C-LIGHT

Light the stage for easy ray tracing.

By Wayland Strickland

C-LIGHT, a three-part program, enables you to create a cast of objects and place them on a set. The first module is C-Light I, an object creation workshop. The Video module lets you set up resolution, picture size, and video standards. C-Light II performs the ray tracing, that is, it plots rays through space as they bounce off your creations. What sets this package apart from its competitors is its all-around simple approach.
C-Light I offers balls (spheres), cans (cylinders), and cubes as building blocks. While this may sound limiting, it is not. You can quickly and easily manipulate the shapes to produce virtually anything. To create a door, for example, you would stretch a cube into a door-size rectangle, and then flatten it. To make the lock plate, follow the same procedure, but shrink the shape and center it on the left edge of the door. For the stem of the handle, take a cylinder, reduce it in size, and place it on the lock plate. Now compress a sphere and place it over the cylinder to complete the door knob.

Raise The Curtain

To select a shape, simply click on its icon at the right of the screen. C-Light I displays your selection in wire-frame mode; you can place it anywhere in the three-dimensional universe with the mouse or by setting coordinates in a pop-up requester. Then you can specify size (in each dimension), color, surface texture (smooth-shaded or mirrored), and angle of rotation (0 to 360 degrees) for each object. Most operations are carried out in real time, although I did experience a lag when using the mouse for complicated maneuvers. If you wish to revise an object you have already generated, you can select and modify (or delete) it in the same manner.
Although you can choose from any of 4096 hues, C-Light I displays only four colors at a time (one background shade and three object colors). From these colors shading is performed. When you are ready to select colors for the palette, C-Light I displays a rainbow made up of default selections that you can change. This method is useful for determining how each of your choices will look next to the others. The feature has a small cosmetic problem though: A flashing purple scan line remains under the menu bar after you exit the mode.
Now that you have set your pieces on stage (each scene accomodates up to 170 objects), you can call in the lighting crew. C-Light I allows as few as one light source and as many as 170. You position light sources the same way as you place objects; the only difference is that you cannot rotate lights or alter their size or color. Lighting instruments radiate in all directions, but are themselves invisible within a scene.
The View gadget in C-Light I lets you manipulate whole scenes in much the same manner as objects. A large cube represents the scene; you can expand or contract it, and rotate it any direction and by any degree. Resulting changes are displayed in a second cube (in a different color), so that you can compare the altered version to the original. This capacity is useful for simple panning; you can generate several pictures with increasing or decreasing X-coordinate values. You can also zoom into or out of scenes by changing the value of the Z coordinates in the same way.
C-Light I's Eye gadget adjusts the viewer's distance from the scene. Perspective increases and distortion decreases the closer you place the "eye" to the stage; the opposite is true for moving away. While you can now move the viewpoint in only two directions, the manual states that others will be added if users request them.

Act Two

The Video module works in much the same way as Preferences in Workbench. The program starts by asking you whether you are using an NTSC (National Television Standards Committee) or PAL Amiga. You must also choose whether your picture will be overscanned (352 x 480) or not, and interlaced or non-interlaced. The settings are stored and used by C-Light II to generate the picture.

C-Light II begins its start-up sequence by requesting you to set (with sliders) the light level for all light sources and an ambient level for the entire scene. (Default settings for the sliders are loaded with the program.) Another slider controls the level to which colors blend into one another. Triggering the Alias control turns on a anti- aliasing routine to reduce jaggies, and selecting Shadow causes objects to cast shadows (otherwise light will pass through undisturbed). Both features add to the time required to generate a picture.
Rendering time also depends a great deal on the number of objects and light sources you have used. In my tests, fairly simple scenes required generation times of about one hour, but complex pictures took up to two days (I do not have a 68020 or 68881 board). All scenes are saved in the standard IFF format. View, a stagehand utility, lets you see completed pictures.
The C-Light package is easy to learn and use. On-line help is included, and the well written manual provides complete explanations and a comprehensive tutorial. 512K is required to generate ray-traced pictures, but to use the on-line help feature, one meg is recommended. The program is fully multitasking and not copy-protected. A new version has come onto the market as we go to press. It includes utilities for creating and replaying animation, and promises to banish menu-bar flicker. I highly recommend C-Light to anyone interested in ray-tracing, and especially to beginners.