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<STRONG>NAME</STRONG>
<STRONG>glSelectBuffer</STRONG> - establish a buffer for selection mode
values
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glSelectBuffer</STRONG>( GLsizei <EM>size</EM>,
GLuint *<EM>buffer</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>size</EM> Specifies the size of <EM>buffer</EM>.
<EM>buffer</EM> Returns the selection data.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glSelectBuffer</STRONG> has two arguments: <EM>buffer</EM> is a pointer to an
array of unsigned integers, and <EM>size</EM> indicates the size of
the array. <EM>buffer</EM> returns values from the name stack (see
<STRONG>glInitNames</STRONG>, <STRONG>glLoadName</STRONG>, <STRONG>glPushName</STRONG>) when the rendering mode
is <STRONG>GL_SELECT</STRONG> (see <STRONG>glRenderMode</STRONG>). <STRONG>glSelectBuffer</STRONG> must be
issued before selection mode is enabled, and it must not be
issued while the rendering mode is <STRONG>GL_SELECT</STRONG>.
A programmer can use selection to determine which primitives
are drawn into some region of a window. The region is
defined by the current modelview and perspective matrices.
In selection mode, no pixel fragments are produced from
rasterization. Instead, if a primitive or a raster position
intersects the clipping volume defined by the viewing
frustum and the user-defined clipping planes, this primitive
causes a selection hit. (With polygons, no hit occurs if
the polygon is culled.) When a change is made to the name
stack, or when <STRONG>glRenderMode</STRONG> is called, a hit record is
copied to <EM>buffer</EM> if any hits have occurred since the last
such event (name stack change or <STRONG>glRenderMode</STRONG> call). The
hit record consists of the number of names in the name stack
at the time of the event, followed by the minimum and
maximum depth values of all vertices that hit since the
previous event, followed by the name stack contents, bottom
name first.
Depth values (which are in the range [0,1]) are multiplied
by 2^32 - 1, before being placed in the hit record.
An internal index into <EM>buffer</EM> is reset to 0 whenever
selection mode is entered. Each time a hit record is copied
into <EM>buffer</EM>, the index is incremented to point to the cell
just past the end of the block of names - that is, to the
next available cell. If the hit record is larger than the
number of remaining locations in <EM>buffer</EM>, as much data as can
fit is copied, and the overflow flag is set. If the name
stack is empty when a hit record is copied, that record
consists of 0 followed by the minimum and maximum depth
values.
To exit selection mode, call <STRONG>glRenderMode</STRONG> with an argument
other than <STRONG>GL_SELECT</STRONG>. Whenever <STRONG>glRenderMode</STRONG> is called while
the render mode is <STRONG>GL_SELECT</STRONG>, it returns the number of hit
records copied to <EM>buffer</EM>, resets the overflow flag and the
selection buffer pointer, and initializes the name stack to
be empty. If the overflow bit was set when <STRONG>glRenderMode</STRONG> was
called, a negative hit record count is returned.
<STRONG>NOTES</STRONG>
The contents of <EM>buffer</EM> is undefined until <STRONG>glRenderMode</STRONG> is
called with an argument other than <STRONG>GL_SELECT</STRONG>.
<STRONG>glBegin</STRONG>/<STRONG>glEnd</STRONG> primitives and calls to <STRONG>glRasterPos</STRONG> can result
in hits.
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_VALUE</STRONG> is generated if <EM>size</EM> is negative.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glSelectBuffer</STRONG> is
called while the render mode is <STRONG>GL_SELECT</STRONG>, or if
<STRONG>glRenderMode</STRONG> is called with argument <STRONG>GL_SELECT</STRONG> before
<STRONG>glSelectBuffer</STRONG> is called at least once.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glSelectBuffer</STRONG> is
executed between the execution of <STRONG>glBegin</STRONG> and the
corresponding execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_NAME_STACK_DEPTH</STRONG>
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glFeedbackBuffer</STRONG>, <STRONG>glInitNames</STRONG>, <STRONG>glLoadName</STRONG>, <STRONG>glPushName</STRONG>,
<STRONG>glRenderMode</STRONG>
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