[webkit-dev] Pixel test experiment

[Maciej Stachowiak]

On Oct 8, 2010, at 12:46 AM, Nikolas Zimmermann wrote:

> 
> Am 08.10.2010 um 00:44 schrieb Maciej Stachowiak:
> 
>> 
>> On Oct 7, 2010, at 6:34 AM, Nikolas Zimmermann wrote:
>> 
>>> Good evening webkit folks,
>>> 
>>> I've finished landing svg/ pixel test baselines, which pass with --tolerance 0 on my 10.5 & 10.6 machines.
>>> As the pixel testing is very important for the SVG tests, I'd like to run them on the bots, experimentally, so we can catch regressions easily.
>>> 
>>> Maybe someone with direct access to the leopard & snow leopard bots, could just run "run-webkit-tests --tolerance 0 -p svg" and mail me the results?
>>> If it passes, we could maybe run the pixel tests for the svg/ subdirectory on these bots?
>> 
>> Running pixel tests would be great, but can we really expect the results to be stable cross-platform with tolerance 0? Perhaps we should start with a higher tolerance level.
> 
> Sure, we could do that. But I'd really like to get a feeling, for what's problematic first. If we see 95% of the SVG tests pass with --tolerance 0, and only a few need higher tolerances
> (64bit vs. 32bit aa differences, etc.), I could come up with a per-file pixel test tolerance extension to DRT, if it's needed.
> 
> How about starting with just one build slave (say. Mac Leopard) that runs the pixel tests for SVG, with --tolerance 0 for a while. I'd be happy to identify the problems, and see
> if we can make it work, somehow :-)

The problem I worry about is that on future Mac OS X releases, rendering of shapes may change in some tiny way that is not visible but enough to cause failures at tolerance 0. In the past, such false positives arose from time to time, which is one reason we added pixel test tolerance in the first place. I don't think running pixel tests on just one build slave will help us understand that risk.

Why not start with some low but non-zero tolerance (0.1?) and see if we can at least make that work consistently, before we try the bolder step of tolerance 0?

Also, and as a side note, we probably need to add more build slaves to run pixel tests at all, since just running the test suite without pixel tests is already slow enough that the testers are often significantly behind the builders.

Regards,
Maciej