This file is indexed.

/usr/share/gtk-doc/html/cogl-2.0-experimental/cogl-Blend-Strings.html is in libcogl-doc 1.16.2-1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Blend Strings</title>
<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
<link rel="home" href="index.html" title="Cogl 2.0 Reference Manual">
<link rel="up" href="cogl-pipeline-apis.html" title="Setting Up A GPU Pipeline">
<link rel="prev" href="cogl-pipeline-apis.html" title="Setting Up A GPU Pipeline">
<link rel="next" href="cogl-2.0-experimental-Pipeline.html" title="Pipeline">
<meta name="generator" content="GTK-Doc V1.19 (XML mode)">
<link rel="stylesheet" href="style.css" type="text/css">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="2">
<tr valign="middle">
<td><a accesskey="p" href="cogl-pipeline-apis.html"><img src="left.png" width="24" height="24" border="0" alt="Prev"></a></td>
<td><a accesskey="u" href="cogl-pipeline-apis.html"><img src="up.png" width="24" height="24" border="0" alt="Up"></a></td>
<td><a accesskey="h" href="index.html"><img src="home.png" width="24" height="24" border="0" alt="Home"></a></td>
<th width="100%" align="center">Cogl 2.0 Reference Manual</th>
<td><a accesskey="n" href="cogl-2.0-experimental-Pipeline.html"><img src="right.png" width="24" height="24" border="0" alt="Next"></a></td>
</tr>
<tr><td colspan="5" class="shortcuts">
                   | 
                  <a href="#cogl-Blend-Strings.description" class="shortcut">Cogl Blend Strings</a>
</td></tr>
</table>
<div class="refentry">
<a name="cogl-Blend-Strings"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="cogl-Blend-Strings.top_of_page"></a>Blend Strings</span></h2>
<p>Blend Strings — A simple syntax and grammar for describing blending and texture
combining functions.</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="cogl-Blend-Strings.description"></a><h2>Cogl Blend Strings</h2>
<p>
Describing GPU blending and texture combining states is rather awkward to do
in a consise but also readable fashion. Cogl helps by supporting
string based descriptions using a simple syntax.
</p>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="id-1.2.5.2.3.3"></a>Some examples</h5></div></div></div>
<p>Here is an example used for blending:</p>
<pre class="programlisting">
"RGBA = ADD (SRC_COLOR * (SRC_COLOR[A]), DST_COLOR * (1-SRC_COLOR[A]))"
</pre>
<p>In OpenGL terms this replaces glBlendFunc[Separate] and
glBlendEquation[Separate]</p>
<p>
Actually in this case it's more verbose than the GL equivalent:
</p>
<pre class="programlisting">
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
</pre>
<p>
But unless you are familiar with OpenGL or refer to its API documentation
you wouldn't know that the default function used by OpenGL is GL_FUNC_ADD
nor would you know that the above arguments determine what the source color
and destination color will be multiplied by before being adding.
</p>
<p>Here is an example used for texture combining:</p>
<pre class="programlisting">
"RGB = REPLACE (PREVIOUS)"
"A = MODULATE (PREVIOUS, TEXTURE)"
</pre>
<p>
In OpenGL terms this replaces glTexEnv, and the above example is equivalent
to this OpenGL code:
</p>
<pre class="programlisting">
  glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
  glTexEnvi (GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_REPLACE);
  glTexEnvi (GL_TEXTURE_ENV, GL_SRC0_RGB, GL_PREVIOUS);
  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND0_RGB, GL_SRC_COLOR);
  glTexEnvi (GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_MODULATE);
  glTexEnvi (GL_TEXTURE_ENV, GL_SRC0_ALPHA, GL_PREVIOUS);
  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND0_ALPHA, GL_SRC_COLOR);
  glTexEnvi (GL_TEXTURE_ENV, GL_SRC1_ALPHA, GL_TEXTURE);
  glTexEnvi (GL_TEXTURE_ENV, GL_OPERAND1_ALPHA, GL_SRC_COLOR);
</pre>
</div>
<div class="section">
<div class="titlepage"><div><div><h5 class="title">
<a name="cogl-Blend-String-syntax"></a>Here's the syntax</h5></div></div></div>
<pre class="programlisting">
&lt;statement&gt;:
  &lt;channel-mask&gt;=&lt;function-name&gt;(&lt;arg-list&gt;)

  You can either use a single statement with an RGBA channel-mask or you can use
  two statements; one with an A channel-mask and the other with an RGB
  channel-mask.

&lt;channel-mask&gt;:
  A or RGB or RGBA

&lt;function-name&gt;:
  [A-Za-z_]*

&lt;arg-list&gt;:
  &lt;arg&gt;,&lt;arg&gt;
  or &lt;arg&gt;
  or ""

  I.e. functions may take 0 or more arguments

&lt;arg&gt;:
  &lt;color-source&gt;
  1 - &lt;color-source&gt;                : Only intended for texture combining
  &lt;color-source&gt; * ( &lt;factor&gt; )     : Only intended for blending
  0                                 : Only intended for blending

  See the blending or texture combining sections for further notes and examples.

&lt;color-source&gt;:
  &lt;source-name&gt;[&lt;channel-mask&gt;]
  &lt;source-name&gt;

  See the blending or texture combining sections for the list of source-names
  valid in each context.

  If a channel mask is not given then the channel mask of the statement
  is assumed instead.

&lt;factor&gt;:
  0
  1
  &lt;color-source&gt;
  1-&lt;color-source&gt;
  SRC_ALPHA_SATURATE
</pre>
</div>
</div>
</div>
<div class="footer">
<hr>
          Generated by GTK-Doc V1.19</div>
</body>
</html>