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glSelectBuffer(3G)
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glSelectBuffer - establish a buffer for selection mode
values
void glSelectBuffer(
GLsizei size,
GLuint *buffer );
Specifies the size of buffer. Returns the selection data.
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 - 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 option
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
option 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.
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
glFeedbackBuffer(3), glInitNames(3), glLoadName(3),
glPushName(3), glRenderMode(3)
glSelectBuffer(3G)
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