Jump to content
  • Advertisement
Sign in to follow this  

Unity Game States Without a Stack

This topic is 4574 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

This post is largely inspired by this thread: http://www.gamedev.net/community/forums/topic.asp?topic_id=361171 I have yet to find a way of managing game states that I really liked. I always had a distaste of the stack method, because juggling back to previous states lower down in the stack is messy. For instance, if I have a menu A which leads to another menu B which leads to C and then to D, but I want a button in D that sends me straight back into A, the stack method does not seem particularly intuitive (obviously those aren't states in the truest sense, but the principle is similar). The method I prefer, and the one which I've been playing with, is more similar to a process manager. Code Complete has something like this. The Enginuity articles also have something similar, although they seem functionally a bit different. Basically, states can be a collection of processes. When you want to change states, you remove some processes and add others. Processes can remove themselves and spawn other processes. Processes can also have children, which only receive events when the parent process is active. Obviously, there is a base process manager which accomodates adding/removing processes. In fact, I have come to like thinking of a game more in terms of an operating system - with processes and resource management and extensibility and such. So I was wondering if there were any major flaws in my thinking or if there was some more you could suggest. Cheers, --Brian

Share this post

Link to post
Share on other sites
Ok, i've never done this with a "menu" system, but something I liked for an adventure game is a "state vector".

for the most part it was a std::vector<string> that I store strings in to represent any information that the game needed to keep track of.
This worked like store("livingroom_light_on"), you would later check that for some trigger event and swap it with "livingroom_light_off". The main benifit of this vector of different strings being that there were no hardcoded states, and there were no limits to the states you could move to.

This could be expanded to a vector of functors that point to all the functions you want to call each update. (Menu1, button1, button2, main_gameloop)

The problems? There is no elegant way to add/remove lots of states (like a whole menu of items), but this could be reduced to having the menu object be the
only state functor that you add to the state vector. Again, there is some added management over a stack, since you still have to have your button
delete the current menu from the state, and add the other menu.

But, at the same time, you can add several menu's or windows into the state vector with each managing itself. You don't have to make up speciial states
for when you want to show an invintory and have the player window open behind it and still running.

I don't think is it the most elegant design, but I found it to be more flexable than a stack when i was making my adventure game.

--edit, re-read your post, and made note that what i said above sounds kinda like the proccess manager idea.
But I think that the process manager should be something seperate, since i think of a process manager controlling the threads that stream in data, take care of resource management, and your main thread. Where as a state manager is linked more to the flow of the game than the lower level managment of resources.

Share this post

Link to post
Share on other sites
I'd go with a list...

I'm currently using the stack method in a game I made for school homeworks and the best thing I've seen that it could be improved is to be able to have a state that is a list of states to implement "layers".

If you're doing it in a (pure) stack only the top element is available. A list would give you access to other states and it will be possible to "sort" the states. If you want to disable a state you could have a flag somewhere to do that. Having a state being a list of states allows interesting things like, for example, the game itself running in the back of a in-game menu. Having the state manager as a state and a list allows the same as having a state being list but can provide more flexibility with the states.

By changing to the list method (from the stack) you will need to see this more like different layers. This is a good way to have a layers in the game, then a layer for the rendering for the UI, then maybe add a layer with a menu, all those could have acces to the game through a pointer.

Share this post

Link to post
Share on other sites
My question would have to be: why do you need to store the previous scene in a menu to begin with? Just use scene pointers, allowing them to switch freely based on options availiable. Then you can do pretty much anything cleanly.

Share this post

Link to post
Share on other sites
Original post by Nairb
I always had a distaste of the stack method, because juggling back to previous states lower down in the stack is messy. For instance, if I have a menu A which leads to another menu B which leads to C and then to D, but I want a button in D that sends me straight back into A, the stack method does not seem particularly intuitive (obviously those aren't states in the truest sense, but the principle is similar).

