Bug 1208023 - Ensure the minimum scale is a sane value greater than zero and add a separate flag to track if the default zoom is valid. r=botond

dom/base/nsViewportInfo.cpp

@@ -17,6 +17,12 @@ nsViewportInfo::ConstrainViewportValues()
   // dev.w3.org/csswg/css-device-adapt section 6.2
   mMaxZoom = std::max(mMinZoom, mMaxZoom);
 
-  mDefaultZoom = mDefaultZoom < mMaxZoom ? mDefaultZoom : mMaxZoom;
+  if (mDefaultZoom > mMaxZoom) {
-  mDefaultZoom = mDefaultZoom > mMinZoom ? mDefaultZoom : mMinZoom;
+    mDefaultZoomValid = false;
+    mDefaultZoom = mMaxZoom;
+  }
+  if (mDefaultZoom < mMinZoom) {
+    mDefaultZoomValid = false;
+    mDefaultZoom = mMinZoom;
+  }
 }

dom/base/nsViewportInfo.h

@@ -12,7 +12,7 @@
 /**
  * Default values for the nsViewportInfo class.
  */
-static const mozilla::LayoutDeviceToScreenScale kViewportMinScale(0.0f);
+static const mozilla::LayoutDeviceToScreenScale kViewportMinScale(0.1f);
 static const mozilla::LayoutDeviceToScreenScale kViewportMaxScale(10.0f);
 static const mozilla::CSSIntSize kViewportMinSize(200, 40);
 static const mozilla::CSSIntSize kViewportMaxSize(10000, 10000);
@@ -27,6 +27,7 @@ class MOZ_STACK_CLASS nsViewportInfo
     nsViewportInfo(const mozilla::ScreenIntSize& aDisplaySize,
                    const mozilla::CSSToScreenScale& aDefaultZoom,
                    bool aAllowZoom) :
+      mDefaultZoomValid(true),
       mDefaultZoom(aDefaultZoom),
       mAutoSize(true),
       mAllowZoom(aAllowZoom)
@@ -44,6 +45,7 @@ class MOZ_STACK_CLASS nsViewportInfo
                    const mozilla::CSSSize& aSize,
                    bool aAutoSize,
                    bool aAllowZoom) :
+                     mDefaultZoomValid(true),
                      mDefaultZoom(aDefaultZoom),
                      mMinZoom(aMinZoom),
                      mMaxZoom(aMaxZoom),
@@ -54,6 +56,7 @@ class MOZ_STACK_CLASS nsViewportInfo
       ConstrainViewportValues();
     }
 
+    bool IsDefaultZoomValid() const { return mDefaultZoomValid; }
     mozilla::CSSToScreenScale GetDefaultZoom() const { return mDefaultZoom; }
     mozilla::CSSToScreenScale GetMinZoom() const { return mMinZoom; }
     mozilla::CSSToScreenScale GetMaxZoom() const { return mMaxZoom; }
@@ -72,6 +75,10 @@ class MOZ_STACK_CLASS nsViewportInfo
      */
     void ConstrainViewportValues();
 
+    // If the default zoom was specified and was between the min and max
+    // zoom values.
+    bool mDefaultZoomValid;
+
     // Default zoom indicates the level at which the display is 'zoomed in'
     // initially for the user, upon loading of the page.
     mozilla::CSSToScreenScale mDefaultZoom;

dom/base/test/test_meta_viewport0.html

@@ -16,12 +16,16 @@
 
     let tests = [];
 
+    function fuzzeq(a, b, msg) {
+      ok(Math.abs(a - b) < 1e-6, msg);
+    }
+
     tests.push(function test1() {
       SpecialPowers.pushPrefEnv(scaleRatio(1.0),
         function() {
           let info = getViewportInfo(800, 480);
-          is(info.defaultZoom, 0,       "initial scale is unspecified");
+          fuzzeq(info.defaultZoom, 0.1, "initial scale is unspecified");
-          is(info.minZoom,     0,       "minumum scale defaults to the absolute minumum");
+          fuzzeq(info.minZoom, 0.1,     "minimum scale defaults to the absolute minimum");
           is(info.maxZoom,     10,      "maximum scale defaults to the absolute maximum");
           is(info.width,       980,     "width is the default width");
           is(info.height,      588,     "height is proportional to displayHeight");

layout/base/MobileViewportManager.cpp

@@ -125,12 +125,17 @@ MobileViewportManager::UpdateResolution(const nsViewportInfo& aViewportInfo,
   if (mIsFirstPaint) {
     CSSToScreenScale defaultZoom = aViewportInfo.GetDefaultZoom();
     MVM_LOG("%p: default zoom from viewport is %f\n", this, defaultZoom.scale);
-    // FIXME/bug 799585(?): GetViewportInfo() returns a default zoom of
+    if (!aViewportInfo.IsDefaultZoomValid()) {
-    // 0.0 to mean "did not calculate a zoom".  In that case, we default
-    // it to the intrinsic scale.
-    if (defaultZoom.scale < 0.01f) {
       defaultZoom = MaxScaleRatio(ScreenSize(aDisplaySize), aViewport);
       MVM_LOG("%p: Intrinsic computed zoom is %f\n", this, defaultZoom.scale);
+      if (defaultZoom < aViewportInfo.GetMinZoom()) {
+        defaultZoom = aViewportInfo.GetMinZoom();
+        MVM_LOG("%p: Clamped to %f\n", this, defaultZoom.scale);
+      }
+      if (defaultZoom > aViewportInfo.GetMaxZoom()) {
+        defaultZoom = aViewportInfo.GetMaxZoom();
+        MVM_LOG("%p: Clamped to %f\n", this, defaultZoom.scale);
+      }
     }
     MOZ_ASSERT(aViewportInfo.GetMinZoom() <= defaultZoom &&
       defaultZoom <= aViewportInfo.GetMaxZoom());