help in fixing convoluted design

Java 2D
#1

First off hi guys, haven’t posted here in a while. OK here is the thing: a while back I figured out ho the game loop and rendering loop were supposed to work. It ran fine on my machine and a few of the other members as well. But some people experienced stutter, which was caused by my code’s poor handling of lag. I figured out the problem and a solution, which is a rudimentary one, but now think that my design is the flaw. Here is the problem and solution:

I have the game tick, client tick loop designed by Marcus Person. I use the game tick to check the keyboard and update the player’s position. The problem is that if there is lag and multiple game ticks happen sequentially, then the character’s position is updated multiple times, without a rendering, so when the render phase finally gets called in client tick, the character jumps to the new position, creating a stutter looking effect.

My rudimentary solution is to create a flag that keeps track making sure that if a game tick happens after a game tick with no client ticks at all in between, then the position update does not happen. This solution is of course crude and slow. This leads me to the following conclusion.

I think that my design is wrong. Currently I have a loop that has a character.update() call in the game tick. The character class checks the keyboard and figures out the new position of the character. I believe this to be the wrong approach. I was wondering what others thought about how to properly abstract the different game mechanics. Which part of the game application should be checking if the direction key is down?

#2

If you use a system where the game logic can run faster than the rendering this will always be a possible issue.

If your rendering interval is too large you will see jumps, nothing you can do apart from make the interval smaller, i.e. render more often.

It might be easier to just tie up the speed of the logic against the speed of rendering since you won’t see any changes until you render anyway. However, if you’re movement is based on time (which I expect it is), you’ll still see jumps if your rendering is the same speed as before and your characters of moving particularly fast.

Kev

#3

[quote]It might be easier to just tie up the speed of the logic against the speed of rendering
[/quote]
What do you mean by that exactly. Curently my loop runs 30 game ticks per sec. So at 85 fps it is:
game
render
render
render
game
render
…

This works fine unless I get some system lag that causes it to be:
game
render
render
game
game
render
game
…

so the 2 game ticks cause the jump. And my movement is based on the interval between game ticks (so yeah it is based on time)

#4

Um, maybe I don’t get this (not unusual), but are you rendering even if nothing has changed?

Kev

#5

[quote] are you rendering even if nothing has changed?
[/quote]
Yes I am. But in the structure there is a game logic tick, then a render tick. The render does not get called from within the game logic. Instead it gets called during the next iteration of the loop. The basic sructure is this (the render is called within the clientTick() ):

clientTick();
                  
      currentTime = timer.getClockTicks();
      passedTime +=  currentTime - previousTime; 
      previousTime = currentTime;
      
      while( passedTime > TICKS_PER_GAMETICK )
      {
            
            gameTick();

            passedTime -= TICKS_PER_GAMETICK;
       }

The code loops through the while loop multiple times if there is any lag, so multiple updates happen with no rendering in between. I am guessing that I should include a render call within my game tick logic, or maybe re work the while loop so that it oes not loop mutiple times in the case of lag.

NOTE: I think I have figured out the solution. Thanx for the replies

#6

I think you should definilty adjust the rendering that is happening despite no game logic change. This should never be the case, as rendering when nothing has changed at all is rather redundant.