Issue #1619 - Convert Intrinsic Ratio to Float

https://bugzilla.mozilla.org/show_bug.cgi?id=1547792

Aspect Ratio handling simplified by using floating point integers:
- Multiplication of value (or inverse value) to a known side for Scaling
- No unequal equal values such as "4/3" vs "8/6" vs "20/15"
- Truly "Empty" aspect ratios, even if one dimension is not 0

15 files changed, 182 insertions, 103 deletions

diff --git a/layout/generic/AspectRatio.h b/layout/generic/AspectRatio.h
new file mode 100644
index 000000000..0056c0620
--- /dev/null
+++ b/layout/generic/AspectRatio.h
@@ -0,0 +1,81 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_AspectRatio_h
+#define mozilla_AspectRatio_h
+
+/* The aspect ratio of a box, in a "width / height" format. */
+
+#include "mozilla/Attributes.h"
+#include "nsCoord.h"
+#include <algorithm>
+#include <limits>
+
+namespace mozilla {
+
+struct AspectRatio {
+  AspectRatio() : mRatio(0.0f) {}
+  explicit AspectRatio(float aRatio) : mRatio(std::max(aRatio, 0.0f)) {}
+
+  static AspectRatio FromSize(float aWidth, float aHeight) {
+    if (aWidth == 0.0f || aHeight == 0.0f) {
+      return AspectRatio();
+    }
+    return AspectRatio(aWidth / aHeight);
+  }
+
+  static AspectRatio FromSize(nsSize aSize) {
+    return FromSize(aSize.width, aSize.height);
+  }
+
+  static AspectRatio FromSize(nsIntSize aSize) {
+    return FromSize(aSize.width, aSize.height);
+  }
+
+  explicit operator bool() const { return mRatio != 0.0f; }
+
+  nscoord ApplyTo(nscoord aCoord) const {
+    MOZ_DIAGNOSTIC_ASSERT(*this);
+    return NSCoordSaturatingNonnegativeMultiply(aCoord, mRatio);
+  }
+
+  float ApplyToFloat(float aFloat) const {
+    MOZ_DIAGNOSTIC_ASSERT(*this);
+    return mRatio * aFloat;
+  }
+
+  // Inverts the ratio, in order to get the height / width ratio.
+  MOZ_MUST_USE AspectRatio Inverted() const {
+    if (!*this) {
+      return AspectRatio();
+    }
+    // Clamp to a small epsilon, in case mRatio is absurdly large & produces
+    // 0.0f in the division here (so that valid ratios always generate other
+    // valid ratios when inverted).
+    return AspectRatio(
+        std::max(std::numeric_limits<float>::epsilon(), 1.0f / mRatio));
+  }
+
+  bool operator==(const AspectRatio& aOther) const {
+    return mRatio == aOther.mRatio;
+  }
+
+  bool operator!=(const AspectRatio& aOther) const {
+    return !(*this == aOther);
+  }
+
+  bool operator<(const AspectRatio& aOther) const {
+    return mRatio < aOther.mRatio;
+  }
+
+ private:
+  // 0.0f represents no aspect ratio.
+  float mRatio;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_AspectRatio_h
diff --git a/layout/generic/moz.build b/layout/generic/moz.build
index ad186ef7a..b830470a3 100644
--- a/layout/generic/moz.build
+++ b/layout/generic/moz.build
@@ -109,6 +109,7 @@ EXPORTS += [
 ]
 
 EXPORTS.mozilla += [
+    'AspectRatio.h',
     'CSSAlignUtils.h',
     'ReflowInput.h',
     'ReflowOutput.h',
diff --git a/layout/generic/nsFlexContainerFrame.cpp b/layout/generic/nsFlexContainerFrame.cpp
index 69200117b..a76097e1e 100644
--- a/layout/generic/nsFlexContainerFrame.cpp
+++ b/layout/generic/nsFlexContainerFrame.cpp
@@ -557,8 +557,8 @@ public:
     return mFlexShrink * mFlexBaseSize;
   }
 
