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Asked: 2026-05-31T05:22:03+00:00

I have been using a few cross-platform GUI libraries (such as FLTK, wxWidgets, GTK++),

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I have been using a few cross-platform GUI libraries (such as FLTK, wxWidgets, GTK++), however I feel like none fulfil my needs as I would like to create something that looks the same regardless of the platform (I understand that there will be people against building GUI’s that don’t have a native look on the platforms but that’s not the issue here).
To build my controls, I usually rely on basic shapes provided by the library and make my way up binding & coding everything together…

So I decided to give it a try and do some opengl for 2D GUI programming (as it would still be cross-platform. With that in mind, I couldn’t help to notice that the applications that I have written using wxWidgets & FLTK usually have a average RAM consume of 1/2MB, whereas a very basic openGL window with a simple background ranges from 6 to 9 MB.

This brings me to the actual question for this thread,
I thought that all the rendering of the screen was made using either opengl/direct (under the covers).

Could someone please explain or link me some sort of article that could give me some insight of how these things actually work?

Thanks for reading!

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1 Answer

  1. Editorial Team

    These multiplatform toolkits usually support quite a lot of backends which does the drawing. Even though some of the toolkits support OpenGL as their backend, the default is usually the “native” backend.

    Take a look eg. at Qt. On Windows it uses GDI for drawing for its native backend. On linux it uses XRender I think. Same on Symbian and Mac. Qt also has its own software rasterizer. And of course there is an OpenGL backend.

    So why the application using some of these GUI toolkits can take less memory than a simple OpenGL application? If the toolkit use the “native” backend, everything is already loaded in memory, because it is very likely that all visible GUI uses the same drawing API. The native APIs can also use only one buffer representing a whole screen in which all applications can draw.

    However when using OpenGL you have your own buffer which represents the application window. Not to mention that an OpenGL application usually has several framebuffers, like z-buffer, stencil buffer, back buffer, which are not essential for 2D drawing, but they take some space (even though its probably the space in graphics card memory). Finally, when using OpenGL, it is possible that the necessary libraries are not yet loaded.

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