Add new pinch gesture patch

mozilla/pdf.js#2582 (comment)
https://gist.github.com/larsneo/bb75616e9426ae589f50e8c8411020f6

Makefile

@@ -43,7 +43,7 @@ content:
 
 	rm content.build/web/compressed.tracemonkey-pldi-09.pdf
 	patch -p1 --no-backup-if-mismatch -d content.build < patches/pdfjs-origin-fix.patch
-	cat patches/pdfjs-pinch-gestures.js >> content.build/web/viewer.js
+	cat patches/pdfjs-pinch-gestures-larsneo.js >> content.build/web/viewer.js
 	mv content.build content
 
 clean:

patches/pdfjs-pinch-gestures-larsneo.js

@@ -0,0 +1,54 @@
+// Pinch gesture workaround for Firefox for Android
+// https://gist.github.com/larsneo/bb75616e9426ae589f50e8c8411020f6
+// https://github.com/M-Reimer/android-pdf-js
+
+(function AndroidPDFJSPinchGesture() {
+  let pinchZoomEnabled = false;
+  function enablePinchZoom(pdfViewer) {
+    let startX = 0, startY = 0;
+    let initialPinchDistance = 0;
+    let pinchScale = 1;
+    const viewer = document.getElementById("viewer");
+    const container = document.getElementById("viewerContainer");
+    const reset = () => { startX = startY = initialPinchDistance = 0; pinchScale = 1; };
+    // Prevent native iOS page zoom
+    //document.addEventListener("touchmove", (e) => { if (e.scale !== 1) { e.preventDefault(); } }, { passive: false });
+    document.addEventListener("touchstart", (e) => {
+      if (e.touches.length > 1) {
+        startX = (e.touches[0].pageX + e.touches[1].pageX) / 2;
+        startY = (e.touches[0].pageY + e.touches[1].pageY) / 2;
+        initialPinchDistance = Math.hypot((e.touches[1].pageX - e.touches[0].pageX), (e.touches[1].pageY - e.touches[0].pageY));
+      } else {
+        initialPinchDistance = 0;
+      }
+    });
+    document.addEventListener("touchmove", (e) => {
+      if (initialPinchDistance <= 0 || e.touches.length < 2) { return; }
+      if (e.scale !== 1) { e.preventDefault(); }
+      const pinchDistance = Math.hypot((e.touches[1].pageX - e.touches[0].pageX), (e.touches[1].pageY - e.touches[0].pageY));
+      const originX = startX + container.scrollLeft;
+      const originY = startY + container.scrollTop;
+      pinchScale = pinchDistance / initialPinchDistance;
+      viewer.style.transform = `scale(${pinchScale})`;
+      viewer.style.transformOrigin = `${originX}px ${originY}px`;
+    }, { passive: false });
+    document.addEventListener("touchend", (e) => {
+      if (initialPinchDistance <= 0) { return; }
+      viewer.style.transform = `none`;
+      viewer.style.transformOrigin = `unset`;
+      PDFViewerApplication.pdfViewer.currentScale *= pinchScale;
+      const rect = container.getBoundingClientRect();
+      const dx = startX - rect.left;
+      const dy = startY - rect.top;
+      container.scrollLeft += dx * (pinchScale - 1);
+      container.scrollTop += dy * (pinchScale - 1);
+      reset();
+    });
+  }
+  document.addEventListener('webviewerloaded', () => {
+    if (!pinchZoomEnabled) {
+      pinchZoomEnabled = true;
+      enablePinchZoom();
+    }
+  });
+})();