Is there a way to program games without depending on fram rate?

Question

Im programming an iOS game and I use the method update for a lot of things, which is called at the game speed refresh (for the moment 60 times per second) but the problem is if the frame rate drops down (for example a notification, or any behavior in the game that, when called, it makes drop down a little bit the fps...) then the bugs comes....

A fast example is if I have an animation of 80 pictures, 40 for jump up and 40 for fall, I would need 1,2 second to run the animation, so if the jump takes 1,2 second it would be ok, the animation would run. But if my fps drop down to 30 then the animation would cut because it would need 2,4 seconds to run the animation but the jump remains 1,2 second. This is only a fast example, there is a lot of unexpected behaviors in the game if the frame rate drops, so my question is, are games developers depending so much on frame rate or there is a way to avoid those fps-bugs? (another way to program or any trick?)

Answer 1

Base your timing on the time, rather than the frame count. So, save a time stamp on each frame, and on the next frame, calculate how much time has elapsed, and based on your ideal frame rate, figure out how many frames of animation to advance. At full speed, you shouldn’t notice a difference, and when the frame rate drops, your animations may get jerky but the motion will never get more than 1 frame behind where it should be.

Edit: as uliwitness points out, be careful what time function you use, so you don’t encounter issues when, for example, the computer goes to sleep or the game pauses.

Answer 2

Always use the delta value in your update method. This is platform and engine independent. Multiply any speed or change value by the delta value (the time interval between the current and the last frames).

In case of the animation, one way to fix the issue could be to multiply the animation counter by delta (and an inverse of the expected interval). Then round this value to get the correct image for the animation.

// currentFrame is a float ivar set to 0 at the beginning of the animation.
currentFrame = currentFrame + delta * 60.0;
int imageIndex = roundf(currentFrame);

However, with Sprite Kit there is a better way to do this kind of animation, as there is a premade SKAction dealing with sprite animation.

[SKAction animateWithTextures:theTextures timePerFrame:someInterval];

With this solution you don't have to deal with timing the images at all. The engine will do that for you.

Answer 3

There's a great discussion about FPS-based and Time-based techniques here:

• Why You Should be Using Time-based Animation and How to Implement it

It's the best on my opinion, very complete, easy to follow and provides JsFiddle examples. I translated those examples to C++/Qt.

Click here to watch a video of my app running: