Radiosity

Although they are effective and relatively efficient, the ray-tracing calculations used in RenderWorks rendering modes cannot produce the full range of lighting effects seen in the real world. The most realistic, yet intensive, rendering effects require radiosity. By adding the indirect lighting and soft lighting effects of radiosity, a rendering can seem highly realistic.

Radiosity is a rendering technique that models light energy transfer between drawing geometry and materials. Radiosity treats each section of drawing geometry as both an absorber and emitter of light. Light energy starts from the light sources present in the drawing; the surfaces that the light illuminates then re-emit the light energy, with changes to the light quality producing softer shadows, color “bleeding” between differently-colored surfaces (because a colored surface re-emits colored light), and softer, diffused lighting. The light energy bounces around until it stops producing an effect.

The radiosity rendering method generates large mesh structures to resolve lighting details in the image. The parameters necessary to create a drawing with radiosity, combined, are called a “radiosity solution.” It is possible for the radiosity solution to require too much detail or such high amounts of mesh data that the rendering cannot take place over a reasonable time period. By balancing the need for sufficient detail in important parts of the image with the exclusion of excess data that is not as necessary, a good radiosity solution can be produced. In addition, the use of final gather rendering with radiosity can improve quality and shorten render times. RenderWorks provides the tools necessary to create the radiosity solution properly, for a high-quality rendering in the shortest possible amount of time.

Radiosity can be highly effective for “matte” drawings. It cannot produce indirect lighting effects for specular reflections, or for light distorted by glass.

Radiosity is available with three RenderWorks commands. For a quicker, lower-quality radiosity solution, select View > Rendering > Fast Radiosity. For a high-quality, but slower, radiosity solution, select View > Rendering > Final Quality Radiosity. Finally, for complex drawings, Custom Radiosity rendering allows the radiosity solution to be controlled by setting up and testing the radiosity solution manually.

Radiosity Workflow

It can take some time to come up with an effective radiosity solution for a drawing. In addition, the rendering process itself can require significant amounts of time. Therefore, certain steps are recommended in order to achieve the best radiosity rendering.

1.	The drawing should be as close to completion as possible. Modifications to the drawing geometry, materials, or lighting will cause the radiosity solution to be deleted, requiring the solution to be regenerated at the next render.

Radiosity solutions for design layers are not saved with the file. For viewports, individual radiosity solutions for each render mode that supports radiosity are stored with the file, if the Save viewport cache option is selected on the Display tab of document preferences.

2.

For a preliminary view of the radiosity solution, select View > Rendering > Fast Radiosity. If the drawing is not too complex, then select View > Rendering > Final Quality Radiosity. The automatic radiosity solution and final gather rendering clean-up provided may be exactly what is required for the final presentation of a drawing.

A rendering made with final quality radiosity may take a considerable amount of time. For a complex model, optimizing the radiosity settings first and then rendering with custom radiosity is recommended.

3.

For a custom radiosity solution, first specify the custom RenderWorks parameters by selecting View > Rendering > Custom Radiosity Options, and make custom settings for the categories in the Custom Radiosity Options dialog box (see Custom RenderWorks Options). Selecting Use Final Gather is recommended, for clean-up of triangular artifacts and light and shadow leaks, and for the indirect lighting of objects which are excluded from the radiosity solution. Like radiosity, final gather rendering creates indirect lighting effects, but from a single light bounce rather than the multiple light energy transfers of radiosity. A combination of “coarse” radiosity and “fine” final gather rendering settings can produce efficient, high-quality rendering effects.

4.

With a specific setting, objects and textures can override the radiosity parameters, so that they always participate in a custom radiosity rendering (this allows radiosity settings to be set to exclude many other objects, without eliminating these specific textures and/or objects, saving unnecessary calculation time). For maximum efficiency, exclude all but the largest or most important objects from the radiosity rendering, and set the final gather rendering to handle the indirect lighting effects of the remaining objects.

Textures and objects can specifically only receive light, or both receive and emit light. Specify these overrides before attempting the radiosity rendering. For these types of textures, click Radiosity Options in the Edit Texture dialog box, and then select Override Radiosity Settings. To allow certain objects to override the radiosity settings, select Override Radiosity on the Render pane in the Object Info palette. An object can override its texture settings; if a texture does not have an override, but the object does, the override applies.

5.	To optimize the radiosity solution, select View > Rendering > Custom Radiosity Options, and then click the Radiosity Options category in the Custom Radiosity Options dialog box. These parameters are described in Setting Custom Radiosity Options.

