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<meta name="Author" content="Mark Danks">
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<title>Basic Objects</title>
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<center>
<h2>
<u>Basic Objects</u></h2></center>
<p><br>There are a number of objects which are the foundation for GEM.
These objects are used in every patch and control the graphics and rendering.
<p><a href="#gemwin">[gemwin]</a> - The window manager
<br><a href="#gemhead">[gemhead]</a> - The start of a rendering chain
<br><a href="#manips">manips</a> - Move an object in the window
<br><a href="#geos">geos</a> - Render a shape
<p><img SRC="tribar.gif" height=13 width=561>
<h3>
<a NAME="gemwin"></a>[gemwin]</h3>
The graphics window is created and destroyed with the <i>[gemwin]</i> object.
With the <i>[gemwin]</i> object, you can set the default size of the graphics
window, create and destroy the graphics window, turn on and off rendering,
etc. All basic GEM patches will have the following <i>[gemwin]</i>
object with these messages:
<center>
<p><img SRC="gemwin.jpg" BORDER=1 height=128 width=78></center>
The create and destroy messages will display and remove the graphics window.
The 1 and 0 messages start and stop rendering.
<p><img SRC="tribar.gif" height=13 width=561>
<h3>
<a NAME="gemhead"></a>[gemhead]</h3>
The <i>[gemhead]</i> object is the start of every rendering chain.
A simple patch, which is located in examples/gem_basic/gem1.redSquare.pd
looks like:
<center>
<p><img SRC="redSquare.jpg" BORDER=1 height=138 width=91></center>
<p>This patch will render a red square. The <i>[gemhead]</i> object
signifies the start of rendering. The <i>[color]</i> object sets the color
for all objects after it in the chain. The <i>[square]</i> object renders
a square into the graphics window based on the current color, texturing,
and transformations. In this case, there is no texturing and no transformation.
<p>Every rendering chain <b>MUST</b> start with a [gemhead]. If you
do not put a <i>[gemhead]</i> at the beginning of the chain, then nothing
will be rendered for that part of the patch.
<p><img SRC="tribar.gif" height=13 width=561>
<h3>
<a NAME="manips"></a>manips</h3>
In the patch 01.basic/02.cube.pd, the <i>[translateXYZ]</i> object is
introduced.
<center>
<p><img SRC="basicCube.jpg" BORDER=1 height=133 width=93></center>
<p>The graphics are transformed and moved by the <i>manipulator</i> objects,
or the manips. GEM has the following manips:
<p><i>[color]</i> - set the color with a vector
<br><i>[colorRGB]</i> - set the color with 3 discrete values
<br><i>[rotate]</i> - rotate with an angle and vector
<br><i>[rotateXYZ]</i> - rotate with 3 discrete values
<br><i>[scale]</i> - scale with a vector
<br><i>[scaleXYZ]</i> - scale with 3 discrete values
<br><i>[translate]</i> - translate with a vector
<br><i>[translateXYZ]</i> - translate with 3 discrete values
<p>To understand the difference between the vector and discrete values
version, realize that everything in is defined in 3 dimensions. These
dimensions can be XYZ values, or RGB colors.
<center>
<p><img SRC="transXYZ.jpg" BORDER=1 height=92 width=201></center>
<p>The two translate objects above will do exactly the same thing in a
patch, but they provide two different ways to do it. <i>[translate]</i> accepts
a scalar and vector. <i>[translateXYZ]</i> accepts three floats which
specify a point in space. The manips will transform any object which
appears after it in the rendering chain.
<p><img SRC="tribar.gif" height=13 width=561>
<h3>
<a NAME="geos"></a>geos</h3>
Up above, we saw the <i>[square]</i> and <i>[cube]</i> objects. The other
primary geos are:
<p><i>[square]</i> - render a square
<br><i>[circle]</i> - render a circle
<br><i>[triangle]</i> - render a triangle
<br><i>[cube]</i> - render a cube
<br><i>[sphere]</i> - render a sphere
<br><i>[cone]</i> - render a cone
<p>The <i>[square]</i>, <i>[circle]</i>, <i>[cube]</i>, and <i>[triangle]</i> objects
have a right-hand inlet to set the size of the shape. The default
size is 1.
<p>The <i>[cone]</i> and <i>[sphere]</i> objects are not perfectly smooth.
They are actually composed of a number of polygons. In order to control
the rendering better, the middle inlet is the size of the object, while
the right-hand inlet is the number of slices to define the shape.
Take a look at the patch gem_basic/gem3.sphere.pd to see how the number
of slices can change the look of a sphere. Don't worry about the
<i><a href="Lighting.html#world_light">[world_light]</a></i>
object, it is just there to make it easier to see the difference in the
number of slices. Make sure to click the 'lighting 0' message before
closing the patch (if you don't, then other patches will probably be completely
black until you quit and restart pd/GEM).
<p>Your graphics window should look like this for 5 and 15 slices:
<center>
<p><img SRC="sphere5.jpg" BORDER=0 height=150 width=150><img SRC="sphere15.jpg" height=150 width=150></center>
Obviously, the more slices that you use, the better the sphere looks.
However, each slice adds more polygons, which can slow down your frame
rate. In computer graphics, there is always a trade off between resolution
and speed.
<p><img SRC="tribar.gif" height=13 width=561>
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