Helper for detecting the correct alpha mode for video textures.
For some reason, some browsers/devices/WebGL implementations premultiply the alpha
of a video before and then a second time if UNPACK_PREMULTIPLY_ALPHA_WEBGL
is true. So the video is premultiplied twice if the alpha mode is UNPACK.
In this case we need the alpha mode to be PMA. This function detects
the upload behavior by uploading a white 2x2 webm with 50% alpha
without UNPACK_PREMULTIPLY_ALPHA_WEBGL and then checking whether
the uploaded pixels are premultiplied.
Helper for detecting the correct alpha mode for video textures. For some reason, some browsers/devices/WebGL implementations premultiply the alpha of a video before and then a second time if
UNPACK_PREMULTIPLY_ALPHA_WEBGLis true. So the video is premultiplied twice if the alpha mode isUNPACK. In this case we need the alpha mode to bePMA. This function detects the upload behavior by uploading a white 2x2 webm with 50% alpha withoutUNPACK_PREMULTIPLY_ALPHA_WEBGLand then checking whether the uploaded pixels are premultiplied.