If not already familiar; you can refer <link linkend="cogl-Blend-Strings">here</link> for an overview of what blend strings are and there syntax.
These are all the functions available for texture combining: <itemizedlist> <listitem>REPLACE(arg0) = arg0</listitem> <listitem>MODULATE(arg0, arg1) = arg0 x arg1</listitem> <listitem>ADD(arg0, arg1) = arg0 + arg1</listitem> < listitem>ADD_SIGNED(arg0, arg1) = arg0 + arg1 - 0.5</listitem> <listitem>INTERPOLATE(arg0, arg1, arg2) = arg0 x arg2 + arg1 x (1 - arg2)</listitem> <listitem>SUBTRACT(arg0, arg1) = arg0 - arg1</listitem> <listitem> < programlisting> DOT3_RGB(arg0, arg1) = 4 x ((arg0[R] - 0.5)) * (arg1[R] - 0.5) + (arg0[G] - 0.5)) * (arg1[G] - 0.5) + (arg0[B] - 0.5 )) * (arg1[B] - 0.5)) </programlisting> </listitem> <listitem> <programlisting> DOT3_RGBA(arg0, arg1) = 4 x ( (arg0[R] - 0.5)) * (arg1[R] - 0.5) + (arg0[G] - 0.5)) * (arg1[G] - 0.5) + (arg0[B] - 0.5)) * (arg1[B] - 0.5)) </programlisting> </listitem> </itemizedlist>
Refer to the <link linkend="cogl-Blend-String-syntax">color-source syntax</link> for describing the arguments. The valid source names for texture combining are: <variablelist> <varlistentry> <term>TEXTURE</term> <listitem>Use the color from the current texture layer</listitem> </varlistentry> <varlistentry> <term>TEXTURE_0, TEXTURE_1, etc</term> <listitem>Use the color from the specified texture layer</listitem> </varlistentry> <varlistentry > <term>CONSTANT</term> <listitem>Use the color from the constant given with set_layer_combine_constant</listitem> </varlistentry > <varlistentry> <term>PRIMARY</term> <listitem>Use the color of the pipeline as set with set_color</listitem> </varlistentry> <varlistentry> < term>PREVIOUS</term> <listitem>Either use the texture color from the previous layer, or if this is layer 0, use the color of the pipeline as set with set_color</listitem> </varlistentry> </variablelist>
<refsect2 id="cogl-Layer-Combine-Examples"> <title>Layer Combine Examples</title> <para>This is effectively what the default blending is:</para> <informalexample><programlisting> RGBA = MODULATE (PREVIOUS, TEXTURE) < /programlisting></informalexample> <para>This could be used to cross-fade between two images, using the alpha component of a constant as the interpolator. The constant color is given by calling set_layer_combine_constant.</para> <informalexample ><programlisting> RGBA = INTERPOLATE (PREVIOUS, TEXTURE, CONSTANT[A]) </programlisting></informalexample> < /refsect2>
<note>You can't give a multiplication factor for arguments as you can with blending.</note>
| this |
A Pipeline object |
| layer_index |
Specifies the layer you want define a combine function for |
| blend_string |
A <link linkend="cogl-Blend-Strings">Cogl blend string</link> describing the desired texture combine function. |
|
true if the blend string was successfully parsed, and the described texture combining is supported by the underlying driver and or hardware. On failure, false is returned and throws is set |