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smart_dropout
- Applies to: TTF
- Fontspector can hotfix?: no
- Fontspector can fix sources?: no
This setup is meant to ensure consistent rendering quality for fonts across all devices (with different rendering/hinting capabilities).
Below is the snippet of instructions we expect to see in the fonts:
B8 01 FF PUSHW 0x01FF
85 SCANCTRL (unconditinally turn on
dropout control mode)
B0 04 PUSHB 0x04
8D SCANTYPE (enable smart dropout control)
"Smart dropout control" means activating rules 1, 2 and 5:
Rule 1: If a pixel's center falls within the glyph outline, that pixel is turned on. Rule 2: If a contour falls exactly on a pixel's center, that pixel is turned on. Rule 5: If a scan line between two adjacent pixel centers (either vertical or horizontal) is intersected by both an on-Transition contour and an off-Transition contour and neither of the pixels was already turned on by rules 1 and 2, turn on the pixel which is closer to the midpoint between the on-Transition contour and off-Transition contour. This is "Smart" dropout control.
For more detailed info (such as other rules not enabled in this snippet), please refer to the TrueType Instruction Set documentation.
Generally this occurs with unhinted fonts; if you are not using autohinting, use gftools-fix-nonhinting (or just gftools-fix-font) to fix this issue.
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universal (in section 'Universal Profile Checks')
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googlefonts (in section 'Universal Profile Checks')