sync code with last improvements from OpenBSD

doc/gl-docs/GL/gl/readbuffer.3gl

@@ -0,0 +1,81 @@
+'\" e
+'\"! eqn | mmdoc
+'\"macro stdmacro
+.ds Vn Version 1.2
+.ds Dt 24 September 1999
+.ds Re Release 1.2.1
+.ds Dp Jan 14 18:30
+.ds Dm 01 readbuffe
+.ds Xs 2004 4 readbuffer.gl
+.TH GLREADBUFFER 3G
+.SH NAME
+.B "glReadBuffer
+\- select a color buffer source for pixels
+
+.SH C SPECIFICATION
+void \f3glReadBuffer\fP(
+GLenum \fImode\fP )
+.nf
+.fi
+
+.SH PARAMETERS
+.TP \w'\f2mode\fP\ \ 'u 
+\f2mode\fP
+Specifies a color buffer.
+Accepted values are
+\%\f3GL_FRONT_LEFT\fP,
+\%\f3GL_FRONT_RIGHT\fP,
+\%\f3GL_BACK_LEFT\fP,
+\%\f3GL_BACK_RIGHT\fP,
+\%\f3GL_FRONT\fP,
+\%\f3GL_BACK\fP,
+\%\f3GL_LEFT\fP,
+\%\f3GL_RIGHT\fP, and
+\%\f3GL_AUX\fP\f2i\fP,
+where \f2i\fP is between 0 and \%\f3GL_AUX_BUFFERS\fP \-1.
+.SH DESCRIPTION
+\%\f3glReadBuffer\fP specifies a color buffer as the source for subsequent
+\%\f3glReadPixels\fP, \%\f3glCopyTexImage1D\fP, \%\f3glCopyTexImage2D\fP,
+\%\f3glCopyTexSubImage1D\fP, \%\f3glCopyTexSubImage2D\fP,
+\%\f3glCopyTexSubImage3D\fP, and
+\%\f3glCopyPixels\fP commands. 
+\f2mode\fP accepts one of twelve or more predefined values.
+(\%\f3GL_AUX0\fP through \%\f3GL_AUX3\fP are always defined.)
+In a fully configured system,
+\%\f3GL_FRONT\fP,
+\%\f3GL_LEFT\fP, and
+\%\f3GL_FRONT_LEFT\fP all name the front left buffer,
+\%\f3GL_FRONT_RIGHT\fP and
+\%\f3GL_RIGHT\fP name the front right buffer, and
+\%\f3GL_BACK_LEFT\fP and
+\%\f3GL_BACK\fP name the back left buffer.
+.P
+Nonstereo double-buffered configurations have only a front left and a
+back left buffer.
+Single-buffered configurations have a front left and a front right 
+buffer if stereo, and only a front left buffer if nonstereo.
+It is an error to specify a nonexistent buffer to \%\f3glReadBuffer\fP.
+.P
+\f2mode\fP is initially \%\f3GL_FRONT\fP in single-buffered configurations,
+and \%\f3GL_BACK\fP in double-buffered configurations.
+.SH ERRORS
+\%\f3GL_INVALID_ENUM\fP is generated if \f2mode\fP is not one of the twelve
+(or more) accepted values.
+.P
+\%\f3GL_INVALID_OPERATION\fP is generated if \f2mode\fP specifies a buffer
+that does not exist.
+.P
+\%\f3GL_INVALID_OPERATION\fP is generated if \%\f3glReadBuffer\fP
+is executed between the execution of \%\f3glBegin\fP
+and the corresponding execution of \%\f3glEnd\fP.
+.SH ASSOCIATED GETS
+\%\f3glGet\fP with argument \%\f3GL_READ_BUFFER\fP
+.SH SEE ALSO
+\%\f3glCopyPixels(3G)\fP,
+\%\f3glCopyTexImage1D(3G)\fP,
+\%\f3glCopyTexImage2D(3G)\fP,
+\%\f3glCopyTexSubImage1D(3G)\fP,
+\%\f3glCopyTexSubImage2D(3G)\fP,
+\%\f3glCopyTexSubImage3D(3G)\fP,
+\%\f3glDrawBuffer(3G)\fP,
+\%\f3glReadPixels(3G)\fP