From 4c7bbd0fef7a94581eaca53dd665cd371a988671 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Ribaudo?= <nribaudo@igalia.com>
Date: Tue, 9 Sep 2025 13:43:01 +0200
Subject: [PATCH] Reduce background canvas resolution

The size of the canvas has significant impact on the rendering
performance. If we are going to render a high-res detail
view on top of the full-page canvas, we can further
reduce the full-page canvas resolution to improve
rendering time without affecting the resolution seen by
the user.

Users will se the lower resolution when quickly scrolling around the
page, but it will then be replaced with the high-res
detail view.
---
 test/integration/viewer_spec.mjs | 16 ++++++++++------
 web/pdf_page_view.js             |  6 ++++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/test/integration/viewer_spec.mjs b/test/integration/viewer_spec.mjs
index f2d3447eb..1e52b65cc 100644
--- a/test/integration/viewer_spec.mjs
+++ b/test/integration/viewer_spec.mjs
@@ -363,12 +363,16 @@ describe("PDF viewer", () => {
               .toBeLessThan(originalCanvasSize * factor ** 2);
 
             expect(canvasSize)
-              .withContext(`In ${browserName}, <= MAX_CANVAS_PIXELS`)
-              .toBeLessThanOrEqual(MAX_CANVAS_PIXELS.get(browserName));
+              .withContext(`In ${browserName}, <= MAX_CANVAS_PIXELS / 100`)
+              .toBeLessThanOrEqual(MAX_CANVAS_PIXELS.get(browserName) / 100);
 
             expect(canvasSize)
-              .withContext(`In ${browserName}, > MAX_CANVAS_PIXELS * 0.99`)
-              .toBeGreaterThan(MAX_CANVAS_PIXELS.get(browserName) * 0.99);
+              .withContext(
+                `In ${browserName}, > MAX_CANVAS_PIXELS / 100 * 0.95`
+              )
+              .toBeGreaterThan(
+                (MAX_CANVAS_PIXELS.get(browserName) / 100) * 0.95
+              );
           })
         );
       });
@@ -565,10 +569,10 @@ describe("PDF viewer", () => {
                 .toBe(2);
               expect(after[0].width)
                 .withContext(`In ${browserName}`)
-                .toBe(582 * pixelRatio);
+                .toBe(Math.floor(58.2 * pixelRatio));
               expect(after[0].height)
                 .withContext(`In ${browserName}`)
-                .toBe(823 * pixelRatio);
+                .toBe(Math.floor(82.3 * pixelRatio));
 
               // The dimensions of the detail canvas are capped to 800x600 but
               // it depends on the visible area which depends itself of the
diff --git a/web/pdf_page_view.js b/web/pdf_page_view.js
index 8a983c0ef..80b47fcf5 100644
--- a/web/pdf_page_view.js
+++ b/web/pdf_page_view.js
@@ -798,6 +798,12 @@ class PDFPageView extends BasePDFPageView {
         this.maxCanvasDim,
         this.capCanvasAreaFactor
       );
+      if (this.#needsRestrictedScaling && this.enableDetailCanvas) {
+        // If we are going to have a high-res detail view, further reduce
+        // the canvas resolution to improve rendering performance.
+        outputScale.sx /= 10;
+        outputScale.sy /= 10;
+      }
     }
   }