glselectbuffer
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glSelectBuffer(3G) OpenGL Reference 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.
Selection is used by a programmer 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 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 zero 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 flag is set. If the name stack is empty when a
hit record is copied, that record consists of zero followed by the
minimum and maximum depth values.
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glSelectBuffer(3G) OpenGL Reference glSelectBuffer(3G)
Selection mode is exited by calling 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 are undefined until glRenderMode is called with an
argument other than GL_SELECT.
glBegin/glEnd primitives and calls to glRasterPos can result in hits.
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
MACHINE DEPENDENCIES
On InfiniteReality systems selection and histogramming are unreliable if
interrupted by a graphics context switch. This will be fixed in the next
software release.
SEE ALSO
glFeedbackBuffer, glInitNames, glLoadName, glPushName, glRenderMode
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