Gl.SelectBuffer (gb.opengl)
Static Sub SelectBuffer ( )
Establish a buffer for selection mode values.
Parameters
- size
-
Specifies the size of buffer.
- buffer
-
Returns the selection data.
Description
Gl.SelectBuffer 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
Gl.InitNames,
Gl.LoadName, Gl.PushName)
when the rendering mode is Gl.SELECT (see
Gl.RenderMode).
Gl.SelectBuffer 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 Gl.RenderMode is called,
a hit record is copied to
buffer if any hits have occurred since the
last such event
(name stack change or
Gl.RenderMode 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
/edit/0,1) are multiplied by
,
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 Gl.RenderMode with an argument
other than Gl.SELECT.
Whenever Gl.RenderMode 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 Gl.RenderMode was called,
a negative hit record count is returned.
Notes
The contents of
buffer is undefined until
Gl.RenderMode is called
with an argument other than Gl.SELECT.
Gl.Begin/Gl.End primitives and calls to Gl.RasterPos
can result in hits. Gl.WindowPos will always generate a selection hit.
Errors
Gl.INVALID_VALUE is generated if
size is negative.
Gl.INVALID_OPERATION is generated if
Gl.SelectBuffer is called while the
render mode is Gl.SELECT,
or if
Gl.RenderMode is called with argument Gl.SELECT before
Gl.SelectBuffer is called at least once.
Gl.INVALID_OPERATION is generated if
Gl.SelectBuffer
is executed between the execution of Gl.Begin
and the corresponding execution of Gl.End.
Associated Gets
Gl.Get with argument Gl.NAME_STACK_DEPTH
Gl.Get with argument Gl.SELECTION_BUFFER_SIZE
Gl.GetPointerv with argument Gl.SELECTION_BUFFER_POINTER
See also
See original documentation on OpenGL website