Friday, November 25, 2016

Engine interview question

My friend know someone who is going to have skype interview for a position as engine junior programmer. I was asked for some guide or hints for this person. I think that this topic is interesting enough to change my long reply into nice post and hear what you think about it:) My email to him looked like this:

" First he should stop being stressful and asking question of others what can be on interview. If he has knowledge and luck he will pass. Sometimes is more about luck than knowledge but generally If he will get too stressful, even luck won’t help him.

About question they can ask whatever they want from just:
  • How are you?
  • Where you were studding?
  • What you were studding?
  • Why do you decide to have interview with us?
To more technical one like:
  • What programming languages you know and how well?
  • What engines you know?
If he sent them CV there will be probably few question about stuff you put there. If he worked previously somewhere I would expect question like:
  • What you done in previous job?
  • Why you decide to change job?
  • What projects you done in university?
  • Why you think this position is for you?
After that may come true technical questions which can by anything from question about: pointers, graphics rendering, memory management, disc access and 1001 other topics. There is just too much of them to be prepare for them. 

So returning to first line if he has knowledge he will answer questions better or worse but he will do this. From my experience, there are always different questions on each interview (but maybe this is just for me). He should chill-out and just see this as learning experience. If he will fail, world don’t end and he should just learn from it and try again. If they will see potential in him there is still big chance they will at least give him programming task.


Tuesday, August 16, 2016

Game development

This time something inspired by this twit:

If you look really general on game development you can compare it to assembling puzzles. A lot of people know about game development from articles, making of videos and few other sources. They also know that there are different options that developer choose when they started:
  • 5000 pieces - Making small game on ready technology.
  • 8000 pieces - Making small game with technology.
  • 12500 pieces - Making game on ready technology.
  • 25000 pieces - Making game with technology. 
This don't sound so bad, so why developer don't make their job properly? People complain about some bugs, some features, about how simple it would be to just add this one feature. This is so frustrating for them because this is so simple (like assembling puzzles).

Wednesday, June 1, 2016

Code pollution

Well time fly by and animation system starting take shape. Thanks to it I could do even some not bad looking animations in game ( but well this is just another milestone in road to finished game. 

Because of this thoughts I already moved to next issue: recovering of movie system. So far its going fine I added new movie resource, movie editor module. No I starting adding basic functionality: adding keys. This operation require list of selected objects in level.

This part was designed great :D Because I can have N levels loaded in memory in the same time I created new level component which exist only in editor. It contain some editor specific data i.e. selection. It's added on loading from editor and it's not saved with level. When you want list of selected objects just pick component from level and I have access to selection. Great idea right ? 

I thought this way when I was writing it. Right now I think it was good direction but it's still "Code pollution". Editor code and game code start mixing which is always harder to manage. On top of that Editor tools component is visible in level properties and yes I know I could hide it in code but then you create hack/some new code path which create new issues. Leaving it is also not any option because this is weird for person who work in tools. When there is something you didn't add you have temptation to remove it (I know what this it and that I shouldn't remove it but still don't like how it pollute my level setup) :D

My another iteration over this problem will be: 

LevelEditorModule would replace level component and thanks to that became independent from level. Advantage of this system is that it should be relatively easy progression from existing code. Just a little bit of time. 

This may look like something stupid to do when I'm already limited by time and doing so many other stuff. Yeah you may be right. I never was too wise in this situations I prefers spending evening or two improving code which works than add new feature to game. Thanks to that I won't have maybe nice feature which will look nice at picture or video but I will have code which will supporting my efforts in creating games. Then features will be easier and funnier to work on :)


Tuesday, May 17, 2016

C++ riddle

This time small C++ riddle which took me some time to figure out :)

My editor currently use sockets connection to pass data between Qt UI and "Editor module" in engine. Inside editor module this happen on two threads:
  1. Processing events on editor module side
  2. Receive data and send result of events back to UI. 
Code of two main function execute on them can found bellow:

This worked fine except my editor were crashing sometimes. This happen on random operations : moving, selecting, changing properties. Visual Studio debugger where showing me that crash were happening in this code:
    eventResult->next = m_eventsToFinalize;
while (wrAtomic::compareexchange(&m_eventsToFinalize, eventResult, eventResult->next) == eventResult->next);

Data in eventResult was looking like corrupted event or already deleted class.

What is wrong with this code :D ?

EDIT: There was small mistake in original version of code which should not be there (I fixed this in post). Line :
while (!wrAtomic::compareexchange(&m_eventsToFinalize, eventResult, eventResult->next) == eventResult->next);
should be:
while (wrAtomic::compareexchange(&m_eventsToFinalize, eventResult, eventResult->next) == eventResult->next);

Wednesday, May 11, 2016

My little monster

This story started long ago while I was still student at University of Technology in Wrocław. It was probably year 2006 but I'm not sure right now. With time passing by all previous years slowly starting blending together but well I'm already at this age where this is pardonable.

