Bouncing Sphere Animation

Modelled and shaded in Emacs, using al-mode for Animation Language, and rendered with BMRT.

Animation based on bouncing ball, AL Animation Language demo by Steve May, T.D. Pixar Inc, while he was teaching at ACCAD, Ohio State University, when he created AL.

"AL is a environment for procedural computer animation which provides a powerful modeling language, a language interpreter, and a set of interactive animation tools.

In addition, AL provides a complete interface to RenderMan compliant renderers including PhotoRealistic RenderMan (tm) and BMRT. The AL software is free and is available on Silicon Graphics workstations and PCs running the Linux operating system."

I wanted to show the automatic changes in reflections and refraction as an object moved, programmed entirely within the Animation Language, using Pixar Renderman Shading Language.

To do this, I replaced the plastic shader of the ball with glass, and set it's opacity very low, to create transparency, then increased reflection and refraction. Then I replaced the wood floor with a checker board, and increased the scale of the Bouncing ball animation from 200x150 to 640x480, and the sphere by 1.5 to create a larger area to show reflection and refraction. Then increased the antialiasing sampling rate by 5x5 and rendered using BMRT - Blue Moon Rendering Tools. Finally, I converted the TIFF images from BMRT to PNG using ImageMagick mogrify, and encoded the 90 frame images as video using mencoder. I didn't create MPEG4 using JPEG images because I feel JPEG is not good enough image quality, and adds artefacts to the checker board, and aliasing and blurs in the resulting video.

"The Blue Moon Rendering Tools (BMRT) are a collection of rendering programs which adhere to the RenderMan(R) interface standard (RenderMan is a registered trademark of Pixar).

The toolkit consists of a full implementation of the RenderMan standard which supports ray tracing, radiosity, area light sources, texture and environment mapping, programmable shading in the RenderMan Shading Language, motion blur, automatic ray cast shadows, CSG, depth of field, support of imager and volume shaders, and other advanced features. The toolkit also contains quick RIB previewers (using GL or X11) to allow "pencil tests" of scenes and animations."

Gritz, L. and Hahn, J.K.
"BMRT: A Global Illumination Implementation of the RenderMan Standard",
Journal of Graphics Tools, Vol. 1, No. 3, pp. 29-47 (1996).

The images to the right are PNG converted from the TIFF original render output. In frames 40 to 50 you can see how the refracted image of the checkered floor, in red and white, moves across the top of the sphere, while the reflection of the floor remains at the bottom within the green colour of the sphere. In frame 55 you see the sphere expand after bouncing off the floor, and the reflection of the spotlight increase in size, and in frame 60 the sphere resumes it's usual shape, and the refracted and reflected images of the floor and spotlight again change relative to this.

Screenshots, and brief descriptions of the software used, AL Bouncesphere II

The scene, animation and shader data, syntax highlighted, AL Bouncesphere III

The original higher quality 640x480 video can be downloaded here bouncesphere.avi

AVI, iPod and Sony PSP versions can be download from Google video

HTML embed code is available from Google video or Youtube