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Overview of the Ambient Occlusion shader

From: Creating Urban Game Environments in 3ds Max

Video: Overview of the Ambient Occlusion shader

When we are rendering ambient occlusion, we want to keep several things in mind so we get a successful bake of our occlusion. The first part of successful ambient occlusion actually starts with modeling. Objects need to be in the real size of the real world object. That is, this door is 10 feet tall. I model that as 10 feet tall in 3ds Max. To tune occlusion, I'll take my warehouse and for this example I have generated some ambient occlusion shaders here in the Material Editor. For games, we would actually use the Render to Texture dialog, but this allowed me to render and show this material a little more clearly.

Overview of the Ambient Occlusion shader

When we are rendering ambient occlusion, we want to keep several things in mind so we get a successful bake of our occlusion. The first part of successful ambient occlusion actually starts with modeling. Objects need to be in the real size of the real world object. That is, this door is 10 feet tall. I model that as 10 feet tall in 3ds Max. To tune occlusion, I'll take my warehouse and for this example I have generated some ambient occlusion shaders here in the Material Editor. For games, we would actually use the Render to Texture dialog, but this allowed me to render and show this material a little more clearly.

To start, I have an AO moody material I'll assign to this warehouse. Ambient Occlusion can be placed in a mental ray shell, which is what I've done here for ease-of-use. In the Ambient Occlusion shader, there are several main factors we need to adjust. The first of these is the Max distance. Max distance in a scene is the distance at which objects cast and then stop casting occlusion on each other. I will render this example. In this rendering, that Max distance of 90 produces deep spreading shadows in the corners and on the base of the building.

Changing that distance to a Max distance of 24 produces far softer occlusion over a smaller area. For comparison, I'll change my Area to Render to a Region and make the region go over part of the garage door, wall, and window. When I hit Render again, we will see a dramatic difference. With the Occlusion Max distance at 24, we get slimmer lines of darkness in the corners and surfaces that were cloudier, such as the slide of the window here, are far clearer and brighter. I will move the region over, just to be able to show this a little closer to the camera.

Once we have decided on a Max distance, which is really affecting how does the gloom spread on the building, we want to look at Spread. For this comparison, I'll put my Max distance back up to 60. For the Spread, the higher that goes, the more the darkness spreads into that zone of occlusion determined by the Max distance. When I take the Spread down to say 0.3 and hit Render again, we will see the darkness really cluster in the corners. We get deeper, harder lines and not as much darkness spreading on the surface. If we look closely where the side wall, the ceiling and the window intersect, you can see this phenomenon.

The darkness is in the corners and curves nicely up to meet versus spreading across the wall. In addition to Spread and Max distance, we want to consider the Bright and Dark values. They don't have to be the black -and-white they start out as. This is an artistic choice. I will jump to Photoshop to illustrate this. In Photoshop, it's very common to take an occlusion map, such as I have several of here, and layer it over a diffuse map to get the proper darkness. This is a raw diffuse map where the color showing is really the raw diffuse channel of that material.

When I lay occlusion over it, I will set the occlusion as a Multiply blending mode. We can do this either here in the texture or in the game engine occasionally. Depending on the blending mode we choose and the Opacity, we get different looks in the occlusion. Changing that blending mode across to Color Burn produces gloom and spreading blackness. We may or may not want this so we need to play with it. Part of that is determined by what color that dark value is. In these renderings, my dark value started out as black.

Here's the raw occlusion. So multiplying the color I have by this gray and black produces that depth in the scene. I will go back to 3ds Max and make a change to this. In 3ds Max if I take the dark color from black and boost it up to a sepia tone, adjusting the Hue and Saturation to give me more of a warm brown. In this case, this will produce that brown in the corner as the maximum dark value. I will hit Render to show this.

When this multiplies over a texture, we will get a far different look and a less heavy rendering than that black. These are the three main things to keep track of in the occlusion when tuning the cinematic look. What does the max distance or how much does the occlusion spread across the objects? Where does the occlusion go? Clustered in the corners or spreading into that zone? And finally, what is the darkest color, because this will lay over another color? The samples in the ambient occlusion shader determine the quality. A low sample rate such as 16 produces dots in the occlusion.

We can start to see some dots right below this sill. We may not want that in our texture. Increasing the samples produces a better quality occlusion at a higher cost and rendering time. Upping the samples to 128 produces very smooth occlusion with an increase correspondingly. With samples of 128, the occlusion is nice and smooth. Ambient occlusion is a terrific tool for us to add more detail. What we need to do is to craft it. It's never just set in stone. We can always change things and what we want to think of as part of our conception or our thinking about the cinematic mood of our imagery when we are playing the game is how do we want to tune the occlusion? Were does it go, what color is it, and how do our corners look?

