Efficient Preview Rendering in Blender

Strategies for efficient preview rendering of stills and animations in Blender.

Preview rendering is an important part of your work flow and needs to be as efficient as possible. It’s important to have strategies and techniques for the earlier stages of scene development that facilitate a smoother work flow. The less time you spend waiting for renders during the early phases of a project, the more time you’ll have for fine-tuning and testing, resulting in better final results for your project. In this article, we’ll take an overview of some of the different tools and techniques that are available in Blender to help you be more efficient with your preview rendering.

This article requires an intermediate knowledge of Blender and is based on the feature set of Blender version 2.48.

Render Preview Window

The Render Preview window will allow you to quickly preview the area within the boundary of its floating window. To activate this tool, move your mousepointer within the boundaries of a 3D view and press Shift-P.

The Render Preview window updates automatically as you change parameters and the viewing angle within the 3D view. The keystroke, Shift-P, will toggle the visibility of the preview window. You can also relocate, resize, and minimize it at will using the intuitive controls found in its interface.

With the preview window visible, you will still have the ability to select objects that are underneath it. This allows you to select and adjust objects in your scene without having to minimize the preview window.

If the preview window doesn’t update, you can press Shift-P twice to unload and reload its interface. This usually happens when updating certain changes (e.g. – lighting).

This tool is not meant for previewing animations.

Border Rendering

The Border render feature can be found in the Scene buttons window (F10) on the Render panel, as shown.

This feature will allow you to draw a box around the desired area for rendering. To use it, you’ll need to switch to a camera view (Numpad-Zero), and press Shift-B. Now, select the desire area for rendering. Be sure to enable the Border option found on the Render panel. The selected area will be denoted by a red dotted-line. Press F12to render the border-selected area.

The selection area will be remembered, so you can feel free to toggle the Border option on/off as needed. To create a different selection area, simply press Shift-B and select a different area.

Approximate Ambient Occlusion (AAO)

AAO is a great way to achieve a fast-rendering GI lighting effect in Blender. The results are similar to Blender’s ray-traced ambient occlusion set to its highest quality setting, but renders in a fraction of the time. The results hold up very well in animated scenes as demonstrated in the Blender Foundation’s “Big Buck Bunny” animated short. If you need ambient occlusion in your render, definitely give AAO a try for much faster previewing and final results.

You can find the AAO controls in the World buttons window, on the “Amb Occ” panel.

For more info:
http://www.blendernation.com/2008/01/23/ambient-occlusion-in-svn/

Override the Material Settings

Blender has a little-known feature that allows you to temporarily assign the same material to every object on a render layer. Each render layer has this feature so you can make them all have the same material or have them all be different. This can be very helpful for fast previews. For example, you can quickly do a “clay” render of an entire scene without having to manually change the material of every object in the scene. Or, you could temporarily color-code different aspects of your scene based on the render layers. The temporary material can be any material that exists in the scene.

To assign a new material to all objects on a render layer, go to the Scene buttons window (F10) and locate the Render Layers panel. In the Layers section, locate the “Mat:” field and enter the name of any material that exists within the scene. To disable this new material assignment, simply clear the “Mat:” field.

Override the Lighting

Similar to overriding the materials in a scene, you can temporarily override the current lighting setup with another group of lights. You can do this using the “Light:” field located to the left of the “Mat:” field shown above. This feature can be used to quickly switch to a simpler lighting setup for faster renders, and then switch to the more complex lighting setup for the final render by simply editing this one field. The overriding lights have to be in a group, though.

To use this feature, simply type in the Group name of desired lighting setup. To go back to the original lighting setup, clear the field.

Adjust Modifier Settings

You can increase the rendering speed for preview renders by setting your modifiers to be disabled when rendering. This works particularly well for the Subsurf modifier because you also have the option to determine the level of the effect for the both the 3D view and the render.

To toggle a modifier’s effects during rendering, use the camera icon found on each modifier’s control panel.

