Solving the Linux multi-monitor problem with SDL 2.0

A few days back I decided to upgrade my Ubuntu 14.04 LTS to Ubuntu 16.04 LTS and the first thing I did, after the upgrade, was to re-build and test AnKi. Everything seemed to work fine except the fullscreen mode. In my dual-monitor setup and with 14.04 SDL was creating a fullscreen SDL_Window in my primary monitor and the second monitor was left alone. In 16.04 though the fulscreen window covered both the monitors and it was placed in a very odd position. This is the code I’m using to create the SDL_Window:

U32 flags = SDL_WINDOW_OPENGL;

if(init.m_fullscreenDesktopRez)
{
	flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
}

m_impl->m_window = SDL_CreateWindow(&init.m_title[0],
	SDL_WINDOWPOS_UNDEFINED,
	SDL_WINDOWPOS_UNDEFINED,
	init.m_width,
	init.m_height,
	flags);

I spend quite a few hours trying to understand the issue and after some digging I found out that SDL was reporting only one display (SDL_GetNumVideoDisplays) with the resolution of my entire desktop. Obviously that was wrong. After trying different stuff I found out the culprit. Apparently SDL 2.0 is using libxinerama.so to query some information related to multi-monitor setups. Since my Ubuntu installation was brand new I didn’t have that library installed. That didn’t stop SDL from building but querying multiple monitors was not working properly.

Hopefully this sort post will help people that have similar problems. If you have multiple monitors and you are using SDL 2.0 install libxinerama-dev.

Game level video demonstration

A video demonstration of a character navigating a real game level. Actually this is a small part of a bigger level. The complete level may be released at some point. Until then, enjoy the video:

PS: Music by almighty Varathron.

Squashing bugs in AnKi

There are some universally accepted truths in software and one of those truths is that all software has bugs. Some people are more careful than others but nobody is perfect and nobody can write 100% bug free code. Another truth is that hunting bugs is rarely a fun job. It shifts the focus and sometimes it forces a mental context switch (graphics guys know that context switches can be slow). I always considered AnKi as a playground. A codebase where I can experiment, learn and have fun. Since the inception of AnKi I knew that bugs and debugging in general will spoil that fun so I had to find a way to have a robust codebase so I can focus on the fun parts. I think to some degree I’ve managed to avoid the endless pains of debugging by using the tricks I’ll describe in the following lines.

The first and, in my opinion, the most powerful tool against bugs is the almighty assertions. AnKi has a ton of assertions. To put it into perspective, there are 852 assertions throughout the code and it’s roughly 1 assertion every 84.8 lines of code. Some subsystems like util (AnKi’s equivalent of STL) have to be extremely robust so this particular subsystem has 1 assertion every 37 lines of code. In practice AnKi almost never segfaults when assertions are enabled. In the majority of cases an assertion is triggered and finding out what’s wrong is a mater of minutes.

Another thing I’ve tried early on and improved over the years is based on the idea that the commonly used subsystems have to be as robust as possible. One of these subsystems is util (contains a list, something like std::vector, hashmap, memory management, strings and other). Util is a widely used subsystem and it’s extremely important to be reliable. As I mentioned earlier, util is rigged with assertions. On top of that there are quite a few unit and performance tests. So unit tests is another weapon against bugs. In AnKi’s case unit testing is not that excessive but they cover some commonly used cases.

AnKi loves wrappers. To protect against common mistakes there are some wrappers that have debug capabilities. One example is anki::Array (something like std::array). anki::Array wraps constant size arrays and it asserts on out of bounds access (unlike std::array). Also, there is SArray that is constructed using a pointer to some memory and a size. SArray will also assert on out of bounds assess. These wrappers, and more, ensure that stupid mistakes will be caught.

The last weapon is the excellent valgrind and more precisely valgrind’s memcheck tool. Once and a white I run a demo on top of valgrind just to make sure that everything is in order. There were some occasions where all of the above methods failed but valgrind found the culprit. Unfortunately in complex workloads valgrind can be quite slow.

Of course C++ bugs are not the only source of bugs. Half of the bugs in AnKi are graphical glitches and rendering problems. Graphics related bugs heavily depend on the GPU and the driver and debugging those can be painful. Spending a whole week debugging can be kind of painful. There are some tools that help graphics related problems but those will not be covered by this article.

To sum up, what worked for AnKi is tons of assertions, robust core subsystems, some unit testing and quality code.

That’s all for now.

Vulkan: The next Khronos graphics API… that is not OpenGL

This year’s GDC proved to be quite exciting. New technologies, new ideas and some heavyweight announcements. According to the press one of the most exciting presentations was Khronos’ Vulkan API and the demos running on top of it. That really depicted the momentum, the support and the commitment behind the new API.

This article gathers all the publicly shared information behind the new API and adds some personal thoughts in the mix. The fact that I had the pleasure to follow the development of Vulkan API very closely (I was involved early on in the development of a prototype Vulkan driver for ARM’s GPUs) will give some credibility to my personal views. But that doesn’t mean that my views reflect those of my employer. So, whatever you read in the following lines doesn’t necessary reflect the views of my current employer.

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Porting AnKi to Android

After months of careful planning, reading the GL specs and waiting for Google to add OpenGL ES 3.0 support, AnKi was finally ported to Android. This article presents the result and briefly expands on the challenges of porting a game engine to Android. More precisely, there is a video showing a demo running on an Android tablet, the second is a pre-build .apk of that demo that you can download and install to your Android device and the third is a few thoughts on Android development and mobile GPUs.

Video

The video is showing a flyby demo running on a Samsung/Google Nexus 10 tablet equipped with Mali T604 GPU. Please note that the demo is a bit slower because of HDMI. The resolution is 720p, the FPS (without HDMI) ~17 and the lights are in the worst case ~10.

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Developing games on and for Linux/SteamOS

Linux, or GNU/Linux as some people want to call it, was born 20+ years ago as an open source desktop operating system and despite its massive success on super-computers, servers, embedded and mobile devices it didn’t manage to gain the same traction on the space that was bred for, on desktop. Many people gave valid arguments on why desktop is a hard market to conquer but deep down I believe that video games is one of the most commonly desired features of a home computing system. Despite some notable efforts over the years Linux gaming never shared the same love as Windows PC gaming and console gaming but that may come to an end mainly due to Valveā€™s efforts to steer developers and gamers to Linux. As a Linux (game) developer for the past 6 years I think I can shed some light on the pros and cons of that system and who knows maybe some people will find this reading useful.

To be able to see and understand the big picture of developing on and for Linux we first need to identify the smaller areas that compose it. Things like tools (compilers, debuggers, libraries), hardware abstractions (graphics and sound APIs) and finally maintaining multiplatform capabilities are some key elements of that process. Keeping the multiplatform aspect of things in the back of our head is an interesting and sensible thing to do mainly because with careful planning and not that much effort a Linux application can be ported to other operating systems where the opposite may not be that easy.

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