-  const nsSize& IntrinsicRatio() const { return mIntrinsicRatio; }
-  bool HasIntrinsicRatio() const { return mIntrinsicRatio != nsSize(); }
+  const AspectRatio IntrinsicRatio() const { return mIntrinsicRatio; }
+  bool HasIntrinsicRatio() const { return !!mIntrinsicRatio; }
 
   // Getters for margin:
   // ===================
@@ -756,7 +756,7 @@ protected:
   const float mFlexGrow;
   const float mFlexShrink;
 
-  const nsSize mIntrinsicRatio;
+  const AspectRatio mIntrinsicRatio;
 
   const nsMargin mBorderPadding;
   nsMargin mMargin; // non-const because we need to resolve auto margins
@@ -1520,22 +1520,20 @@ CrossSizeToUseWithRatio(const FlexItem& aFlexItem,
 }
 
 // Convenience function; returns a main-size, given a cross-size and an
-// intrinsic ratio. The intrinsic ratio must not have 0 in its cross-axis
-// component (or else we'll divide by 0).
+// intrinsic ratio. The caller is responsible for ensuring that the passed-in
+// intrinsic ratio is not zero.
 static nscoord
 MainSizeFromAspectRatio(nscoord aCrossSize,
-                        const nsSize& aIntrinsicRatio,
+                        const AspectRatio& aIntrinsicRatio,
                         const FlexboxAxisTracker& aAxisTracker)
 {
-  MOZ_ASSERT(aAxisTracker.GetCrossComponent(aIntrinsicRatio) != 0,
+  MOZ_ASSERT(aIntrinsicRatio,
              "Invalid ratio; will divide by 0! Caller should've checked...");
+  AspectRatio ratio = aAxisTracker.IsMainAxisHorizontal()
+                          ? aIntrinsicRatio
+                          : aIntrinsicRatio.Inverted();
 
-  if (aAxisTracker.IsCrossAxisHorizontal()) {
-    // cross axis horiz --> aCrossSize is a width. Converting to height.
-    return NSCoordMulDiv(aCrossSize, aIntrinsicRatio.height, aIntrinsicRatio.width);
-  }
-  // cross axis vert --> aCrossSize is a height. Converting to width.
-  return NSCoordMulDiv(aCrossSize, aIntrinsicRatio.width, aIntrinsicRatio.height);
+  return ratio.ApplyTo(aCrossSize);
 }
 
 // Partially resolves "min-[width|height]:auto" and returns the resulting value.
@@ -1584,7 +1582,7 @@ PartiallyResolveAutoMinSize(const FlexItem& aFlexItem,
   // * if the item has an intrinsic aspect ratio, the width (height) calculated
   //   from the aspect ratio and any definite size constraints in the opposite
   //   dimension.
-  if (aAxisTracker.GetCrossComponent(aFlexItem.IntrinsicRatio()) != 0) {
+  if (aFlexItem.IntrinsicRatio()) {
     // We have a usable aspect ratio. (not going to divide by 0)
     const bool useMinSizeIfCrossSizeIsIndefinite = true;
     nscoord crossSizeToUseWithRatio =
@@ -1617,7 +1615,7 @@ ResolveAutoFlexBasisFromRatio(FlexItem& aFlexItem,
   //  - a definite cross size
   // then the flex base size is calculated from its inner cross size and the
   // flex item’s intrinsic aspect ratio.
-  if (aAxisTracker.GetCrossComponent(aFlexItem.IntrinsicRatio()) != 0) {
+  if (aFlexItem.IntrinsicRatio()) {
     // We have a usable aspect ratio. (not going to divide by 0)
     const bool useMinSizeIfCrossSizeIsIndefinite = false;
     nscoord crossSizeToUseWithRatio =
@@ -1693,8 +1691,7 @@ nsFlexContainerFrame::
     // (We'll consider that later, if we need to.)
     resolvedMinSize = PartiallyResolveAutoMinSize(aFlexItem, aItemReflowInput,
                                                   aAxisTracker);
-    if (resolvedMinSize > 0 &&
-        aAxisTracker.GetCrossComponent(aFlexItem.IntrinsicRatio()) == 0) {
+    if (resolvedMinSize > 0 && !aFlexItem.IntrinsicRatio()) {
       // We don't have a usable aspect ratio, so we need to consider our
       // min-content size as another candidate min-size, which we'll have to
       // min() with the current resolvedMinSize.
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 07cdbd7e3..49eea547e 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -4643,10 +4643,10 @@ nsFrame::GetIntrinsicSize()
   return IntrinsicSize(); // default is width/height set to eStyleUnit_None
 }
 
