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Adding Caustics

Caustics can also produce realistic results when applied correctly. This next exercise instructs you in two areas: surfacing glass objects for use with caustics, and applying caustics to objects in a scene.

Exercise 9.4 Tabletop Realism

For this exercise, you can start with the simple glass ball objects from the CD-ROM accompanying this book. You will set the parameters of the glass surface using one area light and a basic set.

Begin by saving any work you’ve done in Layout, and load the BaseCaustic scene from the book’s CD. Figure 9.19 shows the loaded scene.

Figure 9.19. Here, glass balls sit on a set, a reflector object resides in front of the balls, and both are set and ready for refraction and caustics.

The scene contains three glass balls, a small set below them, and an area light above and in back of the objects.

Go to the Surface Editor and select the GlassBall_Teal surface. Set the Color to a bluish green, RGB 192, 226, 215. Leave the Luminosity at 0 percent, and change the Diffuse to 95 percent.

Change the Specularity to 70 percent for a shiny glass surface, and bring the Glossiness to 40 percent. This will create a medium-size hotspot on the glass ball. A higher Glossiness would create a smaller hotspot, giving the surface the appearance of highly glossed ball.

Set the Reflection to 5 percent.

Change the Transparency to 100 percent.

You might think that a 100 percent transparent object would be invisible, right? Well, in fact it wouldn’t show up at all in the render. However, an everyday glass is transparent, but what makes it visible is a combination of reflection and refraction.

Set the Refraction Index to 1.33. The higher the value, the more refraction will occur. Water and glass typically have a refraction value of around 1.33.

Bring Translucency up to 100 percent to help the light pass through the glass ball. Smoothing should be turned on.

You need to tell LightWave to calculate the reflections and refraction. By default, the Environment tab within the Surface Editor lists the Reflection Options as Ray Tracing and Backdrop; however, this setup will use the Ray Tracing and Spherical Map option.

Under the Environment tab of the Surface Editor, for the GlassBall_Teal surface, set the Reflection Options to Ray Tracing and Spherical Map. Make the Reflection Map Fractal Reflections. This is a fractal image on the book’s CD. Simply select Load Image from the Reflection Map drop-down list to load the image.

Click the Shaders tab in the Surface panel, and from the Add Shader drop-down list, select Edge_Transparency. When loaded, double-click it in the list to open its controls. Make sure that the Edge Transparency is set to Opaque, as shown in Figure 9.20.

Figure 9.20. The Edge_Transparency shader for the GlassBall_Teal surface helps give the surface an opaque look.

Under the Advanced tab of the Surface Editor, bring the Color Filter value to 100 percent. The tools in this tabbed area allow you to set features that are not commonly used but are key for certain situations. The Color Filter setting, for example, is perfect for glass. This will color the light source traveling through the transparent surface.

Go to the Render Options panel and make sure that Ray Trace Shadows, Ray Trace Reflection, and Ray Trace Refraction are turned on. These are all heavy-duty render killers, meaning they take a long time to render, but the results are worth it.


You can speed up render times when using Ray Tracing by changing the Extra Ray Trace Optimization value from the default 16 to 8 or lower.

Press F9 to render a frame. Make a low-resolution render to save on rendering time from the Camera panel if you need to. Figure 9.21 shows the rendered image.

Figure 9.21. Although only one light exists in the scene behind the objects, a transparent refractive surface on the glass ball allows the light to pass through.

Feel free to play with the lighting and refraction levels for different looks. When you’re satisfied, save your objects and save your scene.

Now you can copy and paste the surface settings from the GlassBall_Teal surface to the two other glass balls. You can do this in two ways. Either double-click the surface sample preset display at the top of the Surface Editor to save the surface in the Preset shelf or simply right-click the surface listing. Right-clicking on a surface listing in the Surface Editor allows you to copy and paste. Pick a method and copy the surface for GlassBall_Teal.


You can use the Preset shelf for long-term storage and retrieval of surface settings. One-time copy and paste are best handled by using the right mouse button operation. There is a third way that involves loading and saving a surface file by using the Save and Load buttons at the top of the Surface Editor.

Select the GlassBall_Purple surface and paste the copy. Do this by right-clicking and selecting Paste (which will paste what you right clicked and copied). Or, you can double-click the surface preset you made for the Preset shelf.

Once the surface is copied, simply change the color to a soft purple, about 189, 136, 193 RGB. Copy and paste again for the GlassBall_Red surface and make the color 209, 78, 58 RGB.

By copying and pasting the GlassBall_Teal surface, you save a lot of time resetting similar surfaces. All you needed to do is change the color. This also helps keep your objects consistent in all settings.


You also could have selected all three surfaces and changed the parameters for all settings at the same time. Then, you could go back, selecting a specific individual channel and change it’s specific color. If you do this, you’ll need to re-add the Shader in the Shaders tab. Shaders do not apply to multiple surfaces and must be applied one surface at a time.

Go to the Global Illumination panel (Lights tab) and click Enable Caustics. Turn on Cache Caustics (which will save data for subsequent renders, similar to Cache Radiosity discussed earlier) and set the Intensity to 60 percent. This is a scaling factor for the brightness of the caustic.

Set the Accuracy to 200.

This value can range from 1 to 10,000, and the higher it is, the more time is required to calculate the caustic. On a simple water glass, an accuracy of 120 is fine. More complex objects with multiple caustics would require a higher accuracy.

Finally, set Softness to 20.

This evaluates the surrounding caustic rays when rendering. A higher softness results in blurrier caustics, while a lower softness results in sharper caustics. If the caustic appears blotchy and not so smooth, the Softness setting can be increased, but the accuracy setting needs to be increased as well.

Figure 9.22 shows the final rendered image with reflection, refraction, shadows, radiosity, and caustics applied. Load up the Caustic scene from the book’s CD-ROM to see the final scene.

Figure 9.22. Some of LightWave’s heavy render hogs are at work: ray tracing, and caustics. Quite nice, but expensive rendering times.


Try applying Refraction Blurring from the Environment tab of the Surface Editor. A setting of 15 percent or so is a good place to start. What this will do is blur the refraction effects, enhancing realism.



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