Everyone who is anyone seems to be on Discord now, and so are we.

Please join our channel!

Currently listening to GamesQuest podcast by Matt Bauer. Interesting stuff when we are about to enter Early Access.

8-bit vs 16-bit

RetroWar deliberately limits itself to what would be possible to run on an 8-bit computer or console. We believe limitations in visuals produce innovations in gameplay.

Occasionally, after much thought, we break this limits when the benefit offered by modern systems seems worthwhile.

But what exactly is an 8-bit console capable of? Well, in addition to the 8-bit CPU, each system had different chips for graphics and sound, and so capabilities varied greatly, and even overlapped what was possible on 16-bit systems. We have to arbitariliy decide where to draw our lines


Most 8-bit systems could scroll to some degree, but smooth multi-directional scrolling didn't become universal until the 16-bit era. Currently we are not including it, but this is a good candidate to add if we decide to implement more 16-bit type features.

Screen shake

Any 8-bit system that was capable of scrolling was also capable of screen shake, so we include it.

Colour palette

We are using a very simple 16 colour fixed palette. We also try to limit each sprite to 4 colours. Some 8-bit systems had more colours and/or could switch to different palettes. 16-bit systems varied greatly as graphics chips improved. I don't really see the point in doing pixel art with, say, a 4096 colour palette - I think you may as well go right up to 'modern pixelart' in that case and use a 32-bit pallete.

Alpha channel transparency

Makes many nice effects possible, but this was quite advanced even for 16-bit systems. The only transparency 8-bit games had was done by flickering a sprite on and off quickly.


Surprisingly 8-bit systems could do particles! Just look at Defender. They couldn't do vast numbers of them, they couldn't make them glow with transparency, but they could do them. We break the rules slightly here and provide unlimited particle numbers.

Texture scaling

Probably used most famously on the SNES, 2d textures could be resized dynamically and even drawn as pseudo 3d. You could zoom in the display. You could make a sprite bigger or smaller. We are not including it. (Although Retrowar-common library does include one scale effect.)

Dynamic lighting

If you have a large palette and an alpha channel you can dynamically change the light levels, e.g. have a player carrying a torch. It makes a huge improvement to the look of modern pixelart games, but we won't be including it.

Phones as game controllers

The game I am working on is a local multi-player party game for up to 16 players. However not many people have 16 controllers connected to their PC. So I was thinking about using phones as additional controllers.

I can think of a couple of different ways to do this:

  • Create and publish a native app for Android and iOS. The PC game runs a server, the app scans for servers on the LAN and automatically connects. Touch input is sent in UDP packets. Bonus: server could announce "this is a d-pad game" or "this is a twin stick game" and the app could display appropriate input controls.

  • Write the app in JavaScript. Have the game run a webserver, which serves a page containing the app. Tell players to open the IP address of the server in their mobile browser. The browser runs the JavaScript app and uses Websockets to send the touch input to the server.

This seems such a simple, useful re-usable project that I would expect it has been done before. Does anyone know? If not, is anyone interested in working on it? It might make a nice little project for a student.

RetroWar has a Steam page!

Please check it out on Steam.

There is a new trailer too.

Networking strategies for real time games with minimal trust

These my thoughts before doing any research on the topic (other than playing many online games over the years and noting how they perform), because I don't want to be influenced by other people's designs too much. It's quite likely that some of my ideas are wrong, or else they are right but exist already in the literature with better names and better implementations.

0 Pre-requisites

UDP is a protocol for sending packets of data over the internet. The disadvantages of it are: size of each packet is limited, packets may be dropped if the Internet is congested, or even delivered in the wrong order. However it is fast. The alternative is TCP which guarantees delivery but increases latency. Traditionally UDP has always been preferred for action games, although over a good connection TCP may now be fast enough.

1 Dumb terminals

The client sends all input to the server. The server sends back the game output, e.g. Steamlink video stream, Telnet MUD.


  • encoding video stream and rendering graphics needs lots of power on the server,
  • there is latency both directions and also in the encoding/decoding.
  • a buffer is necessary to avoid packet jitter, but the buffer adds more latency.

2 Dumb clients

(Improvement of 1.)

The client sends all input to the server. The server sends back a complete dump of the gamestate. The client runs the game engine locally and used it to draw the output.


  • latency again, jitter again,
  • bandwidth requirements can be substantial if the gamestate is large.

3a Smart clients

(Optimization of 2)

The client sends all input to the server. The server sends back a complete dump of the gamestate. However it doesn't need to do it every frame, because the client runs its own physics simulation in between. If an object is moving it will continue to move, etc. When the next dump from the server arrives it may glitch if it moved in a different direction, but this allows the server tick rate to not be linked to the framerate.


