Learning OpenGL. Log 2

This post is part of a series of logs of my journey in learning OpenGL (or as some say, modern OpenGL).


So far

Quite a bit of work has been done on the engine (briefly mentioned in my last log) over the last week. I did get permission from my coordinator so I will be using the engine for the unit projects. It was mostly bug fixes and getting things to play nice with raw OpenGL. I can’t seem to remember the specifics. My short term memory is seems to be much worse than I remembered… Jokes aside. I will discuss a few things today that might not be directly related to OpenGL.

Windows on Windows

All of the OpenGL development so far, including my engine, has been done using Visual Studio 2012 on a Windows 8 machine. This might be too much information, but on Windows. Interesting things happen when you drag/move and/or re-size a window widget around.

While an user is moving or re-sizing an application’s window, the application’s Win32 message pump enters an other loop that blocks until the user let go of the mouse button. If you’re developing a game or anything alike, it means your game loop would be blocked as well. This blocks your render update, your physics update, and your logic update etc etc. Depending on how things are implemented, and the duration of the window action. Bad things could happen (game is paused when it shouldn’t be, logic break down, network de-sync etc). Of course. Being a perfectionist means that a resolution to this problem is needed if I want a good night sleep.

If you’re creating your window using WinMain, you can hack around it by intercepting and handling the events from the window yourself, instead of passing it to DefWindowProc. If you’re on XNA. You can also hack around it via custom classes instead of using the default XNA provided classes for the related stuff. It’s a bit trickier if you’re using a library such as GLFW and SFML, which provides abstraction on top of the platform specific windowing stuff. I think you could use the refresh callback to resolve the issue in GLFW (I could well be wrong). On SFML is a bit more complicated.

On SFML. sf::Window.pollEvent() also blocks until the window manipulation action is returned. If I guessed correctly, it is probably just a simple wrapper over the windows message pump. I could put some hack into the windows specific code and recompile SFML, but I did not want to do that. Anyway. After some more Googling. I stumbled upon a SFML forum post where someone proposed a solution to do the rendering on a separate thread, leaving all  the event handling and everything else on the main thread. I thought to myself. You might as well do everything on the second thread, and just leave the event handling to the main thread. This was implemented into my engine and now I have the option of running the game in a ‘mainthread’ mode and a ‘dualthread’ mode.

The only thing relevant to OpenGL in this is that the context has to be active on the thread that you’re doing the rendering.

For more information on the Windows message pump issue. Youcan go to this gamedev post where a guy has done some digging and reported his findings. (link: http://www.gamedev.net/topic/488074-win32-message-pump-and-opengl—rendering-pauses-while-draggingresizing/)

God Functions and OpenGL Tutorials

I’ve been encountering an issue that might not actually be an issue. It’s god functions in tutorials and/or minimal examples. It’s the sole reason I hate about reading code. Besides poor code format and bracketing. The tutorials that I’ve been following are full of them. Majority of the typical draw a triangle (equivalent of printing “hello world”)  example tries to stuff everything into as few function as possible, if not into the entire main function. It teaches nothing about the lifetime of any of the OpenGL ‘objects’.

How am I suppose to know that vertex array can be deleted after the data is buffered. How am I suppose to know that the shader source and the shader can be detached and deleted after the shader program is compiled. Wrapping all of these in nice simple classes such a ShaderProgram class, or a Triangle class would have been much more clearer and cleaner.


On the GUI side of things, I’ve discovered and gave SFGUI a try over the last few days and was able to get it semi integrated into my engine.

I did not mention SFGUI in my last log. It’s a GUI library just like the ones mentioned before (AntTweakBar, CEGUI etc). It is built on top of SFML, but it’s on a slow transition to become SFML independent. The widget looks very nice, and is very similar to Valve’s older in game GUI’s. It written in C++ so you don’t get retarded C interfaces that has a gezzalion variants for a single function. The support is awesome and the developers are very active on the forums. It is a new library though.

One issue that I do have with SFGUI is it’s sfg::SFGUI object. At the moment I have the aspect ratio fixed by calling glViewport with the appropriate parameters when a re-size happens. When the GUI is displayed by calling sfg::SFGUI::Display(). It calls glViewport internally which breaks my aspect ratio. I reported the issue on the forum and got a response from one of the developers very quickly. We are currently in the process on finding a workaround before the issue is fixed for the next version.

Qubicle Constructor

I bought a license for Qubicle Constructor last night. It’s a voxel model creator. I plan to use it to create some models for the unit projects.  I have to say. It is quite pricey.. (link)

For those who don’t know what a voxel is. Here’s a wiki link (http://en.wikipedia.org/wiki/Voxel).

In conclusion

I haven’t done much studies on OpenGL lately, so I need to get on with that. Gotta go to sleep a lot more earlier as well..

Note to myself

It might be better to start a different log specifically for my engine development. Instead of contaminating this log with things that are unrelated to OpenGL. Since having a general log seem like a worst idea, but that’s a lot of writing for 2 logs….

According to Murphy’s law: your professor will find your blog, and haunt you in your sleep if you say bad things about them.

Learning OpenGL. Log 1

This is the first, in what will be a series of posts on my journey in learning OpenGL (or as some say, modern OpenGL).


