Flattening: an option leaves colorized images to writers that draw them

Flattening counted every colorized image as transparency, in the art and
in pattern tiles. A new flattener option, keeps_colorize, stops counting
an image colorized with a solid paint whose pixels are grayscale or 1-bit,
for a format whose writer draws such images in their ink. Opacity,
blending modes, opacity masks and effects still flatten them, and pattern
tiles are still expanded for those. The option is off, so exports flatten
as before; the EPS writer that draws colorized images turns it on.

The EPS pattern tile tests now check the exported colors, and a tile
group with opacity for the warning.

crates/engine/src/tests/legacy_ai.rs

@@ -546,7 +546,7 @@ fn a_colorized_grayscale_image_pattern_fill_is_expanded() {
     let keys = crate::cmd::flatten::see_through_images(d);
     assert!(keys.is_empty());
     let layer = d.layers[0].id;
-    assert_eq!(crate::cmd::expand::expand_transparent_image_patterns(d, layer, &keys).unwrap(), 1);
+    assert_eq!(crate::cmd::expand::expand_transparent_image_patterns(d, layer, &keys, &|_, _| true).unwrap(), 1);
     let mut patterns = 0;
     let mut tile_images = 0;
     d.walk(|n| {
@@ -688,7 +688,7 @@ fn only_the_transparent_pattern_fill_of_a_leaf_is_expanded() {
     let d = std::sync::Arc::make_mut(&mut s.doc_mut().unwrap().doc);
     let keys = crate::cmd::flatten::see_through_images(d);
     let layer = d.layers[0].id;
-    assert_eq!(crate::cmd::expand::expand_transparent_image_patterns(d, layer, &keys).unwrap(), 1);
+    assert_eq!(crate::cmd::expand::expand_transparent_image_patterns(d, layer, &keys, &|_, _| true).unwrap(), 1);
     let mut patterns = vec![];
     let mut images = 0;
     d.walk(|n| {
@@ -745,11 +745,10 @@ fn eps_level3_writes_see_through_pattern_tile_images() {
 }
 
 #[test]
-fn eps_flattens_colorized_pattern_tile_images_and_warns() {
+fn eps_writes_colorized_pattern_tile_images_in_their_colors() {
     let mut s = colorized_pattern_over_blue();
     let before = [colour_at(&s.doc().unwrap().doc, 72.0, 72.0), colour_at(&s.doc().unwrap().doc, 88.0, 72.0)];
     let r = s.execute("document.exportEps", &json!({"previewFormat": "none", "useArtboards": true, "level": 3})).unwrap();
-    assert!(warnings(&r).iter().any(|w| w.contains("transparency is flattened")), "{:?}", warnings(&r));
     s.execute("document.open", &json!({"name": "p.eps", "dataBase64": r["dataBase64"], "editingData": false})).unwrap();
     let after = [colour_at(&s.doc().unwrap().doc, 72.0, 72.0), colour_at(&s.doc().unwrap().doc, 88.0, 72.0)];
     for (a, b) in before.iter().zip(after) {
@@ -758,14 +757,31 @@ fn eps_flattens_colorized_pattern_tile_images_and_warns() {
 }
 
 #[test]
-fn eps_warns_for_colorized_image_nested_in_pattern_tile_group() {
+fn flattening_that_keeps_colorize_leaves_colorized_pattern_tile_images_alone() {
+    let s = colorized_pattern_over_blue();
+    let d = &s.doc().unwrap().doc;
+    assert!(crate::cmd::flatten::flatten_document(d, &crate::cmd::FlattenOptions::default()).unwrap().is_some());
+    let o = crate::cmd::FlattenOptions { keeps_colorize: true, ..Default::default() };
+    assert!(crate::cmd::flatten::flatten_document(d, &o).unwrap().is_none(), "the pattern isn't expanded for a colorize paint alone");
+}
+
+#[test]
+fn eps_flattens_colorized_image_in_a_see_through_pattern_tile_group_and_warns() {
     let mut s = colorized_pattern_over_blue();
     let d = std::sync::Arc::make_mut(&mut s.doc_mut().unwrap().doc);
     let id = d.alloc_id();
     let art = std::mem::take(&mut d.patterns[0].art);
-    d.patterns[0].art.push(std::sync::Arc::new(vectorcraft_doc::Node::group(id, art)));
+    let mut group = vectorcraft_doc::Node::group(id, art);
+    group.opacity = 0.5;
+    d.patterns[0].art.push(std::sync::Arc::new(group));
+    let before = [colour_at(&s.doc().unwrap().doc, 72.0, 72.0), colour_at(&s.doc().unwrap().doc, 88.0, 72.0)];
     let r = s.execute("document.exportEps", &json!({"previewFormat": "none", "useArtboards": true, "level": 3})).unwrap();
     assert!(warnings(&r).iter().any(|w| w.contains("transparency is flattened")), "{:?}", warnings(&r));
+    s.execute("document.open", &json!({"name": "p.eps", "dataBase64": r["dataBase64"], "editingData": false})).unwrap();
+    let after = [colour_at(&s.doc().unwrap().doc, 72.0, 72.0), colour_at(&s.doc().unwrap().doc, 88.0, 72.0)];
+    for (a, b) in before.iter().zip(after) {
+        assert!(a.iter().zip(b).all(|(a, b)| a.abs_diff(b) <= 4), "before {before:?} after {after:?}");
+    }
 }
 
 #[test]