If the server is running on a player's machine then that player will have lower latency and have an advantage. The only solution to this, if you care about a fair game, is to add artificial delay to the player's input.

3b Diffs

(Optimization of 2)

The server only sends a complete dump occasionally. In between it just sends diffs. So that would be just the objects that have changed. this was very important in making games possible over dial up modems, but nowadays in most cases it's just an optimization to reduce your bandwidth costs.


If you drop any packets (or receive out of order, which might as well be the same thing) then your gamestate is wrong until the next full dump arrives. To work around this people implemented requests for retransmission of dropped packets, but at some point you have to wonder if they are just re-implementing TCP on top of UDP. And dropped packets really shouldn't be common on modern ISP connections.

Another idea is to assume there will be packet drops and transmit every packet twice. Wastes bandwidth but perhaps saves time (latency).

4 Smarter clients

(Optimization of 3).

If the changes in the objects are entirely predictable, like gravity acting on a projectile, the client can continue to apply them in its own simulation. Only the creation and destruction of the projectiles needs to be sent. Thus you save more bandwidth, but if you drop one of these packets you are even more fucked, so you might want to more strongly consider doing retransmission.

5 Predictive clients

(Improvement of 4.)

The client can predict what its local player is going to do with complete accuracy - it has his input. Therefore it can apply them to the simulation immediately, eliminating the round trip latency to the server and back. So now the client is the apparently the authoritative source for what the player is doing and the server doesn't need to send the player's position anymore, for example. The problem is now the gamestate of the client and server are not in sync. E.g. the position of the player is slightly ahead on the client. Does this matter?

Maybe not. Collisions with the background will not be any different. Collisions with sprites might occasionally be different, so you have to do all collision detection on the server only. The issue with this is that it may result in glitches, where what looks like a hit to the client is actually a miss.

Supposedly it is also possible to predict what other players will do before they do it, but I'm not sure how.

6a Trusted clients

(Improvement of 5, possibly)

One way to reduce these glitches is to trust the client. For certain events that are mostly likely to be annoying glitches, like the player being shot, you make the client the authoritative source. If the client shows the player got hit, then it informs the server, and he did. The problem is that it is then possible to cheat using a hacked client that lies to the server.

6b Glitch merging

(Improvement of 5, possibly)

Another way is when you receive a gamestate dump that differs significantly from the local gamestate, you don't apply it immediately. Instead you generate a new gamestate that is a merger somewhere between the incorrect local state and the correct state. The problem with this is if you got out of sync once you probably will again, so the local game might never catch up to the 'real' state. So you've effectively introduced a permanent increase in latency. I don't know if this method works, I have not tested it myself.

6c Rollback

(Improvement of 5) This also involves trusting the client, but not to generate events. The only thing server trusts is the input from the client. However, the client is trusted to tell the server about input that happened in the past. Each input has a timestamp on it. When the server receives this it rolls back the simulation to the time of the input and then re-runs the simulation with the input applied.

I guess you wouldn't want to rollback on every frame so you'd want to buffer the incoming inputs on the server. Rollback is then only necessary if the buffer empties and you have to generate an update that is missing the input of a player. This method seems to be preferred for fighting games where the order of the inputs received is very important - did the player block 1 frame before the attack or 1 frame after it. But they don't all use it, and I'm not sure if it's helpful for other genres. It doesn't eliminate glitches after all. Also not sure if it can be applied to a game that is not fixed frame rate and the time step is variable.

?Lockstep simulation?

(Alternative to 5?)

If our client gets out of sync with the server it seems inevitable there will be glitches. So how about we keep them locked together? If the client doesn't receive an updated gamestate it waits for a retransmission and freezes until one is received. If the server is awaiting input from any player it does the same. (So there is input buffer needed on server). Any dropped or delayed packets won't cause glitches, the game will just freeze. In that sense it's fair to all players, but it means one player with a crappy connection will slow down the game for everyone.

?Slow motion?

If your buffer runs out with any of these techniques then you have a problem. You could freeze until the next frame arrives, but then you don't have much of a buffer against jitter any more. So you could display 'buffering' like a youtube video and freeze until the buffer fills to full capacity, but then you have a big pause. So I'm wondering if you could instead fake the game timestep while the buffer is filling. If your buffer is full then the game runs normally. If it starts to empty then you make the game run in slow motion until it fills again. Usually this should be unnoticeable to the player, but it should increase the effect as the buffer empties, until the game completely freezes at 0.