NotSoEasyCoding

Foreword

This page shows projects which are considered a good idea by the developers but which have nobody working on them so far. If you think you've got the required skill for a task go on, implement it and you've got a high chance that it'll be accepted. The remaining barrier will only be that it's done well. :-)

If you are such a person, you should feel free to edit this page.

If you're not, you should post a feature request and discuss your idea on the forum or IRC. A coder with better knowledge of the code might give you the green light to add your feature here.

Anybody should feel free to add "clues" to any tasks, that is entry points, traps to avoid, person to contact to discuss and so on.

If you plan to work on a feature, write your name at the bottom of the feature, with the date. Note that if you are too long at working on a feature I'll "free" it back (that is if you're not working on it. If you have problems implementing it, just tell us....)

Game Engine

add a mode to improve OOS detection in MP

We really need an optional 'pedantic mode' for MP which detects OOSes immediately, by comparing all game state information after each action and printing any mismatches. This mode will be optional because of the extra overhead it adds, and it would be very useful for debugging.

Fix a longstanding bug concerning failure to initialize a side in networked mp

(Actually we may have a fix for this now... will post reference)

https://gna.org/bugs/index.php?21397

The problem itself is quite simple -- when the server tells a client that their turn has begun, the client immediately broadcasts [init_side] to all the other players via the server, performing the initial upkeep, healing, and movement point reset actions. However, if this player disconnects / blocks the action by opening a dialog during the prior turn and never closing it, [init_side] is never broadcast. And if the game is then saved by one of the other clients, nothing in the current mechanism detects that this has been overlooked when the game is reloaded. The consequence is that in the reloaded game, that side's turn is *never* initialized -- they get no gold, their units don't heal, and they don't get full move points at the start of the turn.

Propose a mechanism to fix this -- perhaps games which have been loaded should be scanned to see if the current turn failed to initialize. Perhaps a flag in game_state could be used and saved. Perhaps a completely different approach. Check that your mechanism works whether the save is loaded from [snapshot] or [replay_start] and [replay].

This bug has existed since at least Wesnoth 1.8

Make a "replay actions since my last turn" button

It would be very convenient if there an ability to replay everything your opponents just did at the start of your turn, since sometimes things go out of vision or are confusing.

The feature would be like a "replay since my last turn" menu option or button -- most likely, the best approach to implement it is to store a copy of the game_state object in playcontroller.cpp or even in resources, and to refactor the backlog object so that we can hold a "bookmark", i.e. a pointer, to the last position in the replay that we might look to jump back to. The replay process would work by swapping out for the old gamestate, then replaying through the actions since the bookmark until we get back up to speed. The difficult part would be making sure that scenarios with scripted WML events don't break when we do this. For debugging purposes, it might be good to check that at this point we have the same gamestate we did before we clicked the button. The bookmark should only be advanced when we end our turn, and there might be perhaps need to be multiple bookmarks, one for each side, to handle what happens when a side disconnects or is reassigned.

It would be especially helpful for MP play to have this, where special tactics with ambush units are quite common. Part of the design criteria of wesnoth is that it should be a high-level, thoughtful turn based strategy game, but you should be able to play asynchronously and not necessarily give attention to the game until your turn bell rings if you don't want to. Having ambush units and no ability to replay their movements during the opponents turn harms that goal.

For MP play, it will require special attention to make sure that events like "synchronize_choice" are handled correctly so as not to cause out of sync errors, and also that the timer is handled correctly.

Feature request: https://gna.org/bugs/?15334

Thanks to Zappaman for this. https://github.com/wesnoth/wesnoth/pull/270

Improve WML error reporting

There are many programming bugs that give very unclear or cryptic error messages when using WML. Here are some examples:

-- When calling a macro with the wrong number of arguments, wesnoth tells the number it expected, and the number it got, and at which line number it was instantiated. However, it would be helpful if it would also tell the line number of the definition of the macro. This might be helpful if someone is redefining macros.

-- For places where a standard unit filter is expected, if one is not found, the game should point out a problem. For places where such a filter is expected but [filter] child should not appear, if one does it should report an error and a line number. Many users have a hard time with this kind of thing.