In my project I handle such a situation by allowing the top level states (those on the stack) to have child states of their own in a sorted list. Thus it is a hybrid between a stack and a list state scenario. In your situation I would let the menu A be the top level state on the stack and let menues B, C and D be children of A. This way any one of the child menues could send a TerminateChildren command to A. To qualify for being a child state a state would need to exist fully within the context of another state.

Share this post

Link to post
Share on other sites
Original post by PaulCesar
My question would have to be: why do you need to store the previous scene in a menu to begin with? Just use scene pointers, allowing them to switch freely based on options availiable. Then you can do pretty much anything cleanly.

If you want the game to continue in the back when a menu is displayed it could be easily implemented that way. Every layer is independent so I wouldn't even have to care about a scene pointer that way.

Bringing a state to the front would mean to bring that state on the top. Also, like in a process manager it would look like a tree because each states can have childrens and will manage them.

The states would look like they are squeduled and they will run until they send back the control to the manager. If a state blocks (in any of the ways it could) it would block the whole game but anyway this would mean that something is wrong.

Every state layers would act like if they were threads on the same CPU since we implemented a way to have each states to be run (kinda reminds me my first process scheduling experimentation when I tried to make a operating system long time ago). Maybe priorities could also help ordering which state should run first (children shouldn't have higher priorities than parents) so you don't have to reorder anything.

Share this post

Link to post
Share on other sites
I'll use the term 'task' for this discussion, but note that it is the same as 'state' or 'process' above.

I don't like the stack-based approach very much. I prefer to have a manager which exposes the following interface:


Tasks are registered by name. In C++, normally this means passing a name string with an instance of a Task object to link with it. In Java, I usually provide a second form taking a name string to use as a key and a string which is the fully qualified Java name of the class to instantiate ("mypackage.MyTask", for example) - dyanmic instantiation allows for easy configuration of tasks via external data files (this can be done in C++ by implementing and registering TaskFactory instances rather than Task instances). Using dynamic instantiation, you can implement a flexible configuration system that associates menu items/key strokes/events/whatever with different Tasks, thereby eliminating the need to hardcode any flow at all. Or, you could go with something much simpler that just registers all available Tasks at initialization and leaves it up to each task how to manage flow. The other methods of the TaskManager all accept a string which was the key used to register a Task.

Each task exposes the following interface:


When a Task is registered, the TaskManager calls the Task's init method (instantiating it first if using a dynamic system). This is for one-time initialization (which can be anything you deem appropriate). The manager then stores the Task instance away in a hash map for later use.

When TaskManager.activateTask is called, the manager finds the task in the registry. It then calls the Task's activate method. This is where any intialization not handled by the init method should take place. The Task is then added to an active Task list.

Each frame, the game loop calls TaskManager.tick. The manager iterates the active task list and calls the tick method of each task it finds. There is an issue with sequencing here. You could implement it so that when tasks are activated, they are added to the back of the active list. This makes it so that tasks are always ticked in the order they are added. Another option is to assign priority numbers to each Task and use those to sort the active list. Another thing to keep in mind is that you might want some Tasks to temporarily halt processing of the active list, preventing other Tasks from being ticked. For this, I have the tick method return a boolean. A return of false tells the TaskManager to stop iterating the task list.

The rest of the system should be obvious. TaskManager.deactivateTask finds the Task in the registry and if it is active, removes it from the active list and calls its deactivate method. It does not remove it from the registry. TaskManager.deregisterTask removes a Task from the registry and calls its deinit method. In C++, if you are using factories for dynamic instantiation, the manager should also delete the instance. Otherwise, you should put the repsonsiblity on the caller and return the Task instance pointer.

