demo: make a bitmap of blank tiles instead of uploading them#144
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Conserve HTTP connections. Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>
S3 can't negotiate Content-Encoding, but we can precompress objects and unconditionally set the Content-Encoding header. This works for browsers, which always set Accept-Encoding: gzip, but causes problems for curl (without --compressed) and Python requests etc. However, our JSON is really only intended for browsers (and for synctiles itself) and we want to reduce JSON sizes before adding sparse bitmaps. Support uncompressed info.json and slide.json until existing metadata has been converted over. Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>
When tiling, don't upload completely white tiles; add them to a bitmap instead. If the bitmap is non-empty, Base64-encode it and add it to info.json. Then, if a bit is set, tell OpenSeadragon the tile doesn't exist so OSD won't fetch it, using pixels from the next lower resolution instead. We can't simply omit blank tiles because OSD unavoidably logs a console message for every fetch failure. Using the bitmap also saves a round trip. Retile the demo site. Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>
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When tiling, don't upload completely white tiles; add them to a bitmap instead. If the bitmap is non-empty, Base64-encode it and add it to
info.json. Then, if a bit is set, tell OpenSeadragon the tile doesn't exist so OSD won't fetch it, using pixels from the next lower resolution instead.We can't simply omit blank tiles because OSD unavoidably logs a console message for every fetch failure. Using the bitmap also saves a round trip.
To counter the increase in JSON sizes, gzip JSON objects in the S3 bucket. S3 can't negotiate Content-Encoding, but we can precompress objects and unconditionally set the
Content-Encodingheader. This works for browsers, which always setAccept-Encoding: gzip, but causes problems forcurl(without--compressed) and Pythonrequestsetc. However, our JSON is really only intended for browsers (and forsynctilesitself).