Add ScalerBuilder::hint_target to select the hinting target - #137
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showier-drastic wants to merge 1 commit into
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Add ScalerBuilder::hint_target to select the hinting target#137showier-drastic wants to merge 1 commit into
showier-drastic wants to merge 1 commit into
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The hinting mode was hardcoded to HintingMode::Smooth with lcd_subpixel: Some(LcdLayout::Horizontal), which maps to skrifa's SmoothMode::Lcd. That target is only correct when the mask is rasterized for subpixel (LCD) output. swash consumers (e.g. Slint) that render Format::Alpha (grayscale) masks get LCD-tuned grid fitting instead: skrifa documents that this mode widens horizontal stems in ClearType-hinted fonts and 'may lead to blurry images when rendered with an analytical area rasterizer' (skrifa src/outline/hint.rs, Target::Smooth docs). Add a HintingTarget enum and a ScalerBuilder::hint_target() knob so grayscale renderers can request SmoothMode::Normal grid fitting. The default remains HorizontalLcd, so existing users are unaffected. preserve_linear_metrics stays true for both targets: hinting never changes advance widths either way. The hinting instance cache key now includes the target so the same font/size/coords can be hinted for different targets without thrashing a single entry.
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Please see the commit message for the rationale of this change.
Please feel free to edit my branch directly if change is needed. One uncertainty is that I'm not sure if we should even add an option here, or just change the default to be greyscale.
Note: this will be used in a Pull Request to Slint's software renderer, which will demonstrate this PR's usefulness.