glSelectBuffer man page on RedHat
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GLSELECTBUFFER(3G) OpenGL Manual GLSELECTBUFFER(3G)
NAME
glSelectBuffer - establish a buffer for selection mode values
C SPECIFICATION
void glSelectBuffer(GLsizei size, GLuint * buffer);
PARAMETERS
size
Specifies the size of buffer.
buffer
Returns the selection data.
DESCRIPTION
glSelectBuffer 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
glRenderMode()). glSelectBuffer must be issued before selection mode
is enabled, and it must not be issued while the rendering mode is
GL_SELECT.
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 glRenderMode() is called, a hit record is copied to
buffer 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\(emthat 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 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 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 flag and the selection buffer pointer, and
initializes the name stack to be empty. If the overflow bit was set
when glRenderMode() was called, a negative hit record count is
returned.
NOTES
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
hits. glWindowPos() will always generate a selection hit.
ERRORS
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 argument
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 glEnd().
ASSOCIATED GETS
glGet() with argument GL_NAME_STACK_DEPTH
glGet() with argument GL_SELECTION_BUFFER_SIZE
glGetPointerv() with argument GL_SELECTION_BUFFER_POINTER
SEE ALSO
glFeedbackBuffer(), glInitNames(), glLoadName(), glPushName(),
glRenderMode()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLSELECTBUFFER(3G)
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