[gimp-help] Adds in Little Planet and Panorama projection filters

[Julien Hardlin <jhardlin src gnome org>]

commit 108458201e065e0da083b3c254a24b47b5e7ab99
Author: Julien Hardelin <jhardlin orange fr>
Date:   Sat Feb 23 18:30:33 2019 +0100

    Adds in Little Planet and Panorama projection filters

 .../filters/examples/map/little_planet-applied.jpg | Bin 0 -> 14602 bytes
 .../examples/map/little_planet-equirect.jpg        | Bin 0 -> 50424 bytes
 src/filters/map/little-planet.xml                  |  68 +++++++++++++++++----
 src/filters/map/panorama-projection.xml            |  17 ++++++
 4 files changed, 72 insertions(+), 13 deletions(-)
---
diff --git a/images/C/filters/examples/map/little_planet-applied.jpg 
b/images/C/filters/examples/map/little_planet-applied.jpg
new file mode 100644
index 000000000..d80a12b2d
Binary files /dev/null and b/images/C/filters/examples/map/little_planet-applied.jpg differ
diff --git a/images/C/filters/examples/map/little_planet-equirect.jpg 
b/images/C/filters/examples/map/little_planet-equirect.jpg
new file mode 100644
index 000000000..aef4fcee4
Binary files /dev/null and b/images/C/filters/examples/map/little_planet-equirect.jpg differ
diff --git a/src/filters/map/little-planet.xml b/src/filters/map/little-planet.xml
index 41a39a7df..fe47befb3 100644
--- a/src/filters/map/little-planet.xml
+++ b/src/filters/map/little-planet.xml
@@ -21,7 +21,9 @@
     <title>Overview</title>
     <para>
       This filter converts a panorama into a small planet. All images don't fit 
-      this filter.
+      this filter. The ideal image is a 360° x 180° image, also known as 
+      equirectangular image. We will see that it is possible to use normal 
+      images also.
     </para>
   </sect3>
 
@@ -95,8 +97,8 @@
         <term>Inverse transform</term>
         <listitem>
           <para>
-            Do the inverse mapping; useful for touching up zenith, nadir or other 
-            parts of panorama.
+            Do the inverse mapping; useful for touching up zenith, nadir or 
+            other parts of panorama.
           </para>
         </listitem>
       </varlistentry>
@@ -116,23 +118,63 @@
         <term>Use the selection as input/Use the entire layer as input</term>
         <listitem>
           <para>
-            If a selection exists, the filter will use it. Else, the entire layer 
-            will be used.
+            If a selection exists, the filter will use it. Else, the entire 
+            layer will be used.
           </para>
         </listitem>
       </varlistentry>
     </variablelist>
   </sect3>
   <sect3>
-    <title>Using Little Planet filter</title>
+    <title>Using Little Planet filter with an equirectangular image</title>
+    <tip>
+      <para>
+        You can find free equirectangular images at 
+<ulink url="https://commons.wikimedia.org/wiki/Category:360°_panoramas_with_equirectangular_projection"/>.
+      </para>
+    </tip>
+    <mediaobject>
+      <imageobject>
+        <imagedata format="JPG"
+          fileref="images/filters/examples/map/little_planet-equirect.jpg"/>
+      </imageobject>
+      <caption>
+        <para>
+        <subscript>
+          Ettling_Isar_panorama.jpg by © Simon Waldherr under 
+<ulink url="https://creativecommons.org/licenses/by-sa/4.0";>  CC by-sa 4.0</ulink>
+        </subscript>
+        </para>
+        <para>
+        GIMP opened this 16000x8000 pixels original image in a 1000x500 px 
+        frame at zoom 6.25. This is a screenshot scaled to 600x300 px. Note the 
+        empty sky, the horizon perfectly horizontal, the vanishing perspective.
+        </para>
+      </caption>
+    </mediaobject>
+    <mediaobject>
+      <imageobject>
+        <imagedata format="JPG"
+          fileref="images/filters/examples/map/little_planet-applied.jpg"/>
+      </imageobject>
+      <caption>
+        <para>
+          Filter applied
+        </para>
+      </caption>
+    </mediaobject>
+  </sect3>
+
+  <sect3>
+    <title>Using Little Planet filter with a normal image</title>
     <para>
-      The ideal image is a 360° panorama, with an blue empty sky occupying the 
-      upper half of the image and a horizontal horizon. Your image rarely 
-      satisfies these conditions, especially if you cut your panorama off a 
-      larger image. The Little Planet filter brings left and right image sides 
-      together, and creates an unwanted sharp limit if sides are different. An 
-      uneven horizon gives an irregular circle. Usually, you will have to prepare 
-      your panorama before using filter.
+      Your panorama rarely satisfies conditions necessary for this filter, 
+      especially if you cut it off a larger image. The Little Planet filter 
+      brings left and right image sides together, and creates an unwanted sharp 
+      limit if sides are different. An uneven horizon gives an irregular 
+      circle. A blue empty sky occupying the upper half of the image and a 
+      horizontal horizon are perfect. Usually, you will have to prepare your 
+      panorama before using filter.
     </para>
     <figure>
       <title>Original Images</title>
diff --git a/src/filters/map/panorama-projection.xml b/src/filters/map/panorama-projection.xml
index 60edbf225..bc15a75a9 100644
--- a/src/filters/map/panorama-projection.xml
+++ b/src/filters/map/panorama-projection.xml
@@ -54,6 +54,23 @@
     </para>
   </sect3>
   
+  <sect3>
+    <title>Key Modifiers</title>
+    <para>
+      <emphasis role="bold">Click and drag</emphasis> to pan.
+    </para>
+    <para>
+      <emphasis role="bold">Shift + Click and drag</emphasis> to rotate.
+    </para>
+    <para>
+      <emphasis role="bold">Ctrl + Click and drag</emphasis> to pan with a 
+      constrained axis.
+    </para>
+    <para>
+      <emphasis role="bold">Alt + Click and drag</emphasis> to zoom.
+    </para>
+  </sect3>
+  
   <sect3>
     <title>Using Panorama Projection filter</title>
     <tip>