Render Simplification

The Render Simplification feature is a bit “hidden” in Blender. I think that it was originally meant for testing during programming development, but it’s there so why not use it? This feature allows you to reduce the complexity of the render calculations without having to change your parameter settings. You can drastically reduce the effects of several time-consuming aspects of rendering your scene with minimal change to how your rendered scene appears! Yes, there are some differences, but the render still functions very well as a pre-visualization for your final full render.

To use Render Simplification, go to the Scene buttons window (F10) and locate the “Play” button on the Anim panel. To the immediate right, you’ll see a control labeled “rt”. Increment the value to “1”. You will now find that a new panel has been added to the buttons window called Simplification. On this panel, simply enable the Render Simplification feature and lower the values of the parameters. Don’t be afraid to turn them down considerably.

This render was done without Render Simplification (render time: 6 min. 16 sec.).

This render was done with Render Simplification (render time: 2 min. 27 sec.) .

It will take a little experimentation to get a feel for how low you can set things and still get an acceptable render. However, this one feature will save you tremendous amounts of time during scene development.

OpenGL Rendering

Blender offers a feature similar to Maya’s “Playblast” that allows for very fast rendering of the current 3D view. This render can be a still image or an animation. Since this is basically a screen capture of the current 3D view, the quality of the lighting and materials will be limited to the 3D view’s display type setting. In addition to its rendering speed, using OpenGL rendering for your animation previewing will allow you to playback your animations at full speed.

The output format of the OpenGL render is determined by the same settings (located in the Scene buttons window) used for a normal render. Still shots will have to be saved to disc as usual (F3). Rendered animation frames will be saved automatically.

To use the OpenGL rendering features of Blender, orient a 3D view to properly frame the subject. On the Header Bar of the 3D view, locate the “Render this window” button found at the right side. Clicking this button will capture a still image, and Ctrl-Clicking it will capture an animation of the view’s contents.

The render displays in a popup playback window. When displaying an animation, the playback window offers some control via the following keystrokes.

ESC – closes the window.

ENTER – starts playback.

Shift-key (hold) – displays animation file info.

LeftArrow – stops the playback; moves 1 frame back.

RightArrow – stops the playback; moves 1 frame forward.

Shift-LeftArrow – jump to the first frame of the animation.

Shift-RightArrow – jump to the last frame of the animation.

Numpad-Zero – sets the playback at the first frame and switches “cyclical” playback off. Pressing this key again turns cyclical playback on again and starts the playback at the beginning.

Numpad-1 thru Numpad-9 – controls the playback speed. 60, 50, 30, 25, 20, 15, 12, 10 and 6 frames per second, respectively.

LMB drag – dragging the mouse horizontally through the playback window allows you to scrub through the frames.

A-key – toggles the NoSkip mode (all frames will be played instead of skipping frames as needed to maintain the targeted framerate).

P-key – toggles the PingPong playback mode.

Usage Tips:

• After Ctrl-Clicking the render button on the Header Bar, you’ll see the animation’s frames displayed while being saved according to your output settings. Note that the window displayed at this time is NOT the playback window, it’s the standard render window. So, after the animation has been output, press the Esc-key to close the render window and then press Ctrl-F11 to open the playback window. You can use Ctrl-F11 to display the playback window at any time.
• You can also use the “Play” button located in the Scene buttons window on the Anim panel to display the playback window.
• For animations, be sure to specify a location and filename for the output using the filename field located on the Output panel in the Scene buttons window. Otherwise, the file(s) will be saved in the temporary files folder specified in the Preferences window. If you don’t provide a filename, the file(s) will be automatically named based on the range of frames (e.g. – 0001_0060.avi).
• While scrubbing through an animation (LMB drag), the width of the playback window serves as a timeline. In other words, if you want to begin scrubbing from the halfway point of your animation, position the mousepointer at the center of the playback window before beginning to scrub through the frames.

Conclusion

This concludes our look at some of the tools and techniques that are available in Blender for increasing the speed of your preview renderings. Mastering these simple tools and techniques will definitely have a positive impact on your workflow.