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Biromedic
1726c600d2
The canvas built its peniko gradients premultiplied (peniko's default), while Gradient::sample, the PDF export (shading plus SMask) and SVG viewers blend colour and opacity separately: a transparent white stop into black drew grey 127 halfway instead of 191. Opaque gradients are unchanged.
59 lines
3.0 KiB
Rust
59 lines
3.0 KiB
Rust
//! Gradient stops with opacity: colour and opacity blend each on its own (not premultiplied), as
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//! the model samples them ([`Gradient::sample`]) and as the SVG and PDF exports draw them. The colour
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//! of a transparent stop counts: red fading into transparent black darkens as it fades.
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use vectorcraft_color::{Color, Gradient, GradientGeom, GradientKind, GradientPaint, GradientStop, Paint};
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use vectorcraft_doc::{Appearance, Document};
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use vectorcraft_geom::{Point, Rect, shapes};
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use vectorcraft_testkit::fixtures::DocBuilder;
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use vectorcraft_testkit::raster::{Image, render_view};
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/// A 100 pt square filled with `gradient` on `geom`.
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fn filled(gradient: &Gradient, geom: GradientGeom) -> Document {
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let mut gp = GradientPaint::new(gradient.clone());
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gp.geom = Some(geom);
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let mut b = DocBuilder::new(100.0, 100.0);
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b.path(shapes::rectangle(Rect::new(0.0, 0.0, 100.0, 100.0)), Appearance::basic(Paint::Gradient(Box::new(gp)), Paint::None, 0.0), |_| {});
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b.build()
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}
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fn stop(offset: f32, color: Color, opacity: f32, midpoint: f32) -> GradientStop {
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GradientStop { opacity, midpoint, ..GradientStop::new(offset, color) }
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}
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/// Every 7th pixel is the model's colour at its opacity over white (pixel centres).
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fn assert_follows_model(img: &Image, gradient: &Gradient, geom: &GradientGeom) {
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for y in (3..100).step_by(7) {
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for x in (3..100).step_by(7) {
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let t = geom.param_at(gradient.kind, Point::new(x as f64 + 0.5, y as f64 + 0.5)).clamp(0.0, 1.0);
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let (c, o) = gradient.sample(t as f32);
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let want = c.to_rgb().map(|v| ((v * o + 1.0 - o) * 255.0).round() as u8);
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let got = img.over_white(x, y);
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let off = (0..3).map(|k| got[k].abs_diff(want[k])).max().unwrap_or(0);
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assert!(off <= 4, "{:?} ({x},{y}) t={t:.3}: got {got:?}, want {want:?}", gradient.kind);
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}
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}
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}
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#[test]
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fn transparent_stops_blend_colour_and_opacity_apart() {
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let red = Color::rgb(1.0, 0.0, 0.0);
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let fades = [
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// Transparent white into black: mid-grey at half opacity halfway, light over white.
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vec![stop(0.0, Color::WHITE, 0.0, 0.5), stop(1.0, Color::BLACK, 1.0, 0.5)],
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// Red into transparent black: darker red as it fades.
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vec![stop(0.0, red, 1.0, 0.5), stop(1.0, Color::BLACK, 0.0, 0.5)],
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// A midpoint off centre (drawn as an extra stop) follows the same rule.
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vec![stop(0.0, red, 1.0, 0.3), stop(1.0, Color::BLACK, 0.0, 0.5)],
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];
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for stops in fades {
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for (kind, geom) in [
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(GradientKind::Linear, GradientGeom { start: Point::new(0.0, 50.0), end: Point::new(100.0, 50.0), aspect: 1.0, focal: None }),
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(GradientKind::Radial, GradientGeom { start: Point::new(50.0, 50.0), end: Point::new(100.0, 50.0), aspect: 1.0, focal: None }),
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] {
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let gradient = Gradient { kind, stops: stops.clone() };
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assert_follows_model(&render_view(&filled(&gradient, geom), 100, 100), &gradient, &geom);
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}
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}
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}
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