-/* virtual */ nsSize
+/* virtual */ AspectRatio
 nsFrame::GetIntrinsicRatio()
 {
-  return nsSize(0, 0);
+  return AspectRatio();
 }
 
 /* virtual */
@@ -4660,7 +4660,7 @@ nsFrame::ComputeSize(nsRenderingContext* aRenderingContext,
                      const LogicalSize&  aPadding,
                      ComputeSizeFlags    aFlags)
 {
-  MOZ_ASSERT(GetIntrinsicRatio() == nsSize(0,0),
+  MOZ_ASSERT(!GetIntrinsicRatio(),
              "Please override this method and call "
              "nsFrame::ComputeSizeWithIntrinsicDimensions instead.");
   LogicalSize result = ComputeAutoSize(aRenderingContext, aWM,
@@ -4916,13 +4916,15 @@ LogicalSize
 nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingContext,
                                             WritingMode          aWM,
                                             const IntrinsicSize& aIntrinsicSize,
-                                            nsSize               aIntrinsicRatio,
+                                            const AspectRatio&   aIntrinsicRatio,
                                             const LogicalSize&   aCBSize,
                                             const LogicalSize&   aMargin,
                                             const LogicalSize&   aBorder,
                                             const LogicalSize&   aPadding,
                                             ComputeSizeFlags     aFlags)
 {
+  auto logicalRatio =
+      aWM.IsVertical() ? aIntrinsicRatio.Inverted() : aIntrinsicRatio;
   const nsStylePosition* stylePos = StylePosition();
   const nsStyleCoord* inlineStyleCoord = &stylePos->ISize(aWM);
   const nsStyleCoord* blockStyleCoord = &stylePos->BSize(aWM);
@@ -5183,10 +5185,6 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
     intrinsicBSize = 0;
   }
 
-  NS_ASSERTION(aIntrinsicRatio.width >= 0 && aIntrinsicRatio.height >= 0,
-               "Intrinsic ratio has a negative component!");
-  LogicalSize logicalRatio(aWM, aIntrinsicRatio);
-
   // Now calculate the used values for iSize and bSize:
 
   if (isAutoISize) {
@@ -5200,9 +5198,29 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
 
       if (hasIntrinsicISize) {
         tentISize = intrinsicISize;
-      } else if (hasIntrinsicBSize && logicalRatio.BSize(aWM) > 0) {
-        tentISize = NSCoordMulDiv(intrinsicBSize, logicalRatio.ISize(aWM), logicalRatio.BSize(aWM));
-      } else if (logicalRatio.ISize(aWM) > 0) {
+      } else if (hasIntrinsicBSize && logicalRatio) {
+        // (dholbert) <https://phabricator.services.mozilla.com
+        //             /D29244#change-5faEkbsohV7O>
+        // This is wrong -- this ApplyTo call (and probably every ApplyTo call
+        // in this function) would only be valid if we're in a horizontal
+        // writing mode. It's not valid in a vertical writing mode. If this
+        // doesn't break tests, that's a bit concerning, and I think it means
+        // we're missing some test coverage. (That, or I'm misreading things.)
+        //
+        // aIntrinsicRatio is stored in terms of physical axes (width/height),
+        // either of which could be I vs. B axis. So any sort of
+        // aIntrinsicRatio.ApplyTo(someBSize) operation will be
+        // potentially-bogus.
+        //
+        // You probably want to bring back a logicalRatio variable
+        // (like the one we used to have here), but now with type AspectRatio.
+        // It would be equal to either aIntrinsicRatio or
+        // aIntrinsicRatio.Invert() depending on whether aWM is horizontal or
+        // vertical. (And hopefully having logical in its name would be a
+        // reminder that it's in terms of Inline/Block and can be used for
+        // these sorts of ApplyTo(intrinsicBSize) operations.
+        tentISize = logicalRatio.ApplyTo(intrinsicBSize);
+      } else if (logicalRatio) {
         tentISize = aCBSize.ISize(aWM) - boxSizingToMarginEdgeISize; // XXX scrollbar?
         if (tentISize < 0) tentISize = 0;
       } else {
@@ -5219,8 +5237,8 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
 