Click Optimizations to limit the radiosity bounds, if possible; for example, if only one area of a large model is illuminated, the rest of the model can be excluded from the radiosity calculations.

Select Allow Special Overrides to include specially-marked textures and objects regardless of the radiosity settings.

Click Show Color-Coded Preview in the Radiosity Options category of the Custom Radiosity Options dialog box, to preview the drawing while setting the sliders to their optimal positions. Insignificant geometry should be optimized out of the solution, until the preview displays that the final results will have the desired detail sizes.

6.

Test the radiosity solution by setting a Time Limit and Energy percentage, and then press Start. During solution generation, a rendered preview of only the indirect lighting is shown in the drawing window, and solution statistics are displayed. Press the Esc key to further refine the solution, and then press Resume to continue it. Once the preview displays an acceptable solution, press Accept.

7.	Render the customized radiosity solution for final presentation by selecting View > Rendering > Custom Radiosity.

To stop the generation of a radiosity rendering, press the Esc key, or Command-period (Macintosh), Ctrl-period (Windows), and a dialog box opens, asking whether to continue, delete, or accept the current solution.

A radiosity solution is view-independent. The view can be changed, or the Flyover, Pan, and Zoom tools used, for example, and the current solution is used to re-render the drawing. However, changes to the drawing geometry, textures, fill colors, materials, or lighting cause the solution to be deleted.

Setting Custom Radiosity Options

Setting the radiosity options for custom radiosity rendering provides a high level of control over the radiosity solution. The radiosity solution can be tested, stopped, changed, and resumed in order to determine the best parameters for rendering in a reasonable amount of time.

To set custom radiosity options:

1.	Select View > Rendering > Custom Radiosity Options.

2.	The Custom Radiosity Options dialog box opens. Select a category from the list on the left to see the associated parameters on the right.

The Texturing, Geometry, Lighting, Final Gather, and Rendering categories contain parameters described in Custom RenderWorks Options. The parameters set in these categories are identical to the custom RenderWorks settings, but apply to the custom radiosity rendering.

3.	Click the Radiosity Options category to specify the custom radiosity settings.

 

Parameter	Description
Obj Inclusion	Controls the number of objects participating in the radiosity solution; objects below this size receive light energy, but do not emit it. Drag the slider to the right to increase the number of objects included. For maximum efficiency, set the size high enough to include only the largest and most significant objects, and enable final gather rendering to handle the smaller objects.
Init Detail	Controls the size of the emitting surfaces and the starting size of the receiving surfaces; drag the slider to the right to decrease the triangle (mesh) size
Accuracy	Controls the tendency for the mesh to approach the terminating resolution for light and shadow details; increasing this parameter affects the resolution of indirect shadows. In addition, it affects the accuracy of the light transport from surface to surface. Drag the slider to the right to increase the accuracy percentage.
Energy	Sets the amount of indirect light energy for the radiosity solution; when this level is attained, the solution is complete. Drag the slider to the right to further refine an existing solution.
Time Limit	Specifies a time limit in hours and minutes for terminating the radiosity solution. The solution terminates when either the time limit is reached or the desired Energy limit has been achieved (whichever comes first).
Optimizations	Specifies further control over which surfaces participate in the radiosity solution
Ambient Options	Specifies the ambient lighting setting; ambient lighting can have a significant effect on a radiosity rendering
Show Color-Coded Preview	Provides a visual indication of the detail sizes and optimizations applied to the current scene, to quickly be able to eliminate insignificant geometry from the solution. The preview is color-coded to denote object inclusion, bounding volume limit, and initial detail values. Red: Obj Inclusion (shows objects receiving but not emitting light) Yellow: Init Detail Black: Objects that are not included in the radiosity solution and are neither emitting nor receiving light, because they are outside the bounding volume (specified in Optimizations), or have overrides applied to them Grayscale: Objects that are both receiving and emitting light energy are shown in a grayscale relative to their size

4.	To control the ambient light options, click Ambient Options.

The Ambient Options dialog box opens. Normally, ambient lighting should be turned off for a radiosity rendering, to avoid overlighting.

 

Parameter	Description
Use Layer/Viewport Ambient Settings	Uses the ambient lighting setting specified in the Layer Lighting Options dialog box (View > Lighting > Set Layer Lighting Options) or in the Viewport Lighting Options dialog box (click Lighting Options from the Object Info palette Shape tab of a selected viewport)
Create Ambient from Remaining Energy	Converges the solution to the percentage specified in Energy and then applies the remaining light energy to all the objects as ambient light energy (can cause a scene to become overly bright if a significant amount of light energy remains)
Don’t Use Ambient Light	Turns off ambient lighting for the radiosity rendering, which is recommended when emphasizing indirect lighting effects

5.

