Tutorial 4: Advanced Shadowing

Gaffer has added the ability to add realistic shadows to your scene. The soft edges of these shadows are not simple blurs like shadow maps can give, but the true shadowing effect due to partial blocking of area lights. Shadows in LightWave are an expensive option (in rendering time), and these area light shadows are even more expensive. However, Gaffer gives you this new ability as an option allowing you to optimize the look of your scene as you feel best.

We'll go back to the urn scene we've been using for our tests and see how we can change the shadows the urn casts onto the ground.

Load "arealght.lws". The urn's surface is the same as before, with selective lighting used to ignore the fill lights. We want the ground surface to receive the area light shadows, so go to the ground surface, and open Gaffer's options panel. We want the main light to cast these area light shadows.

We do this by typing the light's name ("Main") in the first "Prefix" field in the "Area Light Shadows" section of the panel ( not the Light Intensity Adjustments section.) You should a "1" beside the entry letting you know that there is one light in the scene that matches that prefix.

Area lights cast soft shadows because they have a finite size, so we need to define that size. We also need to tell Gaffer a quality setting for the shadows. A higher quality makes more accurate shadows, but takes longer to render.

For testing purposes let's try a "Quality" value of 10% and a "Radius" of .3. Usually you keep the quality setting very low when you are testing, then set it to a final high value for final rendering. Render the frame and you'll see the effect of this area light.

Obviously the radius setting is to high. The shadow is very broad, and has speckles in it due to the low quality setting. We can make the shadow smoother by raising the quality, but render times will increase, so you usually have to compromise based on your needs.

Let's fix our shadow by reducing the light size and making tighter shadows. This will incidentally increase the shadow quality (at no extra render expense) because tight shadows are more efficient than "loose" ones. Go back to the ground surface's Gaffer settings, change the light radius to .05, and render a frame.

Now the shadow shape is looking good, but we need to decide what quality setting to use. The setting you choose is up to you, and is based on your machine speed and personal patience. Here are some settings to try, along with the render times on a 200 MHz Pentium Pro.Try these to get a feel for the quality you can expect from mixing and matching quality settings with AA settings.

10% Quality - Medium AA - 2 minutes 22 seconds
50% Quality - Medium AA - 4 minutes 12 seconds
100% Quality- Low AA - 3 minutes 41 seconds

When choosing area light qualities, remember that LightWave's own antialiasing helps considerably. One common mistake is deciding the shadow quality settings on a scene that uses no antialiasing, then rendering your final scene with AA turned on. This effectively uses settings that are too high, and therefore too slow.

Judging from the three render tests, a good compromise quality setting would be using Low AA and 100% shadow quality. One advanced trick that can be useful is to use LightWave's "Surface Blur" plug-in, or even the Bloom tool (which comes with Gaffer!) to fuzz the shadows slightly by simply blurring the surface itself.