       if (hasIntrinsicBSize) {
         tentBSize = intrinsicBSize;
-      } else if (logicalRatio.ISize(aWM) > 0) {
-        tentBSize = NSCoordMulDiv(tentISize, logicalRatio.BSize(aWM), logicalRatio.ISize(aWM));
+      } else if (logicalRatio) {
+        tentBSize = logicalRatio.Inverted().ApplyTo(tentISize);
       } else {
         tentBSize = nsPresContext::CSSPixelsToAppUnits(150);
       }
@@ -5231,46 +5249,39 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
         stretchB = (stretchI == eStretch ? eStretch : eStretchPreservingRatio);
       }
 
-      if (aIntrinsicRatio != nsSize(0, 0)) {
+      if (logicalRatio) {
         if (stretchI == eStretch) {
           tentISize = iSize;  // * / 'stretch'
           if (stretchB == eStretch) {
             tentBSize = bSize;  // 'stretch' / 'stretch'
-          } else if (stretchB == eStretchPreservingRatio && logicalRatio.ISize(aWM) > 0) {
+          } else if (stretchB == eStretchPreservingRatio) {
             // 'normal' / 'stretch'
-            tentBSize = NSCoordMulDiv(iSize, logicalRatio.BSize(aWM), logicalRatio.ISize(aWM));
+            tentBSize = logicalRatio.Inverted().ApplyTo(iSize);
           }
         } else if (stretchB == eStretch) {
           tentBSize = bSize;  // 'stretch' / * (except 'stretch')
-          if (stretchI == eStretchPreservingRatio && logicalRatio.BSize(aWM) > 0) {
+          if (stretchI == eStretchPreservingRatio) {
             // 'stretch' / 'normal'
-            tentISize = NSCoordMulDiv(bSize, logicalRatio.ISize(aWM), logicalRatio.BSize(aWM));
+            tentISize = logicalRatio.ApplyTo(bSize);
           }
         } else if (stretchI == eStretchPreservingRatio) {
           tentISize = iSize;  // * (except 'stretch') / 'normal'
-          if (logicalRatio.ISize(aWM) > 0) {
-            tentBSize = NSCoordMulDiv(iSize, logicalRatio.BSize(aWM), logicalRatio.ISize(aWM));
-          }
+          tentBSize = logicalRatio.Inverted().ApplyTo(iSize);
           if (stretchB == eStretchPreservingRatio && tentBSize > bSize) {
             // Stretch within the CB size with preserved intrinsic ratio.
             tentBSize = bSize;  // 'normal' / 'normal'
-            if (logicalRatio.BSize(aWM) > 0) {
-              tentISize = NSCoordMulDiv(bSize, logicalRatio.ISize(aWM), logicalRatio.BSize(aWM));
-            }
+            tentISize = logicalRatio.ApplyTo(bSize);
           }
         } else if (stretchB == eStretchPreservingRatio) {
           tentBSize = bSize;  // 'normal' / * (except 'normal' and 'stretch')
-          if (logicalRatio.BSize(aWM) > 0) {
-            tentISize = NSCoordMulDiv(bSize, logicalRatio.ISize(aWM), logicalRatio.BSize(aWM));
-          }
+          tentISize = logicalRatio.ApplyTo(bSize);
         }
       }
 
