Update vs Draw 1 to 1?

Andres "NEXUS" Chamarra · 2011-01-28T19:03:05

As far as I've read the book, it says that draw will be called immediately after update, which suggests a relationship of 1 to 1 between update and draw calls. However simple testing has proven this to be false, if you place a trace line in both update and draw calls in the platformer demo, you will find that in a fast computer, this relationship tends to be between 3 and 2 to 1. Of course a trace instruction run on every update and draw is on itself dropping down performance, since text print operations tend to be very time consuming, but the point is proven just the same, there is not a direct relationship between update and draw calls. My question comes to the GameTime values, what time interval is it really being measured? is it time between updates? what relevance is in the game time parameter received in the draw call? Would it be possible to track update intervals and draw intervals separately? to for instance update the progression of strictly graphic animations (animations that have no impact on logic) only on draw calls reducing the cost of update and leaving it for other more critical tasks? What are the specific changes of IsFixedTimeStep and SynchronizeWithVerticalRetrace separately and in combination?

Old Archive Archive

Started by NEXUSKill January 18, 2011 04:48 PM

11 comments, last by NEXUSKill 13 years, 2 months ago

superkent

158

January 24, 2011 04:35 PM

Though I don't have any experience, I have read that updating physics systems too quickly can cause floating point errors and erratic behavior, is this true?

pothb

102

January 24, 2011 05:05 PM

Though having more updates than draw isn't necessarily a bad thing, as far as I can tell... isn't it still best to have a 1:1 relationship? With N:1 it would mean that the graphics can't catch up, and with 1:N it would be drawing the same scene too many times.

How would it be marginally better if one is faster than the other unless the drawing can't catch up?

NEXUSKill

475

Author

January 28, 2011 07:03 PM

Though having more updates than draw isn't necessarily a bad thing, as far as I can tell... isn't it still best to have a 1:1 relationship? With N:1 it would mean that the graphics can't catch up, and with 1:N it would be drawing the same scene too many times.

How would it be marginally better if one is faster than the other unless the drawing can't catch up?

The idea behind wondering if N:1 would be better is that update is basically taking frozen samples to simulate something that should be continuous, therefore, the more samples you take, the more the result resembles the real values it is simulating. Think of it like an MP3 file, audio is a continuous wave, MP3 stores music by taking samples of the wave with a given frequency, to save space, the less samples it takes, the less quality the audio file will have, because it resembles less the original audio wave.

However I had not considered floating point error accumulation, that could be an issue, although I would expect a good physics engine to have some countermeasure to that built in.