GLXSWAPBUFFERS(3G)

🌸 NAME 🌸

glXSwapBuffers — ok so this is the one that exchanges front and back buffers, bestie ✨ it lives in section 3G of the GLX manual, and honestly? it's giving main character energy 💅

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🎀 C SPECIFICATION 🎀

void glXSwapBuffers( Display *dpy,
                     GLXDrawable drawable )

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(yeah that delim $$ line is just vibing there at the end, we don't question it, we respect it 🙈)

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🍓 PARAMETERS 🍓

• dpy — the connection to the X server. that's your link to the whole X situation, no cap.
• drawable — the drawable whose buffers are the ones getting swapped. yes, that one. 👑

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✨ DESCRIPTION ✨

okay so here's the tea 🫖 glXSwapBuffers promotes the contents of the back buffer of drawable to become the contents of the front buffer of drawable. like, back buffer → front buffer, glow up complete, slay. 💖

and then?? the contents of the back buffer become undefined. gone. mystery. we do not know her anymore. 😭

the update typically takes place during the vertical retrace of the monitor, rather than immediately after glXSwapBuffers is called. so it's not instant-instant, it's scheduled-instant, iykyk. 🌈

also important: glXSwapBuffers performs an implicit glFlush before it returns. so subsequent OpenGL commands may be issued immediately after calling glXSwapBuffers, but — and this is the key part — they are not executed until the buffer exchange is completed. they're queued, they're waiting their turn, they're in the group chat but nobody's read the message yet. 💀

and if drawable was not created with respect to a double-buffered visual, glXSwapBuffers has no effect, and no error is generated. literally nothing happens. iconic of it. 🙈

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📝 NOTES 📝

the contents of the back buffer become undefined after a swap. and note (fr fr note this): this applies to pbuffers as well as windows. not just windows. pbuffers too. don't forget the pbuffers bestie. 💅

all GLX rendering contexts share the same notion of which are front buffers and which are back buffers. one consequence of that is — and this is the big one — when multiple clients are rendering to the same double-buffered window, all of them should finish rendering before one of them issues the command to swap buffers. 👀

the clients are responsible for implementing this synchronization. the API is not gonna do it for you, she's not your mom. 😤 typically this is accomplished by executing glFinish and then using a semaphore in shared memory to rendezvous before swapping. that's the move. that's the whole plan. 🫶

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💀 ERRORS 💀

• GLXBadDrawable is generated if drawable is not a valid GLX drawable. invalid drawable = instant error, no thoughts. 💀
• GLXBadCurrentWindow is generated if dpy and drawable are respectively the display and drawable associated with the current context of the calling thread, and drawable identifies a window that is no longer valid. that window has left the chat. 🚪

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👀 SEE ALSO 👀

• glFlush
• glXBindSwapBarrierSGIX
• glXJoinSwapGroupSGIX
• glXSwapIntervalSGI

go read those too, bestie, they're all part of the same little friend group 🦋

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and that's the whole page!! footer says GLXSWAPBUFFERS() and it's the GLX manual, section 3G — so yeah, GLXSWAPBUFFERS(3G), exactly as the page signs off at the bottom. periodt. 💖✨🎀