1991-2006
Silicon Graphics, Inc.
glXChooseFBConfig
3G

# glXChooseFBConfig

return a list of GLX frame buffer configurations that match the specified attributes

## C Specification

                    GLXFBConfig * glXChooseFBConfig
                    Display * dpy
                    int screen
                    const int * attrib_list
                    int * nelements

## Parameters

`dpy`

  Specifies the connection to the X server.

`screen`

  Specifies the screen number.

`attrib_list`

  Specifies a list of attribute/value pairs. The last attribute must be `None`.

`nelements`

  Returns the number of elements in the list returned by `glXChooseFBConfig`.

## Description

`glXChooseFBConfig` returns GLX frame buffer configurations that match the attributes specified in `attrib_list`, or `NULL` if no matches are found. If `attrib_list` is `NULL`, then `glXChooseFBConfig` returns an array of GLX frame buffer configurations that are available on the specified screen. If an error occurs, no frame buffer configurations exist on the specified screen, or if no frame buffer configurations match the specified attributes, then `NULL` is returned. Use `XFree` to free the memory returned by `glXChooseFBConfig`.

All attributes in `attrib_list`, including boolean attributes, are immediately followed by the corresponding desired value. The list is terminated with `None`. If an attribute is not specified in `attrib_list`, then the default value (see below) is used (and the attribute is said to be specified implicitly). For example, if `GLX_STEREO` is not specified, then it is assumed to be `False`. For some attributes, the default is `GLX_DONT_CARE`, meaning that any value is OK for this attribute, so the attribute will not be checked.

Attributes are matched in an attribute-specific manner. Some of the attributes, such as `GLX_LEVEL`, must match the specified value exactly; others, such as, `GLX_RED_SIZE` must meet or exceed the specified minimum values. If more than one GLX frame buffer configuration is found, then a list of configurations, sorted according to the ``best'' match criteria, is returned. The match criteria for each attribute and the exact sorting order is defined below.

The interpretations of the various GLX visual attributes are as follows:

`GLX_FBCONFIG_ID`

  Must be followed by a valid XID that indicates the desired GLX frame buffer configuration. When a `GLX_FBCONFIG_ID` is specified, all attributes are ignored. The default value is `GLX_DONT_CARE`.

`GLX_BUFFER_SIZE`

  Must be followed by a nonnegative integer that indicates the desired color index buffer size. The smallest index buffer of at least the specified size is preferred. This attribute is ignored if `GLX_COLOR_INDEX_BIT` is not set in `GLX_RENDER_TYPE`. The default value is 0.

`GLX_LEVEL`

  Must be followed by an integer buffer-level specification. This specification is honored exactly. Buffer level 0 corresponds to the default frame buffer of the display. Buffer level 1 is the first overlay frame buffer, level two the second overlay frame buffer, and so on. Negative buffer levels correspond to underlay frame buffers. The default value is 0.

`GLX_DOUBLEBUFFER`

  Must be followed by `True` or `False`. If `True` is specified, then only double-buffered frame buffer configurations are considered; if `False` is specified, then only single-buffered frame buffer configurations are considered. The default value is `GLX_DONT_CARE`.

`GLX_STEREO`

  Must be followed by `True` or `False`. If `True` is specified, then only stereo frame buffer configurations are considered; if `False` is specified, then only monoscopic frame buffer configurations are considered. The default value is `False`.

`GLX_AUX_BUFFERS`

  Must be followed by a nonnegative integer that indicates the desired number of auxiliary buffers. Configurations with the smallest number of auxiliary buffers that meet or exceed the specified number are preferred. The default value is 0.

`GLX_RED_SIZE`, `GLX_GREEN_SIZE`, `GLX_BLUE_SIZE`, `GLX_ALPHA_SIZE`

  Each attribute, if present, must be followed by a nonnegative minimum size specification or `GLX_DONT_CARE`. The largest available total RGBA color buffer size (sum of `GLX_RED_SIZE`, `GLX_GREEN_SIZE`, `GLX_BLUE_SIZE`, and `GLX_ALPHA_SIZE`) of at least the minimum size specified for each color component is preferred. If the requested number of bits for a color component is 0 or `GLX_DONT_CARE`, it is not considered. The default value for each color component is 0.

`GLX_DEPTH_SIZE`

  Must be followed by a nonnegative minimum size specification. If this value is zero, frame buffer configurations with no depth buffer are preferred. Otherwise, the largest available depth buffer of at least the minimum size is preferred. The default value is 0.

`GLX_STENCIL_SIZE`

  Must be followed by a nonnegative integer that indicates the desired number of stencil bitplanes. The smallest stencil buffer of at least the specified size is preferred. If the desired value is zero, frame buffer configurations with no stencil buffer are preferred. The default value is 0.

`GLX_ACCUM_RED_SIZE`

  Must be followed by a nonnegative minimum size specification. If this value is zero, frame buffer configurations with no red accumulation buffer are preferred. Otherwise, the largest possible red accumulation buffer of at least the minimum size is preferred. The default value is 0.

