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<title>libgfx: Packed Integer Vectors</title>
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<h2>Packed Integer Vectors</h2>
<p>The <a href="vec.html">vector package</a> provides the standard way to
represent and manipulate vector quantities.
These vectors are primarily designed to represent real-valued vectors using
floating point numbers.
However, there are times when it is more convenient to use a packed integer
vector format. That is the purpose of this package, which you can use by
including the header file
<pre>
#include <intvec.h>
</pre>
<p>A <em>packed integer vector</em> is an <i>n</i> element vector, each of whose
elements are <i>k</i>-bit integers. These <i>k</i>-bit integers are
interpreted as representing the range [0, 1] for unsigned types and [-1, 1]
for signed types. For example, suppose we have a vector whose elements are
unsigned 8-bit quantities (e.g., of type <tt>unsigned char</tt>).
Each value would have an integral value in the range [0, 255], but these
values would always be interpreted as real values ranging between [0, 1].
<h3>class IntVec</h3>
<p>Packed integer vectors are declared using the following template class
<pre>
template<class T, int T_MAX, int N> class IntVec;
</pre>
The type <tt>T</tt> is the type of the constituent elements (e.g.,
<tt>unsigned char</tt>) and <tt>T_MAX</tt> is the maxium representable value
for this type (e.g., <tt>UCHAR_MAX</tt>). The number of elements in the
vector is determined by <tt>N</tt>. Note that ANSI C defines appropriate
maximum values of integer types in <limits.h>.
<p>Classes created from the <tt>IntVec</tt> template provide a small set of
fundamental public methods:
<ul>
<li>A default constructor that initializes all elements of the vector to 0.
<li>A C-style [] bracket accessor which returns, as a
<tt>double</tt> the appropriate element of the vector.
<li>A vector assignment operator (<tt>v = w</tt>).
<li>A scalar assignment operator (<tt>v = 3.14</tt>).
</ul>
<h3>class IntVec3</h3>
<p>Because 3-D vectors are particularly common in graphics applications, this
package provides explicit support for them.
<pre>
template <class T, int T_MAX> class IntVec3;
</pre>
<p>In addition to the standard <tt>IntVec</tt> methods, <tt>IntVec3</tt>
provides the following additional constructors, all of which allow the values
of the vector to be explicitly initialized.
<pre>
IntVec3(double x, double y, double z);
IntVec3(const Vec3& v);
IntVec3(const float v[3]);
IntVec3(const double v[3]);
</pre>
<p>It also provides the following methods for manipulating the elements of the
vector:
<pre>
Vec3 unpack() const; <i>// Return vector as Vec3</i>
void pack(const Vec3& v); <i>// Set vector from v</i>
void pack(double x, double y, double z); <i>// Set vector from x,y,z</i>
</pre>
<p>A typical use of this class would be in defining a type for RGB colors
represented with 8 bits per channel. Such a type could be declared as
follows:
<pre>
typedef IntVec3<unsigned char, UCHAR_MAX> byteColor;
</pre>
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