glXGetConfig Subroutine

OpenGL 1.2 for AIX: Reference Manual

glXGetConfig Subroutine

Purpose

Returns information about GLX visuals.

Library

OpenGL C bindings library: libGL.a

C Syntax

int glXGetConfig(Display *dpy
                 XVisualInfo *Visual
                 int Attribute
                 int *Value)

Description

The glXGetConfig subroutine sets the Value provided to the Attribute value of the windows or GLX pixmaps created with respect to the Visual parameter. The glXGetConfig subroutine returns an error code if for any reason it is unsuccessful. If it is successful, 0 (zero) is returned.

The Attribute parameter can be one of the following:

Attribute	Definition
GLX_USE_GL	This attribute is True if OpenGL rendering is supported by this visual. Otherwise, it is False.
GLX_BUFFER_SIZE	This attribute defines the number of bits per color buffer. For red, green, blue, and alpha (RGBA) visuals, it is the sum of GLX_RED_SIZE, GLX_GREEN_SIZE, GLX_BLUE_SIZE, and GLX_ALPHA_SIZE. For color index visuals, this attribute is the size of the color indexes.
GLX_LEVEL	This attribute defines the frame buffer level of the visual. Level 0 is the default frame buffer. Positive levels correspond to frame buffers that overlay the default buffer; negative levels correspond to frame buffers that underlay the default buffer.
GLX_RGBA	This attribute is True if color buffers store RGBA values. It is False if they store color indexes.
GLX_DOUBLEBUFFER	This attribute is True if color buffers exist in front/back pairs that can be swapped. Otherwise, it is False.
GLX_STEREO	This attribute is True if color buffers exist in left/right pairs. Otherwise, it is False.
GLX_AUX_BUFFERS	This attribute defines the number of auxiliary color buffers available. Zero indicates that no auxiliary color buffers exist.
GLX_RED_SIZE	This attribute defines the number of red bits stored in each color buffer. If GLX_RGBA is False, the GLX_RED_SIZE attribute is undefined.
GLX_GREEN_SIZE	This attribute defines the number of green bits stored in each color buffer. If GLX_RGBA is False, the GLX_GREEN_SIZE attribute is undefined.
GLX_BLUE_SIZE	This attribute defines the number of blue bits stored in each color buffer. If GLX_RGBA is False, the GLX_BLUE_SIZE attribute is undefined.
GLX_ALPHA_SIZE	This attribute defines the number of alpha bits stored in each color buffer. If GLX_RGBA is False, the GLX_ALPHA_SIZE attribute is undefined.
GLX_DEPTH_SIZE	This attribute defines the number of bits in the depth buffer.
GLX_STENCIL_SIZE	This attribute defines the number of bits in the stencil buffer.
GLX_ACCUM_RED_SIZE	This attribute defines the number of red bits stored in the accumulation buffer.
GLX_ACCUM_GREEN_SIZE	This attribute defines the number of green bits stored in the accumulation buffer.
GLX_ACCUM_BLUE_SIZE	This attribute defines the number of blue bits stored in the accumulation buffer.
GLX_ACCUM_ALPHA_SIZE	This attribute defines the number of alpha bits stored in the accumulation buffer.
GLX_TRANSPARENT_TYPE_EXT	This attribute defines the type of transparency (if any) in the visual. Return values are:
	GLX_NONE_EXT no transparency GLX_TRANSPARENT_INDEX_EXT PseudoColor transparency GLX_TRANSPARENT_RGB_EXT RGB Transparency
GLX_TRANSPARENT_RED_VALUE_EXT	This attribute returns the red value of the transparent pixel when the transparency type is GLX_TRANSPARENT_RGB_EXT.
GLX_TRANSPARENT_GREEN_VALUE_EXT	This attribute returns the green value of the transparent pixel when the transparency type is GLX_TRANSPARENT_RGB_EXT
GLX_TRANSPARENT_BLUE_VALUE_EXT	This attribute returns the blue value of the transparent pixel when the transparency type is GLX_TRANSPARENT_RGB_EXT.
GLX_TRANSPARENT_ALPHA_VALUE_EXT	This attribute returns the alpha value of the transparent pixel when the transparency type is GLX_TRANSPARENT_RGB_EXT.
GLX_TRANSPARENT_INDEX_VALUE_EXT	This attribute returns the index value of the transparent pixel when the transparency type is GLX_TRANSPARENT_INDEX_EXT.
GLX_X_VISUAL_TYPE_EXT	This attribute returns the visual type:
	GLX_TRUE_COLOR_EXT TrueColor colormap GLX_DIRECT_COLOR_EXT DirectColor colormap GLX_PSEUDO_COLOR_EXT PseudoColor colormap GLX_STATIC_COLOR_EXT StaticColor colormap GLX_GRAY_SCALE_EXT Grayscale colormap GLX_STATIC_GRAY_EXT StaticGray colormap
GLX_VISUAL_CAVEAT_EXT	This attribute returns the visual rating:
	0 or GLX_NONE_EXT no rating GLX_SLOW_VISUAL_EXT not an optimal visual

The X protocol allows a single visual ID to be instantiated with different numbers of bits per pixel. However, windows or GLX pixmaps that will be rendered with OpenGL must be instantiated with a color buffer depth of GLX_BUFFER_SIZE.

Although a GLX implementation can export many visuals that support OpenGL rendering, it must support at least two. The first required visual must be an RGBA visual with 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 required visual. However, the color buffer size of this visual must be as great as the deepest TrueColor, DirectColor, PseudoColor, or StaticColor visual supported on level 0. The visual itself must also be available on level 0.

The other required visual is a color index one with 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. The visual itself must also be available on level 0.

An application is most effective when written to select the visual most closely meeting its requirements. Creating windows or GLX pixmaps with unnecessary buffers can result in reduced rendering performance and poor resource allocation.

Parameters

dpy	Specifies the connection to the X server.
Visual	Specifies the visual to be queried. Visual is a pointer to an XVisualInfo structure, not a visual ID or a pointer to a Visual structure.
Attribute	Specifies the visual attribute to be returned.
Value	Returns the requested value.

Notes

XVisualInfo is defined in the Xutil.h file. It is a structure that includes Visual, VisualID, Screen, and Depth elements.

Return Values

GLXNoExtension	dpy does not support the GLX extension.
GLXBadScreen	The Visual screen does not correspond to a valid screen.
GLXBadAttrib	Attribute is not a valid GLX attribute.
GLXBadVisual	Visual does not support GLX and an attribute other than GLX_USE_GL is requested.

Files

/usr/include/GL/gl.h	Contains C language constants, variable type definitions, and ANSI function prototypes for OpenGL.
/usr/include/GL/glx.h	Contains C language constants, variable type definitions, and ANSI function prototypes for GLX.

Related Information

The glXChooseVisual subroutine, glXCreateContext subroutine.

OpenGL in the AIXwindows (GLX) Environment.

OpenGL Overview.