From 8c021462e6a7c52beb20906b595be52d526d5976 Mon Sep 17 00:00:00 2001 From: Garret Rieger Date: Wed, 7 Dec 2022 22:44:50 +0000 Subject: [PATCH] [subset] Add short document on subset preprocessing. --- docs/subset-preprocessing.md | 226 +++++++++++++++++++++++++++++++++++ 1 file changed, 226 insertions(+) create mode 100644 docs/subset-preprocessing.md diff --git a/docs/subset-preprocessing.md b/docs/subset-preprocessing.md new file mode 100644 index 000000000..6f780dd4b --- /dev/null +++ b/docs/subset-preprocessing.md @@ -0,0 +1,226 @@ +# Introduction + +Subset preprocessing is a mechanism which can significantly speed up font subsetting operations. +It works by prepopulating datastructures from the source font which can be used in later subsetting +operations to more quickly produce the subset. Preprocessing is useful in cases where multiple subsets +will be cut from the same source font. + +# Usage + +```c++ +hb_face_t* preprocessed = hb_subset_preprocess (source_face); + +... + +hb_face_t* subset = hb_subset_or_fail (preprocessed, subset_input); +``` + +# Additional Details + +* A subset produced from a preprocessed face should be identical to a subset produced from only the + original face. The preprocessor does not change the functionality of the subsetter, just speeds + things up. + +* The preprocessing operation may take longer then the time it takes to produce a subset from the + source font. Thus the main performance gains are made when a preprocessed face is reused for multiple + subsetting operations. + +* The preprocessed face may contain references to the memory backing the source face. If this memory + is fully owned by a harfbuzz hb_blob_t* then it will automatically be kept alive for the lifetime + of the preprocessed face. However, if this memory is not fully owned by a harfbuzz hb_blob_t* then + it is necessary to ensure that the memory is kept alive for the lifetime of the preprocessed face. + + +# Performance Improvements + +Here is the performance difference of producing a subset with a preprocessed face vs producing +a subset with the source face: + +Benchmark | Delta Time (%) +----------|----------------- +BM_subset/subset_glyphs/Roboto-Regular.ttf/10_median|-56% +BM_subset/subset_glyphs/Roboto-Regular.ttf/64_median|-33% +BM_subset/subset_glyphs/Roboto-Regular.ttf/512_median|-28% +BM_subset/subset_glyphs/Roboto-Regular.ttf/1000_median|-11% +BM_subset/subset_glyphs/Roboto-Regular.ttf/nohinting/10_median|-56% +BM_subset/subset_glyphs/Roboto-Regular.ttf/nohinting/64_median|-33% +BM_subset/subset_glyphs/Roboto-Regular.ttf/nohinting/512_median|-21% +BM_subset/subset_glyphs/Roboto-Regular.ttf/nohinting/1000_median|-9% +BM_subset/subset_glyphs/Amiri-Regular.ttf/10_median|-67% +BM_subset/subset_glyphs/Amiri-Regular.ttf/64_median|-48% +BM_subset/subset_glyphs/Amiri-Regular.ttf/512_median|-21% +BM_subset/subset_glyphs/Amiri-Regular.ttf/4096_median|-9% +BM_subset/subset_glyphs/Amiri-Regular.ttf/nohinting/10_median|-66% +BM_subset/subset_glyphs/Amiri-Regular.ttf/nohinting/64_median|-50% +BM_subset/subset_glyphs/Amiri-Regular.ttf/nohinting/512_median|-8% +BM_subset/subset_glyphs/Amiri-Regular.ttf/nohinting/4096_median|-9% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/10_median|-85% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/64_median|-71% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/512_median|-3% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/1400_median|4% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/nohinting/10_median|-84% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/nohinting/64_median|-72% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/nohinting/512_median|0% +BM_subset/subset_glyphs/NotoNastaliqUrdu-Regular.ttf/nohinting/1400_median|0% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/10_median|-30% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/64_median|-24% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/512_median|-3% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/1000_median|-3% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/nohinting/10_median|-30% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/nohinting/64_median|-24% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/nohinting/512_median|-3% +BM_subset/subset_glyphs/NotoSansDevanagari-Regular.ttf/nohinting/1000_median|-5% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/10_median|-96% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/64_median|-90% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/512_median|-74% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/4096_median|-25% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/10000_median|-23% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/nohinting/10_median|-95% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/nohinting/64_median|-90% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/nohinting/512_median|-73% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/nohinting/4096_median|-24% +BM_subset/subset_glyphs/Mplus1p-Regular.ttf/nohinting/10000_median|-11% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/10_median|-84% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/64_median|-77% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/512_median|-70% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/4096_median|-80% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/10000_median|-86% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/nohinting/10_median|-84% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/nohinting/64_median|-78% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/nohinting/512_median|-71% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/nohinting/4096_median|-86% +BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/nohinting/10000_median|-88% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/10_median|-59% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/64_median|-55% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/512_median|-67% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/2000_median|-68% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/nohinting/10_median|-60% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/nohinting/64_median|-58% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/nohinting/512_median|-72% +BM_subset/subset_glyphs/SourceSansPro-Regular.otf/nohinting/2000_median|-71% +BM_subset/subset_glyphs/AdobeVFPrototype.otf/10_median|-70% +BM_subset/subset_glyphs/AdobeVFPrototype.otf/64_median|-64% +BM_subset/subset_glyphs/AdobeVFPrototype.otf/300_median|-73% +BM_subset/subset_glyphs/AdobeVFPrototype.otf/nohinting/10_median|-71% 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