       // ComputeAutoSizeWithIntrinsicDimensions preserves the ratio when applying
       // the min/max-size.  We don't want that when we have 'stretch' in either
       // axis because tentISize/tentBSize is likely not according to ratio now.
-      if (aIntrinsicRatio != nsSize(0, 0) &&
-          stretchI != eStretch && stretchB != eStretch) {
+      if (logicalRatio && stretchI != eStretch && stretchB != eStretch) {
         nsSize autoSize = nsLayoutUtils::
           ComputeAutoSizeWithIntrinsicDimensions(minISize, minBSize,
                                                  maxISize, maxBSize,
@@ -5291,8 +5302,8 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
       // 'auto' iSize, non-'auto' bSize
       bSize = NS_CSS_MINMAX(bSize, minBSize, maxBSize);
       if (stretchI != eStretch) {
-        if (logicalRatio.BSize(aWM) > 0) {
-          iSize = NSCoordMulDiv(bSize, logicalRatio.ISize(aWM), logicalRatio.BSize(aWM));
+        if (logicalRatio) {
+          iSize = logicalRatio.ApplyTo(bSize);
         } else if (hasIntrinsicISize) {
           if (!((aFlags & ComputeSizeFlags::eIClampMarginBoxMinSize) &&
                 intrinsicISize > iSize)) {
@@ -5311,8 +5322,8 @@ nsFrame::ComputeSizeWithIntrinsicDimensions(nsRenderingContext*  aRenderingConte
       // non-'auto' iSize, 'auto' bSize
       iSize = NS_CSS_MINMAX(iSize, minISize, maxISize);
       if (stretchB != eStretch) {
-        if (logicalRatio.ISize(aWM) > 0) {
-          bSize = NSCoordMulDiv(iSize, logicalRatio.BSize(aWM), logicalRatio.ISize(aWM));
+        if (logicalRatio) {
+          bSize = logicalRatio.Inverted().ApplyTo(iSize);
         } else if (hasIntrinsicBSize) {
           if (!((aFlags & ComputeSizeFlags::eBClampMarginBoxMinSize) &&
                 intrinsicBSize > bSize)) {
diff --git a/layout/generic/nsFrame.h b/layout/generic/nsFrame.h
index 439e39856..d75555fec 100644
--- a/layout/generic/nsFrame.h
+++ b/layout/generic/nsFrame.h
@@ -264,7 +264,7 @@ public:
   IntrinsicISizeOffsetData
   IntrinsicISizeOffsets(nscoord aPercentageBasis = NS_UNCONSTRAINEDSIZE) override;
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
-  virtual nsSize GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
 
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext*         aRenderingContext,
@@ -285,7 +285,7 @@ public:
               nsRenderingContext*           aRenderingContext,
               mozilla::WritingMode          aWM,
               const mozilla::IntrinsicSize& aIntrinsicSize,
-              nsSize                        aIntrinsicRatio,
+              const mozilla::AspectRatio&   aIntrinsicRatio,
               const mozilla::LogicalSize&   aCBSize,
               const mozilla::LogicalSize&   aMargin,
               const mozilla::LogicalSize&   aBorder,
diff --git a/layout/generic/nsHTMLCanvasFrame.cpp b/layout/generic/nsHTMLCanvasFrame.cpp
index f86ec1136..032b95e5b 100644
--- a/layout/generic/nsHTMLCanvasFrame.cpp
+++ b/layout/generic/nsHTMLCanvasFrame.cpp
@@ -44,21 +44,6 @@ IntrinsicSizeFromCanvasSize(const nsIntSize& aCanvasSizeInPx)
   return intrinsicSize;
 }
 
