unity popcornfx editor ue4 mesh unity3d shape-sampler plugin attribute script unreal rendering particle crash spawn unreal-4 import position animation collision meshsampling effects error baking rotation fbx events android ribbon hh-unityplugin unreal-engine-4 fx bug spawner image camera curve shader billboarding pk-unityplugin build axis velocity sampler event material physics ios projection vr sampler-shape compile-error time popcorn runtime folder backdrop model evolver texture id atlas attributes issues parent-field scaling api delay builder attractor lighting blueprint animtrack distortion unreal-collision spatial-layers fields billboard relative light samplers liferatio life infinite shape kill external scale flux audio draw console samplenormal flipbook pivot track order bake linux preferences