Cogl.Pipeline.prototype.set_blend

function set_blend(blend_string: String): Cogl.Bool {
    // Gjs wrapper for cogl_pipeline_set_blend()
}
  

If not already familiar; please refer <link linkend="cogl-Blend-Strings">here</link> for an overview of what blend strings are, and their syntax.

Blending occurs after the alpha test function, and combines fragments with the framebuffer.

Currently the only blend function Cogl exposes is ADD(). So any valid blend statements will be of the form:

|[ &lt;channel-mask&gt;=ADD(SRC_COLOR*(&lt;factor&gt;), DST_COLOR*(&lt;factor&gt;)) ]|

This is the list of source-names usable as blend factors: <itemizedlist> <listitem><para>SRC_COLOR: The color of the in comming fragment</para></listitem> <listitem><para>DST_COLOR: The color of the framebuffer</para></listitem> <listitem><para>CONSTANT: The constant set via Cogl.Pipeline.prototype.set_blend_constant</para></listitem> </itemizedlist>

The source names can be used according to the <link linkend="cogl-Blend-String-syntax">color-source and factor syntax</link>, so for example "(1-SRC_COLOR[A])" would be a valid factor, as would "(CONSTANT[RGB])"

These can also be used as factors: <itemizedlist> <listitem>0: (0, 0, 0, 0)</listitem> <listitem>1: (1, 1, 1, 1)</listitem> <listitem>SRC_ALPHA_SATURATE_FACTOR: (f,f,f,1) where f = MIN(SRC_COLOR[A],1-DST_COLOR[A])</listitem> </itemizedlist>

<note>Remember; all color components are normalized to the range [0, 1] before computing the result of blending.</note>

<example id="cogl-Blend-Strings-blend-unpremul"> <title>Blend Strings/1</title> <para>Blend a non-premultiplied source over a destination with premultiplied alpha:</para> <programlisting> "RGB = ADD(SRC_COLOR*(SRC_COLOR[A]), DST_COLOR*(1-SRC_COLOR[A]))" "A = ADD(SRC_COLOR, DST_COLOR*(1-SRC_COLOR[A]))" </programlisting> </example>

<example id="cogl-Blend-Strings-blend-premul"> <title>Blend Strings/2</title> <para>Blend a premultiplied source over a destination with premultiplied alpha</para> <programlisting> "RGBA = ADD(SRC_COLOR, DST_COLOR*(1-SRC_COLOR[A]))" </programlisting> </example>

The default blend string is: |[ RGBA = ADD (SRC_COLOR, DST_COLOR*(1-SRC_COLOR[A])) ]|

That gives normal alpha-blending when the calculated color for the pipeline is in premultiplied form.

Since 2.0