Jfgeyelin's dev blog

I wanted to write this post for a while. It describes a C++ technique to implement rollback in the context of multiplayer games that I feel is quite interesting and useful. The tl;dr is: don't bother serializing individual objects, just rollback all the memory. Rollback-based multiplayer I've been working on a multiplayer version of PewPew, and for reasons that are outside of the scope of this post, I chose to implement multiplayer with deterministic lockstep and rollback. The basic idea behind rollback-based multiplayer is that the inputs of players are replicated to all the players. Whenever a player receives the inputs of another player, the state of the game is rolled back to the point where the input happened and fast-forwarded back to the present so that the state shown to a player takes into account the inputs of the other players. Because history is being re-computed, some events get undone. For example, it's possible a player saw themselves taking a bonus, but aft...

You usually use the C library gettext with a _() macro that returns a localized version of the text passed in parameter. For example: puts ( _ ( "Hello" ) ) ; will result in a runtime search of the string "Hello", and _() eventually returns the localized version of the string. I assume the search is implemented using some sort of binary search, so it's probably extremely fast. It's fast, but we can get rid of the search altogether using constexpr functions! The trick is to use a constexpr function that  at compile time gets the ID of the given string. Then it's a matter of doing an array lookup in the table of strings for the desired locale. The array lookup is still unavoidable because we don't know at compile time which locale the app will use. In my case, _() is implemented using I18NStringIndex  which looks like this: constexpr bool I18N_EQ ( char const * a, char const * b ) { return std :: string_view ( a ) == b ; } constexpr int...

Note: This post was initially written in 2013, right after the release of Pacifism. For some reason I never published it. It's still relevant today, so here it is seven years later. In PP2's pacifism mode, you can blow up enemies with bombs. I wanted to encourage people to take risks and not just blow up all the bombs they see, so I decided to give players an incentive to explode large amounts of enemies at the same time. To do that, I crafted a formula that gave players bonuses that exponentially grew along the number of simultaneous kills: x=number of enemies killed.  f(x)=the bonus for x enemies killed. I made sure that the exponential grew slowly: even if a player managed to be twice as good as me and destroy twice as many enemies as me (200), they would only make around 55000 points, which is high but not absurdly so. Once I was pleased with the feeling of the game, I released it and waited for the scores to come in. As the high scores started coming in, I got to se...

PewPew Live was released today on Android ! Let's go over what's new compared to PewPew 2: LAN Multiplayer Multiplayer is the main difference with PewPew 2, and the reason PewPew Live exists in the first place. The initial plan was to support online multiplayer, but this proved to be very complex. For now, the game will only support LAN. Support for custom levels Custom levels are another big new thing. Allowing users to create levels will increase the replayability of the game. I had to choose where on the spectrum would the creation be: should the players be given building blocks that they can remix (low barrier of entry, low variety of levels), or should the players have to directly write code (high barrier of entry, high variety of levels) like I do when creating levels? I chose the latter because that's what I would have liked as a player, it introduces people to programming and tools that lower the barrier of entry can always be built on top. New game modes Unlock-abl...

I'm working on PewPew's sequel, for which I've revamped the graphics. Instead of drawing lines directly using OpenGL, each individual line segment is made up of two triangles whose vertexes are computed with shaders. Getting lines in 3D space to be properly displayed on a 2D screen is not trivial. In PewPew's sequel I use the screen-space projected lines, a technique very well described in the  Drawing Lines is Hard  post. The upside of drawing the lines yourself is that you are fully in control, which allows you to implement nice things such as joints, perspective, and even simulate depth of field. https://en.wikipedia.org/wiki/Depth_of_field Usually depth of field (DoF) in video games is implemented using a post-processing step that blurs the pixels with an intensity that is a function of the depth of the pixels. When we are rendering lines, we can approximate DoF directly when rendering the lines by having the vertex shader increase the width of lines and r...

So! Since my last post I got a new awesome job and thus worked less on PewPew and Rollin' Droid. An update for PewPew is in preparation though. It will feature basic maintenance stuff (iphone 5 support, sound improvements, small optimisations, etc...), and more importantly a new game mode: Pacifism It is  inspired  copied from Geometry Wars' Pacifism game mode, and even in its unfinished form it's really a lot of fun. It will be available only in PewPew 2 when you finish the 3rd Campaign (in any difficulty). Concerning Rollin' Droid, I've expanded my ambitions and need to re-do a part of the engine because I feel that my creativity is limited. I can't simply think of a feature and quickly implement it like I could do in PewPew. The hard part about RD's engine is that I have randomly generated levels that are potentially infinitely wide and height so I can't just alloc enough memory in advance. Also, I absolutely want to maintain 60 fps wit...