Why you must trade off frame rate and quality

Interactive Ray Tracing, like Hardware rendering, displays the scene interactively by rendering the entire image frame over and over at a specific quality level. This “framerate” is typically many times per second, but will decrease as more rays are traced into the scene or as the number of samples per pixel (the smoothness) is increased. In general, a high quality image with many effects takes significantly longer to create and display than a very basic ray traced image with limited quality.

• The number of rays traced per pixel is based on the visible ray tracing effects (shadows, global illumination, etc.), and on the material characteristics (transparent, reflective, etc.) of the objects in the scene. The Performance and Quality ray tracing Quality presets control many of these factors at once.

  

• Samples per pixel determines the number of times each pixel on screen sends rays into the scene to determine the color of that pixel. A fractional amount will group screen pixels together and display less than screen-resolution images very quickly. For higher quality results, each pixel on screen is sampled more than once to insure that fine details and high contrast edges are accurate and smooth.

These settings work together to produce both fast results and high quality visuals, but typically one must be compromised for the other.

Tips for Ray Tracing performance and quality

Improving interactive performance

1. Reduce the Showcase window size. Ray tracing is based on tracing rays from each pixel of the image, so reducing the number of screen pixels will increase the frame rate and any progressive refinement of the image on screen.
2. Click Options > Performance and Quality to open the Performance and Quality dialog box, then click the Interactive Ray Tracing tab. Use the Overall Smoothness sliders as follows:
   • Set Samples per pixel to the lowest possible value (1/16). This is the value at which Showcase will stop ray tracing the view so that you can continue working on the scene. Visual quality will not be optimal, but performance and workflow will be good.
   • Check On idle increase to and specify a value with the slider. This value is the samples per pixel that Showcase will ray trace in the view when you are not interacting with the scene. If you choose to interact with the scene, ray tracing is aborted so that you can continue your work.
3. Set Samples per pixel to the lowest value (1/16). This is the value at which Showcase will stop ray tracing a view and allow you to continue working on the scene. Next, check On idle increase to; its corresponding slider controls the samples per pixel that Showcase will calculate when it is idle. This calculation will be stopped as soon as you try to interact with the scene. In other words, you will not be prevented from working on a scene when this calculation is taking place.
4. In the Options > Selection Display Style menu, select a “wireframe” display method. The “animated grid” will prevent progressive refinement.
5. Move the view away from areas with lots of transparent and refractive surfaces. Transparent and inter-reflective objects will require more rays per pixel than other objects in the scene, and will reduce performance when they are dominant in the view.

Improving output quality

1. In the File > Save Image As... or File > Save Movie As...dialog box, change the quality preset to one ending with “...Ultimate” and set the Sampling quality to be 4 or higher.
2. Test render your scene at smaller pixel dimensions to insure the quality and effects are correct before launching a large output render.
3. Quit all other applications to make as much system RAM available when rendering large output images or long movies.

Ray Tracing Status and Control Panel

The Ray Tracing Control Panel floats in the lower, right corner of the screen and shows feedback on the Interactive Ray Tracing progress, and provides quick access to Ray Tracing Settings and saving the on-screen image.

To open the Ray Tracing Control Panel, select View > Ray Tracing Control Panel or press the Y key.

Progress bar

A horizontal bar shows the current Interactive Ray Tracing progress between sampling settings, along with helpful diagnostic information. The Progress bar includes:

• Elapsed time: the elapsed time from the last Interactive Ray Tracing restart in “hours: minutes: seconds” format.
  NoteThe Interactive Ray Tracing progress will restart when any visual change takes place in the scene. This could be a camera movement, material adjustment, a change to the Ray Tracing quality preset, or many other actions.
• Percentage Done: the amount of the maximum Samples per pixel value that has been attained.
• Samples Min: the minimum Samples per pixel set in the Performance and Quality dialog box. This amount is where the Ray Tracer will begin to display an image on screen.
• Samples Max: the maximum Samples per pixel set in the Performance and Quality dialog box. When this amount is reached, the ray tracer will halt and the image on screen will be “done.”

Save (current screen image and settings)

Pressing the Save button in the Ray Tracing Status control panel will save the current image on screen to disk along with the ray tracing settings needed to reproduce it in a companion XML file.

To save the current screen image with a settings file:

1. Deselect any objects with Ctrl-Shift-A.
2. Press the Save button when the on screen image is desired.
3. Browse to a location on disk to save the image and the Settings XML file.
4. Enter a unique name for the image and settings and choose either JPEG or TIFF as the output format.

Use Saved screen image settings as a quality preset

The Saved screen image quality preset XML can be used to reproduce the exact quality level seen in that image for a larger image or animation.

1. Locate the saved settings XML file on disk. (It is saved in the same location as the screen image, with the same name appended with “.xml”)
2. Move this XML file to the My Documents\Autodesk Showcase 2011\InteractiveRaytracingSettings folder.
3. Close and reopen the Performance and Quality dialog, or Save Image As or Save Movie As dialog boxes.

