PICK_APERTURE(3G)

NAME

pick_aperture − define pick aperture for pick_from_segment(3G) and hit_mode(3G)

SYNOPSIS

C Syntax:

void set_pick_window(fildes,px_min,py_min,px_max,py_max)
int fildes;
float px_min,py_min,px_max,py_max;

void set_pick_depth(fildes,p_front,p_back)
int fildes;
float p_front,p_back;

void inq_pick_window(fildes,px_min,py_min,px_max,py_max)
int fildes;
float *px_min,*py_min,*px_max,*py_max;

void inq_pick_depth(fildes,p_front,p_back)
int fildes;
float *p_front,*p_back;

FORTRAN77 Syntax:

subroutine set_pick_window(fildes,px_min,py_min,px_max,py_max)
integer*4 fildes
real px_min,py_min,px_max,py_max

subroutine set_pick_depth(fildes,p_front,p_back)
integer*4 fildes
real p_front,p_back

subroutine inq_pick_window(fildes,px_min,py_min,px_max,py_max)
integer*4 fildes
real px_min,py_min,px_max,py_max

subroutine inq_pick_depth(fildes,p_front,p_back)
integer*4 fildes
real p_front,p_back

Pascal Syntax:

procedure set_pick_window(fildes:integer;
px_min,py_min,px_max,py_max:real);

procedure set_pick_depth(fildes:integer; p_front,p_back:real);

procedure inq_pick_window(fildes:integer;
var px_min,py_min,px_max,py_max:real);

procedure inq_pick_depth(fildes:integer; var p_front,p_back:real);

DESCRIPTION

Input Parameters

fildes Integer file descriptor returned by gopen when an I/O path to a graphics device is opened.

px_min minimum x limit for pick window in VDC units.

py_min minimum y limit for pick window in VDC units.

px_max maximum x limit for pick window in VDC units.

py_max maximum y limit for pick window in VDC units.

p_front specifies the front pick apperture plane in perspective coordinates; i.e., comparison with the pick aperture is performed after the primitives are transformed by the current transformation matrix. Perspective divide occurs after the front and back clip.

p_back specifies the back pick aperture plane in perspective coordinates; i.e., comparison with the pick aperture performed after the primitives are transformed by the current transformation matrix. Perspective divide is performed after the front and back clip.

Discussion

Set_pick_window and set_pick_depth set a 2-dimensional rectangular window and a front and back z plane which together define the pick aperture. Inquire_pick_window and inq_pick_depth return the current set values for the pick aperture.

The pick aperture is used for hit testing when the Starbase hit mode is enabled (see hit_mode(3G)). Hit testing is also done by pick_from_segment(3G).

Note that some picking modes (see set_pick_mode(3G)) may cause pick_from_segment(3G) to alter the pick aperture.

ERRORS

1 Graphics device is not initialized for this operation.

DEFAULTS

px_min: 0.0

py_min: 1.0

px_max: 0.0

py_max: 1.0

p_front: −10000.0

p_back: 10000.0

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