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<a href="#cogl-2.0-experimental-Vertex-Attributes.description" class="shortcut">Description</a>
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<a name="cogl-2.0-experimental-Vertex-Attributes"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle"><a name="cogl-2.0-experimental-Vertex-Attributes.top_of_page"></a>Vertex Attributes</span></h2>
<p>Vertex Attributes — Functions for declaring and drawing vertex
attributes</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<a name="cogl-2.0-experimental-Vertex-Attributes.synopsis"></a><h2>Synopsis</h2>
<pre class="synopsis"><span class="returnvalue">CoglAttribute</span> * <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-new" title="cogl_attribute_new ()">cogl_attribute_new</a> (<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> *attribute_buffer</code></em>,
<em class="parameter"><code>const <span class="type">char</span> *name</code></em>,
<em class="parameter"><code><span class="type">gsize</span> stride</code></em>,
<em class="parameter"><code><span class="type">gsize</span> offset</code></em>,
<em class="parameter"><code><span class="type">int</span> components</code></em>,
<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-Common-Types.html#CoglAttributeType" title="enum CoglAttributeType"><span class="type">CoglAttributeType</span></a> type</code></em>);
<span class="returnvalue">gboolean</span> <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-is-attribute" title="cogl_is_attribute ()">cogl_is_attribute</a> (<em class="parameter"><code><span class="type">void</span> *object</code></em>);
<span class="returnvalue">void</span> <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-set-normalized" title="cogl_attribute_set_normalized ()">cogl_attribute_set_normalized</a> (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>,
<em class="parameter"><code><span class="type">gboolean</span> normalized</code></em>);
<span class="returnvalue">gboolean</span> <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-get-normalized" title="cogl_attribute_get_normalized ()">cogl_attribute_get_normalized</a> (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>);
<a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="returnvalue">CoglAttributeBuffer</span></a> * <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-get-buffer" title="cogl_attribute_get_buffer ()">cogl_attribute_get_buffer</a> (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>);
<span class="returnvalue">void</span> <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-set-buffer" title="cogl_attribute_set_buffer ()">cogl_attribute_set_buffer</a> (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>,
<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> *attribute_buffer</code></em>);
</pre>
</div>
<div class="refsect1">
<a name="cogl-2.0-experimental-Vertex-Attributes.description"></a><h2>Description</h2>
<p>
FIXME
</p>
</div>
<div class="refsect1">
<a name="cogl-2.0-experimental-Vertex-Attributes.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="cogl-attribute-new"></a><h3>cogl_attribute_new ()</h3>
<pre class="programlisting"><span class="returnvalue">CoglAttribute</span> * cogl_attribute_new (<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> *attribute_buffer</code></em>,
<em class="parameter"><code>const <span class="type">char</span> *name</code></em>,
<em class="parameter"><code><span class="type">gsize</span> stride</code></em>,
<em class="parameter"><code><span class="type">gsize</span> offset</code></em>,
<em class="parameter"><code><span class="type">int</span> components</code></em>,
<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-Common-Types.html#CoglAttributeType" title="enum CoglAttributeType"><span class="type">CoglAttributeType</span></a> type</code></em>);</pre>
<p>
Describes the layout for a list of vertex attribute values (For
example, a list of texture coordinates or colors).
</p>
<p>
The <em class="parameter"><code>name</code></em> is used to access the attribute inside a GLSL vertex
shader and there are some special names you should use if they are
applicable:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">"cogl_position_in" (used for vertex positions)</li>
<li class="listitem">"cogl_color_in" (used for vertex colors)</li>
<li class="listitem">"cogl_tex_coord0_in", "cogl_tex_coord1", ...
