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Scale

read_fonts::model::metrics::scaled

Trait Scale 

Source 
pub trait Scale {
    type Value: Copy;

    // Required methods
    fn add(a: Self::Value, b: Self::Value) -> Self::Value;
    fn sub(a: Self::Value, b: Self::Value) -> Self::Value;
    fn half(value: Self::Value) -> Self::Value;
    fn scale_x(&self, value: F48Dot16) -> Self::Value;
    fn scale_y(&self, value: F48Dot16) -> Self::Value;
    fn scale_glyph_extents(
        &self,
        extents: GlyphExtents<F48Dot16>,
    ) -> GlyphExtents<Self::Value>;
    fn scale_rect(
        &self,
        bounds: BoundingBox<F48Dot16>,
    ) -> BoundingBox<Self::Value>;

    // Provided method
    fn ppem(&self) -> Option<f32> { ... }
}
Expand description

Converts a measurement in font units into a caller’s own units.

Written by whatever owns scaling in a text stack: a shaper, or the bridge between one and this crate. Callers that want font units read them from GlyphMetrics, Metrics and StyleMetrics and never implement this.

An implementation chooses the number format, the rounding, and the order of operations for each axis. This crate defines how measurements combine into a metric.

The arithmetic is part of the trait for the same reason: an implementation decides what an overflowing sum does and which way a halved odd number rounds.

Required Associated Types§

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type Value: Copy

What a scaled measurement is expressed as.

Required Methods§

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fn add(a: Self::Value, b: Self::Value) -> Self::Value

Returns a plus b.

This and the two below take no scale. They describe Value itself, so every scale of that type answers them alike.

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fn sub(a: Self::Value, b: Self::Value) -> Self::Value

Returns a less b.

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fn half(value: Self::Value) -> Self::Value

Returns half of value.

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fn scale_x(&self, value: F48Dot16) -> Self::Value

Scales a measurement along the x axis.

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fn scale_y(&self, value: F48Dot16) -> Self::Value

Scales a measurement along the y axis.

Separate from scale_x because the two axes need not agree, and because a caller whose y runs down the page says so here.

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fn scale_glyph_extents( &self, extents: GlyphExtents<F48Dot16>, ) -> GlyphExtents<Self::Value>

Scales where a glyph’s ink sits.

One call rather than four, so that a scale running the other way up settles in one place what that means for a bearing and a size. The scale also decides whether to round the box’s corners before scaling.

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fn scale_rect(&self, bounds: BoundingBox<F48Dot16>) -> BoundingBox<Self::Value>

Scales a region given by its corners.

One call for the same reason as scale_glyph_extents: a scale running the other way up decides here which corner ends up least.

Provided Methods§

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fn ppem(&self) -> Option<f32>

Returns the size in pixels per em, if the scale has one.

Embedded bitmaps are measured from the strike selected for this size. None, the default, selects the largest strike.

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors§