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harfbuzz/docs/subset-preprocessing.md

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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

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 than 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.

  • Currently the largest performance gains are seen when using a preprocessed face for CFF subsetting.

  • 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%
BM_subset/subset_glyphs/AdobeVFPrototype.otf/nohinting/64_median -68%
BM_subset/subset_glyphs/AdobeVFPrototype.otf/nohinting/300_median -72%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/10_median -90%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/64_median -82%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/512_median -31%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/4096_median -9%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/6000_median -22%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/nohinting/10_median -88%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/nohinting/64_median -83%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/nohinting/512_median -31%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/nohinting/4096_median -16%
BM_subset/subset_glyphs/MPLUS1-Variable.ttf/nohinting/6000_median -18%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/10_median -44%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/64_median -18%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/512_median -2%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/900_median -6%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/nohinting/10_median -45%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/nohinting/64_median -17%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/nohinting/512_median -15%
BM_subset/subset_glyphs/RobotoFlex-Variable.ttf/nohinting/900_median -3%
BM_subset/subset_codepoints/Roboto-Regular.ttf/10_median -20%
BM_subset/subset_codepoints/Roboto-Regular.ttf/64_median -16%
BM_subset/subset_codepoints/Roboto-Regular.ttf/512_median -12%
BM_subset/subset_codepoints/Roboto-Regular.ttf/1000_median -10%
BM_subset/subset_codepoints/Roboto-Regular.ttf/nohinting/10_median -24%
BM_subset/subset_codepoints/Roboto-Regular.ttf/nohinting/64_median -14%
BM_subset/subset_codepoints/Roboto-Regular.ttf/nohinting/512_median -15%
BM_subset/subset_codepoints/Roboto-Regular.ttf/nohinting/1000_median -9%
BM_subset/subset_codepoints/Amiri-Regular.ttf/10_median -51%
BM_subset/subset_codepoints/Amiri-Regular.ttf/64_median -37%
BM_subset/subset_codepoints/Amiri-Regular.ttf/512_median -12%
BM_subset/subset_codepoints/Amiri-Regular.ttf/4096_median -1%
BM_subset/subset_codepoints/Amiri-Regular.ttf/nohinting/10_median -49%
BM_subset/subset_codepoints/Amiri-Regular.ttf/nohinting/64_median -35%
BM_subset/subset_codepoints/Amiri-Regular.ttf/nohinting/512_median -6%
BM_subset/subset_codepoints/Amiri-Regular.ttf/nohinting/4096_median -1%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/10_median -82%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/64_median -9%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/512_median 0%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/1400_median 0%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/nohinting/10_median -82%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/nohinting/64_median -13%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/nohinting/512_median -3%
BM_subset/subset_codepoints/NotoNastaliqUrdu-Regular.ttf/nohinting/1400_median 2%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/10_median -40%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/64_median -26%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/512_median -5%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/1000_median 3%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/nohinting/10_median -43%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/nohinting/64_median -24%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/nohinting/512_median -2%
BM_subset/subset_codepoints/NotoSansDevanagari-Regular.ttf/nohinting/1000_median 2%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/10_median -83%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/64_median -67%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/512_median -39%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/4096_median -20%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/10000_median -25%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/nohinting/10_median -83%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/nohinting/64_median -65%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/nohinting/512_median -42%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/nohinting/4096_median -34%
BM_subset/subset_codepoints/Mplus1p-Regular.ttf/nohinting/10000_median -21%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/10_median -69%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/64_median -69%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/512_median -70%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/4096_median -84%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/10000_median -83%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/nohinting/10_median -71%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/nohinting/64_median -68%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/nohinting/512_median -70%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/nohinting/4096_median -86%
BM_subset/subset_codepoints/SourceHanSans-Regular_subset.otf/nohinting/10000_median -88%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/10_median -45%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/64_median -48%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/512_median -57%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/2000_median -66%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/nohinting/10_median -43%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/nohinting/64_median -50%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/nohinting/512_median -63%
BM_subset/subset_codepoints/SourceSansPro-Regular.otf/nohinting/2000_median -72%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/10_median -69%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/64_median -66%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/300_median -74%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/nohinting/10_median -70%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/nohinting/64_median -71%
BM_subset/subset_codepoints/AdobeVFPrototype.otf/nohinting/300_median -75%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/10_median -66%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/64_median -46%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/512_median -15%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/4096_median -5%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/6000_median -16%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/nohinting/10_median -66%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/nohinting/64_median -45%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/nohinting/512_median -14%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/nohinting/4096_median -11%
BM_subset/subset_codepoints/MPLUS1-Variable.ttf/nohinting/6000_median -27%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/10_median -38%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/64_median -9%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/512_median -3%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/900_median -16%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/nohinting/10_median -39%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/nohinting/64_median -12%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/nohinting/512_median -4%
BM_subset/subset_codepoints/RobotoFlex-Variable.ttf/nohinting/900_median -2%
BM_subset/instance/MPLUS1-Variable.ttf/10_median -68%
BM_subset/instance/MPLUS1-Variable.ttf/64_median -45%
BM_subset/instance/MPLUS1-Variable.ttf/512_median -18%
BM_subset/instance/MPLUS1-Variable.ttf/4096_median -2%
BM_subset/instance/MPLUS1-Variable.ttf/6000_median 4%
BM_subset/instance/MPLUS1-Variable.ttf/nohinting/10_median -69%
BM_subset/instance/MPLUS1-Variable.ttf/nohinting/64_median -46%
BM_subset/instance/MPLUS1-Variable.ttf/nohinting/512_median -11%
BM_subset/instance/MPLUS1-Variable.ttf/nohinting/4096_median 4%
BM_subset/instance/MPLUS1-Variable.ttf/nohinting/6000_median -5%
BM_subset/instance/RobotoFlex-Variable.ttf/10_median -34%
BM_subset/instance/RobotoFlex-Variable.ttf/64_median -12%
BM_subset/instance/RobotoFlex-Variable.ttf/512_median 6%
BM_subset/instance/RobotoFlex-Variable.ttf/900_median -6%
BM_subset/instance/RobotoFlex-Variable.ttf/nohinting/10_median -33%
BM_subset/instance/RobotoFlex-Variable.ttf/nohinting/64_median -11%
BM_subset/instance/RobotoFlex-Variable.ttf/nohinting/512_median 3%
BM_subset/instance/RobotoFlex-Variable.ttf/nohinting/900_median 0%