New issue 1129: [experimental] Opaque sources fade volume sources https://bitbucket.org/yt_analysis/yt/issues/1129/experimental-opaque-sources... Suoqing Ji: When opaque sources are rendered with ``alpha=1`` in default, the volume sources would not be visible. In plane parallel lens, the objects in the middle are not visible.  In perspective lens, the entire volume sources are not visible.