-- When doing scenario transitions in a campaign, if the side definitions don't matchup exactly the game tends to give unintelligible error messages. For instance, if one is transitioning and there is an AI side which does not have a leader (but it has a starting location in the map) it must have "no_leader = yes" in its [side] tag, or else when the team_builder objects enter stage two, the game will try to create a unit with an empty type, and the constructor of class unit will fail giving the error message "game::game_error tried to create unit with empty type". This really needs to be much better. For instance, giving a line number of a problem, or suggesting that no_leader should be used. (Note that, it is often possible to debug problems like this by turning on --log-debug=team_construction at commandline but I doubt that there are any users that know about this, you would only learn from reading the C++... without such debug info, fixing things like this can literally take hours.) For that matter it's some question why the team_builder doesn't just stop trying to build a unit when it sees it doesn't have enough info...

-- Recursive macros break the game, and not by stack overflow but by exhausting the heap. It would be nice if we could catch this and report an error.

Many of the users of WML are students or beginners to programming, it is a big help to them to improve the error reporting of this nature -- not to mention that many veterans would appreciate as well. In part we need fixits here and there but more broadly we need a smarter system that can figure out what's really wrong when things go wrong and give helpful suggestions.

Map label "groups" which can be selectively turned on and off by the user

It would be nice if the user could have more control over how map labels are displayed, for instance to be able to check on / off labels made by certain players, and for custom scenarios, to be able to make custom classes which the use can turn on or off. This might be helpful for custom scenarios esp. which might have some technical info they want to show, but which it might be messy to display all of the time. The hard part of this is that there should ideally be a gui to work with the map labels, although maybe this need could be worked around or simplified somehow.

Add a new damage stats calculation mode to support scenarios with extremely high stats

Most players use the damage calculation window constantly when they play so that they can see what to expect from various attacks. The way the game is currently set up, when a unit is selected, as soon as another unit is moused over the stats for an attack will be calculated, whether or not the user actually brings up the window.

The probabilities for the various outcomes are calculated by explicitly calculating the distribution of attacker and defender hp / slowed status after each swing by either party, one swing at a time. Thus at the end we get exact probabilities of the possible outcomes.

However, this comes at a cost -- the running time of the calculation can in the worst case be something like O( attacker_hp * defender_hp * total_number_of_strikes). In default era wesnoth (and in much of UMC) this is fine because units don't get extremely high hp values. However in some UMC units do get extremely high hp, and many will also have specials like drain and berzerk, and may have many different weapons as well. At some point these scenarios become unplayable even on a machine of moderate specs because mousing over any unit causes > 10 seconds of lag during which the game becomes unresponsive, trying to calculate attack outcomes.

In these cases, it would be better to give an "inexact" damage prediction, based on just simulating a few thousand attacks and plotting the results. Since it's a monte carlo algorithm rather than an exact algorithm, there will be some error, but if it makes the game playable then it's clearly an improvement, and anyways for "extreme stats" battles with high strikes and damage, the outcome is in a sense less random anyways because the outcomes with inordinate amounts of hits and misses are more and more rare (law of large numbers), so the error shouldn't actually be terribly significant.

If there were an advanced preference that caused the predictions to use such an algorithm instead of the current one, so that the user could turn it on if they start to get problems, it would eliminate a significant headache for some UMC.

MP Related

Automatically resolve add-on dependencies

In 1.11 add-ons may declare dependencies. A related easy coding task is to allow the user to force breaking dependencies.

A related goal which would be greatly beneficial would be that wesnoth can automatically resolve the dependencies by fetching the add-ons from the download server, when in the MP-lobby the user tries to join a game with a dependency they don't meet. A dialog would ideally be provided as well, or perhaps a preference.

https://gna.org/bugs/?21705

Even older: https://gna.org/bugs/?9683

Gold graph

Make a graph feature, presumably in a dialog, that helps depict the history of the game. For example it could display army value, army + bank value, number of villages tagged, luck swings... the purpose would be to assist spectators of a live game / spectators of a replay to understand the history of the game. It would be particularly helpful with AI development, by helping AI developers to identify key points where one of the AI is making a big mistake.