On one of C++ courses we got exercise to do program of our choice to show that we learned language. I decided that isometric game in SDL software mode will be great idea. And so I started working on it. What a great joy I had when everything finally started working together and I was able to send it to person conducting classes. I got passing marks and this was end of story. 

Well at least for a lot of project this would be truth but in this cases there is a lot more. Some time passed and with friend we decided to make casual game. Code from course project was really useful but software rendering were too slow so I switched whole stuff on OpenGL and some time later we finished "Pirate Crystal's: Adventure of Julia".

Another semester started and in advance C++ course I decided to connect physics to engine which at this point had already some basic 3D functionality. This wasn't easy because this was my first encounter with proper physics implementation. But well all of that couldn't prepare me for what came on other course conducted by Kornel Kisielewicz about shaders. I still remember his comment when he was rejecting my idea of doing normal mapping: but this is standard now. 

This may sound silly but for me this meant a lot. I was hiding in save zone avoiding shaders however I could but then I was informed that I'm far behind what happening in industry. This was crucial moment for me because I quickly get out of my save bubble, learned shaders and decided that I never want to stop learning new stuff and ending in this bubble again.

But what the hell this post is about? This is for sure not post about me but "My little monster". I sometimes hate it, sometimes need break from it sometimes I messing with it but in the end this is my "little monster" which I put a lot effort into and try to make it the best engine I can.

Why Monster ? 

People who done work on bigger projects probably know this feeling of being lost in code. In my case it often happen when I move to new part of code which I never had occasion to work on. Now imagine the same situation happening in your own code base. This is moment when you start understanding how big project you working on really is.

Other thing is that a lot of people seeing personal projects as "toys" they don't treat it seriously when you talk that you work on them. In my case I don't see difference between my personal project and projects I worked on in work. Of course code base is smaller but if you look on how much code is handled by programmer then I'm sure that I handle a lot more in my personal project.

There are also issues which you need to deal with yourselves:
  • Code paths that aren't used quickly became broken. 
  • There is issue of tools that you don't compile when I do some changes in engine.
  • Differences between GPU vendors.
  • Memory management,
  • Threading issue like: timing, race conditions.
  • Multi platform development.
  • Code which you don't even know how worked in first place.
  • Build system.
  • Building of game package (ideal if it was automatic).
  • And a lot more.
I personally don't try hack any of this or just do quick prototype. I try to make proper solution which I would also create if I needed to resolve this issue in work. And this change really a lot. 

This was really visible when I were changing work. The first time when I was doing it and mentioned my project people were like good you do something on your own but what you done in previous job. Things changed last time. When I was showing it to people that interview me they sometimes even skipped some tests and we ended talking how I done stuff or they give me their opinion how they would do something. This project was seen as one of projects that I was working on commercially and I think this was great.

Why Little Monster ? 

Well this is not name of engine because its called White Rabbit Engine. This is name that I using when I end in bed after doing some work for engine and finally realizing what kind of technology I creating. I'm scared of it complexity because sometimes I got lost in my own code. What will future bring I don't know but this project carring ten years of development, all my knowledge and well it still my "little monster". I may sometimes have enough of but but I still like what I do and will carry work on it for a little bit more :)

Friday, April 29, 2016

My bookshelves.

I realize recently that I'm weird programmer. If you would look on my bookshelves you will find there:
  • manga, 
  • fantasy books,
  • movies art books,
  • games art books,
  • books about drawing, 
  • books about anatomy,
  • books about animations,
  • D&D manuals.
What you won't find there is any programming book. My only book kind of in this topic is Showstopper about development of windows NT on my kindle. Which is in the fact not programming book but more story of people who created it and I'm still in middle of reading it :) 

The other book I reading is  "The Animator's Survival Kit: A Manual of Methods, Principles and Formulas for Classical, Computer, Games, Stop Motion and Internet Animators." which is for me really interesting. So far I finding there a lot of interesting advice which some even apply to programming.

And this is weird because as programmer I probably should read some books in my field of work. But I don't fell any push into this direction. I don't wan't to read book about programming language because what for? I tried long time ago and they are boring like hell :/ If I need to learn syntax I can just look into online tutorials.

All new stuff about C++ I learning when I searching online for solutions of problems or discuss with others. Sometimes I spend more time on trying understand small piece of example code than on fixing the initial issue. This happening mostly because I go from one page to another and finding more and more interesting stuff.

I would really love to read programming book which is not about language or algorithms but more about programming itself. I imagine such a book would contain stories of development, tips and tricks how to be better programmer. You know this kind of book which you start reading and before you noticing its ends.

Do you know book like that ? If you know I would really like to know its title.


Sunday, April 24, 2016

Plans, real life and monkey job.