I find this system to be more flexible than a purely stack-based approach. You can do some neat stuff with it. Assuming that you separate the actual game state (and by game state in this case I mean player stats, entity positions, etc...) from the Tasks, then you can get even more flexibility. One Task could be used to handle the management and display of the game world, while another task could be used to overlay the UI. You could split things up further, having one Task manage user input and player state, another to update game logic, another to render the game world, and a final one to display the UI. This basically breaks up the game loop into different Task objects, keeping things logically divided and pluggable. When a menu is displayed, an additional Task can be added to the list to show it. You can override the exisiting Tasks to display only the menu, or pause the game logic so that game world and existing UI are still displayed behind the menu but nothing is updating. Lots of different things you can do.

This system can be as simple or as complex as you want it. For a different perspective, take a look at Scott Patterson's article in Game Programming Gems 3: An Object-Composition Game Framework.

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Similar Content

    • By D34DPOOL
      Edit Your Profile D34DPOOL 0 Threads 0 Updates 0 Messages Network Mod DB GameFront Sign Out Add jobEdit jobDeleteC# Programmer for a Unity FPS at Anywhere   Programmers located Anywhere.
      Posted by D34DPOOL on May 20th, 2018
      Hello, my name is Mason, and I've been working on a Quake style arena shooter about destroying boxes on and off for about a year now. I have a proof of concept with all of the basic features, but as an artist with little programming skill I've reached the end of my abilities as a programmer haha. I need someone to help fix bugs, optomize code, and to implent new features into the game. As a programmer you will have creative freedom to suggest new features and modes to add into the game if you choose to, I'm usually very open to suggestions :).
      What is required:
      Skill using C#
      Experience with Unity
      Experience using UNET (since it is a multiplayer game), or the effort and ability to learn it
      Since the game currently has no funding, we can split whatever revenue the game makes in the future. However if you would perfer I can create 2D and/or 3D assets for whatever you need in return for your time and work.
      It's a very open and chill enviornment, where you'll have relative creative freedom. I hope you are interested in joining the team, and have a good day!
      To apply email me at mangemason@yahoo.com
    • By davejones
      Is there a way to automatically change the start position of an animation? I have a bunch of animations set up on 3D models in unity. The issue is that I need to move the 3D models, however when I do so the animation start positions are not updated and I have to do it manually.

      Changing the transform of key frames is time consuming with the amount of animations I have, so I was wondering if there was a way to do it automatically?
    • By MoreLion
      hey all! We are looking for members for our Unity horror game! 
      Here’s the story:
      After a deadly virus plunges the world into chaos killing 85% of the human population there are now what they call “zones” these zones are watched very closely by the surviving government, people are checked every day for the virus, even if you touch the spit or any human waste or fluids of the victim who is infected, you will die. But one day, people in the west zone start to go missing, 1 woman goes outside the walls to uncover the mystery, is there more to the virus than meets the eye?, That is where your story starts.
      This game is not a long development game, I have loads other game ideas,
      I will also allow you to have a bit of creative freedom if you wish to add or share a idea!
      And no, it’s not a zombie game lol I feel like zombie games are too generic, in this game you will encounter terrifying beasts!
      There is some concept art one of our concept artists have made
      If interested email liondude12@gmail.com
    • By Canadian Map Makers
      GOVERNOR is a modernized version of the highly popular series of “Caesar” games. Our small team has already developed maps, written specifications, acquired music and performed the historical research needed to create a good base for the programming part of the project.

      Our ultimate goal is to create a world class multi-level strategic city building game, but to start with we would like to create some of the simpler modules to demonstrate proof of concept and graphical elegance.


      We would like programmers and graphical artists to come onboard to (initially) create:

      A module where Province wide infrastructure can be built on an interactive 3D map of one of the ancient Roman Provinces.
      A module where city infrastructure can be built on a real 3D interactive landscape.
      For both parts, geographically and historically accurate base maps will be prepared by our team cartographer. Graphics development will be using Blender. The game engine will be Unity.


      More information, and examples of the work carried out so far can be found at http://playgovernor.com/ (most of the interesting content is under the Encyclopedia tab).


