Fix Docker build

Fixes #17

README.md

@@ -6,6 +6,7 @@ Data files for packaging the [Solarus Snap image](https://snapcraft.io/solarus)
 
 * Ensure that [snapd is installed](https://docs.snapcraft.io/installing-snapd/6735) (Ubuntu has this by default).
 * Run `sudo snap install solarus`
+* (optional) Run `sudo snap connect solarus:joystick` to enable controller support.
 
 You should now have icons in your applications menu for the Quest Editor and Launcher programs.
 
@@ -21,8 +22,8 @@ You should now have icons in your applications menu for the Quest Editor and Lau
 
 ### Building
 
-* First [install snapd](https://docs.snapcraft.io/installing-snapd/6735) and snapcraft.
-* To build, simply run `snapcraft`.
+* First [install snapd](https://docs.snapcraft.io/installing-snapd/6735), snapcraft, and [Docker](https://docs.docker.com/install/).
+* To build, run `docker run --rm -v "$PWD":/build -w /build snapcore/snapcraft bash -c "apt update && snapcraft"`.
 * To test your build, run: `sudo snap install solarus_*.snap --dangerous`
 
 ### Publishing

snap/snapcraft.yaml

@@ -44,6 +44,14 @@ apps:
       - joystick
 
 parts:
+  prepare:
+    plugin: nil
+    prepare: |
+      echo "deb http://ppa.launchpad.net/litenstein/sdl2-xenial/ubuntu xenial main" | tee /etc/apt/sources.list.d/litenstein-ubuntu-sdl2-xenial-xenial.list
+      apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 1E0A4B32AA748B9D11C4528301A509285F2EA337
+      apt-get update
+      apt-get install -y libsdl2-2.0-0
+    prime: [-*]
   launcher:
     plugin: cmake
     source-type: git
@@ -64,7 +72,7 @@ parts:
       - qttools5-dev
       - qttools5-dev-tools
       - libglm-dev
-    after: [desktop-qt5]
+    after: [prepare, desktop-qt5]
     override-prime: |
       set -eu
       snapcraftctl prime