Funny thing about planning is that sometimes its not working out the way you want. This was case this week I planned to work on animations and ended doing small upgrade for resource system. The best thing is that I don't even feel bad about stuff ending this way :D 

How I ended doing that is other story. Because I have policy of moving everything what I can to resource system which I have (this make stuff more consistent) I moved my rendering script to it. Everything would be good if not the fact that render script is initialized on main thread and my resource system never was prepared for request from other thread than game thread. So it was time to do improvement to allow for this :D

This was even more important because there were sometimes crashes at startup of game. I split my task on 3 sub task:

  1. Access to resource data require locking of resource (i.e. meshRes->lock()->getMaterial();)
  2. Separation of resource from data so you could have resource handle and it was still loading 
  3. Moving prepared stuff on multithreading.
First two task were robust :/ required iterating over all my resource types and changing it's interface. This was boring like hell but well programming is not only about interesting stuff.

My mind was blank when I was doing this so I had time to think and came to conclusion:
Some people saying that programming is about creating stuff. But reality is different. We as programmer spend most of our time improving existing stuff, changing them, fixing and redesigning. When we do all of this we make small piece of code which do something new and we once again starting whole thing again. This is also true in personal projects.
Few hour later changes were ready and I could start preparing functions which worked on one thread but were already separated in a way part of it could be moved to other thread. This was more interesting task which resulted in changes for some of resources. Generally my resource system look like this:

class ResourceXYZ
     ResourceId  m_id;
     DataType*  m_privateData;

Till now private data was part which control whole resource but now in some cases I want to hold some data in resource so even when private data change it will still be the same. I.e. LevelID (Yes level is also resource).

Another hour later I was ready. I know that my game worked because I were changes step by step with running game to be sure it at least work. Next step was mutli-threaded code which went smoothly.

Thanks to lock system I would add simple wait for loading of resource if it was still loading. There were small issue with dependencies of compiling GPU programs (they expected other resources to be already loaded) but well thanks to my split on soft and hard references fixing it was also easy.

And so my code working now and my previous 700 ms loading on debug configuration resulted in 600 ms loading now :) There are still few things I want to make:

  • File asynchronous loading with forward loading for better performance.
  • Reloading of resources
  • Cleanup iteration over whole system
But well you cannot have everything in life but some day I will make this all work :) For now I will return to animation topic to push everything forward :)


Thursday, April 14, 2016

After break

I took some break from writing on this blog but I had busy last few months. In this time I done a lot of changes in engine one of biggest "finished" one are changes in file system. But this time I don't to talk about what I done but more about what will come and what I working on right now.

And I do some stuff with which I'm not feel most comfortable: Animation system. So I decided to seek some advice and explain what I do, why and how I would like to improve it. So be free to comment and critique.

I don't fell that system I have right now is what I really want to have.

This is this weird felling when you fell that system that you created is working but you fell that it's limiting you. Because of this felling recently more often I turn of computer and sit down with pen and notebook and think what I really want to do with this system. So far my conclusion is because I'm iterative develop White Rabbit Engine technology I didn't notice till now that what was I searching for was different thing from what I have now. 

What I have now is "decent" system for playing animation using blends trees. And what I was searching for are behavior trees. I already have some idea how to make this system part of existing code. This will require some changes because I want blend trees to be just input nodes for behaviors nodes. Everything so whole system was consistent on all levels.

New movement system
Right now there is simple system which apply on character: orientation from pad/keyboard relative to camera direction and then play walk/run animation. This work but don't look nice when you try to change direction.

Because of that currently I started experimenting with simple system which based on direction vector try to choose the animation which will allow to get root bone position to destiny point. How it will work I don't know this is more R&D. So far I'm still not convinced by result. I will also probably postpone this "task" to first do proper behavior tree which will allow me on easier experimenting.

I am doing animations so if it possible I want to optimize whole workflow as much as I can.

This is for more simpler problem than it may sound. Currently I can create "Animation Database" (AnimDB) resource which contain link to animations resource and blends trees inside. 

Sound good but it's not because I cannot reuse the same blend tree between different AnimDB. This was one of this problem I didn't thought so much when I was doing initial system and if I decide to do different animations for each race in Little Big Adventure: Remake it would require from me supporting multiple copies of the same tree which would be really inefficient. So I need to fix :)

Animations in White Rabbit Engine are used to locomotion of character.

Right now this happening by calculating root bone relative movement and applying this to kinematic physics in each frame. This works nice but you need to be really careful how you do animations because slight foot movement may result in sliding effects of foots.

What I would like to experiment with is possibility to lock one of bones in world space and retrieving root offset from this.This would look like we have animation with marked when left or right foot touch ground and when it do it I lock position of marked bone in world space (b.w.s.) and store local animation position (b.l.a.p) of it. Bone is locked as long as distance between stored (b.l.a.p) and current (b.l.a.p) won't be bigger then some delta. I would use this lock to apply corrections to root offset so even if foot slightly move in animation in engine it would still look good


As you can see I think about a lot of stuff and try to improve a lot of different issues. Right now we redoing assets for Little Big Adventure: Remake. Thanks to that we don't need to put extra effort into changing content. But once I will define whole workflow there will be only place for small improvement. 

There will be no second chance so it would be nice to do it right so I'm going back to my pen and notebook to figure out in my head how I want this whole stuff to work. When whole idea will be in my head coding should be the easiest part.