      This project represents a good opportunity for upcoming programmers and 3D modeling artists to develop something for their portfolios in a relatively short time span, working closely with one of Canada’s leading cartographers. There is also the possibility of being involved in this project to the point of a finished game and commercial success! Above all, this is a fun project to work on.


      Best regards,

      Steve Chapman (Canadian Map Makers)

    • By Scouting Ninja
      So I have hundreds of moving objects that need to check there speed. One of the reasons they need to check there speed is so they don't accelerate into oblivion, as more and more force is added to each object.
      At first I was just using the Unity vector3.magnitude. However this is actually very slow; when used hundreds of times.
      Next I tried the dot-product check:  vector3.dot(this.transform.foward, ShipBody.velocity) The performance boost was fantastic. However this only measures speed in the forward direction. Resulting in bouncing objects accelerating way past the allowed limit.
      I am hoping someone else knows a good way for me to check the speed with accuracy, that is fast on the CPU. Or just any magnitude calculations that I can test when I get home later.
      What if I used  vector3.dot(ShipBody.velocity.normalized, ShipBody.velocity)?
      How slow is it to normalize a vector, compared to asking it's magnitude?
    • By Ds ds
      Hi, my name is Andres, I'm a programmer with a technician degree and a Diploma in C#, looking for a project in Unity to start my career in game development. I don't do it for a paid but a recognition and start a portfolio, preferably a 2D game. Thanks for read, have a nice day. 
    • By Victor Rodriguez
      Hi there! Is the first time that I'm posting here so I'm sorry if I'm doing it wrong ha. 
      So here it comes, my doubt is, I'm doing a game with different levels, each of these levels in one different scene. Each scene contains to cameras that you can change pressing a button. Everything works fine. 
      The only problem is that I would like it to look a bit more professional, and I would like that if you finish the level with camera2, the next level start the same way. I've been thinking about using dontdestroyonloadon both cameras, but obviously this cameras need to be attached to the player to make the movement work, what do you recommend? Sorry If I've explained it in a messy way, and feel free to dm me for anything. Thanks in advance! 
    • By Ike aka Dk
      Hello everyone 
      I am a programmer from Baku.
      I need a 3D Modeller for my shooter project in unity.I have 2 years Unity exp.
      Project will paid when we finish the work 
      If you interested write me on email:
    • By markoal
      I'm Unity developer from Croatia and I'm looking to work on the paid project in my spare time.
      I have 5+ years of experience in Unity and I'm familiar with almost anything, including all platforms (also Switch, PS4 and Xbox).
      Feel free to contact me.
    • By bartekm777
      About me
      Lvl 28   Programmer (day job: non-gamedev-programmer, making games as a hobby for about 2 years) Some vector art experience - tried to make some assets on my own using vector software and scripts   Some design experience (designing my own games ) About game
      Turn-based fantasy rpg inspired by games like Heroes 3 (also WoG mod), NEO Scavenger, Battle Brothers I would like to create easy to use editor for creating custom scenarios (similar to the one from Heroes 3) World and story are clean slate, I did some drafts but I'm not good at it so it's possibly subject to change I decided to create graphics using vector software + scripts to make it faster (rpg's tend to have lots of assets), also it's more precise and easier to create tileable graphics (for example: rivers, paths) No sound/music work has been done yet Who do I look for?
      Definitely someone with 2d art skills  I would like to focus more on programming 2D animator (skletal animations are preferred) Additional programmer could make development faster Someone for creating sounds/music/both It's a hobby project, I work on it in my free time. In case the project make it to the finish line and get shipped  - I can offer rev-share  
      Below should be few screens of what I already did (about 2 months of work) - some graphics, editor prototype screenshot and game prototype screenshot

  • Advertisement
  • Popular Now

  • Forum Statistics

    • Total Topics
    • Total Posts

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

Participate in the game development conversation and more when you create an account on GameDev.net!

Sign me up!