(used for vertex texture coordinates)</li>
<li class="listitem">"cogl_normal_in" (used for vertex normals)</li>
</ul></div>
<p>
</p>
<p>
The attribute values corresponding to different vertices can either
be tightly packed or interleaved with other attribute values. For
example it's common to define a structure for a single vertex like:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1
2
3
4
5</pre></td>
<td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwc">typedef</span> <span class="gtkdoc kwb">struct</span>
<span class="gtkdoc opt">{</span>
<span class="gtkdoc kwb">float</span> x<span class="gtkdoc opt">,</span> y<span class="gtkdoc opt">,</span> z<span class="gtkdoc opt">;</span> <span class="comment">/* position attribute */</span>
<span class="gtkdoc kwb">float</span> s<span class="gtkdoc opt">,</span> t<span class="gtkdoc opt">;</span> <span class="comment">/* texture coordinate attribute */</span>
<span class="gtkdoc opt">}</span> MyVertex<span class="gtkdoc opt">;</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
And then create an array of vertex data something like:
</p>
<div class="informalexample">
<table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
<tbody>
<tr>
<td class="listing_lines" align="right"><pre>1</pre></td>
<td class="listing_code"><pre class="programlisting">MyVertex vertices<span class="gtkdoc opt">[</span><span class="number">100</span><span class="gtkdoc opt">] = { .... }</span></pre></td>
</tr>
</tbody>
</table>
</div>
<p>
</p>
<p>
In this case, to describe either the position or texture coordinate
attribute you have to move <span style="color: red"><pre>sizeof (MyVertex)</pre></span> bytes to
move from one vertex to the next. This is called the attribute
<em class="parameter"><code>stride</code></em>. If you weren't interleving attributes and you instead had
a packed array of float x, y pairs then the attribute stride would
be <span style="color: red"><pre>(2 * sizeof (float))</pre></span>. So the <em class="parameter"><code>stride</code></em> is the number of
bytes to move to find the attribute value of the next vertex.
</p>
<p>
Normally a list of attributes starts at the beginning of an array.
So for the <span style="color: red"><pre>MyVertex</pre></span> example above the <em class="parameter"><code>offset</code></em> is the
offset inside the <span style="color: red"><pre>MyVertex</pre></span> structure to the first
component of the attribute. For the texture coordinate attribute
the offset would be <span style="color: red"><pre>offsetof (MyVertex, s)</pre></span> or instead of
using the offsetof macro you could use <span style="color: red"><pre>sizeof (float) * 3</pre></span>.
If you've divided your <em class="parameter"><code>array</code></em> into blocks of non-interleved
attributes then you will need to calculate the <em class="parameter"><code>offset</code></em> as the
number of bytes in blocks preceding the attribute you're
describing.
</p>
<p>
An attribute often has more than one component. For example a color
is often comprised of 4 red, green, blue and alpha <em class="parameter"><code>components</code></em>, and a
position may be comprised of 2 x and y <em class="parameter"><code>components</code></em>. You should aim
to keep the number of components to a minimum as more components
means more data needs to be mapped into the GPU which can be a
bottlneck when dealing with a large number of vertices.
</p>
<p>
Finally you need to specify the component data type. Here you
should aim to use the smallest type that meets your precision
requirements. Again the larger the type then more data needs to be
mapped into the GPU which can be a bottlneck when dealing with
a large number of vertices.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute_buffer</code></em> :</span></p></td>
<td>The <a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> containing the actual
attribute data</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>name</code></em> :</span></p></td>
<td>The name of the attribute (used to reference it from GLSL)</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>stride</code></em> :</span></p></td>
<td>The number of bytes to jump to get to the next attribute
value for the next vertex. (Usually
<span style="color: red"><pre>sizeof (MyVertex)</pre></span>)</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>offset</code></em> :</span></p></td>
<td>The byte offset from the start of <em class="parameter"><code>attribute_buffer</code></em> for
the first attribute value. (Usually
<span style="color: red"><pre>offsetof (MyVertex, component0)</pre></span>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>components</code></em> :</span></p></td>
<td>The number of components (e.g. 4 for an rgba color or
3 for and (x,y,z) position)</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>type</code></em> :</span></p></td>
<td>FIXME</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>A newly allocated <span class="type">CoglAttribute</span> describing the
layout for a list of attribute values stored in <em class="parameter"><code>array</code></em>.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 1.4</p>
<p class="stability">Stability Level: Unstable</p>
</div>
<hr>
<div class="refsect2">
<a name="cogl-is-attribute"></a><h3>cogl_is_attribute ()</h3>
<pre class="programlisting"><span class="returnvalue">gboolean</span> cogl_is_attribute (<em class="parameter"><code><span class="type">void</span> *object</code></em>);</pre>
<p>
Gets whether the given object references a <span class="type">CoglAttribute</span>.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>object</code></em> :</span></p></td>
<td>A <a class="link" href="cogl-2.0-experimental-The-Object-Interface.html#CoglObject" title="CoglObject"><span class="type">CoglObject</span></a>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>
<code class="literal">TRUE</code> if the handle references a <span class="type">CoglAttribute</span>,
<code class="literal">FALSE</code> otherwise</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="cogl-attribute-set-normalized"></a><h3>cogl_attribute_set_normalized ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> cogl_attribute_set_normalized (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>,
<em class="parameter"><code><span class="type">gboolean</span> normalized</code></em>);</pre>
<p>
Sets whether fixed point attribute types are mapped to the range
0→1. For example when this property is TRUE and a
<a class="link" href="cogl-2.0-experimental-Common-Types.html#COGL-ATTRIBUTE-TYPE-UNSIGNED-BYTE:CAPS"><code class="literal">COGL_ATTRIBUTE_TYPE_UNSIGNED_BYTE</code></a> type is used then the value 255
will be mapped to 1.0.
