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 GLSELECT (see glRenderMode).
glSelectBuffer must be issued before selection mode is enabled, and it
must not be issued while the rendering mode is GLSELECT.
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
- 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 0 followed by the minimum
and maximum depth values.
Page 1
glSelectBuffer(3G) OpenGL Reference glSelectBuffer(3G)
To exit selection mode, call glRenderMode with an argument other than
GLSELECT. Whenever glRenderMode is called while the render mode is
GLSELECT, 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 -1 is returned.
NOTES
The contents of buffer is undefined until glRenderMode is called with an
argument other than GLSELECT.
glBegin/glEnd primitives and calls to glRasterPos can result in hits.
ERRORS
GLINVALIDVALUE is generated if size is negative.
GLINVALIDOPERATION is generated if glSelectBuffer is called while the
render mode is GLSELECT, or if glRenderMode is called with argument
GLSELECT before glSelectBuffer is called at least once.
GLINVALIDOPERATION is generated if glSelectBuffer is executed between
the execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GLNAMESTACKDEPTH
SEE ALSO
glFeedbackBuffer, glInitNames, glLoadName, glPushName, glRenderMode
Page 2