GLXCREATECONTEXT(3G)

💖 GLXCREATECONTEXT 💖

okay bestie, gather round, because today we're reading the manual page for glXCreateContext — yeah it's a GLX one, the 3G kind, so it's living over in OpenGL/X11 library land. and it does exactly what it says on the tin: it makes you a brand new GLX rendering context ✨

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🎀 NAME 🎀

glXCreateContext — create a new GLX rendering context 🦋

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🌸 C SPECIFICATION 🌸

GLXContext glXCreateContext( Display *dpy,
                             XVisualInfo *vis,
                             GLXContext shareList,
                             Bool direct )

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(yes the delim $$ is just sitting there in the middle of the synopsis block. not me pointing at it. it's part of the page, we keep it, periodt 💅)

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🦋 PARAMETERS 🦋

• dpy — the connection to the X server. like, which server are we even talking to, bestie.
• vis — the visual that defines the frame buffer resources your rendering context gets to play with. and listen, this one trips people up: it is a pointer to an XVisualInfo structure. it is not a visual ID, and it is not a pointer to a Visual. okay? okay. 🫶
• shareList — the context you wanna share display lists with. NULL means no sharing is to take place, so it's giving solo main character energy.
• direct — whether rendering is to be done with a direct connection to the graphics system if possible (True) or through the X server (False).

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💫 DESCRIPTION 💫

glXCreateContext creates a GLX rendering context and hands you back its handle. and the vibe? this context can render into both windows and GLX pixmaps. iconic. but if glXCreateContext fails to create a rendering context, it returns NULL, which is the saddest possible return value 😭

now, if direct is True, then a direct rendering context is created if the implementation supports direct rendering, if the connection is to an X server that is local, and if a direct rendering context is available. and heads up — an implementation may return an indirect context when direct is True. like, it's allowed to do that. no cap.

if direct is False, then a rendering context that renders through the X server is always created. and yes, direct rendering provides a performance advantage in some implementations — but there's a catch, and it's a big one: direct rendering contexts cannot be shared outside a single process, and they may be unable to render to GLX pixmaps. so, trade-offs, bestie.

if shareList is not NULL, then all display-list indexes and definitions are shared by context shareList and by the newly created context. and an arbitrary number of contexts can share a single display-list space — the more the merrier, fr fr. however, all rendering contexts that share a single display-list space must themselves exist in the same address space. two rendering contexts share an address space if both are nondirect using the same server, or if both are direct and owned by a single process. and note this lil detail: in the nondirect case, it is not necessary for the calling threads to share an address space — only for their related rendering contexts to share an address space. the way that's so specific. 💅

and if the GL version is 1.1 or greater, then all texture objects except object 0 are shared by any contexts that share display lists. not object 0 though. object 0 said no thank you. 🙈

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🌈 NOTES 🌈

XVisualInfo is defined in Xutil.h. it is a structure that includes visual, visualID, screen, and depth elements. there they are. that's the whole list.

a process is a single execution environment, implemented in a single address space, consisting of one or more threads.

a thread is one of a set of subprocesses that share a single address space, but maintain separate program counters, stack spaces, and other related global data. and a thread that is the only member of its subprocess group is equivalent to a process. cute, right?

⚠️ it may not be possible to render to a GLX pixmap with a direct rendering context. so like, don't be shocked, bestie. it's in the notes for a reason.

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💀 ERRORS 💀

• NULL is returned if execution fails on the client side. yeah. NULL. again. 💔
• BadMatch is generated if the context to be created would not share the address space or the screen of the context specified by shareList.
• BadValue is generated if vis is not a valid visual — for example, if a particular GLX implementation does not support it.
• GLXBadContext is generated if shareList is not a GLX context and is not NULL.
• BadAlloc is generated if the server does not have enough resources to allocate the new context. server said "no room", basically.

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🫶 SEE ALSO 🫶

• glXDestroyContext
• glXGetConfig
• glXIsDirect
• glXMakeCurrent

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and that's the whole page, babes 🧚 the footer down there just says GLXCREATECONTEXT() right back at us — same as the top, no version number, no date, nothing, so we're keeping it consistent. now go forth and create contexts responsibly, bestie. 💜✨