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<span id="Colors"></span><div class="header">
<p>
Next: <a href="Textures.html" accesskey="n" rel="next">Textures</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr />
<span id="Colors-1"></span><h4 class="subsection">5.3.1 Colors</h4>
<p>Merriam-Webster defines color as “a phenomenon of light (such as red,
brown, pink, or gray) or visual perception that enables one to
differentiate otherwise identical objects.” In this essay, I
will…
</p>
<p>Okay, okay. We all know what colors are. Chickadee provides a data
type to represent color and some convenient procedures to work with
them in the <code>(chickadee graphics color)</code> module. Colors are made
up of four components, or channels: red, green, blue, and alpha
(transparency.) Each of these values is expressed as a uniform
floating point value in the range [0, 1]. 0 means that color channel
is unrepresented in the resulting color, whereas 1 means that color
channel is at full intensity.
</p>
<p>Making a color object is easy, and there’s a few ways to do it
depending on what’s most convenient. The first is <code>make-color</code>,
where you specify each channel exactly as described above. This is
fully opaque magenta:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">make-color</span> <span class="syntax-symbol">1.0</span> <span class="syntax-symbol">0.0</span> <span class="syntax-symbol">1.0</span> <span class="syntax-symbol">1.0</span><span class="syntax-close">)</span>
</pre></div>
<p>Many people are used to representing colors as 6 or 8 digit
hexadecimal numbers, so Chickadee also allows that. Here’s magenta,
again:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">rgba</span> <span class="syntax-symbol">#xFF00FFFF</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">rgb</span> <span class="syntax-symbol">#xFF00FF</span><span class="syntax-close">)</span> <span class="syntax-comment">; equivalent to the above
</span></pre></div>
<dl>
<dt id="index-make_002dcolor">Procedure: <strong>make-color</strong> <em>r g b a</em></dt>
<dd><p>Return a new color object with a red value of <var>r</var>, a green value
of <var>g</var>, a blue value of <var>b</var>, and an alpha (transparency) value
of <var>a</var>. All values are clamped to the range [0, 1].
</p></dd></dl>
<dl>
<dt id="index-rgba">Procedure: <strong>rgba</strong> <em>color-code</em></dt>
<dd><p>Return a new color object using the values of the first 32 bits of
<var>color-code</var>. Each channel occupies 8 bits. Starting from the
most significant bit, red is first, followed by green, then blue, then
alpha. Color codes are often represented as 6 or 8 digit hexadecimal
numbers in various other programs.
</p></dd></dl>
<dl>
<dt id="index-rgb">Procedure: <strong>rgb</strong> <em>color-code</em></dt>
<dd><p>Like <code>rgba</code>, but <var>color-code</var> is a 24 bit code with no alpha
channel.
</p></dd></dl>
<dl>
<dt id="index-color_003f">Procedure: <strong>color?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a color object.
</p></dd></dl>
<dl>
<dt id="index-color_002dr">Procedure: <strong>color-r</strong> <em>color</em></dt>
<dd><p>Return the red channel of <var>color</var>.
</p></dd></dl>
<dl>
<dt id="index-color_002dg">Procedure: <strong>color-g</strong> <em>color</em></dt>
<dd><p>Return the green channel of <var>color</var>.
</p></dd></dl>
<dl>
<dt id="index-color_002db">Procedure: <strong>color-b</strong> <em>color</em></dt>
<dd><p>Return the blue channel of <var>color</var>.
</p></dd></dl>
<dl>
<dt id="index-color_002da">Procedure: <strong>color-a</strong> <em>color</em></dt>
<dd><p>Return the alpha channel of <var>color</var>.
</p></dd></dl>
<dl>
<dt id="index-transparency">Procedure: <strong>transparency</strong> <em>alpha</em></dt>
<dd><p>Return a new color that is white (RGB channels set to 1) with an alpha
channel value of <var>alpha</var>. This can be useful for creating a color
that can be multiplied against another color to make it more
transparent.
</p></dd></dl>
<dl>
<dt id="index-string_002d_003ecolor">Procedure: <strong>string->color</strong> <em>s</em></dt>
<dd><p>Convert the hexadecimal color code in the string <var>s</var> to a color
object. The following string formats are supported:
</p>
<div class="lisp">
<pre class="lisp"><span class="syntax-open">(</span><span class="syntax-symbol">string->color</span> <span class="syntax-string">"#FF00FFFF"</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">string->color</span> <span class="syntax-string">"FF00FFFF"</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">string->color</span> <span class="syntax-string">"#FF00FF"</span><span class="syntax-close">)</span>
<span class="syntax-open">(</span><span class="syntax-symbol">string->color</span> <span class="syntax-string">"FF00FF"</span><span class="syntax-close">)</span>
</pre></div>
</dd></dl>
<dl>
<dt id="index-color_002a">Procedure: <strong>color*</strong> <em>a b</em></dt>
<dd><p>Multiply the color <var>a</var> with the color or number <var>b</var> and return
a new color with the result.
