fix(print,engine): read the page tree once when finding which pages' text reads up

crates/engine/src/session/files.rs

@@ -171,7 +171,13 @@ impl Session {
                 Err(_) => return Vec::new(),
             },
         };
-        (0..doc.info.pages.len()).map(|i| pages.contains(&i) && pdfcraft_print::text_reads_up(&cos, i)).collect()
+        // The page tree is read once, and each page is looked up, not searched for, in `pages`.
+        let mut out = vec![false; doc.info.pages.len()];
+        let wanted: Vec<usize> = pages.iter().copied().filter(|&p| p < out.len()).collect::<std::collections::BTreeSet<_>>().into_iter().collect();
+        for (p, up) in wanted.iter().zip(pdfcraft_print::texts_read_up(&cos, &wanted)) {
+            out[*p] = up;
+        }
+        out
     }
 
     /// Combine whole files, in order, into new PDF bytes (one bookmark per file).

crates/print/src/lib.rs

@@ -42,4 +42,4 @@ pub use settings::{
 };
 #[cfg(test)]
 use sheets::text_direction;
-pub use sheets::{LABEL_MARGIN, MARGIN, Placement, Sheet, layout, matching_paper, text_reads_up};
+pub use sheets::{LABEL_MARGIN, MARGIN, Placement, Sheet, layout, matching_paper, text_reads_up, texts_read_up};

crates/print/src/sheets.rs

@@ -7,7 +7,17 @@ use super::{DecodeBudget, Dict, Document, Matrix, Object};
 /// sideways on a letter or A4 sheet), counting each text-showing operator once; form XObjects
 /// are followed a few levels deep.
 pub fn text_reads_up(doc: &Document, index: usize) -> bool {
-    let Some(page) = pdfcraft_model::pages(doc).into_iter().nth(index) else { return false };
+    texts_read_up(doc, &[index]).first().copied().unwrap_or(false)
+}
+
+/// [`text_reads_up`] for each of `indices`, reading the page tree once: once per page, the
+/// whole tree would be walked for every page asked about.
+pub fn texts_read_up(doc: &Document, indices: &[usize]) -> Vec<bool> {
+    let pages = pdfcraft_model::pages(doc);
+    indices.iter().map(|&i| pages.get(i).is_some_and(|page| page_reads_up(doc, page))).collect()
+}
+
+fn page_reads_up(doc: &Document, page: &pdfcraft_model::Page) -> bool {
     let to_display = Matrix(page.view_matrix(doc)).invert().unwrap_or_default();
     let res = page.dict.get(b"Resources").and_then(|r| doc.resolve(r).as_dict().cloned()).unwrap_or_default();
     let mut score = 0i64;

crates/print/src/tests.rs

@@ -1245,3 +1245,17 @@ fn contents_pieces_join_with_a_space_across_a_trailing_comment() {
     let printed_ctrl = impose(&with_newline, &settings(vec![0], Layout::Size(SizeMode::Actual))).unwrap();
     assert_eq!(form_strings(printed_ctrl), [b"HIDDEN".to_vec(), b"SHOWN".to_vec()]);
 }
+
+/// Many pages asked about at once are answered from one walk of the page tree, each as
+/// [`text_reads_up`] answers it alone; a page past the end is `false`.
+#[test]
+fn texts_read_up_answers_many_pages_from_one_walk() {
+    let doc = fixture(3_000);
+    let all: Vec<usize> = (0..3_001).collect();
+    let started = std::time::Instant::now();
+    let up = texts_read_up(&doc, &all);
+    assert!(started.elapsed() < std::time::Duration::from_secs(20), "{:?}", started.elapsed());
+    assert_eq!(up.len(), all.len());
+    assert!(up.iter().all(|u| !u), "upright text, and no page 3000");
+    assert_eq!(up[1], text_reads_up(&doc, 1));
+}