Monthly Archives: February 2017

Anatomy of a bug fix

February 09, 2017 | Filed under: production line | programming

I thought it might be interesting to just brain dump my thoughts as I do them for a Production Line bug.

The bug is an error message which I get triggering thus:

GERROR(“No room to TrashLowPriorityResource from stockpile”);

Which is handy, as I know exactly WHAT is happening, and where in the code. Thats 95% of the work done already. Amen to asserts! I know that inside the function SIM_ResourceStockpile::TrashLowPriorityResource(), I am not able to actually do what the function needs to do. So firstly what does this function do anyway? I can’t remember… Thankfully there is a comment:

//if we find a resource not needed by current task, destroy it (only one)

Which is pretty handy. So this is a stockpile at a production task (working on a vehicle) and it needs room for a new resource presumably. The code goes through all of the objects currently in the stockpile to check we really need them. here is the code:

    iter it;
    for (it = Objects.begin(); it != Objects.end(); ++it)
    {
        SIM_ResourceObject* pobject = *it;

        //is this object needed?
        bool bneeded = false;
        SIM_ProductionTask::iter rit;
        for (int c = 0; c < SIM_ProductionSlot::MAX_RESOURCE_QUANTITIES; c++)
        {
            SIM_ResourceQuantity req = PSlot->CurrentResources[c];
            if (req.Quantity <= 0)
            {
                continue;
            }
            if (req.PResource == pobject->GetResource())
            {
                if (GetQuantity(req.PResource) > req.Quantity)
                {
                    bneeded = false;
                }
                else
                {
                    bneeded = true;
                }
            }
        }
        if (!bneeded)
        {
            RemoveObject(pobject->GetResource());
            return;
        }
    }

Thats the first half of the function, it then tries to do a simialr thing with requests, rather thanm objects. However I think I see an issue already. That GetQuantity() is checking the total quantity, not for this single object. Nope…thjat makes sense. I guess I really need to trigger the error and step through it, so time to fire up a save game from a player and run it in *slooooow* debug mode. Ok… an immediate crash from a save game..where we have 16 requests and no objects. So there seems to be a bug in the latter code:

    //ok we need to destroy a request instead of a current object.
    reqit qit;

    for (qit = Requests.begin(); qit != Requests.end(); qit++)
    {
        SIM_ResourceRequest* preq = *qit;
        //is this object needed?
        bool bneeded = false;
        for (int c = 0; c < SIM_ProductionSlot::MAX_RESOURCE_QUANTITIES; c++)
        {
            SIM_ResourceQuantity req = PSlot->CurrentResources[c];
            if (req.Quantity <= 0)
            {
                continue;
            }
            if (req.PResource == preq->PObject->GetResource())
            {
                //sure we ordered it, but do we actually have enough for this task, when com,bining requests with objects?
                int stock_and_ordered = GetStockAndOrdered(req.PResource);
                if (stock_and_ordered >= req.Quantity)
                {
                    Requests.remove(preq);
                    preq->PObject->Trash();
                    return;
                }
                bneeded = true;
            }
        }
        if (!bneeded)
        {
            Requests.remove(preq);
            preq->PObject->Trash();
            return;
        }
    }

So what could be wrong here? Ok…well hang on a darned minute. This code is just saying ‘do we really need resources of this type right now???’ rather than ‘do we need ALL of these right now?’  which is more of a problem. We are clearly somehow ‘over-ordering’. The slot in question is ‘fit trunk’. presumably it only needs trunks… They do all indeed appear to be the same type. 4 are ‘intransit’ the rest are queued up at some resource importer or a supply stockpile or component stockpile somewhere.

So the ‘solution’ is easy. First kill off (delete) a request that is not in transit yet, to make room, or if that is not possible, kill one that actually is in transit. This then frees up the required place in our stockpile. But hold on? this is just patching over the wound? how on earth did this happen? The calling code is requesting new resources, when clearly 16 are already on the way! in fact its requesting a servo…

AHAHAHAHA!

what a beautiful bug. The player obviously upgraded to a powered tailgate, which means a servo is needed for every trunk, and yet 16 trunks were already on order. Error! error! I have special code that handles when an upgrade makes an existing resource requirement obsolete (climate control replaces aircon), but not code to handle this case, where additional stuff is needed. This is FINE, I can implement the above mentioned code without worrying how it happened.

That actually wasn’t too bad at all :D

Jake Birkett, one of the developers behind Shadowhand is going to be at GDC this year, shortly before the final (yay!) release of the game. If you haven’t already heard about it, check out the website or read the announcement on Jakes blog:

http://greyaliengames.com/blog/going-to-gdc-want-to-try-shadowhand/

Its a very interesting game, because its a sort of RPG/Card game/Visual Novel mashup with cool characters and a very interesting combat mechanic. I think it will appeal to casual card game players and Darkest-Dungeon lovers alike.

I’ll also be there, wearing a REALLY BRIGHT jacket, and pretending to be networking.

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This week has been tough. I’ve been busy, also been ill, and been totally rewriting a core bit of code in Production Line to fix some obscure bugs. I think the code is way better now, but the proof is in the play-testing. I didn’t want to keep the improvements I *know* I’ve made hidden from people any longer so today I released 1.05 and also this video…

Here is the complete changelist:

[version alpha  1.05]
1) Resource conveyors now have feint shadows.
2) New design and car stock dialogs now prevent autosave from triggering.
3) Powerplant efficiency upgrade now works in a more obvious way.
4) Massive speed-up to the delay between a stockpile needing resources, and them being ordered.
5) Floating values and particles no longer visible when quitting a game.
6) Fixed crash bug when preparing to place a new slot over a conveyor belt loop.
7) Game now paused whilst in R&D screen.
8) Erroneous robot upgrades removed from make windows slot.
9) Changes to floating values rendering makes zoomed out GUI less messy.
10) Fixes for possible causes of crashing when saving really big games.
11) Some crude rebalancing of starting funds for the first two missions.
12) ‘R’ as well as ‘r’ now rotates.
13) Clicking current balance now acts as an on/off toggle on finance window, which is no longer modal.
14) Various minor GUI fixes.
15) ‘Make valve’ is now visible on the slot picker.
16) Save game GUI now much more consistent with the load game GUI.

