Snap on Ubuntu RPi3 fails to render on Wayland

[AlanGriffiths]

This can be reproduced on Ubuntu Core 20 and Ubuntu Server 20.04

Steps to Reproduce

On desktop

With the demo app and the snapcraft YAML below:

snapcraft remote-build --launchpad-accept-public-upload
scp super-cool-app_0.1.0_arm64.snap <the RPi>:~

on the RPi

If you are reproducing on Ubuntu Server, you need to add kms support. E.g.

sudo echo "dtoverlay=vc4-kms-v3d" >> /boot/firmware/usercfg.txt
sudo reboot

sudo snap install mir-kiosk
sudo snap set mir-kiosk daemon=true # not needed on Core
unsquashfs -d super-cool-app_0.1.0_arm64 super-cool-app_0.1.0_arm64.snap
sudo snap try super-cool-app_0.1.0_arm64
sudo snap set super-cool-app daemon=true # not needed on Core

Expected results: The demo displays correctly
Actual results: Only the decorations display

Additional details:

Something goes wrong using the vc4_dri.so driver on ARM64/RPi3

There's a relevant log line:

2021-03-17T17:00:41Z -[16793]: Failed to start Flutter renderer: Unable to create a GL context

Logs can be accessed with:

sudo snap logs super-cool-app

Additional logging can be obtained by editing super-cool-app_0.1.0_arm64/bin/wayland-launch and adding export EGL_LOG_LEVEL=debug before the final exec command.

The problem can be hidden by adding export LIBGL_ALWAYS_SOFTWARE=true in the same place.

snapcraft.yaml

name: super-cool-app
version: 0.1.0
summary: Super Cool App
description: Super Cool App that does everything!

architectures:
  - build-on: amd64
  - build-on: arm64

confinement: strict
base: core18
grade: stable

apps:
  daemon:
    daemon: simple
    restart-condition: always
    command-chain:
      - bin/run-daemon
      - bin/wayland-launch
    command: bin/flutterdemo
    extensions: [flutter-master] # Where "master" defines which Flutter channel to use for the build

  super-cool-app:
    command-chain:
      - bin/wayland-launch
    command: flutterdemo
    extensions: [flutter-master] # Where "master" defines which Flutter channel to use for the build

parts:
  super-cool-app:
    plugin: flutter
    source: flutterdemo
    flutter-target: lib/main.dart # The main entry-point file of the application

  mir-kiosk-snap-launch:
    plugin: dump
    source: https://github.com/MirServer/mir-kiosk-snap-launch.git
    override-build:  $SNAPCRAFT_PART_BUILD/build-with-plugs.sh opengl pulseaudio wayland
    stage-packages:
      - inotify-tools

  assets:
    plugin: nil
    stage-packages:
      - dmz-cursor-theme
      - fonts-dejavu
      - fonts-freefont-ttf
      - fonts-ubuntu

layout:
  /usr/share/fonts:
    bind: $SNAP/usr/share/fonts
  /etc/fonts:
    bind: $SNAP/etc/fonts
  /usr/share/icons:
    bind: $SNAP/usr/share/icons

[christiancfifi]

flutter/flutter#76178 (comment)
I had this problem also, and I think it is caused by a small issue that we were looking into on the flutter engine github ^

In env.sh LIBGL_DRIVERS_PATH is set to /usr/... instead of $SNAP/usr/...

[MarcusTomlinson]

flutter/flutter#76178 (comment)
I had this problem also, and I think it is caused by a small issue that we were looking into on the flutter engine github ^

In env.sh LIBGL_DRIVERS_PATH is set to /usr/... instead of $SNAP/usr/...

This issue is Wayland-specific. I've commented on the linked bug though.