OpenGL Rendering performance and other question..

[online.0227]

Hello.

1ST QUESTION:
I am game programmer student and quite interested in QT right now becuz I heard that Valve is going to use both QT and SDL for their next Source 2 game engine. (i guess they would use QT for level editor things..) also heard that Dota 2 on steam used SDL for linux port.

Well I am a student dealing with directX on windows much more, I made small game and its engine on windows. It has simple level editor and launcher (for the purpose of updating game prior to start just like common mmorpg games) used prior to start game as well.

Now, I want to port them into linux for study purpose. However I am considering either implementing them all using QT, or QT + SDL. I heard latest SDL 2.0 boosted rendering speed a lot, however, I also heard QT also boosted opengl rendering speed a lot since its version of 5.0. I will definitely use QT for game laucher prior to start game and level editor, however, what I meant here is game windowing.

If OpenGL rendering speed isn't that different, I would NOT use SDL but will have everything done using QT. However, I would use SDL if SDL is faster than QT by 5~10 fps point. (where fps 60 is standard). So that is my concern, how much speed difference for OpenGL rendering between them, QT and SDL?

2ND QUESTION:
And 2nd question is just for curious, I heard LGPL software can re-license back to GPL anytime. If QT suddenly do that, all the softwares that are written using QT and already being sold in the market has to get commercial qt license immediately or release their source code if they don't want to pay? just wonder lol

thank you.

[sierdzio]

1. SDL is pretty much made for games. Qt is made for standard applications, but can be used for creating games. Keep that in mind :-)

I would recommend testing both solutions before making a choice. Perhaps SDL and Qt can even be combined together?

2. Qt 5.4 is licensed under LGPL2, LGPL3, GPL2, GPL3, and commercial licenses. Digia, the company who owns the trademark and copyright, is doing rather good job, expanding our freedoms, not dimishing them. So in that regard, I would not worry too much. In any case, Qt source code is protected by the KDE agreemend, which states that whenever any company owning Qt does something nasty, the KDE foundation has all the power to fork and use the code, and keep it Free.

Also, once you release a product based on Qt, any changes to Qt licensing of future Qt versions do not affect you at all. "Lex retro non agit":http://en.wikipedia.org/wiki/Nullum_crimen,_nulla_poena_sine_praevia_lege_poenali ;-)

Lastly, even when using GPL license, you do not need to publish your source code to everybody.