A possible nice feature for this purpose would be to allow the user to click on the graph at key points which would trigger the "back to turn" mechanism to jump back in the replay, or automatically play the replay forwards from the beginning to that point... etc.

Related email on dev-talk: https://mail.gna.org/public/wesnoth-dev/2014-02/msg00089.html

Automatically link up to wesnothd server on a local network

The feature request was to use ZeroConf technology, if available, to publish info of a running wesnothd instance to other machines on a local network. Then when they are searching to connect to an unofficial server, they won't have to learn the IP address.

The extra code should be guarded with preprocessor flags so that ZeroConf does not become a build dependency of wesnoth.

https://gna.org/bugs/?13703

Create a set of "common" mp messages which players can use when they don't share a language

Most users speak english, however, wesnoth also has large Polish and Hungarian communities, and many Brazilian players, not all of whom speak english. It would be nice we could have a set of messages that could be chatted, but which will be translated by our translators and displayed always in the current locale on each client, to make it easier to communicate in mp games / on the mp server.

The hard part is that if you don't already know about the gettext translation system, you will have to learn about it. The messages should be stored in a .cfg file in the data folder so that they can be easily modified and can be handled in the same way that other in-game text is translated -- they should perhaps go in their own gettext-domain however. Ideally there would be a gui dialog of some kind to select from them.

Improve server wml processing

The wesver uses an alternative implementation to store and process wml objects see http://wiki.wesnoth.org/WesnothdDesign#simple_wml. This is for performance. However, the simple_wml sometimes messes up translation for mp scenarios / campaigns, resulting in mp scenarios/campaigns beeing untranslated for non-hosts in networked mp (http://gna.org/bugs/?22989). Fixing this is not easy becasue of the performance requirements.

Improvements to AI

Move and targeting phase

AI needs to move units which are not within range of the enemy. This is generally a sequence of moves (some interesting things like 'ambush!' or 'WML event' might happen as a result of those moves, which should interrupt this phase). The problem is that simply doing those moves 1-by-1 is very slow, for two reasons:

1. movement maps are invalidated after each move, and are recalculated from the start. yet, if we are doing just a sequence of moves, we can just 'remove moved unit from moves' after each move and avoid expensive recalculation of the movement map.
   • Note that WML could mess with the game state at any time, so at the very least, movement will need to be recalculated after a WML event blocks undo (that is, indicates that it changed game state). --Brilliand 01:30, 28 May 2012 (UTC)
2. most tasks need devoting more than one unit to execute (i.e., it's meaningless to go for the enemy position with just 1 unit). So, making individual decisions just does some repeating calculations, which is slow.

A practical demonstration of these concerns are LoW 2 (dwarf ai is slow due to large avoid aspect) and NR:Showdown (orc AIs there are slow because of huge number of units)

we need a fast and effective 'move and targeting stage' - both ideas and implementations are wanted. Here's Sirp's idea (more in 2009-aug-15 irclog):

--

Eval-based AI

The AI system would be based around an 'eval' function -- a formula which is given a position, and returns a number saying how attractive that position is.

There would also be a 'candidate_moves' function -- a formula which is given a unit and returns a list of 'candidate moves' -- i.e. moves for that unit that the AI should consider making.

The aim of the system is to come up with the combination of candidate moves that gives the best possible evaluation. By doing this, the AI will work in a team, since the 'eval' function can give bonuses for units being close together, protecting each other, etc.

There are likely to be, of course, a very large combination of possible moves, and not every one can possibly be evaluated. Instead, we take a monte carlo approach.

If an AI has N units that it can move, that is an N-dimension matrix of possible moves. We would choose some cells in this matrix at random and then evaluate them. Then, of these cells evaluated we would choose cells that evaluated well, and discard those that did not evaluate well. Then, we would begin with those cells that evaluated well, and choose a scattering of 'close by' cells -- i.e. cells where we only vary some of the dimensions, at random. We would continue to evaluate cells at random, starting with those cells that evaluated well, and evaluating cells nearby. After several iterations, we would hope to arrive at a cell that evaluates very well, and we would use this as our set of moves.