   The new preset will be shown in the list of Quality presets in all dialog boxes, and can be used to recreate the exact quality level.

   NoteA saved screen image Quality Preset XML file only contains one Samples per pixel setting, and is not recommended for Interactive Ray Tracing. This disables progressive improvement and the image on screen will not be displayed until that sampling level is reached.

Settings (for Interactive Ray Tracing)

Press the Settings button to open the Performance and Quality dialog to the Interactive Ray Tracing tab. If the dialog box is already open, it will switch to the Interactive Ray Tracing tab.

Interactive Ray Tracing Performance and Quality

Insure maximum interactivity for the scene

1. Select Options > Performance and Quality or press the Settings button in the Ray Tracing Status UI (Y), to open the Performance and Quality dialog box.
2. Select the Interactive Ray Tracing tab to show the ray tracing controls.
3. Select a Quality preset labeled “...Interactive” with the effects desired.

   

   NoteRay Tracing quality presets included with Showcase are tuned either for an interactive experience, or for final output. The included presets are grouped by the various major ray tracing effects (shadows, ambient shadows, global illumination) activated by each.

Maintain a minimum interactive quality level

A minimum screen image quality can be maintained while allowing progressive improvements to the image.

1. Select a Quality preset with the effects desired.
2. Set the Samples per pixel slider to the desired minimum number of samples. The scene will update to show this level.

Locking display quality to a constant level

Lock the display quality

1. Select Options > Performance and Quality or press the Settings button in the Ray Tracing Status UI (Y), to open the Performance and Quality dialog box.
2. Select Quality preset with the effects desired.
3. Set the Samples per pixel slider to the desired minimum number of samples. The scene will update to show this level.

   

4. Deselect the On idle increase to: option to lock the quality to the Samples per pixel number above.

Preset Properties (Advanced)

Each quality preset includes detailed settings for many aspects of the Interactive Ray Tracing process. The Preset Properties fold-down exposes these controls to tune the ray tracing for quality and performance.

Reflections and Transparency

Ray Tracing includes reflections and transparency in all presets, and these settings have a large effect on interactivity. Because the same “ray” that bounces to show reflection may instead pass through objects to show transparency, one set of controls affects both.

• Max limit: for efficiency in ray tracing, a limit is placed on how “deep” a ray will continue into the scene when it is reflected or passes through a transparent object. If transparent objects in the scene look opaque or object reflections do not seem correct, increase this value.
  NoteFor objects that are both reflective and transparent, when the Max limit of transparency is reached, the ray will “bounce back” as a reflection. This avoids “black holes” in multi-layered transparencies, but can make objects look too shiny.
• Accuracy level: the quality of a ray traced reflection or transparency is based on the number of rays it uses to sample objects in the scene. If objects appear pixelated in reflections or transparency, or if Blurred Reflections look very rough, increase this value. See also:

Shadows and Illumination

Additional ray tracing effects can be activated to add shadowing and inter-object illumination to your scene. The default quality presets will activate these features, but they can be set individually.

• Object shadows: on/off and Quality level. The quality of a ray traced shadow is based on the number of rays it uses to sample the edges of objects. Soft shadows require more rays, and will show erratic edges when the quality level is not high enough.
• Use precalculated ambient shadows: if checked, precalculated shadows (see Add ambient shadows to surfaces) will be displayed when present. Precalculated ambient shadows will override ray tracing ambient shadows if this is checked.
• Ambient shadows: on/off and Quality level. Ray traced ambient shadows are not “baked” to geometry, so they will update as items are moved or animated. The Ambient Shadows Quality level determines how many rays are cast for these types of shadows, and will show dots or speckled shading when the quality level is not high enough.
• Global Illumination: on/off and Quality level. Global Illumination is a combination of ambient light collection and “light bouncing” from one surface to another. The Global Illumination Quality level determines how many rays are cast to find and disperse this illumination, and will show dots or speckled shading when the quality level is not high enough.

Saving presets

Quality presets for interactive and offline Ray Tracing can be saved from the Performance and Quality dialog box. This is a good way to preserve temporary modifications to other presets (denoted by a * in front of the name), or to create presets based on computer capabilities or special needs.

To save a custom quality preset:

1. Select Options > Performance and Quality or press the Settings button in the Ray Tracing Status UI (Y), to open the Performance and Quality dialog box.
2. Select Quality preset to start your preset from, or adjust the properties individually.
3. Press the Save Preset As... button.

   A file browser opens to My Documents\Autodesk Showcase 2011\InteractiveRaytracingSettings.

   NotePreset files saved in other locations will not be loaded by Showcase. If moved to this default location, they will be recognized.
4. Give the preset XML file a descriptive name, and press Save.

   The new preset will appear in the quality preset drop-down list for Interactive Ray Tracing, Save Image As..., and Save Movie As... output types.

• To share a custom quality preset with another Showcase user, simply copy the XML file and place it in the same “InteractiveRaytracingSettings” folder in their Showcase 2011 user directory.
• To remove a custom quality preset from the drop-down list, move or delete the XML file from the default “InteractiveRaytracingSettings” folder.