-/* Helper for our nsIFrame::GetIntrinsicRatio() impl. Takes the result of
- * "GetCanvasSize()" as a parameter, which may help avoid redundant
- * indirect calls to GetCanvasSize().
- *
- * @param aCanvasSizeInPx The canvas's size in CSS pixels, as returned
- *                        by GetCanvasSize().
- * @return The canvas's intrinsic ratio, as a nsSize.
- */
-static nsSize
-IntrinsicRatioFromCanvasSize(const nsIntSize& aCanvasSizeInPx)
-{
-  return nsSize(nsPresContext::CSSPixelsToAppUnits(aCanvasSizeInPx.width),
-                nsPresContext::CSSPixelsToAppUnits(aCanvasSizeInPx.height));
-}
-
 class nsDisplayCanvas : public nsDisplayItem {
 public:
   nsDisplayCanvas(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
@@ -92,7 +77,7 @@ public:
       // Need intrinsic size & ratio, for ComputeObjectDestRect:
       nsIntSize canvasSize = f->GetCanvasSize();
       IntrinsicSize intrinsicSize = IntrinsicSizeFromCanvasSize(canvasSize);
-      nsSize intrinsicRatio = IntrinsicRatioFromCanvasSize(canvasSize);
+      AspectRatio intrinsicRatio = AspectRatio::FromSize(canvasSize);
 
       const nsRect destRect =
         nsLayoutUtils::ComputeObjectDestRect(constraintRect,
@@ -211,10 +196,15 @@ nsHTMLCanvasFrame::GetIntrinsicSize()
   return IntrinsicSizeFromCanvasSize(GetCanvasSize());
 }
 
-/* virtual */ nsSize
+/* virtual */ AspectRatio
 nsHTMLCanvasFrame::GetIntrinsicRatio()
 {
-  return IntrinsicRatioFromCanvasSize(GetCanvasSize());
+/*
+  if (StyleDisplay()->IsContainSize()) {
+    return AspectRatio();
+  }
+ */
+  return AspectRatio::FromSize(GetCanvasSize());
 }
 
 /* virtual */
@@ -234,7 +224,7 @@ nsHTMLCanvasFrame::ComputeSize(nsRenderingContext *aRenderingContext,
   intrinsicSize.width.SetCoordValue(nsPresContext::CSSPixelsToAppUnits(size.width));
   intrinsicSize.height.SetCoordValue(nsPresContext::CSSPixelsToAppUnits(size.height));
 
-  nsSize intrinsicRatio = GetIntrinsicRatio(); // won't actually be used
+  AspectRatio intrinsicRatio = GetIntrinsicRatio();
 
   return ComputeSizeWithIntrinsicDimensions(aRenderingContext, aWM,
                                             intrinsicSize, intrinsicRatio,
@@ -340,7 +330,7 @@ nsHTMLCanvasFrame::BuildLayer(nsDisplayListBuilder* aBuilder,
     return nullptr;
 
   IntrinsicSize intrinsicSize = IntrinsicSizeFromCanvasSize(canvasSizeInPx);
-  nsSize intrinsicRatio = IntrinsicRatioFromCanvasSize(canvasSizeInPx);
+  AspectRatio intrinsicRatio = AspectRatio::FromSize(canvasSizeInPx);
 
   nsRect dest =
     nsLayoutUtils::ComputeObjectDestRect(area, intrinsicSize, intrinsicRatio,
diff --git a/layout/generic/nsHTMLCanvasFrame.h b/layout/generic/nsHTMLCanvasFrame.h
index b2d159627..8432ad224 100644
--- a/layout/generic/nsHTMLCanvasFrame.h
+++ b/layout/generic/nsHTMLCanvasFrame.h
@@ -58,7 +58,7 @@ public:
   virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
-  virtual nsSize GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
 
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext *aRenderingContext,
diff --git a/layout/generic/nsIFrame.h b/layout/generic/nsIFrame.h
index 82bcf563a..b3606d0b4 100644
--- a/layout/generic/nsIFrame.h
+++ b/layout/generic/nsIFrame.h
@@ -27,6 +27,7 @@
 #include "FrameProperties.h"
 #include "LayoutConstants.h"
 #include "mozilla/layout/FrameChildList.h"
+#include "mozilla/AspectRatio.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/WritingModes.h"
 #include "nsDirection.h"
@@ -2047,15 +2048,14 @@ public:
   virtual mozilla::IntrinsicSize GetIntrinsicSize() = 0;
 
