glGetError returns the value of the error flag. Each
detectable error is assigned a numeric code and symbolic
name. When an error occurs, the error flag is set to the
appropriate error code value. No other errors are recorded
until glGetError is called, the error code is returned, and
the flag is reset to GL_NO_ERROR. If a call to glGetError
returns GL_NO_ERROR, there has been no detectable error
since the last call to glGetError, or since the GL was
initialized.
To allow for distributed implementations, there may be
several error flags. If any single error flag has recorded
an error, the value of that flag is returned and that flag
is reset to GL_NO_ERROR when glGetError is called. If more
than one flag has recorded an error, glGetError returns and
clears an arbitrary error flag value. Thus, glGetError
should always be called in a loop, until it returns
GL_NO_ERROR, if all error flags are to be reset.
Initially, all error flags are set to GL_NO_ERROR.
The following errors are currently defined:
GL_NO_ERROR No error has been recorded.
The value of this symbolic
constant is guaranteed to be
0.
GL_INVALID_ENUM An unacceptable value is
specified for an enumerated
argument. The offending
command is ignored, and has no
other side effect than to set
the error flag.
GL_INVALID_VALUE A numeric argument is out of
range. The offending command
is ignored, and has no other
side effect than to set the
error flag.
GL_INVALID_OPERATION The specified operation is not
allowed in the current state.
The offending command is
ignored, and has no other side
effect than to set the error
flag.
GL_STACK_OVERFLOW This command would cause a
stack overflow. The offending
command is ignored, and has no
other side effect than to set
the error flag.
GL_STACK_UNDERFLOW This command would cause a
stack underflow. The
offending command is ignored,
and has no other side effect
than to set the error flag.
GL_OUT_OF_MEMORY There is not enough memory
left to execute the command.
The state of the GL is
undefined, except for the
state of the error flags,
after this error is recorded.
When an error flag is set, results of a GL operation are
undefined only if GL_OUT_OF_MEMORY has occurred. In all
other cases, the command generating the error is ignored and
has no effect on the GL state or frame buffer contents. If
the generating command returns a value, it returns 0. If
glGetError itself generates an error, it returns 0.