GLSELECTBUFFER(3G) UNIX Programmer's Manual GLSELECTBUFFER(3G)
glSelectBuffer - establish a buffer for selection mode
values
void glSelectBuffer( GLsizei size,
GLuint *buffer )
size Specifies the size of buffer.
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 ras-
terization. Instead, if a primitive or a raster position
intersects the clipping volume defined by the viewing frus-
tum 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 selec-
tion 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
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GLSELECTBUFFER(3G) UNIX Programmer's Manual GLSELECTBUFFER(3G)
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.
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 exe-
cuted 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(3G), glInitNames(3G), glLoadName(3G),
glPushName(3G), glRenderMode(3G)
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