[gimp-help] Add Perlin Noise filter

[Julien Hardlin <jhardlin src gnome org>]

commit c3df80cee49f159b210ec1b0cb66c5d056061371
Author: Julien Hardelin <jhardlin orange fr>
Date:   Sat Mar 9 17:36:05 2019 +0100

    Add Perlin Noise filter

 .../examples/render/perlin_noise-alpha-1.png       | Bin 0 -> 40469 bytes
 .../examples/render/perlin_noise-alpha-2.png       | Bin 0 -> 10078 bytes
 .../examples/render/perlin_noise-default.png       | Bin 0 -> 15999 bytes
 .../filters/examples/render/perlin_noise-iter.png  | Bin 0 -> 38309 bytes
 .../C/filters/examples/render/perlin_noise-z-1.png | Bin 0 -> 27081 bytes
 .../C/filters/examples/render/perlin_noise-z-2.png | Bin 0 -> 29187 bytes
 images/C/filters/render/perlin_noise-dialog.png    | Bin 0 -> 19173 bytes
 src/filters/render.xml                             |   2 +-
 src/filters/render/perlin-noise.xml                | 167 +++++++++++++++++++++
 9 files changed, 168 insertions(+), 1 deletion(-)
---
diff --git a/images/C/filters/examples/render/perlin_noise-alpha-1.png 
b/images/C/filters/examples/render/perlin_noise-alpha-1.png
new file mode 100644
index 000000000..f92a66c2b
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-alpha-1.png differ
diff --git a/images/C/filters/examples/render/perlin_noise-alpha-2.png 
b/images/C/filters/examples/render/perlin_noise-alpha-2.png
new file mode 100644
index 000000000..573d2b846
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-alpha-2.png differ
diff --git a/images/C/filters/examples/render/perlin_noise-default.png 
b/images/C/filters/examples/render/perlin_noise-default.png
new file mode 100644
index 000000000..7b82767fe
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-default.png differ
diff --git a/images/C/filters/examples/render/perlin_noise-iter.png 
b/images/C/filters/examples/render/perlin_noise-iter.png
new file mode 100644
index 000000000..ac9d04c29
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-iter.png differ
diff --git a/images/C/filters/examples/render/perlin_noise-z-1.png 
b/images/C/filters/examples/render/perlin_noise-z-1.png
new file mode 100644
index 000000000..3015f6038
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-z-1.png differ
diff --git a/images/C/filters/examples/render/perlin_noise-z-2.png 
b/images/C/filters/examples/render/perlin_noise-z-2.png
new file mode 100644
index 000000000..5b767d070
Binary files /dev/null and b/images/C/filters/examples/render/perlin_noise-z-2.png differ
diff --git a/images/C/filters/render/perlin_noise-dialog.png b/images/C/filters/render/perlin_noise-dialog.png
new file mode 100644
index 000000000..1c9e1b631
Binary files /dev/null and b/images/C/filters/render/perlin_noise-dialog.png differ
diff --git a/src/filters/render.xml b/src/filters/render.xml
index f5e7c0e3f..6b897382d 100644
--- a/src/filters/render.xml
+++ b/src/filters/render.xml
@@ -14,7 +14,7 @@
 
