GLXGETCONFIG(3gl)

✨ GLXGETCONFIG ✨

okay bestie, buckle up — this is the GLXGETCONFIG page from the 3G manual, and it's literally the "hey what's up with this visual" function 💅

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🌸 NAME 🌸

glXGetConfig — returns info about GLX visuals 🦋

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🎀 C SPECIFICATION 🎀

int glXGetConfig( Display *dpy,
                  XVisualInfo *vis,
                  int attrib,
                  int *value )

delim $$

(yes the delim $$ is in there, we don't make the rules, we just report them 💖)

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🫶 PARAMETERS 🫶

• dpy — the connection to the X server. your lil phone line to X 📞
• vis — the visual you're asking about. heads up: it's a pointer to an XVisualInfo structure, not a visual ID and not a pointer to a Visual. this trips people up fr fr, so read it twice 🙈
• attrib — which visual attribute you want back.
• value — where the requested value gets written. it returns the value, as in it fills this in for you ✨

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💜 DESCRIPTION 💜

glXGetConfig sets value to the attrib value of windows or GLX pixmaps created with respect to vis. If it fails for literally any reason, glXGetConfig returns an error code. Otherwise? zero. that's it, zero, we love a clean success 🫶

So attrib is one of these, bestie 👇

• GLX_USE_GL — True if OpenGL rendering is supported by this visual, False otherwise.
• GLX_BUFFER_SIZE — number of bits per color buffer. For RGBA visuals, GLX_BUFFER_SIZE is the sum of GLX_RED_SIZE, GLX_GREEN_SIZE, GLX_BLUE_SIZE, and GLX_ALPHA_SIZE. For color index visuals, GLX_BUFFER_SIZE is the size of the color indexes.
• GLX_LEVEL — frame buffer level of the visual. Level zero is the default frame buffer. Positive levels correspond to frame buffers that overlay the default buffer, and negative levels correspond to frame buffers that underlay the default buffer. so like, above and below the default, iconic 🎀
• GLX_RGBA — True if color buffers store red, green, blue, and alpha values. False if they store color indexes.
• GLX_DOUBLEBUFFER — True if color buffers exist in front/back pairs that can be swapped, False otherwise.
• GLX_STEREO — True if color buffers exist in left/right pairs, False otherwise.
• GLX_AUX_BUFFERS — number of auxiliary color buffers that are available. Zero indicates that no auxiliary color buffers exist.
• GLX_RED_SIZE — number of bits of red stored in each color buffer. Undefined if GLX_RGBA is False. ⚠️ undefined, not "zero", not "we'll guess" — undefined.
• GLX_GREEN_SIZE — number of bits of green stored in each color buffer. Undefined if GLX_RGBA is False.
• GLX_BLUE_SIZE — number of bits of blue stored in each color buffer. Undefined if GLX_RGBA is False.
• GLX_ALPHA_SIZE — number of bits of alpha stored in each color buffer. Undefined if GLX_RGBA is False.
• GLX_DEPTH_SIZE — number of bits in the depth buffer.
• GLX_STENCIL_SIZE — number of bits in the stencil buffer.
• GLX_ACCUM_RED_SIZE — number of bits of red stored in the accumulation buffer.
• GLX_ACCUM_GREEN_SIZE — number of bits of green stored in the accumulation buffer.
• GLX_ACCUM_BLUE_SIZE — number of bits of blue stored in the accumulation buffer.
• GLX_ACCUM_ALPHA_SIZE — number of bits of alpha stored in the accumulation buffer.

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The X protocol allows a single visual ID to be instantiated with different numbers of bits per pixel. Windows or GLX pixmaps that will be rendered with OpenGL, however, must be instantiated with a color buffer depth of GLX_BUFFER_SIZE. like, no negotiating on that one 🌈

Although a GLX implementation can export many visuals that support GL rendering, it must support at least one RGBA visual. This visual must have at least one color buffer, a stencil buffer of at least 1 bit, a depth buffer of at least 12 bits, and an accumulation buffer. Alpha bitplanes are optional in this visual. However, its color buffer size must be as great as that of the deepest TrueColor, DirectColor, PseudoColor, or StaticColor visual supported on level zero, and it must itself be made available on level zero. 👑

In addition, if the X server exports a PseudoColor or StaticColor visual on framebuffer level 0, a color index visual is also required on that level. It must have at least one color buffer, a stencil buffer of at least 1 bit, and a depth buffer of at least 12 bits. This visual must have as many color bitplanes as the deepest PseudoColor or StaticColor visual supported on level 0.

Applications are best written to select the visual that most closely meets their requirements. Creating windows or GLX pixmaps with unnecessary buffers can result in reduced rendering performance as well as poor resource allocation. translation: don't be greedy with buffers, it's giving messy 💀

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🦋 NOTES 🦋

XVisualInfo is defined in Xutil.h. It is a structure that includes visual, visualID, screen, and depth elements. that's your lil cheat sheet 🎀

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💅 ERRORS 💅

• GLX_NO_EXTENSION is returned if dpy does not support the GLX extension.
• GLX_BAD_SCREEN is returned if the screen of vis does not correspond to a screen.
• GLX_BAD_ATTRIBUTE is returned if attrib is not a valid GLX attribute.
• GLX_BAD_VISUAL is returned if vis doesn't support GLX and an attribute other than GLX_USE_GL is requested.

so if you ask for GLX_DEPTH_SIZE on a visual that doesn't do GLX, that's a GLX_BAD_VISUAL for you. the only thing you're allowed to ask a non-GLX visual is GLX_USE_GL, and spoiler, the answer's gonna be False 🙈

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🌟 SEE ALSO 🌟

glXChooseVisual, glXCreateContext

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and that's the whole page, bestie, no cap 💖 this was GLXGETCONFIG() from the 3G manual — go forth and vibe-check your visuals, you're the main character of your own framebuffer 👑✨🌸