This code has been hell to get right. Its all to do with the resource items that get delivered around the factory. They can be created new (nothing is actually new() for memory reasons) and imported from an importer (or held in an importers queue), then can be in transit, then can be used up, they can be created by manufacturing slots, or heading to/from a supply stockpile or in an export queue for either of those things. Thats all EASY to manage. The code hell comes from the fact that the player can delete ANYTHING at any time, or change any route which makes some of those items ‘stranded’. You can delete the source of a resource, or some part of its current route, or its destination at any point, and code chaos ensues.

I think its much better now… I really hoper so, its actually stressed me quite a bit.

Ultimately all bugs can be fixed, but its frustrating because a) I have a lot of people playing and want them to be happy and b) I have a long list of ‘cool things’ I want to improve and tweak and add, and I’m not letting myself do any of that stuff until I have little or no bug reports, so its been really frustrating. I’ll be sooo happy if people say I’ve fixed some of the bugs and I can go back to doing some GUI improvements and some play balancing and tech tree fun and games!

The alpha continues to be really, really popular, almost entirely by word of mouth (not much press has come our way), so that’s really encouraging and I’d like to thank everyone who has tweeted, posted in forums, and generally told their friends about the game, it is much appreciated. I’m really hoping next week my video will be all ‘look at all the coool stuff we added!’.

This has been the softest launch of a game I’ve ever done. I spent about $100 total on facebook post boosts, I tweeted, I blogged and I posted to the ProductionLine facebook page. Since then…thats it, I’ve been pretty much going along on word of mouth, and even then, sales have exceeded my expectations! This is really good news, because so far the development of the game has gone exactly as I had hoped, with a lot more focus on what actual players of the game want, rather than me guessing, or doing just want I want, or me trying to guess what makes the press happiest.

This has resulted in a lot of bug reports! (many thanks for that) and some really good suggestions and ideas, some of which have already made it into the game. People do seem to be surprised how quickly stuff goes in or gets improved, but frankly thats because I worked on this game for about a year in silence so there is this whole huge library of decent engine code in the background that is *done* and thus I only really have to code new features and GUI stuff now. New GUI does not take that long, and thankfully I’ve got good enough at debugging multi-threading and recursive stuff that this is not a huge bottleneck either. I’m almost disappointed nobody is having frame-rate issues, because I love optimizing :D

This is just as well as there have been a LOT of ideas and suggestions. I’ve already seen factories way bigger and more efficient than anything I have managed to create. It never occurred to me to re-use the conveyor belts in cunning roundabout-style loops with the individual processing elements happening at different junctions…until someone found a bug in it.

Users feedback has been excellent, encouraging and invaluable.

But anyway! I’m actual;y sending out a puny mailing list today with 7,500 recipients, so that should open things up a bit, especially as some are press. I don’t expect massive press coverage, but I’m not relying on it either. The game remains very much in Alpha (not even beta) so I expect a lot of people, gamers and press alike will stay in a ‘wait and see’ mode.

In the meantime, I have just set a big patch(1.04) live, and here is the fairly hefty changelist. (not bad for about 4 days work).

[version alpha  1.04]
1) The task ‘make fuel tanks’ now unlocks when researched correctly.
2) Fixed some crashes and routing bugs caused by deleting resource importer bays.
3) Pop-up details on the slot-picker now should show decimal places for times.
4) Vehicle details windows limited to one per vehicle and can now be dragged by the player.
5) Fixed minute format bug in save games.
6) Pause now works as a toggle, and all speed controls have hotkeys.
7) Escape key now closes slot picker.
8) Slot picker has less visual ‘padding’.
9) Double-click on the relevant window now loads a save game.
10) The upgrades section of a slot details dialog is now hidden if there are no upgrades available for selection.
11) Any open dialogs are now correctly closed when going to the main menu.
12) Fixed crash bug when a single stretch of uninterrupted conveyor belt was over 64 tiles long.
13) Added new efficiency dialog which shows efficiency over time and also a snapshot of current slot efficiency.
14) Fixed bug where slots could be placed ‘spilling’ over into a locked factory area.
15) Fixed bug on low resolutions where the slot upgrades window did not fit on the screen.
16) Floating numbers fade out now even when paused.
17) Improvements to ‘load-balancing’ at junctions.
18) New ‘Efficiency’ dialog currently just showing global state of all slots now and over time.
19) Slight speedup of creating the load-game dialog.
20) New vehicle pop-ups show the reason a vehicle is stuck.
21) Some conveyor belt graphics now have darker, more obvious direction arrows.
22) Fixed incorrect sizes of some delivered resources.
23) New upgrade for painting slot: ‘High pressure paint nozzles’
24) Fixed bug where components built inside the factory at ‘make’ slots did not survive a save and load.
25) Corrupt resource deliveries to roof making and similar slots fixed.
26) New graphics for the tyre-making slot and the window making slot.

 

Thanks for everyone pre-ordering, and I also really appreciate it when people tweet or post online about the game, its really helpful. If you don’t have the game yet, here is the order form :D