Sponsored Feature: The All-Important Import Pipeline
July 23, 2009 Page 1 of 4
[In this sponsored feature, part of Intel's Visual Computing section, Rod Green discusses the creation of art pipelines for the firm's Project Offset engine/game, explaining why studios "should be aiming to sever the umbilical cord" and implement a 'common format' approach to art pipelines.]
It's no secret that the world of art development for games is getting more complicated, with dynamic rig LODs, real-time tessellation, sub-d surfaces, mega-textures, and the like. The complexity of assets is increasing, while at the same time, there's a drive to simplify the process to create them.
If the initial technical hurdle is lowered, artists will be free to be more creative and spend more time iterating art, and less time wrangling their tools to try and just get the assets into the game (or so the thinking goes).
One really good initial step toward helping your artists do what they do best is to alleviate their dependency on one specific software package. Long gone are the days when a studio could get by just with a copy of [insert your favorite package here].
Studios should be aiming to sever the umbilical cord and let their art teams work with what they know or what's best for any given task. Beyond the implicit benefits, there's also a world of good to be had in using this approach when working with outsourced employees.
The trick to making the switch is to change the studio's mentality by breaking down the export barrier and implementing an import-based pipeline.
Export vs. Import
What's the real difference between export- and import-based pipelines?
An export-based pipeline is typically structured so that assets are exported directly to a custom first-party priority native format. Once exported, the asset is loaded directly into the engine to be binarized. The format is often spec'ed in such a way that the content is written in a very specific structure dictated mainly by the engine's internal data structures. An example would be to de-index vertex data, triangulate, then section out materials, normals, and tangents.
Creating your own custom exporter initially seems like the path of least resistance. Why should we try to interpret or work with someone else's exporter? We can just quickly write our own and make it do exactly what we need!
While this is true and can help jumpstart production, it will ultimately confine and limit your production team.
One of the problems with an export-based pipeline is it becomes challenging to support artists who are working in multiple art packages. A unique exporter has to be built and maintained for each software application.
Some studios avoid this maintenance nightmare by establishing one core package as the gatekeeper of data (see Figure 1), a practice that utilizes a range of third-party established formats to transfer between external packages while ultimately forcing all content to be passed through one primary package's exporter before it can be loaded in the engine.
But what if, during production, a superstar programmer develops tech for the engine that will allow you to render all meshes via subdivision surfaces? The programmer tells you that triangulated meshes aren't optimal for this new tech and the system would really prefer quads. You'll now have to update the engine's native mesh structures to support quads, modify the external exporter(s), and -- you guessed it -- re-export all the mesh assets!
Another more common example is that your project is targeted for multiple hardware platforms. You're going to have to maintain multiple exporters for different targets and at the very least re-export the assets in a way that suits that target platform, most commonly down sampling the assets in the process. Needless to say, in an export-based pipeline, managing two distinct sets of exported assets and art pipelines can get quite complicated (see Figure 2).
On the other hand, an import-based pipeline shifts the task of native conversion from the export step to the import through a transparent background process. Rather than defining a custom export format, the pipeline makes use of a standardized format (for example, FBX or Collada for models and PSD or TIFF for textures).
The asset is saved to this common format and then sourced in the engine. The act of sourcing the "loading" of the asset in the engine triggers a background process that converts and imports the data from the source asset as needed. It might, for example, convert units, de-index vert data, Y-up to Z-up, combine, flatten, resize, recolor, and so forth.
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