m 56s
    6. Compositing in After Effects
      6m 41s
    7. Rendering the EXR image format
      3m 35s
  8. 23m 3s
    1. Anti-Aliasing Quality
      6m 44s
    2. Setting color profiles
      2m 53s
    3. Diagnosing raytracing
      5m 7s
    4. Adjusting motion blur
      6m 57s
    5. Finding mental ray help
      1m 22s
  9. 21s
    1. Goodbye
      21s

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