This section describes the various RTrace pull-menus (in the menu bar) and what they do.
The File Menu
The File menu allows you to open a new scene description, to save an image or animation file, or to quit from RTrace. The menu options are:
Open .sff file...: This prompts you for a scene description file (a text file ending in .sff). Use this when you want to tell RTrace which scene to work with.
Save Image...: This allows you to save the image which RTrace has generated to a file. Use this when RTrace has finished rendering an image, and you want to save it to disk. This gives you the choice of saving the image as a PICT file or as a PPM file. You will usually want to save it as a PICT file, since that is the file format recognized by most Macintosh applications.
Quit: When you choose this option, RTrace aborts any rendering in progress and quits. Use this option when you no longer want to use RTrace.
The Edit Menu
The Edit menu allows you to copy the image to the clipboard, or to change the preferences for RTrace. All other options in the Edit menu are for compatibility with Desk Accessories only. The only options you can use are:
Copy: This option copies the image to the clipboard. This is only available if you have 32-bit QuickDraw. If you do not have 32-bit QuickDraw, you should use the Save Image command to save the image, and then open it from another application.
Preferences...: This option brings up the Preferences Window, and allows you to change the preferences. See Preferences Window.
The Windows Menu
The Windows menu lets you show or hide any of the five major windows. When a window is visible, its corresponding menu item will read “Show ... Window.” When it is not visible, the menu item will read “Hide ... Window.”
The available menu options are:
Show/Hide Options Window:This option will show or hide the Options Window . Hiding the Options Window during rendering can prevent the windows from cluttering up the screen. It has no impact on performance. See the Preferences section for information on how to automatically hide the Options Window during each rendering.
Show/Hide Status Window:This option will show or hide the Status Window. Since the Status Window provides continual feedback during scene reading and rendering, hiding it can speed thing up significantly. However, it does give valuable information on how much RTrace has done, and how much remains to be done. See the Preferences section for information on how to automatically show the Options Window during each rendering.
Show/Hide Log Window:This option will show or hide the Log Window. Since the Log Window provides some technical information feedback during scene reading and rendering, hiding it can speed thing up a little.
Show/Hide Animation Window:This option will show or hide the Animation Window. Generally, the Animation Window will show itself when necessary, and hide itself when it is no longer needed.
Show/Hide Image Window:This option will show or hide the Image Window. Since the Image Window is continuously updated during rendering, hiding it can speed thing up a little. Note, however, that if the image is not being kept in memory, the image in the Image Window will be incomplete if it is hidden, and then later shown. This does not affect any saved image, which will always be complete. See the Preferences section for information on how to automatically show the Image Window during each rendering.
The Windows
The Options Window lets you change any of the multiple options RTrace uses to generate the image. The Options Window looks like this:
Figure 3: The Options Window
The options (alphabetically) are:
Aliasing Threshold: This is one of the three major controls of image quality, the other two being shading threshold and ambient threshold. It controls pixel supersampling, and ranges from 0 (best) to 1 (poor). The good range is 0.1 to 0.03 (see Shading Threshold, Ambient Threshold, and Supersampling).
Ambient Levels: This option defines the number of shading levels (shading tree depth) in which ambient lighting calculations will be done through ray distribution. Use low values for this option.
Ambient Threshold: This is one of the three major controls of image quality, the other two being aliasing threshold and shading threshold. It controls ambient rays distribution caching, and ranges from 0 (best) to 1 (poor). The good range is 0.01 to 0.00001. A value of 0 means that there is no ambient threshold. (see Aliasing Threshold and Shading Threshold).
Ambient Samples: This option defines the maximum number of distributed rays to be used in ambient lighting calculations. Use low values for this option.
Animate: When this option is checked, RTrace uses the values in the Animation Window to generate multiple scenes. When it is not checked, the values in the Animation Window are ignored.
