fix(html): probe the text size adjustment in a document of its own

docs/design/lazy-loading.md

@@ -243,12 +243,13 @@ the first chunk of a sheet with shapes is always near: the writer states
 
 **What stays.** The limits (`spreadsheet_limit`, `spreadsheet_cell_limit`)
 stay as they are in this step. A sheet of 500 K cells
-(`efficiency-big-1.ods`) took 7.0 s to its first frame, and takes 4.0 s
-with chunks. About 2 s of the rest is `viewport.js`: to find whether the
-browser adjusts the text size, it sets the zoom of the body twice. Each
-set makes the browser compute the style and the layout of the whole
-document again. Whether the limits can go up is a measurement after that
-is fixed.
+(`efficiency-big-1.ods`) took 7.0 s to its first frame, and takes 2.2 s
+with chunks. The same page without its scripts takes 2.0 s. Before, the
+page with chunks took 4.0 s, and 1.8 s of that was `viewport.js`. To find
+whether the browser adjusts the text size, it set the zoom of the body
+twice, and each set made the browser compute the style and the layout of
+the whole document again. It now probes in an `iframe` of its own. Whether
+the limits can go up is the next measurement.
 
 ## Order of work
 

src/odr/internal/html/frontend/viewport.js

@@ -57,30 +57,42 @@
   // A run against a stated length, so no rect convention enters. True in webkit
   // and in the engines that ignore the property; false where it scales the text
   // a second time.
+  //
+  // In a document of its own: a zoom on the body and an adjustment on the root
+  // are inherited, so in the page they would restyle and lay out all of it,
+  // twice.
   function textAdjustHolds() {
-    var ruler = document.createElement("div");
+    var frame = document.createElement("iframe");
+    frame.style.cssText =
+      "position:absolute;top:0;left:0;width:400px;height:0;border:0;" +
+      "visibility:hidden";
+    body.appendChild(frame);
+    var probe = frame.contentDocument;
+    if (probe === null || probe.body === null) {
+      body.removeChild(frame);
+      return false;
+    }
+    probe.body.style.margin = "0";
+    var ruler = probe.createElement("div");
     ruler.style.cssText =
       "position:absolute;top:0;left:0;width:400px;height:0;overflow:hidden";
-    var run = document.createElement("span");
+    var run = probe.createElement("span");
     run.style.cssText = "font:100px/1 monospace;white-space:pre";
     run.textContent = "MMMMMMMMMM";
     ruler.appendChild(run);
-    body.appendChild(ruler);
+    probe.body.appendChild(ruler);
 
     function ratio() {
       var length = ruler.getBoundingClientRect().width;
       return length ? run.getBoundingClientRect().width / length : 0;
     }
 
-    var zoom = body.style.zoom;
-    body.style.zoom = "1";
     var unzoomed = ratio();
-    body.style.zoom = "0.5";
-    textAdjust("50%");
+    probe.body.style.zoom = "0.5";
+    probe.documentElement.style.setProperty("-webkit-text-size-adjust", "50%");
+    probe.documentElement.style.setProperty("text-size-adjust", "50%");
     var zoomed = ratio();
-    textAdjust("");
-    body.style.zoom = zoom;
-    body.removeChild(ruler);
+    body.removeChild(frame);
 
     return unzoomed > 0 && Math.abs(zoomed - unzoomed) < unzoomed / 50;
   }

test/data.cmake

@@ -17,9 +17,9 @@ odr_test_data(
 odr_test_data(
         PATH "reference-output/odr-public"
         URL "https://github.com/opendocument-app/OpenDocument.test.output.git"
-        REVISION "1ff01470c6b43a1962d6f934a9d6a46600e3b72e")
+        REVISION "1ae5868d991da48d23b44be6d4e99264258dfd95")
 
 odr_test_data(
         PATH "reference-output/odr-private"
         URL "https://github.com/opendocument-app/OpenDocument.test-private.output.git"
-        REVISION "07c9ef2bb3b2397249ef0ff0dec15baa9fc5d887")
+        REVISION "32f5ee77f480a8e21a4dfce80fc9a267a1034493")