The following will show you how to use the "Auto Occlusion" option in the "Render Cache" section of Brazil. The above examples rendered in Brazil beta 20 are available for you to download in order to try these settings on your own computer. This technique is especially useful in situations such as making renderings for an animation or producing large format renderings for print. The use of Auto Occlusion in the Render Cache can speed things up greatly. For example, the LC2 chair rendering above was output at 2000x2000 pixels (translating to a 7x7 inch print at 300dpi) in 12 minutes.
The key concept to understand is that the settings in the Render Cache as well as those in the Auto Occlusion section will need to change depending on the physical size of your model. The Render Cache is another method of calculating global illumination in Brazil. In short, it makes renderings happen really fast. This is of course at a price of seeing non realistic shadows where your model makes contact with the ground plane. The default setting for the Render Cache is set to the "No Enhancement" option. The shadows created with this default will often not appear dark enough and as a result your model may look like it's floating slightly. A more useful option available to you in the Render Cache is called Auto Occlusion. This option will create shadows based on an objects proximity to other objects in the scene. You can control the color of the shadow and how far the shadow will spread where objects meet. To start using the Render Cache in Brazil simply "enable" it in the Brazil settings dialog and expand the section to show the full "detailed controls". You'll likely need to review the Brazil Getting Started Guide as well to learn how to turn on the sky light if you haven't done so already.
In the screen shot above there are two measurements which had to be made first when setting up the "Rhino Drive" scene for rendering. The first measurement to make is the distance of the shadow created where two objects meet. In this case the Rhino jump drive is making contact with a ground plane. Using the "Distance" command in Rhino is a quick way to get an idea of how far you'll want the shadow to be calculated. This distance, represented by the blue line, is the end value for the Auto Occlusion settings in the "Detail Enhancement" section of the Render Cache.
The second measurement to make, represented by the red line, is the distance you want Brazil to resample the shadow created. In general, a value of 10 is a good place to start and should be raised if splotches or uneven areas in the shadows are seen. A common reason to increase this value is when the ground plane can be seen in the distance to look pixelated because Brazil is not resampling far enough in the scene.
It is easier to see the shadows made with the Auto Occlusion option if we change the start color. In example A above, the color swatch for the start value was selected and assigned a green color. Keep in mind that a dark gray shadow is usually best for more realistic results. In example B, the "Attenuate" option has been turned off. This means that the shadow will not begin to fade out until it reaches the end distance set. Compare this to the rendering made with Attenuation on. The shadow instead blends into transparency starting at the half way point over it's length.
The examples above show the results of using different end values for the Auto Occlusion. The size of your model is important when determining the right setting to use. Also note that the distance values in the Brazil options use the same units as your active Rhino file.... millimeters, inches etc.
Another area of the Render Cache panel to be familiar with is the section titled "Creation Shade Rate". The settings here correspond to the level of detail calculated by the Render Cache. Higher values will produce more detail but will take longer to calculate. For the examples provided here, a setting of -4 was used for both min and max values. When other sampling values in the Render Cache are high, the difference in creation shade rates is hard to see. The time differences can be significant however as shown above.
The smoothness of the detail in the shadow gradients is mainly controlled by the number of samples specified for the Auto Occlusion enhancement. Above are examples of 2 through 10 samples respectively. The graininess produced at lower sample rates is most noticeable at the setting of 2 in this case. The render time will be even faster at lower settings but at the price of quality. Generally a setting of 5-10 is best for most models.
The resolution of shadow areas can be further improved by raising the number of samples in the "Resampling Filtering" section of the Render Cache. Higher values will smooth out splotches in the shadow gradients.
This technique may not be as realistic as just using the sky light with GI and a high sample rate in the Luma Server but it sure can be fast. Using Auto Occlusion in conjunction with an HDR image in a GI environment can be very impressive and is certainly worth a try if you need to make some renderings quickly.