Antialiasing: Antialiasing is a method which smoothes out rough edges caused by visible pixels, eliminating the “jaggies.” RTrace can use any of three antialiasing methods: normal supersampling antialiasing, semi-adaptive supersampling antialiasing, or adaptive supersampling antialiasing. Normal supersampling antialiasing should be used with non-zero focal apertures (see Focal Aperture, Supersampling, Intersect).
Cluster Size: As part of RTrace’s scene processing, it groups scene objects in clusters. This option lets you specify how many objects there should be in a cluster. Use a low value for sparse scenes, and a high value for dense scenes.
Correct Texture Normals:When this option is checked, RTrace corrects texture normals when textures that modify normals are used, as they may sometimes create strange surface effects. This tends to happen if the scale of the normal perturbation is big.
Eye Separation: This controls the separation between the right and left eyes when using Right eye or Left eye View. It can be either an actual distance, or a percentage of the distance from the Eye point to the Look point (see View).
Focal Aperture: This option lets you set the focal aperture of the “camera” which is taking the picture. The default, 0.0, is a pinhole camera. If this is non-zero, there is depth of field, so adaptive supersampling antialiasing will not work so well (see Antialiasing).
Focal Distance: This option specifies the focal distance of the “camera” which is taking the picture. If the option is not checked, the distance from the Eye point to the Look point is used.
Image Width: This option lets you select the width of the rendered image, in pixels.
Image Height: This option lets you select the height of the rendered image, in pixels.
Intersect: This option chooses, in adaptive supersampling antialiasing mode, between testing all scene objects or only the objects found at the pixel corners and inside. Testing only at corners and inside greatly reduces CPU time, but with very small objects, is sometimes fails (see Antialiasing).
Intersect Adjust: When this option is checked, RTrace avoids some problems with invalid self-intersections. Scenes with text objects should be traced with this option checked.
Lighting: This option controls the generation of shadow rays through non-opaque objects. There may be either no such shadow rays, partial shadow rays, or full shadow rays. If a scene has translucent objects, full or partial shadow rays should be used for the most realistic image.
Normal: Normal is used here in the sense of “perpendicular.” This option lets you control the correction of surface normals, so that it points against the incident ray. With “correct” objects, you should use 1.
Shading: This option chooses between shading models. The options are Normal Phong or Strauss. The Strauss model, developed by Paul Strauss of SGI, is default but slower.
Shading Levels: This option establishes a maximum shading tree depth. When a scene has transparent or reflective objects, it may be important to lower this parameter, or else the tracing never stops. In most cases, there should be no problem allowing it to be large.
Shading Threshold: This is one of the three major controls of image quality, the other two being aliasing threshold and ambient threshold. It controls shading rays propagation, and ranges from 0 (best) to 1 (poor). The good range is 0.01 to 0.001 (see Aliasing Threshold and Ambient Threshold).
Supersampling: Supersampling refers to the antialiasing process where a single pixel is sampled many times, at slightly different positions inside the pixel. A greater number of samples results in smoother edges. However, supersampling significantly slows the rendering process. The choices are none, low, medium, and high. Choosing higher supersampling values improves the image quality, but slows rendering. “Medium” is a good choice for high resolutions, but “High” gives the highest image quality (and takes the longest time). (See Antialiasing, Aliasing Threshold).
Texture: This option lets you specify where the texture information appears in the scene description (.sff) file. There may be either no textures, or textures defined inside the objects field, or textures defined after the objects field. If you try to read a file with the wrong texture format, RTrace will generate an error. In that case, just change this option and try again.
Use Jittered Sampling:When this option is checked, RTrace uses jittered sampling. Sometimes checking this produces better images from scenes with small tricky details.
View: RTrace supports stereoscopic viewing, where two images are rendered from slightly different viewpoints, to emulate the separation of human eyes. This option lets you choose to render from the Left eye’s view point or from the Right eye’s viewpoint. If the view is Normal, no stereoscopic offset takes place (see Eye Separation).
There are also three buttons in the Options dialog:
Render: This begins a new rendering, using the current options on the most recently opened scene description (.sff) file.
Defaults: This resets all options in the Options Window to their default settings.
