Add snapcraft information for building snaps

Snaps are a universal packaging format for Linux platforms
and is available for most major Linux distributions.

This commit adds support for building OpenRocket as a snap. The
snap convention is to place snap relevant information in the top
level snap directory. The snapcraft.yaml file provides information
regarding what should be in the snap and how to build it.

Signed-off-by: Billy Olsen <billy.olsen@gmail.com>

.gitignore

@@ -89,3 +89,5 @@ crashlytics-build.properties
 fabric.properties
 
 openrocket.log
+
+*.snap

snap/gui/openrocket.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Type=Application
+Name=openrocket
+Comment=Design and simulate model rockets
+Icon=${SNAP}/meta/gui/openrocket.png
+Exec=openrocket
+Terminal=false
+Categories=Utility;

snap/local/launcher

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+JAVA_BIN="$JAVA_HOME/bin/java"
+
+export DESKTOP_SESSION=gnome
+export XDG_SESSION_DESKTOP=gnome
+export XDG_CURRENT_DESKTOP=GNOME
+
+# Fix font / theme
+export _JAVA_OPTIONS='-Dsun.java2d.xrender=true -Dprism.useFontConfig=false -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel -Dswing.crossplatformlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel'
+export JAVA_FONTS=$SNAP/usr/share/fonts/truetype
+exec $JAVA_BIN -jar $SNAP/OpenRocket.jar "$@"
+

snap/snapcraft.yaml

@@ -0,0 +1,77 @@
+name: openrocket
+adopt-info: openrocket
+grade: stable
+summary: A free, fully featured model rocket simulator.
+description: |
+  OpenRocket is a free, fully featured model rocket simulator that allows you
+  to design and simulate your rockets before actually building and flying them.
+
+  The main features include
+
+    * Six-degree-of-freedom flight simulation
+    * Automatic design optimization
+    * Realtime simulated altitude, velocity and acceleration display
+    * Staging and clustering support
+    * Cross-platform (Java-based)
+    * Read more about it on the OpenRocket.info.
+license: GPL-3.0
+base: core18
+
+grade: stable
+confinement: strict
+
+apps:
+  openrocket:
+    extensions:
+      - gnome-3-28
+    command: bin/launcher
+    plugs:
+      - home
+      - network
+      - cups-control
+      - opengl
+    environment:
+      JAVA_HOME: "$SNAP/usr/lib/jvm/java-11-openjdk-amd64"
+
+parts:
+  openrocket:
+    plugin: ant
+    source: .
+    ant-build-targets:
+      - clean
+      - check
+      - unittest
+      - jar
+    override-pull: |
+      # Override the pull in order to set the version and the grade.
+      # In the future, the releases can be annotated tags and snapcraft
+      # will use those for the version numbers.
+      #
+      # This can be extended to other parts of OpenRocket (to use the
+      # git describe --tags command) but the build should be updated at
+      # the same time so its consistent across all artifacts. Will defer
+      # that to a later pull request.
+      #
+      # Until then, just use the build.version value
+      snapcraftctl pull
+      VERSION=$(cat core/resources/build.properties | awk -F'=' '/build\.version/ { print $2 }')
+      snapcraftctl set-version "$VERSION"
+    override-build: |
+      snapcraftctl build
+      mv swing/build/jar/OpenRocket.jar $SNAPCRAFT_PART_INSTALL/OpenRocket.jar
+    build-packages:
+      - wget
+    stage-packages:
+      - openjdk-11-jre
+      - ca-certificates
+      - ca-certificates-java
+    prime:
+      - -usr/lib/jvm/java-*/lib/security/cacerts
+      - -usr/lib/jvm/java-*/jre/lib/security/cacerts
+
+  launcher:
+    plugin: dump
+    source: snap/local
+    organize:
+      'launcher': 'bin/'
+