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<title>Tutorial - Geomview Manual</title>
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<h2 class="chapter">2 Tutorial</h2>
<p>This chapter leads you through some of the basics of using Geomview.
Work through this chapter in front of a computer where you can try
out the examples given here to get a feel for what you can do with
Geomview.
<p>To start Geomview, login to the computer and get a shell window. A
shell window is a window in which you can type Unix commands; the prompt
in the window usually ends with a '%'. In the shell window (the mouse
cursor must be in the window) type the following (<kbd><Enter></kbd> here
means hit the "Enter" key):
<pre class="example"> geomview tetra dodec <Enter>
</pre>
<p>This command starts up Geomview and loads two example objects, a
tetrahedron and a dodecahedron. After a few seconds three windows
should appear; see <a href="figinitial.html#figinitial">Figure</a>.
<div class="float">
<a name="figinitial"></a><img src="figs/initial.png" alt="figs/initial.png">
<p><strong class="float-caption">Figure 2.1: Initial Geomview display.</strong></p></div>
<p>The panel on the left is Geomview's main control panel; it's called
the <em>Main</em> panel. The skinny panel in the middle is the
<em>Tools</em> panel and is for selecting different kinds of motions.
The window on the right is the camera window and in it you see a
large tetrahedron and a dodecahedron which is partially obscured
by the tetrahedron.
<p>Geomview has lots of panels but by default it displays only these three.
We'll describe some aspects of these and a couple of the others in this
tutorial. You can read more about these and other panels in the later
chapters of this manual.
<p>Put the mouse cursor in the camera window and press down and hold the
left mouse button. Now, while holding down the button, slowly move the
mouse around. You should see the picture rotate in the direction you
move the mouse. If you lift up on the mouse button while moving the
mouse, the picture continues rotating. To stop it, hold the mouse very
still and click down and up on the left mouse button.
<p>Geomview uses the <em>glass sphere</em> model for mouse-based motion. This
means you are supposed to think of the object as being inside an
invisible sphere and the mouse cursor is a gripper outside the sphere.
When you hold down the left mouse button, the gripper grabs the
sphere; when you let go of the button, the gripper releases the
sphere. Moving the mouse while holding the button down causes the
sphere (and hence the object) to move in the same direction as the
mouse.
<p>In addition to the two solids you should also see two wire-frame
boxes in the camera window. These are the "bounding boxes" of the two
objects. By default Geomview puts a bounding box around each object
that it displays so that you have an idea of how large it is.
<p>Notice that as you move the mouse around the tetrahedron and
dodecahedron move as a unit. That is because by default what you are
actually moving is the "World". To move an individual object instead of
the whole world, move the mouse cursor to the <em>Targets</em> browser in
the <em>Main</em> panel. Click (any button) on the word <em>tetra</em>.
This makes the tetrahedron be the "target object". Now move the cursor
back to the camera window and you can rotate just the tetrahedron.
<p>The motion that you have been applying up to now has been rotation,
because that is the motion mode that is selected in the <em>Tools</em>
panel. To translate instead, click on the <em>Translate</em> button.
Now when you move the mouse in the camera window while holding down the
left button, the tetrahedron (which should still be the target object
from before) will translate in the direction you move the mouse. Notice
that you can translate it beyond the edge of the window as long as you
keep holding the left mouse button down. If you lift up on the mouse
button while moving the mouse, the tetrahedron will keep going. It
moves rather rapidly so it is very easy to lose track of where it is.
<p>If you accidentally lose the tetrahedron by translating it too far out
of the view of the window, you can get it back by clicking on the
<em>Center</em> button in the <em>Tools</em> panel. This causes it to
come back to its initial position.
<p>Click on the <em>Center</em> button to bring the tetrahedron home, and
then translate it off to one side so that you can completely see the
dodecahedron.
<p>Your world now has two objects in it that are beside each other. You
should see the dodecahedron in the middle of the window and maybe part
of the tetrahedron off to one side. Go back to the <em>Targets</em>
browser in the <em>Main</em> panel and click on "World" to select the
whole world again. Now click on the <em>Look At</em> button in the
<em>Tools</em> panel. You should see the dodecahedron and the tetrahedron
in the middle of the window next to each other (see <a href="figlookatworld.html#figlookatworld">Figure</a>). The <em>Look At</em> button positions the camera in such a way
that the target object is centered in the window.
<div class="float">
<a name="figlookatworld"></a><img src="figs/fig2.png" alt="figs/fig2.png">
<p><strong class="float-caption">Figure 2.2: Looking at the world.</strong></p></div>
Now put the cursor over the middle of the dodecahedron and double-click
the right mouse button. This means click it down-and-up two times in
rapid succession. Notice that the dodecahedron becomes the target
object; you can see this in the <em>Targets</em> browser in the
<em>Main</em> panel. Double-clicking the right mouse button on an object
is another way to make it the target object.