`GLX_ACCUM_GREEN_SIZE`

  Must be followed by a nonnegative minimum size specification. If this value is zero, frame buffer configurations with no green accumulation buffer are preferred. Otherwise, the largest possible green accumulation buffer of at least the minimum size is preferred. The default value is 0.

`GLX_ACCUM_BLUE_SIZE`

  Must be followed by a nonnegative minimum size specification. If this value is zero, frame buffer configurations with no blue accumulation buffer are preferred. Otherwise, the largest possible blue accumulation buffer of at least the minimum size is preferred. The default value is 0.

`GLX_ACCUM_ALPHA_SIZE`

  Must be followed by a nonnegative minimum size specification. If this value is zero, frame buffer configurations with no alpha accumulation buffer are preferred. Otherwise, the largest possible alpha accumulation buffer of at least the minimum size is preferred. The default value is 0.

`GLX_RENDER_TYPE`

  Must be followed by a mask indicating which OpenGL rendering modes the frame buffer configuration must support. Valid bits are `GLX_RGBA_BIT` and `GLX_COLOR_INDEX_BIT`. If the mask is set to `GLX_RGBA_BIT` | `GLX_COLOR_INDEX_BIT`, then only frame buffer configurations that can be bound to both RGBA contexts and color index contexts will be considered. The default value is `GLX_RGBA_BIT`.

`GLX_DRAWABLE_TYPE`

  Must be followed by a mask indicating which GLX drawable types the frame buffer configuration must support. Valid bits are `GLX_WINDOW_BIT`, `GLX_PIXMAP_BIT`, and `GLX_PBUFFER_BIT`. For example, if mask is set to `GLX_WINDOW_BIT` | `GLX_PIXMAP_BIT`, only frame buffer configurations that support both windows and GLX pixmaps will be considered. The default value is `GLX_WINDOW_BIT`.

`GLX_X_RENDERABLE`

  Must be followed by `True` or `False`. If `True` is specified, then only frame buffer configurations that have associated X visuals (and can be used to render to Windows and/or GLX pixmaps) will be considered. The default value is `GLX_DONT_CARE`.

`GLX_X_VISUAL_TYPE`

  Must be followed by one of `GLX_TRUE_COLOR`, `GLX_DIRECT_COLOR`, `GLX_PSEUDO_COLOR`, `GLX_STATIC_COLOR`, `GLX_GRAY_SCALE`, or `GLX_STATIC_GRAY`, indicating the desired X visual type. Not all frame buffer configurations have an associated X visual. If `GLX_DRAWABLE_TYPE` is specified in `attrib_list` and the mask that follows does not have `GLX_WINDOW_BIT` set, then this value is ignored. It is also ignored if `GLX_X_RENDERABLE` is specified as `False`. RGBA rendering may be supported for visuals of type `GLX_TRUE_COLOR`, `GLX_DIRECT_COLOR`, `GLX_PSEUDO_COLOR`, or `GLX_STATIC_COLOR`, but color index rendering is only supported for visuals of type `GLX_PSEUDO_COLOR` or `GLX_STATIC_COLOR` (i.e., single-channel visuals). The tokens `GLX_GRAY_SCALE` and `GLX_STATIC_GRAY` will not match current OpenGL enabled visuals, but are included for future use. The default value for `GLX_X_VISUAL_TYPE` is `GLX_DONT_CARE`.

`GLX_CONFIG_CAVEAT`

  Must be followed by one of `GLX_NONE`, `GLX_SLOW_CONFIG`, `GLX_NON_CONFORMANT_CONFIG`. If `GLX_NONE` is specified, then only frame buffer configurations with no caveats will be considered; if `GLX_SLOW_CONFIG` is specified, then only slow frame buffer configurations will be considered; if `GLX_NON_CONFORMANT_CONFIG` is specified, then only nonconformant frame buffer configurations will be considered. The default value is `GLX_DONT_CARE`.

`GLX_TRANSPARENT_TYPE`

  Must be followed by one of `GLX_NONE`, `GLX_TRANSPARENT_RGB`, `GLX_TRANSPARENT_INDEX`. If `GLX_NONE` is specified, then only opaque frame buffer configurations will be considered; if `GLX_TRANSPARENT_RGB` is specified, then only transparent frame buffer configurations that support RGBA rendering will be considered; if `GLX_TRANSPARENT_INDEX` is specified, then only transparent frame buffer configurations that support color index rendering will be considered. The default value is `GLX_NONE`.

`GLX_TRANSPARENT_INDEX_VALUE`

  Must be followed by an integer value indicating the transparent index value; the value must be between 0 and the maximum frame buffer value for indices. Only frame buffer configurations that use the specified transparent index value will be considered. The default value is `GLX_DONT_CARE`. This attribute is ignored unless `GLX_TRANSPARENT_TYPE` is included in `attrib_list` and specified as `GLX_TRANSPARENT_INDEX`.

`GLX_TRANSPARENT_RED_VALUE`

  Must be followed by an integer value indicating the transparent red value; the value must be between 0 and the maximum frame buffer value for red. Only frame buffer configurations that use the specified transparent red value will be considered. The default value is `GLX_DONT_CARE`. This attribute is ignored unless `GLX_TRANSPARENT_TYPE` is included in `attrib_list` and specified as `GLX_TRANSPARENT_RGB`.

