glSelectBuffer(3G)glSelectBuffer(3G)NAMEglSelectBuffer - establish a buffer for selection mode values
GLuint *buffer );
Specifies the size of buffer. Returns the selection data.
DESCRIPTIONglSelectBuffer() has two arguments: buffer is a pointer to an array of
unsigned integers, and size indicates the size of the array. buffer
returns values from the name stack (see glInitNames(), glLoadName(),
glPushName()) when the rendering mode is GL_SELECT (see glRender‐
Mode()). glSelectBuffer() must be issued before selection mode is
enabled, and it must not be issued while the rendering mode is
A programmer can use selection to determine which primitives are drawn
into some region of a window. The region is defined by the current mod‐
elview 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 glRenderMode() is called, a hit record is copied to buf‐
fer if any hits have occurred since the last such event (name stack
change or glRenderMode() 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 buffer is reset to 0 whenever selection mode is
entered. Each time a hit record is copied into buffer, 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 buffer, as much data
as can fit is copied, and the overflow option is set. If the name stack
is empty when a hit record is copied, that record consists of 0 fol‐
lowed by the minimum and maximum depth values.
To exit selection mode, call glRenderMode() with an argument other than
GL_SELECT. Whenever glRenderMode() is called while the render mode is
GL_SELECT, it returns the number of hit records copied to buffer,
resets the overflow option and the selection buffer pointer, and ini‐
tializes the name stack to be empty. If the overflow bit was set when
glRenderMode() was called, a negative hit record count is returned.
The contents of buffer is undefined until glRenderMode() is called with
an argument other than GL_SELECT.
glBegin()/glEnd() primitives and calls to glRasterPos() can result in
GL_INVALID_VALUE is generated if size is negative.
GL_INVALID_OPERATION is generated if glSelectBuffer() is called while
the render mode is GL_SELECT, or if glRenderMode() is called with argu‐
ment GL_SELECT before glSelectBuffer() is called at least once.
GL_INVALID_OPERATION is generated if glSelectBuffer() is executed
between the execution of glBegin() and the corresponding execution of
ASSOCIATED GETSglGet() with argument GL_NAME_STACK_DEPTH
glGet() with argument GL_SELECTION_BUFFER_SIZE
glGetPointerv() with argument GL_SELECTION_BUFFER_POINTER
SEE ALSOglFeedbackBuffer(3), glInitNames(3), glLoadName(3), glPushName(3),