glXMakeContextCurrent Subroutine

OpenGL 1.2 for AIX: Reference Manual

glXMakeContextCurrent Subroutine

Purpose

Attaches a GLX context to one or more GLX drawables.

Library

OpenGL C bindings library: libGL.a

C Syntax

Bool glXMakeContextCurrent(Display *dpy,

                           GLXDrawable draw,

                           GLXDrawable read,

                           GLXContext context)

Description

The glXMakeContextCurrent subroutine does two things: (1) it makes the specified context parameter the current GLX rendering context of the calling thread, replacing the previously current context if one exists, and (2) it attaches context to the GLX drawables draw and read. As a result of these two actions, subsequent OpenGL rendering calls use context as a rendering context to modify the draw and read GLX drawables. Since the glXMakeContextCurrent subroutine always replaces the current rendering context with the specified context, there can be only one current context per thread.

draw is used for all OpenGL operations except:

Any pixel data that is read based on the value of GL_READ_BUFFER. Note that accumulation operations use the value GL_READ_BUFFER but are not allowed unless draw is identical to read.
Any depth values that are retrieved by glReadPixels or glCopyPixels.
Any stencil values that are retrieved by glReadPixels or glCopyPixels.

These frame buffer values are taken from read. Note that the same GLX Drawable may be specified for both draw and read.

Pending commands to the previous context, if any, are flushed before it is released.

The first time context is made current to any thread, its viewport is set to the full size of draw. Subsequent calls by any thread to the glXMakeContextCurrent subroutine using context have no effect on its viewport.

To release the current context without assigning a new one, call the glXMakeContextCurrent subroutine with the draw, read and context parameters set to None, None and Null, respectively.

The glXMakeContextCurrent subroutine returns True if it is successful, False otherwise. If False is returned, the previously current rendering context and drawables (if any) remain unchanged.

Parameters

dpy	Specifies the connection to the X server.
draw	Specifies a GLX drawable to be used for draw operations. This value must reflect either a GLX window ID, a GLX pixmap ID or a GLX pbuffer ID.
read	Specifies a GLX drawable to be used for read operations. This value must reflect either a GLX window ID, a GLX pixmap ID or a GLX pbuffer ID.
context	Specifies a GLX rendering context to be attached to the specified draw and read GLX drawables.

Return Values

True	Returned if the glXMakeContextCurrent subroutine is successful.
False	Returned if the glXMakeContextCurrent subroutine is not successful. The previously current rendering context and drawable (if any) remain unchanged.

Notes

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. A thread is the only member of its subprocess group that is equivalent to a process.

Error Codes

BadAccess	context is current to another thread at the time that the glXMakeContextCurrent subroutine is called.
BadAlloc	The server has delayed allocation of ancillary buffers until glXMakeContextCurrent is called, only to find that it has insufficient resources to complete the allocation.
BadMatch	It is generated by a number of conditions: draw or read is not compatible with context. draw or read is a GLX Pixmap. and context is a direct rendering context. draw and read are None and context is not None. This may be generated for implementation-specific reasons.
GLXBadContext	The specified context is not a valid GLX context.
GLXBadContextState	The rendering context current to the calling thread has an OpenGL renderer state of GL_FEEDBACK or GL_SELECT.
GLXBadCurrentDrawable	Pending OpenGL commands exist for the previous context, and the previous draw or read is no longer valid.
GLXBadDrawable	draw or read is not a valid GLX drawable.
GLXBadWindow	The X window underlying either draw or read is no longer valid.

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 glCopyPixels subroutine, glReadPixels subroutine, glXCreateNewContext subroutine, glXCreatePbuffer subroutine, glXCreatePixmap subroutine and glXCreateWindow subroutine.

OpenGL in the AIXwindows (GLX) Environment.

OpenGL Overview.