Of course, this system will be made more complex by the uncertainty of attacks. There are a number of ways to handle attacks, probably the easiest being to consider attacks as types of moves, and then if a move combination involving an attack is chosen, perform the attack and then re-run the entire AI algorithm before moving again. (Something similar to what the current AI does).

This is effectively an AI framework, not an AI in itself. How well it performs will correlate strongly with how good an eval() function one can write, and is also based on the notion that generally certain combinations of moves are 'similar' to other combinations.

--

Village grabbing

Improve AI village grabbing algorithm to assign villages that are farther than one turn from current unit location. Idea how to do would be value villages so that it can filter out villages that belongs to enemies/allies sides. Those villages are stored in memory and used in 2nd pass that determines how AI should dispatch units to get villages if it should at all in this turn. This should be close to optimal solution with currently available units but performance limits should be taken into account. Good solution would be that village grabbing value could be calculated with attack ratings and if some village has high value it would make unit go for that village instead

This should help AI in begin of scenario. Currently AI might not grab all of villages that belong to its area which results quite large incoming loses. In later game enemy might have large number of units in one part of map so village grabbing should be avoided in that are. Single unit would be easy pray for enemy so moving there would result just to loses.

Data Structures

Config Writer

The speed of saving Wesnoth games is dominated by the time to marshall all the config structures. This involves deep copying them many times as each subsystem returns its config bundle; far better would be to have a "config_writer" class which is handed to each subsystem which iterates through its structures and does the writing (to file or network) directly to the config_writer instance.

Stop by #wesnoth-dev on freenode irc if you want to help with this, or post in the Coder's Corner.

Config memory optimisation

Right now, most of the memory used by wesnoth when using low_memory configuration flag is used by the config object trees. It would be possible to drop unused "branches" of that trees by using boost smart pointers in the config structure

come and discuss that change on #wesnoth-dev. Sirp is the one that knows the most about that...

Improvements to Unit Map

As described here: [1] (cjhopman has submitted a patch on that already)

Make the lua state persistent

Wesnoth is designed to make all data files as simple and human-readable as possible, including savefiles. WML is designed so that it is always very easy to write the entire WML state as plaintext and reload it correctly. There are many benefits of this, but especially

• It makes it easy for beginners / students to read the files and see what's going on
• It makes it easy for us to debug problems without needing special tools to read the savefiles
• It makes it easy to edit save files to work around any possible bugs. Users have even reported opening savefiles from version 1.10 in microsoft word (!) to correct minor bugs in mp and resaving them, as a policy for tournament games.

This was unfortunately somewhat lost when we added lua. If you use lua in your scenarios, things become more complicated because we can't save the lua state at all. If you rely on lua variables to save information, then when your scenario is saved and reloaded those variables will get wiped. The wesnoth engine provides places for lua to hook into "onsave" and "onload" so that the scenario developer can write their own serialization routines, but this is just punting the problem to scenario developers.

We also provide the "preload" event type specifically to work around the issue -- unlike all other events, preload is called exactly once for every time the scenario is loaded. The purpose is to give another way that lua users can initialize a table of lua functions used by their addon and guarantee that this happens before the functions are called. But to non-lua users this event is basically unsafe for normal use otherwise -- if there is a preload event which e.g. increments a WML variable, then the WML state now depends on how many times the scenario is saved or reloaded. In a normal scenario, save / reload events should be invisible, and normally if this isn't the case it indicates a bug similar to an OOS.

A nice solution to this would be if we properly serialized the lua state alongside the WML in a savefile. The most suitable solution is probably this library: https://github.com/fnuecke/eris It would require significant additional work as well to find a good way to serialize the C functions that we expose to lua, and the userdata like units held by lua.

See Also

Frequently Proposed Good Ideas

Check the B.W.H. list in the Ideas Forum. Be aware that some entries there are old and have already been implemented, so you will need to investigate that before beginning work.