</p></dd></dl>
<dl>
<dt id="index-color_002b">Procedure: <strong>color+</strong> <em>a b</em></dt>
<dd><p>Add the color <var>a</var> to the color <var>b</var> and return a new color with
the result.
</p></dd></dl>
<dl>
<dt id="index-color_002d">Procedure: <strong>color-</strong> <em>a b</em></dt>
<dd><p>Subtract the color <var>b</var> from the color <var>a</var> and return a new
color with the result.
</p></dd></dl>
<dl>
<dt id="index-color_002dinverse">Procedure: <strong>color-inverse</strong> <em>color</em></dt>
<dd><p>Invert the red, green, and blue channels of <var>color</var> and return a
new color with the result.
</p></dd></dl>
<dl>
<dt id="index-color_002dlerp">Procedure: <strong>color-lerp</strong> <em>start end alpha</em></dt>
<dd><p>Linearly interpolate the colors <var>start</var> and <var>end</var> using the
factor <var>alpha</var>, a number in the range [0, 1].
</p></dd></dl>
<span id="Stock-Colors"></span><h4 class="subsubsection">5.3.1.1 Stock Colors</h4>
<p>For convenience, Chickadee comes with some basic colors predefined:
</p>
<dl>
<dt id="index-white">Variable: <strong>white</strong></dt>
</dl>
<dl>
<dt id="index-black">Variable: <strong>black</strong></dt>
</dl>
<dl>
<dt id="index-red">Variable: <strong>red</strong></dt>
</dl>
<dl>
<dt id="index-green">Variable: <strong>green</strong></dt>
</dl>
<dl>
<dt id="index-blue">Variable: <strong>blue</strong></dt>
</dl>
<dl>
<dt id="index-yellow">Variable: <strong>yellow</strong></dt>
</dl>
<dl>
<dt id="index-magenta">Variable: <strong>magenta</strong></dt>
</dl>
<dl>
<dt id="index-cyan">Variable: <strong>cyan</strong></dt>
</dl>
<p>For fun, there are also predefined colors for the classic
<a href="https://en.wikipedia.org/wiki/Tango_Desktop_Project#Palette">Tango color palette</a>.
</p>
<dl>
<dt id="index-tango_002dlight_002dbutter">Variable: <strong>tango-light-butter</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dbutter">Variable: <strong>tango-butter</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dbutter">Variable: <strong>tango-dark-butter</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dorange">Variable: <strong>tango-light-orange</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dorange">Variable: <strong>tango-orange</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dorange">Variable: <strong>tango-dark-orange</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dchocolate">Variable: <strong>tango-light-chocolate</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dchocolate">Variable: <strong>tango-chocolate</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dchocolate">Variable: <strong>tango-dark-chocolate</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dchameleon">Variable: <strong>tango-light-chameleon</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dchameleon">Variable: <strong>tango-chameleon</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dchameleon">Variable: <strong>tango-dark-chameleon</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dsky_002dblue">Variable: <strong>tango-light-sky-blue</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dsky_002dblue">Variable: <strong>tango-sky-blue</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dsky_002dblue">Variable: <strong>tango-dark-sky-blue</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dplum">Variable: <strong>tango-light-plum</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dplum">Variable: <strong>tango-plum</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dplum">Variable: <strong>tango-dark-plum</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dlight_002dscarlet_002dred">Variable: <strong>tango-light-scarlet-red</strong></dt>
</dl>
<dl>
<dt id="index-tango_002dscarlet_002dred">Variable: <strong>tango-scarlet-red</strong></dt>
</dl>
<dl>
<dt id="index-tango_002ddark_002dscarlet_002dred">Variable: <strong>tango-dark-scarlet-red</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d1">Variable: <strong>tango-aluminium-1</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d2">Variable: <strong>tango-aluminium-2</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d3">Variable: <strong>tango-aluminium-3</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d4">Variable: <strong>tango-aluminium-4</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d5">Variable: <strong>tango-aluminium-5</strong></dt>
</dl>
<dl>
<dt id="index-tango_002daluminium_002d6">Variable: <strong>tango-aluminium-6</strong></dt>
</dl>
<hr />
<div class="header">
<p>
Next: <a href="Textures.html" accesskey="n" rel="next">Textures</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
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