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This video is part of

Image for Creating Urban Game Environments in 3ds Max
Creating Urban Game Environments in 3ds Max

78 video lessons · 6219 viewers

Adam Crespi
Author

 
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  1. 4m 47s
    1. Welcome
      55s
    2. Understanding the design process
      47s
    3. What you should know before watching this course
      14s
    4. Software requirements
      47s
    5. Using the exercise files
      2m 4s
  2. 14m 36s
    1. Identifying key contours and shadows in concept art
      1m 59s
    2. Analyzing concept art for texture
      2m 28s
    3. Choosing between modeling and texturing
      1m 43s
    4. Understanding the limitations of normal maps
      2m 26s
    5. Analyzing concept art for key shadow details
      3m 10s
    6. Identifying shadow details as generated or painted
      2m 50s
  3. 44m 57s
    1. Planning the visible overlaid history in a city
      3m 6s
    2. Planning a "wedding cake" building: Base, middle, and top
      2m 50s
    3. Planning a modern building: Base and shaft
      3m 1s
    4. Designing the zoning: Planning the visible uses of buildings
      6m 43s
    5. Laying out city blocks
      2m 36s
    6. Planning modular textures and geometry: Streets and sidewalks
      4m 1s
    7. Texturing intersections
      3m 13s
    8. Modeling modular curbs, gutters, and ramps
      5m 7s
    9. Modeling modular street elements
      3m 14s
    10. Modeling corners with ramps
      5m 56s
    11. Unwrapping sidewalk elements
      5m 10s
  4. 38m 9s
    1. Laying out rectangles and planning how to clone geometry and texture
      4m 59s
    2. Using layers to organize construction elements and actual models
      3m 51s
    3. Extruding edges to form major shadow lines
      5m 17s
    4. Testing the module for correct floor-to-floor heights
      1m 41s
    5. Trimming down the module and cloning
      4m 10s
    6. Stretching the vertical elements to minimize geometry
      7m 10s
    7. Unwrapping the elements for correct proportion
      7m 48s
    8. Laying out a texture sheet for a façade
      3m 13s
  5. 39m 50s
    1. Making brick texture
      6m 23s
    2. Adding detail to the diffuse texture: Sills and arches
      4m 24s
    3. Adding stone accents
      7m 47s
    4. Layering color in window frames and doorways
      8m 39s
    5. Copying diffuse layers for normal map foundations
      2m 7s
    6. Desaturating the diffuse map copies and prepping for normal maps
      3m 42s
    7. Converting bump maps to normal maps using nDO
      6m 48s
  6. 1h 2m
    1. Analyzing the necessary silhouette and geometry
      5m 24s
    2. Examining existing buildings in different lighting conditions
      3m 8s
    3. Planning cornice elements
      3m 32s
    4. Extruding cornice elements from polygon edges
      9m 12s
    5. Assigning smoothing groups for optimal shading
      4m 31s
    6. Unwrapping cornices for lighting
      8m 43s
    7. Modeling sloped roofs
      7m 16s
    8. Adding fascias and soffits
      5m 21s
    9. Adding fascias and soffits for gable ends
      7m 31s
    10. Texture sheets for roofs
      8m 1s
  7. 13m 55s
    1. Arranging, aligning, and cloning modular elements
      3m 26s
    2. Setting pivot points for buildings
      5m 48s
    3. Reusing elements: Exploring possibilities in modular building design
      4m 41s
  8. 40m 3s
    1. Creating a texture library
      36s
    2. Creating rusty corrugated metal texture
      7m 53s
    3. Creating stone texture
      4m 42s
    4. Creating wood texture
      9m 50s
    5. Creating rough brick texture
      7m 44s
    6. Creating roads
      9m 18s
  9. 38m 44s
    1. Using the Walkthrough Assistant to assess texture needs
      4m 46s
    2. Drawing detail at the right size
      3m 30s
    3. Understanding tiling and non-tiling textures
      2m 57s
    4. Deciding when to use tiling and non-tiling textures
      3m 2s
    5. Using multiple mapping coordinates
      4m 3s
    6. Using multiple unwrap modifiers
      6m 47s
    7. Unwrapping objects a second time: Planning an unwrap for a light map
      7m 46s
    8. Unwrapping a building façade using overlapping texture elements
      5m 53s
  10. 30m 25s
    1. Understanding ambient occlusion
      1m 50s
    2. Assessing the quality of occlusion as a cinematic mood
      2m 48s
    3. Overview of the Ambient Occlusion shader
      5m 9s
    4. Baking maps using the Render To Texture dialog
      3m 15s
    5. Using occlusion as a foundation for dirt
      5m 28s
    6. Using occlusion from detailed models for texture
      5m 54s
    7. Baking lighting
      6m 1s
  11. 25m 18s
    1. Preparing for Unity as a world builder
      2m 26s
    2. Importing into Unity and recognizing limitations
      4m 12s
    3. Importing elements with detailed materials
      5m 59s
    4. Setting optimal texture sizes and resizing in Unity
      3m 12s
    5. Setting up a naming convention and scene management
      7m 40s
    6. Renaming tools in 3ds Max
      1m 49s
  12. 1m 21s
    1. What's next
      1m 21s

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