   /**
-   * Get the intrinsic ratio of this element, or nsSize(0,0) if it has
-   * no intrinsic ratio.  The intrinsic ratio is the ratio of the
-   * height/width of a box with an intrinsic size or the intrinsic
-   * aspect ratio of a scalable vector image without an intrinsic size.
+   * Get the intrinsic ratio of this element, or a default-constructed
+   * AspectRatio if it has no intrinsic ratio.
    *
-   * Either one of the sides may be zero, indicating a zero or infinite
-   * ratio.
+   * The intrinsic ratio is the ratio of the width/height of a box with an
+   * intrinsic size or the intrinsic aspect ratio of a scalable vector image
+   * without an intrinsic size.
    */
-  virtual nsSize GetIntrinsicRatio() = 0;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() = 0;
 
   /**
    * Bit-flags to pass to ComputeSize in |aFlags| parameter.
diff --git a/layout/generic/nsImageFrame.cpp b/layout/generic/nsImageFrame.cpp
index 03fcbd8e3..68076ce1e 100644
--- a/layout/generic/nsImageFrame.cpp
+++ b/layout/generic/nsImageFrame.cpp
@@ -138,7 +138,6 @@ NS_IMPL_FRAMEARENA_HELPERS(nsImageFrame)
 nsImageFrame::nsImageFrame(nsStyleContext* aContext) :
   nsAtomicContainerFrame(aContext),
   mComputedSize(0, 0),
-  mIntrinsicRatio(0, 0),
   mDisplayingIcon(false),
   mFirstFrameComplete(false),
   mReflowCallbackPosted(false),
@@ -325,11 +324,11 @@ nsImageFrame::UpdateIntrinsicRatio(imgIContainer* aImage)
   if (!aImage)
     return false;
 
-  nsSize oldIntrinsicRatio = mIntrinsicRatio;
+  AspectRatio oldIntrinsicRatio = mIntrinsicRatio;
 
   // Set intrinsic ratio to match aImage's reported intrinsic ratio.
   if (NS_FAILED(aImage->GetIntrinsicRatio(&mIntrinsicRatio)))
-    mIntrinsicRatio.SizeTo(0, 0);
+    mIntrinsicRatio = AspectRatio();
 
   return mIntrinsicRatio != oldIntrinsicRatio;
 }
@@ -557,7 +556,7 @@ nsImageFrame::OnSizeAvailable(imgIRequest* aRequest, imgIContainer* aImage)
     // Have to size to 0,0 so that GetDesiredSize recalculates the size.
     mIntrinsicSize.width.SetCoordValue(0);
     mIntrinsicSize.height.SetCoordValue(0);
-    mIntrinsicRatio.SizeTo(0, 0);
+    mIntrinsicRatio = AspectRatio();
     intrinsicSizeChanged = true;
   }
 
@@ -672,7 +671,7 @@ nsImageFrame::NotifyNewCurrentRequest(imgIRequest *aRequest,
     // Have to size to 0,0 so that GetDesiredSize recalculates the size
     mIntrinsicSize.width.SetCoordValue(0);
     mIntrinsicSize.height.SetCoordValue(0);
-    mIntrinsicRatio.SizeTo(0, 0);
+    mIntrinsicRatio = AspectRatio();
   }
 
   if (mState & IMAGE_GOTINITIALREFLOW) { // do nothing if we haven't gotten the initial reflow yet
@@ -808,7 +807,7 @@ nsImageFrame::EnsureIntrinsicSizeAndRatio()
               ICON_SIZE + (2 * (ICON_PADDING + ALT_BORDER_WIDTH)));
           mIntrinsicSize.width.SetCoordValue(edgeLengthToUse);
           mIntrinsicSize.height.SetCoordValue(edgeLengthToUse);
-          mIntrinsicRatio.SizeTo(1, 1);
+          mIntrinsicRatio = AspectRatio(1.0f);
         }
       }
     }
@@ -932,7 +931,7 @@ nsImageFrame::GetIntrinsicSize()
   return mIntrinsicSize;
 }
 
