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C++, SDL2, OpenGL ES 2 (GLES2), CMake, Git

Background, CMake

Two C++ OpenGL side projects I’ve posted about in the last two years are…  One uses (Qt + OpenGL + Qt Creator with qmake .pro build files) for an STL model viewer in Qt Creator for (Windows, Mac OS X, Linux).  The other uses (SDL2 + OpenGL) for cross-platform demos such as a bookshelf style grid view and a shadow mapping demo (using assimp for models).  The build system for this latter project was a bit messy because I started from SDL2 sample projects for (Windows Visual Studio, Linux make files, Android nmake, XCode OSX, XCode iOS).  This made sense at the time (because my real job keeps me busy so I wanted a faster short-term path to see my cross-platform code running).  However, I decided I wanted a cleaner long-term build solution, so I gave this SDL2 project a complete “reboot”.

I started a new (but similar) project from scratch using CMake.  This was a great way to get some experience using CMake.  At my job, we use Visual Studio for Windows and Makefiles for Linux (with GCC).  For this side project there’s a lot more native build systems, so it makes more sense to use a tool like CMake (or SCons etc).


To make the cross-platform aspect simpler at this stage, I’m doing all the OpenGL stuff with OpenGL ES 2 core profile (obviously in the long-term I could have multiple rendering paths).  The current list of platforms is – Windows (ANGLE), Linux, OS X, Android, iOS, Emscripten.  I kind of wanted to use GLES3 because of new features like (vertex array objects) and (texture arrays).  However, there is currently better cross-platform support for GLES2.  In particular, for Emscripten GLES3, better WebGL 2 browser support is required.

ANGLE is also currently lacking in GLES3 support.  Wikipedia says OpenGL 4.3 provides full compatibility with OpenGL ES 3.0, but I’m not sure whether it’s 100% true.  Plus I’m eventually planning to use ANGLE for Windows Mobile 10 support (or Universal Windows Platform) too.

OSX is lacking in terms of GLES2 support.  GL_ARB_ES2_compatibility does not provide full compatibility with GLES2.  I found that even simple GLES2 code requires changes to work on OSX – for example, a VAO (vertex array object) must be bound for OSX, while GLES2 core does not support VAOs.  GL_ARB_ES2_compatibility Overview states “will ease the process of porting applications from OpenGL ES 2.0 to OpenGL”, so it’s not full ES2 support.

So for OSX I will need some conditionals (or an alternate rendering path).  Or I could wait for ANGLE to add GLES2 support.  Or I could try MetalGL.  With the release of OSX 10.11 (just a few days ago), OSX now supports Metal, and there is a project MetalGL that can map GLES2 to Metal.  The day OSX 10.11 came out (9/30) I was able to run the demo (DrawLoadDemo) for MetalGL on OSX.  I was able to connect my own project to it (using CMake), but there is some compatibility issue with SDL2.  I’m not yet sure how easy it will be to get MetalGL to work with SDL2 on OSX.  TBD on this.

Qt Creator

I’m using Qt Creator as my primary editor and IDE (when possible).  Qt Creator has support for CMake.


I’m using Git (instead of Subversion).  For basic use, the main difference between Git and Subversion is that Git is not designed around a centralized server.  So when I do a git commit, I also do a git push to push my local commit to the online central server.  Another obvious difference I noticed is that when I check svn log using TortoiseSVN it takes a long time to get the log from the central server (unless you use something to cache it).

Modern C++

An interesting aside is that Linus Torvald (who initially designed and developed git) likes C better than C++.  I actually have some sympathy with that view – C is simpler than C++ (so it’s less likely to result in pointlessly complex code) and it’s lower level (so it’s easier to know what the compiler will do).  Plus my job (GPU modeling) relates to systems software, and systems software programmers (eg computer engineers) tend to like lower layer code (ie closer to the hardware).

For my job we haven’t upgraded our project yet from Visual Studio 2010.

For this side project, I’m making a conscious effort to use more modern C++ features (eg C++11) when useful.

Screen Shots

I’ll figure out later how best to post the Emscripten version (uses JavaScript and WebGL).  For now I’ll just share a screenshot.  I’m also sharing a photo of the same demo running on a Kindle Fire HD 6.  This simple demo also runs on Linux, Windows, iOS, OSX.  A lot of the changes (ie the rewrite) I describe here relate to the cross-platform support (eg CMake usage), so I’m also including a screen shot of CMake in Qt Creator.  I’m also  including a screen shot of SourceTree for Git

image image image  image

Next Steps

I had a great time and learned a lot building this cross-platform infrastructure from the ground up.  I’m tempted to just focus more on that aspect.  I could make it an open source project, focus on making it more robust and better designed as a generic engine base.  Make it simpler and more streamlined for others to use for their projects.  Take feedback and contributions.  Add features and general-use functionality that isn’t specific to a particular application.  Integrate additional libraries (make some parts optional).  It might become more like a game engine or similar to Marmalade ( ).

Another path I’d love to pursue is writing additional graphics demos (eg beyond the basic shadow map demo seen in an earlier post).

However, the path I’ve decided to focus on next is to make a playable game.  I’ve been playing “Clash of Clans”, so I’ve decided to write a cross-platform tower defense game similar to CoC.  Here’s a random screen shot of CoC to give an idea – it’s an isometric tile-based tower defense strategy game.  I’m making it 3D so the rendering may look more like “Galaxy Control”.

image image

To keep things simple, I’m planning to focus on the rendering, basic UI, and a basic single player demo.  This means things like (art, sound, networking, content, game design details) are lower priority (at least initially).  I suspect if my goal was to release a commercial game as a solo developer, then using a pre-existing game engine (like Unity) (or at least Marmalade) would make more sense.  And going all crazy with the ground-up cross-platform support wouldn’t be necessary.  I also have a busy real job (GPU model development) and this project is just for fun and learning…  So we’ll see how far I get :-).  However far I get, I’ll at least expect to get some more great experience and learning 🙂

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