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bflatasticandClaude Opus 5.5
54427d7a92
On screen, a group (or object) with opacity, a blend mode, an opacity mask or knockout whose content blends is drawn offscreen over a copy of its backdrop and mixed back in by its opacity, mask and clip (a group blend mode then applies to the backdrop-free result, as PDF defines it). Isolate Blending keeps the content starting from transparency. Clip groups no longer isolate their children (blending content is clipped per drawing), and non-isolated knockout groups composite their elements against the art below the group. Groups without blending inside still render as plain layers. In PDF, such groups are written as non-isolated transparency groups (a constant-alpha soft mask instead of the writer's isolated opacity group), knockout groups included. doc: Node::blends_through / children_blend. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
100 lines
3.8 KiB
Rust
100 lines
3.8 KiB
Rust
//! Blend modes and transparency groups in PDF export.
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use vectorcraft_color::{BlendMode, Color, Paint};
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use vectorcraft_doc::{Appearance, Document, Node, NodeId};
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use vectorcraft_geom::{Rect, shapes};
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use crate::*;
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fn rect(r: Rect, rgb: (f32, f32, f32)) -> Node {
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Node::path(NodeId(0), shapes::rectangle(r), Appearance::basic(Paint::solid(Color::rgb(rgb.0, rgb.1, rgb.2)), Paint::None, 0.0))
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}
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fn add(d: &mut Document, mut n: Node) {
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n.id = d.alloc_id();
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let l = d.layers[0].id;
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d.insert(Some(l), usize::MAX, n).unwrap();
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}
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/// The file's text with spaces removed (content streams uncompressed).
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fn text(d: &Document) -> String {
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let bytes = export(d, &PdfOptions { compress: false, ..Default::default() }).unwrap();
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String::from_utf8_lossy(&bytes).replace(' ', "")
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}
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#[test]
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fn every_blend_mode_is_written_under_its_pdf_name_and_read_back() {
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for mode in BlendMode::ALL.into_iter().filter(|m| *m != BlendMode::Normal) {
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let mut d = Document::new(100.0, 100.0);
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add(&mut d, rect(Rect::new(0.0, 0.0, 100.0, 100.0), (0.2, 0.5, 0.9)));
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let mut top = rect(Rect::new(20.0, 20.0, 80.0, 80.0), (0.6, 0.25, 0.5));
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top.blend = mode;
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add(&mut d, top);
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let name = mode.label().replace(' ', "");
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assert!(text(&d).contains(&format!("/BM/{name}")), "{mode:?}");
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let back = import(&export(&d, &PdfOptions::default()).unwrap()).unwrap();
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let mut found = BlendMode::Normal;
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back.walk(|n| {
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if n.blend != BlendMode::Normal {
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found = n.blend;
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}
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});
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assert_eq!(found, mode);
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}
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}
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/// The backdrop and a 50% group (isolated or not) holding a Multiply square.
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fn half_group(isolate: bool) -> Document {
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let mut d = Document::new(100.0, 100.0);
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add(&mut d, rect(Rect::new(0.0, 0.0, 100.0, 100.0), (0.8, 0.6, 0.2)));
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let mut m = rect(Rect::new(20.0, 20.0, 80.0, 80.0), (0.5, 0.5, 1.0));
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(m.id, m.blend) = (d.alloc_id(), BlendMode::Multiply);
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let mut g = Node::group(NodeId(0), vec![std::sync::Arc::new(m)]);
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(g.opacity, g.isolate) = (0.5, isolate);
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add(&mut d, g);
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d
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}
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#[test]
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fn a_group_is_written_non_isolated_unless_it_isolates_blending() {
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let open = text(&half_group(false));
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// A transparency group without /I, its 50% carried by a constant alpha soft mask.
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assert!(!open.contains("/Itrue"), "{open}");
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assert!(open.contains("/SMask") && open.contains("/Alpha") && open.contains("/BM/Multiply"), "{open}");
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let isolated = text(&half_group(true));
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assert!(isolated.contains("/Itrue") && isolated.contains("/ca0.5"), "{isolated}");
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assert!(!isolated.contains("/Alpha"), "{isolated}");
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// Either way the child's blend mode reads back.
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for d in [half_group(false), half_group(true)] {
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let back = import(&export(&d, &PdfOptions::default()).unwrap()).unwrap();
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let mut bm = BlendMode::Normal;
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back.walk(|n| {
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if n.blend != BlendMode::Normal {
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bm = n.blend;
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}
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});
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assert_eq!(bm, BlendMode::Multiply);
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}
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}
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#[test]
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fn groups_without_blending_inside_stay_isolated_groups() {
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let mut d = half_group(false);
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let g = d.layers[0].children().unwrap()[1].id;
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let m = d.node(g).unwrap().children().unwrap()[0].id;
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d.node_mut(m).unwrap().blend = BlendMode::Normal;
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let t = text(&d);
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assert!(t.contains("/Itrue") && t.contains("/ca0.5") && !t.contains("/SMask"), "{t}");
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}
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#[test]
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fn a_knockout_group_with_blending_elements_is_non_isolated_unless_isolated() {
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for isolate in [false, true] {
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let mut d = half_group(isolate);
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let g = d.layers[0].children().unwrap()[1].id;
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let n = d.node_mut(g).unwrap();
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(n.opacity, n.knockout) = (1.0, vectorcraft_doc::Knockout::On);
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assert_eq!(text(&d).contains("/Itrue"), isolate, "isolate {isolate}");
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}
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}
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