</p>
<p>
The default value of this property depends on the name of the
attribute. For the builtin properties cogl_color_in and
cogl_normal_in it will default to TRUE and for all other names it
will default to FALSE.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute</code></em> :</span></p></td>
<td>A <span class="type">CoglAttribute</span>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>normalized</code></em> :</span></p></td>
<td>The new value for the normalized property.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 1.10</p>
<p class="stability">Stability Level: Unstable</p>
</div>
<hr>
<div class="refsect2">
<a name="cogl-attribute-get-normalized"></a><h3>cogl_attribute_get_normalized ()</h3>
<pre class="programlisting"><span class="returnvalue">gboolean</span> cogl_attribute_get_normalized (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>);</pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute</code></em> :</span></p></td>
<td>A <span class="type">CoglAttribute</span>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the value of the normalized property set with
<a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-set-normalized" title="cogl_attribute_set_normalized ()"><code class="function">cogl_attribute_set_normalized()</code></a>.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 1.10</p>
<p class="stability">Stability Level: Unstable</p>
</div>
<hr>
<div class="refsect2">
<a name="cogl-attribute-get-buffer"></a><h3>cogl_attribute_get_buffer ()</h3>
<pre class="programlisting"><a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="returnvalue">CoglAttributeBuffer</span></a> * cogl_attribute_get_buffer (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>);</pre>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute</code></em> :</span></p></td>
<td>A <span class="type">CoglAttribute</span>
</td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>Returns</em></span> :</span></p></td>
<td>the <a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> that was set with
<a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-set-buffer" title="cogl_attribute_set_buffer ()"><code class="function">cogl_attribute_set_buffer()</code></a> or <a class="link" href="cogl-2.0-experimental-Vertex-Attributes.html#cogl-attribute-new" title="cogl_attribute_new ()"><code class="function">cogl_attribute_new()</code></a>.</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 1.10</p>
<p class="stability">Stability Level: Unstable</p>
</div>
<hr>
<div class="refsect2">
<a name="cogl-attribute-set-buffer"></a><h3>cogl_attribute_set_buffer ()</h3>
<pre class="programlisting"><span class="returnvalue">void</span> cogl_attribute_set_buffer (<em class="parameter"><code><span class="type">CoglAttribute</span> *attribute</code></em>,
<em class="parameter"><code><a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> *attribute_buffer</code></em>);</pre>
<p>
Sets a new <a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a> for the attribute.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute</code></em> :</span></p></td>
<td>A <span class="type">CoglAttribute</span>
</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>attribute_buffer</code></em> :</span></p></td>
<td>A <a class="link" href="cogl-2.0-experimental-CoglAttributeBuffer---Buffers-of-vertex-attributes.html#CoglAttributeBuffer" title="CoglAttributeBuffer"><span class="type">CoglAttributeBuffer</span></a>
</td>
</tr>
</tbody>
</table></div>
<p class="since">Since 1.10</p>
<p class="stability">Stability Level: Unstable</p>
</div>
</div>
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