   <!--Noise-->
   <xi:include href="render/cell-noise.xml"/>
-  <!--<xi:include href="render/perlin_noise.xml"/>-->
+  <xi:include href="render/perlin-noise.xml"/>
   <xi:include href="render/plasma.xml"/>
   <!--<xi:include href="render/simplex_noise.xml"/>-->
   <xi:include href="render/solid-noise.xml"/>
diff --git a/src/filters/render/perlin-noise.xml b/src/filters/render/perlin-noise.xml
new file mode 100644
index 000000000..42a8e5676
--- /dev/null
+++ b/src/filters/render/perlin-noise.xml
@@ -0,0 +1,167 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE sect2 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+                       "http://www.docbook.org/xml/4.3/docbookx.dtd";>
+<!-- section history:
+  2019-03-08 j.h: create. I am not sure my interpretation of functions are 
+  correct
+-->
+<sect2 xmlns:xi="http://www.w3.org/2001/XInclude"; id="gimp-filter-noise-perlin">
+  <title>Perlin Noise</title>
+
+  <indexterm>
+    <primary>Filters</primary>
+    <secondary>Render</secondary>
+    <tertiary>Perlin Noise</tertiary>
+  </indexterm>
+  <indexterm>
+    <primary>Grid</primary>
+    <secondary>Perlin Noise</secondary>
+  </indexterm>
+
+  <sect3>
+    <title>Overview</title>
+    <para>
+      This filter generates a noise texture using the Perlin Noise algorithm. 
+      Results don't depend on the image you opened.
+      <mediaobject>
+        <imageobject>
+          <imagedata format="PNG"
+            fileref="images/filters/examples/render/perlin_noise-default.png"/>
+        </imageobject>
+        <caption>
+          <para>
+            Filter applied with default options: Alpha=1.200  Scale=1.800 
+            Z offset=-1.000  Iterations=3
+          </para>
+        </caption>
+      </mediaobject>
+    </para>
+  </sect3>
+  
+  <sect3>
+    <title>Activating the filter</title>
+    <para>
+      This filter is found in the image window menu under
+      <menuchoice>
+        <guimenu>Filters</guimenu>
+        <guisubmenu>Render</guisubmenu>
+        <guisubmenu>Noise</guisubmenu>
+        <guimenuitem>Perlin Noise…</guimenuitem>
+      </menuchoice>.
+    </para>
+  </sect3>
+  
+  <sect3>
+    <title>Options</title>
+    <figure>
+      <title><quote>Perlin Noise</quote> filter options</title>
+      <mediaobject>
+        <imageobject>
+          <imagedata format="PNG"
+            fileref="images/filters/render/perlin_noise-dialog.png"/>
+        </imageobject>
+      </mediaobject>
+    </figure>
+    <variablelist>
+      <varlistentry>
+        <term>Presets, Preview, Split view, Use selection as input</term>
+        <listitem>
+          <xi:include href="../about-common-features.xml"/>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Alpha</term>
+        <listitem>
+          <para>
+            Low values give sharper noise
+          </para>
+          <figure>
+            <title><quote>Alpha </quote> option examples</title>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+            fileref="images/filters/examples/render/perlin_noise-alpha-1.png"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Alpha = 0.300
+                </para>
+              </caption>
+            </mediaobject>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+            fileref="images/filters/examples/render/perlin_noise-alpha-2.png"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Alpha = 3.600
+                </para>
+              </caption>
+            </mediaobject>
+          </figure>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Scale</term>
+        <listitem>
+          <para>
+            Scale of the noise function: works like a zoom.
+          </para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Z offset</term>
+        <listitem>
+          <para>
+            Vary noise.
+          </para>
+          <figure>
+            <title><quote>Z offset</quote> option examples</title>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+              fileref="images/filters/examples/render/perlin_noise-z-1.png"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Z offset = -1000
+                </para>
+              </caption>
+            </mediaobject>
+            <mediaobject>
+              <imageobject>
+                <imagedata format="PNG"
+              fileref="images/filters/examples/render/perlin_noise-z-2.png"/>
+              </imageobject>
+              <caption>
+                <para>
+                  Z offset = 0.900
+                </para>
+              </caption>
+            </mediaobject>
+          </figure>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
+        <term>Iterations</term>
+        <listitem>
+          <para>
+            The number of noise octaves.
+          </para>
+          <mediaobject>
+            <imageobject>
+              <imagedata format="PNG"
+                fileref="images/filters/examples/render/perlin_noise-iter.png"/>
+            </imageobject>
+            <caption>
+              <para>
+                Iterations = 7
+              </para>
+            </caption>
+          </mediaobject>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </sect3>
+</sect2>