To control which surfaces participate in the radiosity solution, click Optimizations. Before the solution is generated, visibility information is gathered to exclude insignificant objects from the solution, either because they are not visible, or they are not participating in the indirect lighting scheme. If textures and/or objects have radiosity overrides, enable the overrides.

 

Parameter	Description
Optimize for Static View	Enables optimization options for rendering a static view with radiosity (deselect if planning to change views or create a movie from the rendering)
Include Visible Surfaces Only	Only visible surfaces participate in receiving and emitting indirect light; use overrides to include specific non-visible objects in the rendering
Limit Radiosity Bounds	Limits the radiosity solution to a 3D bounding volume (for example, the rest of a building may not need to participate in the rendering, when only one room is of interest)
Derive from Static View	Automatically determines the radiosity bounds using visibility data of objects in the current view gathered for static view optimization; includes objects behind the viewer
Manually	Specifies manual coordinates for the bounding volume. The bounding volume is previewed with dotted lines; objects outside the bounding volume are shown in black. Specify the minimum and maximum X, Y, and Z coordinates to determine the bounding volume.
Allow Special Overrides	Allows specific objects to participate in emitting or receiving indirect lighting during radiosity processing
Special Overrides	Sets the participation of objects with radiosity overrides set in the Object Info palette and textures with overrides set in the Edit Texture dialog box
Obj Info and Texture	Enables the override options in both the Edit Texture dialog box and the Render tab of the Object Info palette to allow objects and textures with overrides to emit or receive indirect lighting during radiosity processing, regardless of the custom radiosity parameters
Texture Only	Enables the Override Radiosity Settings option in the Edit Texture dialog box to allow objects with that texture applied to emit or receive indirect lighting during radiosity processing, regardless of the custom radiosity parameters
Obj Info Only	Enables the Override Radiosity option on the Render tab of the Object Info palette to allow specific objects to emit or receive indirect lighting during radiosity processing, regardless of the custom radiosity parameters
Other Items	Sets the emit/receive properties of objects and textures without overrides Emitting surfaces are processed from brightest to darkest
May Emit and Receive	Allows objects and textures without overrides to possibly receive and re-emit light energy, depending on the radiosity settings
May Only Receive	Allows objects and textures without overrides to possibly receive light energy, depending on the radiosity settings, but not re-emit it
May Neither Emit Nor Receive	Allows objects without overrides to neither emit nor receive light energy, excluding them from participating in the radiosity solution. These objects and textures are rendered only by direct lighting.
Update Preview	Updates the color-coded preview (Show Color-Coded Preview must be selected in the Radiosity Options category of the Custom Radiosity Options dialog box)

6.	Click the Radiosity Solution category to generate the solution.

The radiosity settings are used for a rendering with radiosity when View > Rendering > Custom Radiosity is selected. However, the radiosity solution can be generated from the Custom Radiosity Options dialog box first, if desired, in order to refine a solution until it is acceptable. By using the color-coded preview and the Solution Info controls (Start/Resume, Accept, Delete, and the Esc key), the radiosity solution can be refined until the best quality is achieved in the shortest amount of time.

 

Parameter	Description
Solution Info	Displays statistics gathered from the current solution, while a solution is being generated and once it is complete Energy: displays the solution’s indirect light energy value; when this value reaches the Energy setting, the current solution has been produced. Emitting: shows the number of triangles emitting light energy Receiving: shows the number of triangles receiving light energy Time Used: displays the elapsed solution time Time Remaining (Est.): displays an estimate of the remaining time until the Energy level has been reached and the solution is complete Median Obj Size: displays the median size of objects in the model, and sets the halfway position for the Obj. Inclusion, Init Detail, and Small Detail parameter sliders
Start/Resume	Begins generating the radiosity solution, or proceeds with a paused solution if the Energy percentage has not been achieved. To pause the generation of a radiosity solution, press the Esc key, or Command-period (Macintosh), Ctrl-period (Windows).
Accept	When a solution exists, but the specified Energy value has not been reached, pressing Accept changes the Energy slider to the current solution’s energy value
Delete	Deletes a solution; press Start to restart the solution from the beginning

Once a solution has been completed, the radiosity parameters cannot be changed. Click Delete if changes are desired, and then generate the solution again by pressing Start.