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Tema: Split Frame rendering on the ResPower Super Farm

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    Fecha de ingreso
    Apr 2002

    Split/Frame rendering on the ResPower Super/Farm

    Split/Frame rendering on the ResPower Super/Farm.
    by - Cory King and Early Ehlinger

    I - What is Split/Frame rendering?
    II - How does ResPower accomplish Split/Frame rendering with Blender?
    III - What about re-assembly?
    IV - How much speedup does Split/Frame provide?
    V - Real world examples.
    VI - Known Issues.

    I - What is Split/Frame rendering?

    ResPower is constantly searching for ways to speed up the process of 3D content creation, specifically in the área of rendering. Speeding up the render times of animations with hundreds or thousands of frames is fairly straightforward; simply render each frame on a different computer so that múltiple frames run in parallel. Split/Frame rendering is básically the same process, only it is designed for still frame images.

    The basic idea behind Split/Frame rendering is to breaque a single frame into múltiple chunks called "buckets". Each bucket is then rendered on a separate computer so that several (possibly one hundred or more) chunks can be run in parallel. This speedup is linear in theory, meaning that a frame split into 100 buckets should render 100 times faster than the same frame rendered as 1 bucket. Unfortunately, because of Amdahl's Law, this is not the case, although the speedup can still be quite remarkable. Chek the sidebar for more information on Amdahl.

    Split/Frame rendering is not a new concept and has been available for many 3D rendering engines for years. Professional 3D packages such as 3DStudio and Lightwave support Split/Frame natively, but even with one of these packages the advantages of Split/Frame are only seen when using a render farm like ResPower.

    II - How does ResPower accomplish Split/Frame rendering with Blender?

    The Blender Python API has facilities to perform a "Border Render." This básically means that a rectangular section of pixels from any image can be selected and the render engine will only render the pixels within that rectangle, leaving everything else black. Using this method, ResPower can split an image into any arbitrary number of buckets, and render each bucket on a separate computer. Then, using another open source software package called ImageMagick, the frame is automatically cropped to remove all the extra blak space. Each individual bucket's output is saved as a separate image in the user's Renders folder.

    The ability to render separate portions of a single frame in parallel allows 3D artists who work with still frames to take full advantage of a render farm. With this technique, a single frame can be rendered at full resolution in a matter of minutes at ResPower where it might take hours, or even days, to render at the same size and quality on a single computer. On top of that, an artist can continue to tweaque his scene, or work on something completely different while his frame is rendering because his machine won't be bogged down with the arduous tasque of rendering.

    III - What about re-assembly?

    ResPower has recently introduced the ability to re-assemble all the buckets from a Split/Frame render with a process we call "stitching". For frames submitted as Split/Frame, there is a command on the jobs page called Stitch. Stitching once again uses ImageMagik to programmatically pull all of the individual bucket images together and append them into one full-size image. All of the individual bucket images remain available for download if the user wishes, but an additional image called "frame_x.stitched.ext" will appear in the Renders folder once the stitching is finished, where 'x' is the frame number and 'ext' is the file extension, i.e. png, jpg, bmp, etc.

    ImageMagik works from the command line so that overhead associated with starting a graphical user interface is completely eliminated. This means more resources are available to devote to the process of restitching, and that means customers get the finished product faster. Another advantage of ImageMagik running from the command line is that restitching can be almost completely automated. With a single command, the farm will fetch every image required, give them to ImageMagick, and wait for the final output.

    This ability is vastly superior to the old way of re-assembling bucket images where users had to use photo editing software such as Photoshop and manually put all the images together to get the finished product.

    IV - How much speedup does Split/Frame provide?

    As I said before, the theoretical speedup for Split/Frame rendering is linear, so that a 50 x 50 split should render 2500 times faster than no split. Unfortunately, ResPower hasn't been able to secure any real estate in Theory (prices are *incredibly* high there), and things that work in Theory don't always work here. The speedup is considerable with splits in the range of 16 buckets all the way up to 400 buckets. Unfortunately there are many factors involved in determining the best split, and trial and error is generally the best way to find the optimal split.

    Because Blender is only usable on the ResPower Super/Farm by purchasing a subscription, customers don't have to worry about picking the wrong split. If a 2 x 2 split isn't fast enough, you can try a 4 x 4. If you start with 10x10, and you've passed the point of diminishing returns, you can bak it up for a 8x8 split.

    V - Real world examples.

    The file used for determining these times can be found here. It is provided so you may render on your own system to determine the speedup you can expect when using Split/Frame on the ResPower Super/Farm.

    These are the times required to render this file at different splits using only the fastest rendering nodes available on the farm. The resolution of each rendered frame is somewhere close to 2048 pixels x 2048 pixels. The slight changes are due to the fact that the width and height in pixels must be a múltiple of the number of buckets for stitching to work properly. For instance, an 800 pixel x 600 pixel frame should not be rendered with a 7 x 7 split because 7 doesn't divide evenly into 800 or 600.

    Please note that render times depend on several factors including scene complexity, network stress, the availability of render nodes, and more. Because of these factors, this very small set of data is fairly inconsistent. A more robust data set would show a smoother curve of progression between data points.

    1 x 1 (no split) - 2048 pixels x 2048 pixels
    render 11 hrs 06 min 46 sec

    2 x 2 - 2048 pixels x 2048 pixels
    render 05 hrs 34 min 08 sec

    3 x 3 - 2048 pixels x 2048 pixels
    render 01 hrs 53 min 11 sec

    4 x 4 - 2048 pixels x 2048 pixels
    render 01 hrs 32 min 55 sec

    5 x 5 - 2050 pixels x 2050 pixels
    render 01 hrs 13 min 21 sec

    6 x 6 - 2046 pixels x 2046 pixels
    render 01 hrs 01 min 11 sec

    7 x 7 - 2051 pixels x 2051 pixels
    render 00 hrs 27 min 17 sec

    8 x 8 - 2048 pixels x 2048 pixels
    render 00 hrs 40 min 53 sec

    9 x 9 - 2052 pixels x 2052 pixels
    render 00 hrs 17 min 17 sec

    10 x 10 - 2050 pixels x 2050 pixels
    render 00 hrs 27 min 54 sec

    10 x 20 - 2040 pixels x 2050 pixels
    render 00 hrs 13 min 27 sec

    20 x 20 - 2040 pixels x 2040 pixels
    render 00 hrs 33 min 21 sec

    20 x 30 - 2040 pixels x 2040 pixels
    00 hrs 10 min 10 sec

    20 x 40 - 2040 pixels x 2040 pixels
    render 00 hrs 9 min 27 sec

    30 x 30 - 2040 pixels x 2040 pixels
    render 00 hrs 16 min 31 sec

    Miniaturas adjuntadas Miniaturas adjuntadas Split Frame rendering on the ResPower Super Farm-chart.png  
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