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Geomview lets you manipulate objects with the mouse. There are six
different mouse motion modes: Rotate, Translate,
Cam Fly, Cam Zoom, Geom Scale, and
Cam Orbit. The tools panel has a button for each of these
modes; to switch modes, click on the corresponding button. You can also
select these through the Motion Mode browser on the
Main panel.
This section describes basic mouse interaction. For details,
see section The Commands Panel.

The Tools Panel
Each of the motion modes uses a common paradigm for how the motion is
applied. In particular, each depends on the current target
object and the current center object. These are explained in the
following paragraphs.
The current target object is shown in the Target field in the
Tools panel. This is the same as the selected object in the
Targets browser in the Main panel, and you can
change it by either selecting a new object in the browser, by typing
a new entry in the field, or by picking an object in a camera
window by double-clicking the right mouse button with the cursor over
the object.
The current center object is shown in the Center field in the
Tools panel. Its default value is the special word "target",
which means that the center object is whatever the target object is.
You can change the center to any object by typing it in the Center
field. The origin of the center object is held fixed in Rotate and
Orbit modes. Normally the center object is one of the existing
geoms listed in the Targets browser, and the actual center of
rotations is the origin of that object's coordinate system.
It is possible, however, to select an arbitrary point of interest on
an object as the center. For details, see section Selecting a Point of Interest.
You apply a mouse motion by holding down either the left or middle mouse
button with the cursor in a camera window and moving the mouse. Most of
the modes have inertia, which means that if you let go of the
button while moving the mouse, the motion will continue. It may be
helpful to imagine the mouse cursor as being a gripper; when you hold a
mouse button down, it grips the target object and you can move it. When
you let go of the mouse button, the gripper releases the object.
Letting go of the mouse button while moving the mouse is like throwing
the object -- the object continues moving independent of the mouse.
Inertia can be turned off; see the Main panel's Motion menu,
described below.
Generally, the left mouse button controls motion in the screen plane,
while the middle mouse controls motion along or around the forward direction.
Pressing the shift key while dragging with left or middle mouse buttons
in most motion modes gives slow-speed motions, useful for fine adjustment.
You can pick any point on an object (not just its origin) as the center of
motion by holding down the shift key while clicking the right mouse button;
this chooses a point of interest.
- Rotate
-
In Rotate mode, hold the left mouse button down to rotate the
target object about the center object. Rotation proceeds in the
direction that you move the mouse. Specifically, the axis of rotation
passes through the origin of the center object, is parallel to the
camera view plane, and is perpendicular to the direction of motion of
the mouse. When the center is "target", this means that the target
object rotates about its own origin.
The middle mouse button in Rotate mode rotates the target
object about an axis perpendicular to the view plane.
- Translate
-
In Translate mode, hold the left mouse button down to translate
the target object in the direction of mouse motion. The middle mouse
button translates the target along an axis perpendicular to the view
plane.
In Euclidean space, the center object is essentially irrelevant for
translations. In hyperbolic and spherical spaces, where translations
have a unique axis, this axis is chosen to go through the origin of the
center object.
- Cam Fly
-
Cam Fly is a crude flight simulator that lets you fly around
the scene. It works by moving the camera.
Move the mouse while holding the left mouse button down to
point the camera in a different direction. To move forward or backward,
hold down the middle button and move the mouse vertically. Both of
these motions have inertia; typically the easiest way to fly around a
scene is to give the camera a slight forward push by letting go of the
middle button while moving the mouse upward, and then using the left
button to steer.
Cam Fly affects the camera window that the mouse is in; it
ignores the target object and the center object.
- Cam Orbit
-
Cam Orbit mode lets you rotate the current camera around the
current center. The left mouse button does this rotation. The middle
mouse button in Cam Orbit mode acts as in
Cam Fly mode: it moves the camera forward or backward.
In general Cam Orbit does not move the target object, although
if the current camera is selected as the target and the center is also
the target, it will pivot that camera about itself just as in
Cam Fly mode.
- Cam Zoom
-
Cam Zoom mode lets you change the current camera's field of
view with the mouse; hold the left mouse button down and move the mouse
to change it. The numeric value of the field of view is shown in the
FOV field in the Camera panel.
- Geom Scale
-
Geom Scale mode lets you enlarge or shrink a geom. It operates
on the target object if that object is a geom. If the target is a
camera, Geom Scale operates on the geom that was most recently
the target object. Moving the mouse while holding down the left mouse button
scales the object either up or down, depending on the direction of
mouse motion. The center of the applied scaling transformation is the
center object.
Scaling is meaningful only in Euclidean space; attempts to scale are
ignored in other spaces.
Geom Scale mode does not have inertia.
The Stop, Look At, Center, and Reset
buttons on the Tools panel perform actions related to motions
but do not change the current motion mode.
- Stop
-
The Stop button causes all motions to stop. It affects all
moving objects, not just the target object. Its keyboard shortcut
is H.
The keyboard command h, which does not correspond to a
panel button, stops the current motion for the target object only.
- Look At
-
The Look At button causes the current camera to be moved
to a position such that it is looking at the target object, and such
that the target object more or less fills the window.
The Look At command is unreliable in non-Euclidean spaces.
- Center
-
The Center button undoes the target object's transformation,
moving it back to its home position, which is where it was when you
originally loaded it into Geomview.
- Reset
-
The Reset button stops all motion and causes all objects to
move back to their home positions.
The Tools panel also sports a Main button, to invoke the
main panel in case it was dismissed or buried, and a Done button
to close the Tools panel.
The Main panel's Motion Style menu has special controls
affecting how mouse motions are interpreted.
- [ui] Inertia
-
Normally, moving objects have inertia: if the mouse is still moving
when the button is released, the selected object continues to move.
When Inertia is off, objects cease to move as soon as you release
the mouse.
- [uc] Constrain Motion
-
It's sometimes handy to move an object in a direction aligned with a
coordinate axis: exactly horizontally or vertically. Selecting
Constrain Motion changes the interpretation of mouse motions
to allow this; approximately-horizontal or approximately-vertical mouse dragging
becomes exactly horizontal or vertical motion. Note that the motion is
still along the X or Y axes of the camera in which you move the mouse,
not necessarily the object's own coordinate system.
- [uo] Own Coordinates
-
It's sometimes handy to move objects with respect to the coordinate system
where they were defined, rather than with respect to some camera's view. While
Own Coordinates is selected, all motions are interpreted that way:
dragging the mouse rightward in translate mode moves the object in its own +X
direction, and so on. May be especially useful in conjunction with
the Constrain Motion button.
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