HP c3700 - Workstation, Reference Manual, Page: 398 / 486

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glSelectBuffer
Chapter 17
398
glSelectBuffer
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.
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.
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.