UPDATE 14/8/14 6:28pm: Yesterday, Blizzard contacted Eurogamer to say that the dual frame-rate issue we uncovered in Diablo 3 was a bug it was looking into patching as soon as possible, and offered to talk us through it one-on-one at Gamescom. Thomas Morgan met up with production director John Hight in Cologne earlier today for a quick chat.
"First off, I want to thank you for going through it, digging through it. As it turns out we do have an interesting bug in the game," Hight explains. "Essentially what's going on is we're updating at 60 frames per second, except on the consoles it's 59.94. Effectively it's like a round-off here - we're updating 59 frames on the first second, and 61 frames on the next [meaning] we're literally double-writing a frame."
So it appears as though elements of the renderer operate at a pure 60fps, while the HDMI standard actually incorporates the legacy NTSC drop-frame standard, running at 59.94fps. The discrepancy is apparent on both versions, but according to Hight differences in the way they handle the rendering account for the more pronounced hit to PS4 performance.
"After we we read your article we went back through, looked at the code, and determined that we made mistake on, essentially, updates. So we're now at full 60 frames. We're now posting an update that will go up before the day one patch, and will be part of the day one patch," Hight continues.
"As soon as we saw your article I sent it over to our core engineering lead, and I'm saying 'hey what's this this about?' Those guys are awesome - they jumped right on it, looked through the code, and were like 'I'll be darned we actually have a problem here with the way we're updating'... So our goal is to have that out day one, so on the 19th. We actually put the Sony [PS4 patch] into format today, and Sony's going to give us a pretty quick turnaround on it. I don't think we're going to have a problem getting it day one."