Enum Coverage 

pub enum Coverage {
    Exact,
    Thresholded,
    Full,
}

How an integrated coverage becomes an alpha byte — AGG’s three modes.

See AntiAlias, whose three variants these mirror one for one; this is the integrator’s own spelling of the same choice, so scanline does not depend on the device vocabulary.

use pdfrum_render::scanline::{Coverage, FillRule, Rasterizer};

// A half-covered pixel: `Exact` keeps the partial alpha, `Full`
// pushes any touched pixel to 255.
let alpha = |coverage| {
    let mut rasterizer = Rasterizer::new();
    rasterizer.move_to(0.0, 0.0);
    rasterizer.line_to(0.5, 0.0);
    rasterizer.line_to(0.5, 1.0);
    rasterizer.line_to(0.0, 1.0);
    rasterizer.close_polygon();
    let mut out = 0u8;
    rasterizer.sweep(FillRule::Winding, coverage, |_, _, _, a| out = a);
    out
};
assert!(alpha(Coverage::Exact) < 255);
assert_eq!(alpha(Coverage::Full), 255);

Variants

Exact

Coverage becomes alpha: min(255, floor(cov * 256)).

Thresholded

aliased_path: the same coverage thresholded at its midpoint.

Full

full_cover: any touched pixel at 255, whatever its coverage.

Trait Implementations

impl Clone for Coverage

fn clone(&self) -> Coverage

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Coverage

impl Debug for Coverage

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Coverage

fn default() -> Coverage

Returns the “default value” for a type.

impl Eq for Coverage

impl PartialEq for Coverage

fn eq(&self, other: &Coverage) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Coverage