Make sure the gain map metadata is towards the start of the file. #2479
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The 'tmap' item data containing the gain map metadata was mistakenly being put at the end of the file.
tests/gtest/avifincrtest_helpers.cc
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| available_byte_count -= byte_count / 2; | ||
| byte_count -= byte_count / 2; | ||
| // Extra planes (alpha, gain map), if any, are assumed to be located before | ||
| // the other planes and to represent at most 50% of the payload. |
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Not sure if this still holds with monochrome+alpha+gainmap, but this function is hard to tune anyway. Feel free to change or remove conditions if they are cumbersome.
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Yeah I changed it a bit randomly, but after a while I realized the problem was not this formula but actually this part:
// There is no valid AV1 payload smaller than 10 bytes, so all but one cell
// should be decoded if at most 10 bytes are missing.
if ((available_byte_count + 10) >= byte_count) {Because my image had tiles that were all identical, and so all the tiles pointed to the same blob in mdat and were all decoded at once. So I fixed it by changing the test image.
I left this just in case, although looking at it again my change was wrong (and I changed it again), but I'm not sure this code is really exercised right now.
| @@ -2195,8 +2195,8 @@ static avifResult avifEncoderWriteMediaDataBox(avifEncoder * encoder, | |||
| const size_t mdatStartOffset = avifRWStreamOffset(s); | |||
| for (uint32_t itemPasses = 0; itemPasses < 3; ++itemPasses) { | |||
| // Use multiple passes to pack in the following order: | |||
| // * Pass 0: metadata (Exif/XMP) | |||
| // * Pass 1: alpha, gain map (AV1) | |||
| // * Pass 0: metadata (Exif/XMP/gain map metadata) | |||
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Unrelated to this PR: Shouldn't Exif/XMP be at the end?
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It's the same as the gain map metadata: if we put it at the end of the file, avifDecoderParse() will block untill it receives the whole file, unless ignoreExif and ignoreXMP are set. In the documentation for those fields we say some of these payloads are (unfortunately) packed at the end of the file so we consider this to be a bad thing.
The 'tmap' item data containing the gain map metadata was mistakenly being put at the end of the file.