76 lines
1.9 KiB
Text
76 lines
1.9 KiB
Text
|
.TH QBALL 2
|
||
|
|
.SH NAME
|
||
|
|
qball \- 3-d rotation controller
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.B
|
||
|
|
#include <draw.h>
|
||
|
|
.br
|
||
|
|
.B
|
||
|
|
#include <geometry.h>
|
||
|
|
.PP
|
||
|
|
.B
|
||
|
|
void qball(Rectangle r, Mouse *mousep,
|
||
|
|
.br
|
||
|
|
.B
|
||
|
|
Quaternion *orientation,
|
||
|
|
.br
|
||
|
|
.B
|
||
|
|
void (*redraw)(void), Quaternion *ap)
|
||
|
|
.SH DESCRIPTION
|
||
|
|
.I Qball
|
||
|
|
is an interactive controller that allows arbitrary 3-space rotations to be specified with
|
||
|
|
the mouse. Imagine a sphere with its center at the midpoint of rectangle
|
||
|
|
.IR r ,
|
||
|
|
and diameter the smaller of
|
||
|
|
.IR r 's
|
||
|
|
dimensions. Dragging from one point on the sphere to another specifies the endpoints of a
|
||
|
|
great-circle arc. (Mouse points outside the sphere are projected to the nearest point
|
||
|
|
on the sphere.) The axis of rotation is normal to the plane of the arc, and the
|
||
|
|
angle of rotation is twice the angle of the arc.
|
||
|
|
.PP
|
||
|
|
Argument
|
||
|
|
.I mousep
|
||
|
|
is a pointer to the mouse event that triggered the interaction. It should
|
||
|
|
have some button set.
|
||
|
|
.I Qball
|
||
|
|
will read more events into
|
||
|
|
.IR mousep ,
|
||
|
|
and return when no buttons are down.
|
||
|
|
.PP
|
||
|
|
While
|
||
|
|
.I qball
|
||
|
|
is reading mouse events, it calls out to the caller-supplied routine
|
||
|
|
.IR redraw ,
|
||
|
|
which is expected to update the screen to reflect the changing orientation.
|
||
|
|
Argument
|
||
|
|
.I orientation
|
||
|
|
is the orientation that
|
||
|
|
.I redraw
|
||
|
|
should examine, represented as a unit Quaternion (see
|
||
|
|
.IR quaternion(9.2)).
|
||
|
|
The caller may set it to any orientation.
|
||
|
|
It will be updated before each call to
|
||
|
|
.I redraw
|
||
|
|
(and on return) by multiplying by the rotation specified with the mouse.
|
||
|
|
.PP
|
||
|
|
It is possible to restrict
|
||
|
|
.I qball's
|
||
|
|
attention to rotations about a particular axis.
|
||
|
|
If
|
||
|
|
.I ap
|
||
|
|
is null, the rotation is unconstrained.
|
||
|
|
Otherwise, the rotation will be about the same axis as
|
||
|
|
.IR *ap .
|
||
|
|
This is accomplished by projecting points on the sphere to
|
||
|
|
the nearest point also on the plane through the sphere's center
|
||
|
|
and normal to the axis.
|
||
|
|
.SH SOURCE
|
||
|
|
.B /sys/src/libgeometry/qball.c
|
||
|
|
.SH SEE ALSO
|
||
|
|
.IR quaternion (2)
|
||
|
|
.br
|
||
|
|
Ken Shoemake,
|
||
|
|
``Animating Rotation with Quaternion Curves'',
|
||
|
|
.I
|
||
|
|
SIGGRAPH '85 Conference Proceedings.
|