[tor-commits] [tor-browser/tor-browser-60.6.1esr-9.0-1] Bug 1548634 - Update the default letterboxing behavior to use stepped ranges r=johannh

[gk@xxxxxxxxxxxxxx]

commit 166a752ab22ef1415c250eff37e1ada3f2f24915
Author: Tom Ritter <tom@xxxxxxxxxxx>
Date:   Tue May 7 16:06:43 2019 +0000

    Bug 1548634 - Update the default letterboxing behavior to use stepped ranges r=johannh
    
    Differential Revision: https://phabricator.services.mozilla.com/D29759
---
 .../browser/browser_dynamical_window_rounding.js   | 11 ++++------
 .../components/resistfingerprinting/RFPHelper.jsm  | 25 +++++++++++++++++-----
 2 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/browser/components/resistfingerprinting/test/browser/browser_dynamical_window_rounding.js b/browser/components/resistfingerprinting/test/browser/browser_dynamical_window_rounding.js
index ae8055a49ce5..784fb42b8631 100644
--- a/browser/components/resistfingerprinting/test/browser/browser_dynamical_window_rounding.js
+++ b/browser/components/resistfingerprinting/test/browser/browser_dynamical_window_rounding.js
@@ -11,9 +11,7 @@
  */
 
 const TEST_PATH = "http://example.net/browser/browser/components/resistfingerprinting/test/browser/";;
-
-const DEFAULT_ROUNDED_WIDTH_STEP  = 200;
-const DEFAULT_ROUNDED_HEIGHT_STEP = 100;
+const { RFPHelper } = ChromeUtils.import("resource://gre/modules/RFPHelper.jsm");
 
 // A set of test cases which defines the width and the height of the outer window.
 const TEST_CASES = [
@@ -50,10 +48,9 @@ function handleOSFuzziness(aContent, aTarget) {
 
 function checkForDefaultSetting(
   aContentWidth, aContentHeight, aRealWidth, aRealHeight) {
-  // The default behavior for rounding is to round window with 200x100 stepping.
-  // So, we can get the rounded size by subtracting the remainder.
-  let targetWidth = aRealWidth - (aRealWidth % DEFAULT_ROUNDED_WIDTH_STEP);
-  let targetHeight = aRealHeight - (aRealHeight % DEFAULT_ROUNDED_HEIGHT_STEP);
+  // We can get the rounded size by subtracting twice the margin.
+  let targetWidth = aRealWidth - (2 * RFPHelper.steppedRange(aRealWidth));
+  let targetHeight = aRealHeight - (2 * RFPHelper.steppedRange(aRealHeight));
 
   // This platform-specific code is explained in the large comment below.
   if (getPlatform() != "linux") {
diff --git a/toolkit/components/resistfingerprinting/RFPHelper.jsm b/toolkit/components/resistfingerprinting/RFPHelper.jsm
index 2f3a1dd0e659..5f23d0679b53 100755
--- a/toolkit/components/resistfingerprinting/RFPHelper.jsm
+++ b/toolkit/components/resistfingerprinting/RFPHelper.jsm
@@ -21,9 +21,6 @@ const kPrefLetterboxingTesting =
 const kTopicDOMWindowOpened = "domwindowopened";
 const kEventLetterboxingSizeUpdate = "Letterboxing:ContentSizeUpdated";
 
-const kDefaultWidthStepping = 200;
-const kDefaultHeightStepping = 100;
-
 var logConsole;
 function log(msg) {
   if (!logConsole) {
@@ -338,6 +335,24 @@ class _RFPHelper {
   }
 
   /**
+   * Given a width or height, returns the appropriate margin to apply.
+   */
+  steppedRange(aDimension) {
+    let stepping;
+    if (aDimension <= 50) {
+      return 0;
+    } else if (aDimension <= 500) {
+      stepping = 50;
+    } else if (aDimension <= 1600) {
+      stepping = 100;
+    } else {
+      stepping = 200;
+    }
+
+    return (aDimension % stepping) / 2;
+  }
+
+  /**
    * The function will round the given browser by adding margins around the
    * content viewport.
    */
@@ -373,8 +388,8 @@ class _RFPHelper {
       // stepping size.
       if (!this._letterboxingDimensions.length) {
         result = {
-          width: (aWidth % kDefaultWidthStepping) / 2,
-          height: (aHeight % kDefaultHeightStepping) / 2,
+          width: this.steppedRange(aWidth),
+          height: this.steppedRange(aHeight),
         };
         log("_roundContentView[" + logId + "] calcMargins(" + aWidth + ", " + aHeight + ") = " + result.width + " x " + result.height);
         return result;

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