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glSelectBuffer — establish a buffer for selection mode values
void glSelectBuffer( | GLsizei | size, |
| GLuint * | buffer); |
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
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.
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.
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.
glGet with argument GL_NAME_STACK_DEPTH
glGet with argument GL_SELECTION_BUFFER_SIZE
glGetPointerv with argument GL_SELECTION_BUFFER_POINTER
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/.