It’s been 2 weeks since Uni started. As I am doing an Interactive Computer Graphics this semester, which uses OpenGL. I have therefore, started it.

Besides learning to draw the basic primitives and the usual rainbow colored triangles. Plus a little bit of shader programming. I’ve spent a lot of the time in the past 2 weeks just playing and experimenting with a couple of utility tool kits and  graphics libraries for window creation and input handling. Namely Freeglut, GLFW, and SFML. Today, I will talk about my experience with them so far, and what not.

From a beginner point of view, getting started with learning how to setup a basic window and OpenGL context up was such a pain. Going from a C++ programmer to using libraries/API’s that are written in C also made me quite uncomfortable. To those who are a novice like me. Fear not, you will get used to it after a while. The hardest part is actually just getting the few concepts down.  Specifically window and context initialization and the way OpenGL’s API is defined. This is not a tutorial, so I won’t go into the details, but I will provide a list of the online tutorials I’ve been using that are very good.

Freeglut (Wiki link)

Freeglut is an API compatible clone of the now obsolete Glut. It is under active development, where as work on Glut halted back in 2005. All it does is providing means to create a window which an OpenGL context will be attached to. The reason I took a dip into Freeglut is because the Interactive Computer Graphics unit uses it (because the text book uses it…). It has been the de facto choice for tutorials and teaching materials, even though it should just die after the original project halted. now Just a quick rank: the lecturer seems like a nice guy, but he is just NOT lecturer materials. The textbook that he chose is also horrible. From what I’ve gathered, the same textbook has been used for the last couple years for this unit, which is sad. The text attempts to teach theories and concepts in computer graphics and tries to mix OpenGL into it.

The way Freeglut/Glut works is by providing a couple callbacks for different things while keeping completely control over it’s own main loop. This is good for making applications like interactive graphics render and model viewers, application which it was designed for developing.  If you intend to develop applications such as games, that are much more interactive and resource intensive, then Freeglut is not for you. At first I wasn’t too sure why, but control over the main loop is very important.

To use Freeglut, you initialize the library and set your call backs, and then you begin Freeglut’s mainloop. At this point, Freeglut takes over control until it exits.

GLFW (link)

The next tool kit I tried is GLFW. It is a very minimal tool kit and does not do as much as what Freeglut give you, but it does give you control over your mainloop. Instead of entering Freeglut’s mainloop, you have something along the line of “pollevents()”, which it internally calls callbacks that can you set, just like Freeglut. GLFW and Freeglut are quite similar with their functions, in terms of initialization and configurating the window. I spent about a week on Freeglut. By the time I moved to GLFW, it wasn’t too hard picking it up.

What I did was I ended up wrapping the GLFW stuff into a RenderWindow class, and wrote a simple event queue and wrote custom callbacks to translate most of the call backs into my own events, which I then handled by polling my own event queue. I modeled it after SFML because I’ve been using it for a while now and the OOP aspect of it made it very elegant.

One thing that I do miss that Freeglut has and GLFW doesn’t is menu creation. Pop-up menus will be used extensively for this unit so I spent a lot of time investigating what alternative there is for GLFW besides writting my own. The problem is, there isn’t really any. I did managed to discover CEGUI, nui3, glui2 and AntTweakBar.  The AntTweakBar library seems like the easiest to implement with the others looking quite complicated. I did not give any of them a try so I could be wrong. What bothered me is that they were GUI/widget tool kits and do not provide the ‘traditional’ menu.

SFML (link)

Finally. I remember that  SFML uses OpenGL internally. SFML (short for simple, fast, multi-media library). It’s popular for creating 2D games and applications. Bit of a rival to SDL. Best of all, it’s written in C++, and under active development. The library provides a lot to developers with 5 different modules. Providing classes for not just handling 2D graphics, but there are also classes for handling audio, network and other things. SFML allows you to use the OpenGL API directly, and it’s very simple to do some. What’s nice is that you can use it’s 2D graphics module along side of it. There are quite a few GUI libraries built for SFML but I havn’t look too deep into yet. The best thing yet is that I’ve been using SFML for the last couple dozen weeks on my 2D game engine project.

I spent the afternoon today and extended the engine enough to get some basic OpenGL primitive drawn. The engine is no where near completion. If I could use SFML for the interactive computer graphics unit then I will have the opportunity to develop and grow the engine along side the course project, instead of pausing work on my game project.


This blog has turned out to be a lot more formal and a bit more longer than I expected, but that’s cool. In closing, the libraries I mentioned today are not all there is out there. They are simply the ones that I’ve discovered and explored so far. There are many more out there that can be used for creating window and OpenGL context. The ones that I could think of on top of my head are Qt and SDL. I’ve used Qt before and it’s awesome for lots of things.

The next thing I will do is work a bit more on OpenGL with SFML for a bit more, and do so by extending my engine. I will also have to contatct my unit coordinator to accquire permission on developing on VS2012 with SFML on Windows (the project is meant to be done on a POSIX system with Freeglut). Lastly, I will continue learning OpenGL.

Stay tuned for the next log. Peace out!

List of tutorials

(in order of most favored):

List of libraries mentioned

(no particular order):

  • Freeglut
  • GLFW
  • SFML
  • SDL
  • Qt
  • nui3
  • glui2
  • AntTweakBar