Rendering problems with OIT (Order Independent Translucency)

[Vanessa_A_]

I work for a company called Create, and we’re building a SaaS for Real Estate Development. Our product is a 3d environment where a user can interact with a city environment and build prospective properties on a selected parcel. We’ve chosen to use an open-source 3d engine called CesiumJS:

http://cesiumjs.org/

Recently CesiumJS changed the way they support alpha rendering. They currently use a method called Order-Independent Transparency. They previously used a method called Alpha-Blending.

Here’s some information on Alpha Weighted Blending/Order Independent Rendering:

https://cesiumjs.org/2014/03/14/Weighted-Blended-Order-Independent-Transparency/

http://casual-effects.blogspot.com/2014/03/weighted-blended-order-independent.html

The Problem:

When we upgraded to the newest Cesium release we found that we had inconsistent yet very drastic rendering issues with the transparent primitives in our map. In what seemed like random occurrences transparent surface that overlapped another transparent surface would show snow, glitching, poor color rendering, or other artifacts. 

Here are some screen shots of rendering issues:

After some investigation we isolated the issues to Macs that are using the Intel GPU:

- Macbook Airs that do not offer NVIDIA cards

- Other Macs that have had their Intel cards forced by using GFXCardStatus: http://gfx.io/

The issues were never seen in PCs or in Macs using graphics cards other than Intel. 

Here are the results of a small survey we hosted. Attendees at our talk at the JS.Geo conference in Portland as well as members of our Create team filled out the survey:

410669

Here is a demo that shows the effects of both OIT and alpha blending approach and glitches with Intel GPUs:

http://bagnell.github.io/cesium/Apps/Sandcastle/gallery/OIT.html

Our Request:

Our team and Cesium is reaching out to Intel to help solve these graphics issues. Could Intel please investigate this and bring the OIT rendering correctly to Macs using Intel GPUs? If this, indeed, is an Apple issue could Apple collaborate with Intel to solve this problem?

OIT rendering and WebGL support is a very important element for modern applications. Mapping has become ubiquitous and ongoing mapping applications and technologies like Create and others will require GPUs to support modern approaches to rendering.

Any input would be greatly appreciated!

best,

Vanessa Archambault

[Bradley_W_Intel]

Thank you for bring this to our attention. We've been using your testcase at http://bagnell.github.io/cesium/Apps/Sandcastle/gallery/OIT.html to try and replicate this on Windows hardware. Thus far we haven't been able to replicate it on Windows, which is the only GL driver that Intel creates. If the error cases are showing up in OS X, then you'll need to raise the issue with Apple, because they create the driver for OS X. We don't have the insight to know the code paths taken by that driver.

I'm sorry we can't be of more help. Good luck.