Introduction
Rendering an image can be a very time consuming process, since it requires an enormous number of calculations to mathematically trace the rays of light around your 3D design. The best available method for speeding up this process is to avoid calculations which are not really necessary. This chapter explains how program settings and the characteristics of your design will affect these calculations and the overall rendering time. Note that the "Render -> Estimate Render Time..." menu item can give you an estimate of what the overall rendering time will be under the current program settings.

Image Size
Each pixel in a rendered image requires an individual ray-tracing computation to determine what color it should be. All else being equal, the rendering time will always be proportional to the number of pixels in the image. Thus, it makes sense to let the image be as small as practical for what you are trying to accomplish. If you are just checking lighting, shadows, or intersections, a quarter or half screen image is often big enough. Remember that a one-quarter screen image contains only one-sixteenth as many pixels as a full screen image. So, if the image doesn't need to be big, don't make it big. You can also save a lot of time by only rendering small rectangles in the eye view window. This is often a very quick method of making sure that the full size rendering will be correct.

The Number Of Objects
An image which contains many objects will take longer to render than an image which contains only a few. Note that if the computations for reflection, refractions, and shadows (described below) are not being performed, then the rendering time will be roughly proportional to the number of objects. For example, twice as many objects might only take twice as long to render. However, if the more complex calculations (shadows, refraction, reflections, etc) are being performed, then the overall rendering time will increase more dramatically with the number of objects. For example, twice as many objects might take four times as long to render.

The Number Of Light Source Objects & Shadows
The existence of light source objects make it necessary to compute the locations of shadows and spectral reflections. This, more than anything else, can greatly increase the rendering time, especially as the total number of light sources increase. For example, the addition of each light source object can easily increase the rendering time by fifty percent.  Turning off these computations in the "Render Settings" dialog box will greatly speed up the rendering process. This is useful when you are rendering a test image which contains one or more light source objects, but you do not feel it is important to see spectral reflections or shadows.  I recommend never using more than two or three light source objects, since more than that doesn't improve the image much (usually), it just makes it take a really long time to render.

Note that light sources which do not generate shadows (described in the Modify Object Behavior" section of the "Object Manipulation" chapter) will do little to increase the rendering time.  Likewise, setting regular objects to not cast shadows will also decrease the rendering time, since unecessary shadow calculations can be avoided.  In short, the fewer objects and lights which can generate shadows, the faster the rendering will be.

Reflective And Refractive Objects
The existence of objects which reflect or refract light will also greatly increase the rendering time. This is especially true as the total number of objects increases. This is because the light which hits these objects will continue traveling, and the ray-tracing computations must continue until the light stops. Turning off these computations in the "Render Settings" dialog box will speed up the rendering process. This is a wise thing to do if you are testing lighting, object intersections, or other aspects of an image which do not depend on reflections or refractions. 

Background Tasks
All Power-Mac applications must cooperate with each other by sharing that wonderful (faster than Pentium :-) PowerPC processor. An application does this by allowing "background tasks". The "Rendering In Progress" menu allows you to specify the number of background tasks which are allowed each second. More background tasks per second will improve the response of other applications, but will also increase the rendering time. If you want the rendering process to go as fast as possible, then you will want fewer background tasks. To further maximize speed, you will want to avoid using other applications while RenderBoy is rendering an image. Also, if you are not using any other applications, you will want to leave RenderBoy (not the Finder) as the active application. This lets RenderBoy get as much CPU time as possible.