glXMakeCurrentReadSGI(3G) OpenGL Reference - GLX glXMakeCurrentReadSGI(3G)
NAME
glXMakeCurrentReadSGI - attach a GLX context to separate read and write
drawables
C SPECIFICATION
Bool glXMakeCurrentReadSGI( Display *dpy,
GLXDrawable draw,
GLXDrawable read,
GLXContext gc )
PARAMETERS
dpy Specifies the connection to the X server.
draw A GLX drawable that receives the results of OpenGL drawing
operations.
read A GLX drawable that provides pixels for glReadPixels and
glCopyPixels operations.
gc A GLX rendering context to be attached to draw and read.
DESCRIPTION
glXMakeCurrentReadSGI performs the same functions as glXMakeCurrent, with
one important difference: it attaches a GLX context to two drawables,
rather than one. The second drawable serves as the source for any pixel
data that are read by glReadPixels, glCopyPixels, and OpenGL extension
commands that read color, depth, or stencil data from the framebuffer.
It may be an ordinary GLX drawable, or it may be a GLX video source (see
glXCreateGLXVideoSourceSGIX). Accumulation operations (see glAccum) are
not allowed when draw is not identical to read.
It is not necessary for draw and read to have the same ancillary buffers.
It is also not necessary for read to contain a buffer corresponding to
the current GLREADBUFFER of gc. For example, the current
GLREADBUFFER of gc might be GLBACK, and read might be single-buffered.
If there is no corresponding buffer in read, then the pixel values
extracted from read will be undefined, but no error will be generated.
Operations that query the value of GLREADBUFFER use the value set last
in gc, regardless of whether read has the corresponding buffer.
glXMakeCurrentReadSGI returns True if it is successful, False otherwise.
If False is returned, the previously current rendering context and
drawables (if any) remain unchanged.
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glXMakeCurrentReadSGI(3G) OpenGL Reference - GLX glXMakeCurrentReadSGI(3G)
ERRORS
BadMatch is generated if any of the following conditions hold:
1. draw was not created on the same X screen and visual as gc.
2. read was not created on the same X screen as gc.
3. draw is None and gc is not None.
4. draw is a GLX video source.
BadAccess is generated if gc was current to another thread at the time
glXMakeCurrentReadSGI was called.
GLXBadDrawable is generated if either draw or read is not a valid GLX
drawable.
GLXBadContext is generated if gc is not a valid GLX context.
GLXBadContextState is generated if glXMakeCurrentReadSGI is called
between a glBegin and the corresponding call to glEnd.
GLXBadContextState is also generated if the rendering context current to
the calling thread has OpenGL renderer state GLFEEDBACK or GLSELECT.
GLXBadCurrentWindow is generated if there are pending OpenGL commands for
the previous context and the current drawable is a window that is no
longer valid.
BadAlloc may be generated if the server has delayed allocation of
ancillary buffers until glXMakeCurrentReadSGI is called, only to find
that it has insufficient resources to complete the allocation.
MACHINE DEPENDENCIES
The SGImakecurrentread extension is supported on RealityEngine,
RealityEngine2, and VTX systems with the following restrictions:
1. A BadMatch error is generated if
a. draw is RGBA and read is not, or vice versa. A video
source (see glXCreateGLXVideoSourceSGIX) is considered to
be RGBA.
b. read is not a video source and it does not have the same
color component resolution or the same number of index bits
as draw;
c. Either draw or read is not at buffer level 0 (the main
frame buffer planes, rather than overlay planes).
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glXMakeCurrentReadSGI(3G) OpenGL Reference - GLX glXMakeCurrentReadSGI(3G)
d. draw is multisample capable and readP is a pbuffer (see
glXCreateGLXPbufferSGIX).
2. When draw is a pixmap then read must be the same pixmap. A
BadAlloc error is generated otherwise.
On RealityEngine, RealityEngine2, and VTX, on InfiniteReality, on High
Impact and Maximum Impact, on Solid Impact systems, and on O2 systems, it
is not possible to use a context for rendering to both windows and
pixmaps.
SEE ALSO
glXMakeCurrent, glXCreateContext, glXGetCurrentContext,
glXGetCurrentDisplay, glXGetCurrentDrawable, glXGetCurrentReadDrawable
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