ef60979258
This pulls in the experimental cogl 2.0 reference manual from the clutter repository since it wasn't included in the filter-branch when we split cogl out.
130 lines
3.7 KiB
XML
130 lines
3.7 KiB
XML
<?xml version="1.0"?>
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
|
|
<!ENTITY version SYSTEM "version.xml">
|
|
]>
|
|
|
|
<refentry id="cogl-Blend-Strings">
|
|
<refmeta>
|
|
<refentrytitle role="top_of_page" id="cogl-Blend-Strings.top_of_page">Blend Strings</refentrytitle>
|
|
<manvolnum>3</manvolnum>
|
|
<refmiscinfo>COGL Library</refmiscinfo>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>Blend Strings</refname>
|
|
<refpurpose>A simple syntax and grammar for describing blending and texture
|
|
combining functions.</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsect1 id="cogl-Blend-Strings.description" role="desc">
|
|
<title>Cogl Blend Strings</title>
|
|
<para>
|
|
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.
|
|
</para>
|
|
|
|
<section>
|
|
<title>Some examples</title>
|
|
|
|
<para>Here is an example used for blending:</para>
|
|
<programlisting>
|
|
"RGBA = ADD (SRC_COLOR * (SRC_COLOR[A]), DST_COLOR * (1-SRC_COLOR[A]))"
|
|
</programlisting>
|
|
<para>In OpenGL terms this replaces glBlendFunc[Separate] and
|
|
glBlendEquation[Separate]</para>
|
|
<para>
|
|
Actually in this case it's more verbose than the GL equivalent:
|
|
</para>
|
|
<programlisting>
|
|
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
|
|
</programlisting>
|
|
<para>
|
|
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.
|
|
</para>
|
|
|
|
<para>Here is an example used for texture combining:</para>
|
|
<programlisting>
|
|
"RGB = REPLACE (PREVIOUS)"
|
|
"A = MODULATE (PREVIOUS, TEXTURE)"
|
|
</programlisting>
|
|
<para>
|
|
In OpenGL terms this replaces glTexEnv, and the above example is equivalent
|
|
to this OpenGL code:
|
|
</para>
|
|
<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);
|
|
</programlisting>
|
|
|
|
</section>
|
|
|
|
<section id="cogl-Blend-String-syntax">
|
|
<title>Here's the syntax</title>
|
|
|
|
<programlisting>
|
|
<statement>:
|
|
<channel-mask>=<function-name>(<arg-list>)
|
|
|
|
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.
|
|
|
|
<channel-mask>:
|
|
A or RGB or RGBA
|
|
|
|
<function-name>:
|
|
[A-Za-z_]*
|
|
|
|
<arg-list>:
|
|
<arg>,<arg>
|
|
or <arg>
|
|
or ""
|
|
|
|
I.e. functions may take 0 or more arguments
|
|
|
|
<arg>:
|
|
<color-source>
|
|
1 - <color-source> : Only intended for texture combining
|
|
<color-source> * ( <factor> ) : Only intended for blending
|
|
0 : Only intended for blending
|
|
|
|
See the blending or texture combining sections for further notes and examples.
|
|
|
|
<color-source>:
|
|
<source-name>[<channel-mask>]
|
|
<source-name>
|
|
|
|
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.
|
|
|
|
<factor>:
|
|
0
|
|
1
|
|
<color-source>
|
|
1-<color-source>
|
|
SRC_ALPHA_SATURATE
|
|
</programlisting>
|
|
|
|
</section>
|
|
|
|
|
|
</refsect1>
|
|
|
|
|
|
</refentry>
|