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.
hb_face_t* preprocessed = hb_subset_preprocess (source_face); ... hb_face_t* subset = hb_subset_or_fail (preprocessed, subset_input);
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.
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% |