Bug 1101628 - Refactor snapshotting code to allow reusing it across tests. r=botond

MozReview-Commit-ID: BRSUNn5gxSX

gfx/layers/apz/test/mochitest/apz_test_native_event_utils.js

@@ -90,6 +90,20 @@ function coordinatesRelativeToScreen(aX, aY, aElement) {
   };
 }
 
+// Get the bounding box of aElement, and return it in device pixels
+// relative to the screen.
+function rectRelativeToScreen(aElement) {
+  var targetWindow = aElement.ownerDocument.defaultView;
+  var scale = targetWindow.devicePixelRatio;
+  var rect = aElement.getBoundingClientRect();
+  return {
+    x: (targetWindow.mozInnerScreenX + rect.left) * scale,
+    y: (targetWindow.mozInnerScreenY + rect.top) * scale,
+    w: (rect.width * scale),
+    h: (rect.height * scale)
+  };
+}
+
 // Synthesizes a native mousewheel event and returns immediately. This does not
 // guarantee anything; you probably want to use one of the other functions below
 // which actually wait for results.

gfx/layers/apz/test/mochitest/apz_test_utils.js

@@ -267,3 +267,48 @@ function runContinuation(testFunction) {
     });
   };
 }
+
+// Take a snapshot of the given rect, *including compositor transforms* (i.e.
+// includes async scroll transforms applied by APZ). If you don't need the
+// compositor transforms, you can probably get away with using
+// SpecialPowers.snapshotWindowWithOptions or one of the friendlier wrappers.
+// The rect provided is expected to be relative to the screen, for example as
+// returned by rectRelativeToScreen in apz_test_native_event_utils.js.
+// Example usage:
+//   var snapshot = getSnapshot(rectRelativeToScreen(myDiv));
+// which will take a snapshot of the 'myDiv' element. Note that if part of the
+// element is obscured by other things on top, the snapshot will include those
+// things. If it is clipped by a scroll container, the snapshot will include
+// that area anyway, so you will probably get parts of the scroll container in
+// the snapshot. If the rect extends outside the browser window then the
+// results are undefined.
+// The snapshot is returned in the form of a data URL.
+function getSnapshot(rect) {
+  function parentProcessSnapshot() {
+    addMessageListener('snapshot', function(rect) {
+      Components.utils.import('resource://gre/modules/Services.jsm');
+      var topWin = Services.wm.getMostRecentWindow('navigator:browser');
+
+      // reposition the rect relative to the top-level browser window
+      rect = JSON.parse(rect);
+      rect.x -= topWin.mozInnerScreenX;
+      rect.y -= topWin.mozInnerScreenY;
+
+      // take the snapshot
+      var canvas = topWin.document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
+      canvas.width = rect.w;
+      canvas.height = rect.h;
+      var ctx = canvas.getContext("2d");
+      ctx.drawWindow(topWin, rect.x, rect.y, rect.w, rect.h, 'rgb(255,255,255)', ctx.DRAWWINDOW_DRAW_VIEW | ctx.DRAWWINDOW_USE_WIDGET_LAYERS | ctx.DRAWWINDOW_DRAW_CARET);
+      return canvas.toDataURL();
+    });
+  }
+
+  if (typeof getSnapshot.chromeHelper == 'undefined') {
+    // This is the first time getSnapshot is being called; do initialization
+    getSnapshot.chromeHelper = SpecialPowers.loadChromeScript(parentProcessSnapshot);
+    SimpleTest.registerCleanupFunction(function() { getSnapshot.chromeHelper.destroy() });
+  }
+
+  return getSnapshot.chromeHelper.sendSyncMessage('snapshot', JSON.stringify(rect)).toString();
+}

gfx/layers/apz/test/mochitest/test_touch_listeners_impacting_wheel.html

@@ -27,26 +27,6 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=1203140
 
 const kResponseTimeoutMs = 2 * 60 * 1000; // 2 minutes
 
-function parentProcessSnapshot() {
-  addMessageListener('snapshot', function(rect) {
-    Components.utils.import('resource://gre/modules/Services.jsm');
-    var topWin = Services.wm.getMostRecentWindow('navigator:browser');
-
-    // reposition the rect relative to the top-level browser window
-    rect = JSON.parse(rect);
-    rect.x -= topWin.mozInnerScreenX;
-    rect.y -= topWin.mozInnerScreenY;
-
-    // take the snapshot
-    var canvas = topWin.document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
-    canvas.width = rect.w;
-    canvas.height = rect.h;
-    var ctx = canvas.getContext("2d");
-    ctx.drawWindow(topWin, rect.x, rect.y, rect.w, rect.h, 'rgb(255,255,255)', ctx.DRAWWINDOW_DRAW_VIEW | ctx.DRAWWINDOW_USE_WIDGET_LAYERS | ctx.DRAWWINDOW_DRAW_CARET);
-    return canvas.toDataURL();
-  });
-}
-
 function takeSnapshots(e) {
   // Grab some snapshots, and make sure some of them are different (i.e. check
   // the page is scrolling in the compositor, concurrently with this wheel
@@ -58,18 +38,12 @@ function takeSnapshots(e) {
   var lastSnapshot = null;
   var success = false;
 
-  var chromeHelper = SpecialPowers.loadChromeScript(parentProcessSnapshot);
-  SimpleTest.registerCleanupFunction(function() { chromeHelper.destroy() });
-
   // Get the position of the 'content' div relative to the screen
-  var contentDiv = document.getElementById('content');
-  var rect = coordinatesRelativeToWindow(0, 0, contentDiv);
-  rect.w = contentDiv.getBoundingClientRect().width * window.devicePixelRatio;
-  rect.h = contentDiv.getBoundingClientRect().height * window.devicePixelRatio;
+  var rect = rectRelativeToScreen(document.getElementById('content'));
 
   for (var i = 0; i < 10; i++) {
     SpecialPowers.DOMWindowUtils.advanceTimeAndRefresh(16);
-    var snapshot = chromeHelper.sendSyncMessage('snapshot', JSON.stringify(rect)).toString();
+    var snapshot = getSnapshot(rect);
     //dump("Took snapshot " + snapshot + "\n"); // this might help with debugging
 
     if (lastSnapshot && lastSnapshot != snapshot) {