<div class="float">
<a name="figappearance"></a><img src="figs/ap.png" alt="figs/ap.png">
<p><strong class="float-caption">Figure 2.3: The Appearance Panel.</strong></p></div>
Go to the <em>Inspect</em> menu at the top of the <em>Main</em> panel and select
<em>Appearance</em>. This brings up the <em>Appearance</em>
panel. When it appears, if it partially obscures another Geomview window
you can move it off to one side by dragging its frame with the middle
mouse button down.
<p>The <em>Appearance</em> panel lets you control various things about the
way Geomview draws objects. Note the buttons labeled <em>[af] Faces</em> and
<em>[ae] Edges</em>. Click on the <em>[ae] Edges</em> one, and notice
that Geomview is now drawing the edges of the dodecahedron. Click on it
again and the edges go away. Click several times and watch the edges
come and go. When you've had enough of this, leave the edges on
and click the <em>[af] Faces</em> button. This toggles the faces
on and off. Click the button again to turn them back on.
<p>Now click on the <em>[Cf] Faces</em> button under the word <em>COLOR</em>. A
color chooser panel should appear (see <a href="figcolorchooser.html#figcolorchooser">Figure</a>).
<div class="float">
<a name="figcolorchooser"></a><img src="figs/color.png" alt="figs/color.png">
<p><strong class="float-caption">Figure 2.4: Color Chooser Panel.</strong></p></div>
<p>Note the three sliders, <em>H</em>, <em>S</em>, and <em>V</em>,
controlling the color's hue, saturation, and value (lightness).
Clicking the <em>HSV</em> button gives a different set of sliders,
one each for red, green, and blue.
Numerical values for both RGB and HSV color systems
can be seen or edited at the bottom of the panel.
The dodecahedron's previous colors were specified in the file
<samp><span class="file">dodec</span></samp> that you loaded when we started Geomview. The color that
you specify with the color
panel overrides the old colors. You can adjust the intensity of the
color with the <em>Intensity</em> slider. When you find a color that
you like, click the <em>Done</em> button.
<p>Now put the cursor somewhere over the gray background and double-click
the right mouse button; this picks "World" as the target object.
Click the <em>Look At</em> button to look at the world again.
<p>Notice that in the <em>Appearance</em> panel the settings of the buttons
have changed from the way you left them with the dodecahedron. That's
because the <em>Appearance</em> panel always displays the settings for
the target object, which is now the world, which still has its
default settings.
<p>Click on the <em>[ab] BBox</em> button under the word <em>Draw</em>.
The bounding boxes go away. Now put the cursor back in the camera
window. At the keyboard, type the keys <kbd>a </kbd>b. Notice that the
bounding boxes come back. <kbd>a </kbd>b is the keyboard shortcut for
the bounding box toggle button; the string "[ab]" appears on the
button to indicate this. Most of Geomview's buttons have keyboard
shortcuts that you can use instead if you want. This is useful once
you are familiar with Geomview and don't want to have to move around
among lots of panels.
<p>Now select the tetrahedron, either by double-clicking the right mouse
button on it, or by selecting "tetra" in the <em>Targets</em> browser.
Then click on the <em>Delete</em> button in the <em>Main</em> panel. The
tetrahedron should disappear. This is how you get rid of an object.
<p>You can also load objects from within Geomview. Click on the <em>File</em>
menu in the <em>Main</em> panel and choose <em>Open</em>.
The <em>Files</em> panel will appear.
Below the middle of this panel is a browser with three lines in it; the
second line is a directory with lots of Geomview example files in it.
Click on that second line; see <a href="figfilespanel.html#figfilespanel">Figure</a>. Scroll down in
the list of files until you see <samp><span class="file">tref.off</span></samp>. Click on that line,
and then click on the <em>OK</em> button. A large trefoil-shaped tube
will appear in your window. Click the <em>Hide</em> button in the
<em>Files</em> panel to dismiss the panel.
<div class="float">
<a name="figfilespanel"></a><img src="figs/secondlinelist.png" alt="figs/secondlinelist.png">
<p><strong class="float-caption">Figure 2.5: The Files Panel.</strong></p></div>
<p>Now click on the <em>Reset</em> button in the <em>Tools</em> panel. This
causes everything to return to its home position. You should see a
dodecahedron and a trefoil knot (see <a href="figtrefdodec.html#figtrefdodec">Figure</a>).
<p>Play around with the trefoil knot and the dodecahedron. Experiment with
some of the other buttons in the <em>Tools</em> panel. Try coloring the
trefoil knot with the <em>Appearance</em> panel.
<p>For a tutorial on how to create your own objects to load into Geomview,
see file <samp><span class="file">doc/oogltour</span></samp> distributed with Geomview. The things in
that file will be incorporated into a future version of this manual.
<div class="float">
<a name="figtrefdodec"></a><img src="figs/trefdodecinter.png" alt="figs/trefdodecinter.png">
<p><strong class="float-caption">Figure 2.6: Trefoil and Dodecahedron.</strong></p></div>
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