message: Reflection maps must be 256x256.
  This makes the web samples comply with the size requirement in
  `filament/src/IndirectLight.cpp`.
diff: @@ -98,7 +98,7 @@ function(add_envmap SOURCE TARGET)
  set(target_skyboxes ${target_skyboxes} ${target_skybox} PARENT_SCOPE)
  add_custom_command(
  OUTPUT ${target_skybox} ${target_envmap}
  - COMMAND cmgen -x public --format=rgbm --size=512 --extract-blur=0.1 ${source_envmap}
  + COMMAND cmgen -x public --format=rgbm --size=256 --extract-blur=0.1 ${source_envmap}
  MAIN_DEPENDENCY ${source_envmap}
  DEPENDS cmgen)
  set(target_envmaps ${target_envmaps} ${target_envmap} PARENT_SCOPE)
  