From 1450446d110c90a2e80434feff49314b14afdc78 Mon Sep 17 00:00:00 2001
From: Brad Werth <bwerth@mozilla.com>
Date: Wed, 27 Sep 2017 14:06:37 -0700
Subject: [PATCH] Bug 1376931 Part 2: Extend ContentViewer to allow reporting
 of effective full zoom level as determined by the device context. r=bz,heycam

MozReview-Commit-ID: EoVp1DwAl0j

--HG--
extra : rebase_source : b0bdf52adb0e44b51c4bbeb33668c35f559b8464
---
 docshell/base/nsIContentViewer.idl            | 12 ++++++++++++
 layout/base/nsDocumentViewer.cpp              | 19 +++++++++++++++++++
 layout/base/nsPresContext.cpp                 |  6 ++++++
 layout/base/nsPresContext.h                   |  6 ++++++
 .../specialpowers/content/specialpowersAPI.js |  3 +++
 toolkit/content/widgets/browser.xml           |  7 +++++++
 6 files changed, 53 insertions(+)

diff --git a/docshell/base/nsIContentViewer.idl b/docshell/base/nsIContentViewer.idl
index 75f457d2d9c7..8cfe7955533e 100644
--- a/docshell/base/nsIContentViewer.idl
+++ b/docshell/base/nsIContentViewer.idl
@@ -212,6 +212,18 @@ interface nsIContentViewer : nsISupports
   /** The amount by which to scale all lengths. Default is 1.0. */
   attribute float fullZoom;
 
+  /**
+   * The actual full zoom in effect, as modified by the device context.
+   * For a requested full zoom, the device context may choose a slightly
+   * different effectiveFullZoom to accomodate integer rounding of app units
+   * per dev pixel. This property returns the actual zoom amount in use,
+   * though it may not be good user experience to report that a requested zoom
+   * of 90% is actually 89.1%, for example. This value is provided primarily to
+   * support media queries of dppx values, because those queries are matched
+   * against the actual native device pixel ratio and the actual full zoom.
+   */
+  readonly attribute float deviceFullZoom;
+
   /**
    * The value used to override devicePixelRatio and media queries dppx.
    * Default is 0.0, that means no overriding is done (only a positive value
diff --git a/layout/base/nsDocumentViewer.cpp b/layout/base/nsDocumentViewer.cpp
index 1d4242d12996..856e6957292b 100644
--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -3226,6 +3226,25 @@ nsDocumentViewer::GetFullZoom(float* aFullZoom)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDocumentViewer::GetDeviceFullZoom(float* aDeviceFullZoom)
+{
+  NS_ENSURE_ARG_POINTER(aDeviceFullZoom);
+#ifdef NS_PRINT_PREVIEW
+  if (GetIsPrintPreview()) {
+    // Print Preview overrides all zoom; if specified, we use the print preview
+    // zoom, no matter what.
+    *aDeviceFullZoom = mPrintPreviewZoom;
+    return NS_OK;
+  }
+#endif
+  // If not in print preview, ask the prescontext for the device zoom, if a
+  // prescontext is available.
+  nsPresContext* pc = GetPresContext();
+  *aDeviceFullZoom = pc ? pc->GetDeviceFullZoom() : mPageZoom;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsDocumentViewer::SetOverrideDPPX(float aDPPX)
 {
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 71d5b1e30eb9..c0b59693abf5 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1364,6 +1364,12 @@ nsPresContext::UpdateEffectiveTextZoom()
   }
 }
 
+float
+nsPresContext::GetDeviceFullZoom()
+{
+  return mDeviceContext->GetFullZoom();
+}
+
 void
 nsPresContext::SetFullZoom(float aZoom)
 {
diff --git a/layout/base/nsPresContext.h b/layout/base/nsPresContext.h
index 32fc9ac1eed4..d654b259a936 100644
--- a/layout/base/nsPresContext.h
+++ b/layout/base/nsPresContext.h
@@ -604,6 +604,12 @@ public:
   }
 
   float GetFullZoom() { return mFullZoom; }
+  /**
+   * Device full zoom differs from full zoom because it gets the zoom from
+   * the device context, which may be using a different zoom due to rounding
+   * of app units to device pixels.
+   */
+  float GetDeviceFullZoom();
   void SetFullZoom(float aZoom);
 
   float GetOverrideDPPX() { return mOverrideDPPX; }
diff --git a/testing/specialpowers/content/specialpowersAPI.js b/testing/specialpowers/content/specialpowersAPI.js
index a528bd6a8183..df009255c765 100644
--- a/testing/specialpowers/content/specialpowersAPI.js
+++ b/testing/specialpowers/content/specialpowersAPI.js
@@ -1422,6 +1422,9 @@ SpecialPowersAPI.prototype = {
   getFullZoom(window) {
     return this._getMUDV(window).fullZoom;
   },
+  getDeviceFullZoom(window) {
+    return this._getMUDV(window).deviceFullZoom;
+  },
   setFullZoom(window, zoom) {
     this._getMUDV(window).fullZoom = zoom;
   },
diff --git a/toolkit/content/widgets/browser.xml b/toolkit/content/widgets/browser.xml
index 8ac9d3adacc0..74c3b2ca6092 100644
--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@@ -554,6 +554,13 @@
         ]]></setter>
       </property>
 
+      <property name="deviceFullZoom"
+                readonly="true">
+        <getter><![CDATA[
+          return this.markupDocumentViewer.deviceFullZoom;
+        ]]></getter>
+      </property>
+
       <property name="textZoom">
         <getter><![CDATA[
           return this.markupDocumentViewer.textZoom;