Frame dropping

What it is

Frame dropping (or “frame skipping”, “lag” [incorrectly], etc.) is a problem that occurs if a graphical computer program cannot perform all the calculations it needs to in order to display another frame on time.

It happens in very nearly all games (a full-on freeze being the worst case), but particularly in action games such as fighting games, a minor glitch in timing becomes a big problem for players.

Summary

Frame dropping and minor delays come about due to less-than-optimal program design. Because programs must execute a certain amount of code to be considered “ready”, calculations that are not in time pose a problem to the software engineer: either the calculations must be stopped and the results displayed, or the display must be delatyed until the calculations finish. However, most fighting games take the latter approach because it is much simpler to conceptualize, and because incomplete calculations will not usually be of any use in them.

 

For example, a single frame’s difference in displaying will create animation, but if this is delayed in any way, it will feel like the movement was delayed, and if a frame gets lost, the motion will feel more choppy.

If time takes precedence, then the motion will seem strange, and if proper actions take precedence, then the motion will be delayed.

 

One of the problems sometimes introduced when an arcade game is ported to a home console is that differing system hardware causes different locations for frameskips. And unfortunately, that usually means that it’s the the ports that have these issues.

In SNK games

Because SNK stuck with the NEO·GEO hardware for over a decade, some of their new-fangled fighting games on their old-fangled hardware proved a little taxing for what the CPU (long surpassed during the system’s lifetime) could take. Particularly bad instances include KOF 2000 with the MAX versions of Raikōken, Gōran Enpō, and Shining Crystal Bit (cause frame drops every time). It was bad in KOF ’97 as well.

The “Village of Twilight” stage in Last Blade 2(not particularly helped by Lee Rekka’s pretty flames) and the (normally very smooth) third-round graphics in Terry’s stage in Mark of the Wolves make this very apparent when the problem is easily compounded by something so simple as a special move’s graphics being added on top of the stage’s (don’t look for this in the console ports, by the way; see the next paragraph).

During these temporary freezes, command input is not usually recognized, tending to screw up counterattack attempts.

 

What is particularly infuriating about this is that a simple overclocking of the main CPU in an otherwise accurate emulator (or if you have the skill and the hardware, the actual board) will go to show that these issues were caused by having just a little too much work put on the CPU. Indeed, the PlayStation 2 port of Mark of the Wolves does not have the slowdown issue referred to above, for example. (This is not to say that the original SNK could have avoided bankruptcy by slightly upgrading the NEO·GEO, but it could have made a better selling point late in the system’s life if they had given the option...).

Further reading

Original CSS design by
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Attributed (but not necessarily endorsed) under
Creative Commons 3.0.
Based off the article on the kakuge.com wiki, edited on or before 5 January 2009.
Unofficial translation published by BRPXQZME / Alfie Parthum 16 February 2009. No unauthorized redistribution permitted.