`GLX_TRANSPARENT_GREEN_VALUE`

  Must be followed by an integer value indicating the transparent green value; the value must be between 0 and the maximum frame buffer value for green. Only frame buffer configurations that use the specified transparent green value will be considered. The default value is `GLX_DONT_CARE`. This attribute is ignored unless `GLX_TRANSPARENT_TYPE` is included in `attrib_list` and specified as `GLX_TRANSPARENT_RGB`.

`GLX_TRANSPARENT_BLUE_VALUE`

  Must be followed by an integer value indicating the transparent blue value; the value must be between 0 and the maximum frame buffer value for blue. Only frame buffer configurations that use the specified transparent blue value will be considered. The default value is `GLX_DONT_CARE`. This attribute is ignored unless `GLX_TRANSPARENT_TYPE` is included in `attrib_list` and specified as `GLX_TRANSPARENT_RGB`.

`GLX_TRANSPARENT_ALPHA_VALUE`

  Must be followed by an integer value indicating the transparent alpha value; the value must be between 0 and the maximum frame buffer value for alpha. Only frame buffer configurations that use the specified transparent alpha value will be considered. The default value is `GLX_DONT_CARE`.

When more than one GLX frame buffer configuration matches the specified attributes, a list of matching configurations is returned. The list is sorted according to the following precedence rules, which are applied in ascending order (i.e., configurations that are considered equal by a lower numbered rule are sorted by the higher numbered rule):

1.

  By `GLX_CONFIG_CAVEAT` where the precedence is `GLX_NONE`, `GLX_SLOW_CONFIG`, and `GLX_NON_CONFORMANT_CONFIG`.

2.

  Larger total number of RGBA color components (`GLX_RED_SIZE`, `GLX_GREEN_SIZE`, `GLX_BLUE_SIZE`, plus `GLX_ALPHA_SIZE`) that have higher number of bits. If the requested number of bits in `attrib_list` is zero or `GLX_DONT_CARE` for a particular color component, then the number of bits for that component is not considered.

3.

  Smaller `GLX_BUFFER_SIZE`.

4.

  Single buffered configuration (`GLX_DOUBLEBUFFER` being `False` precedes a double buffered one.

5.

  Smaller `GLX_AUX_BUFFERS`.

6.

  Larger `GLX_DEPTH_SIZE`.

7.

  Smaller `GLX_STENCIL_SIZE`.

8.

  Larger total number of accumulation buffer color components (`GLX_ACCUM_RED_SIZE`, `GLX_ACCUM_GREEN_SIZE`, `GLX_ACCUM_BLUE_SIZE`, plus `GLX_ACCUM_ALPHA_SIZE`) that have higher number of bits. If the requested number of bits in `attrib_list` is zero or `GLX_DONT_CARE` for a particular color component, then the number of bits for that component is not considered.

9.

  By `GLX_X_VISUAL_TYPE` where the precedence order is `GLX_TRUE_COLOR`, `GLX_DIRECT_COLOR`, `GLX_PSEUDO_COLOR`, `GLX_STATIC_COLOR`, `GLX_GRAY_SCALE`, `GLX_STATIC_GRAY`.

## Examples

`attrib_list` =

  {`GLX_RENDER_TYPE`, `GLX_RGBA_BIT`, `GLX_RED_SIZE`, 4, `GLX_GREEN_SIZE`, 4, `GLX_BLUE_SIZE`, 4, `None`};

Specifies a frame buffer configuration that supports RGBA rendering and exists in the normal frame buffer, not an overlay or underlay buffer. The returned visual supports at least four bits each of red, green, and blue, and possibly no bits of alpha. It does not support stereo display. It may or may not have one or more auxiliary color buffers, a back buffer, a depth buffer, a stencil buffer, or an accumulation buffer.

## Notes

`glXChooseFBConfig` is available only if the GLX version is 1.3 or greater.

If the GLX version is 1.1 or 1.0, the GL version must be 1.0. If the GLX version is 1.2, then the GL version must be 1.1. If the GLX version is 1.3, then the GL version must be 1.2.

glXGetFBConfigs and glXGetFBConfigAttrib can be used to implement selection algorithms other than the generic one implemented by `glXChooseFBConfig`. Call `glXChooseFBConfig` to retrieve all the frame buffer configurations on a particular screen or, alternatively, all the frame buffer configurations with a particular set of attributes. Next, call glXGetFBConfigAttrib to retrieve additional attributes for the frame buffer configurations and then select between them.

GLX implementations are strongly discouraged, but not proscribed, from changing the selection algorithm used by `glXChooseFBConfig`. Therefore, selections may change from release to release of the client-side library.

## Errors

`NULL` is returned if an undefined GLX attribute is encountered in `attrib_list`, if `screen` is invalid, or if `dpy` does not support the GLX extension.

## See Also

glXGetFBConfigAttrib, glXGetFBConfigs, glXGetVisualFromFBConfig

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.