-/* virtual */ nsSize
+/* virtual */ AspectRatio
 nsImageFrame::GetIntrinsicRatio()
 {
   return mIntrinsicRatio;
diff --git a/layout/generic/nsImageFrame.h b/layout/generic/nsImageFrame.h
index 59af1be32..2414d89df 100644
--- a/layout/generic/nsImageFrame.h
+++ b/layout/generic/nsImageFrame.h
@@ -86,7 +86,7 @@ public:
   virtual nscoord GetMinISize(nsRenderingContext *aRenderingContext) override;
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
-  virtual nsSize GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
   virtual void Reflow(nsPresContext*           aPresContext,
                       ReflowOutput&     aDesiredSize,
                       const ReflowInput& aReflowInput,
@@ -333,7 +333,7 @@ private:
   nsCOMPtr<imgIContainer> mPrevImage;
   nsSize mComputedSize;
   mozilla::IntrinsicSize mIntrinsicSize;
-  nsSize mIntrinsicRatio;
+  mozilla::AspectRatio mIntrinsicRatio;
 
   bool mDisplayingIcon;
   bool mFirstFrameComplete;
diff --git a/layout/generic/nsLineLayout.cpp b/layout/generic/nsLineLayout.cpp
index 6a15a9cfa..60e4e8c96 100644
--- a/layout/generic/nsLineLayout.cpp
+++ b/layout/generic/nsLineLayout.cpp
@@ -784,7 +784,7 @@ IsPercentageAware(const nsIFrame* aFrame)
     //   is calculated from the constraint equation used for
     //   block-level, non-replaced elements in normal flow. 
     nsIFrame *f = const_cast<nsIFrame*>(aFrame);
-    if (f->GetIntrinsicRatio() != nsSize(0, 0) &&
+    if (f->GetIntrinsicRatio() &&
         // Some percents are treated like 'auto', so check != coord
         pos->mHeight.GetUnit() != eStyleUnit_Coord) {
       const IntrinsicSize &intrinsicSize = f->GetIntrinsicSize();
diff --git a/layout/generic/nsSubDocumentFrame.cpp b/layout/generic/nsSubDocumentFrame.cpp
index fd9a7d32c..31d04a335 100644
--- a/layout/generic/nsSubDocumentFrame.cpp
+++ b/layout/generic/nsSubDocumentFrame.cpp
@@ -671,7 +671,7 @@ nsSubDocumentFrame::GetIntrinsicSize()
   return nsAtomicContainerFrame::GetIntrinsicSize();
 }
 
-/* virtual */ nsSize
+/* virtual */ AspectRatio
 nsSubDocumentFrame::GetIntrinsicRatio()
 {
   nsIFrame* subDocRoot = ObtainIntrinsicSizeFrame();
@@ -771,7 +771,7 @@ nsSubDocumentFrame::Reflow(nsPresContext*           aPresContext,
     // Size & position the view according to 'object-fit' & 'object-position'.
     nsIFrame* subDocRoot = ObtainIntrinsicSizeFrame();
     IntrinsicSize intrinsSize;
-    nsSize intrinsRatio;
+    AspectRatio intrinsRatio;
     if (subDocRoot) {
       intrinsSize = subDocRoot->GetIntrinsicSize();
       intrinsRatio = subDocRoot->GetIntrinsicRatio();
diff --git a/layout/generic/nsSubDocumentFrame.h b/layout/generic/nsSubDocumentFrame.h
index 93d908dcc..907d33710 100644
--- a/layout/generic/nsSubDocumentFrame.h
+++ b/layout/generic/nsSubDocumentFrame.h
@@ -51,7 +51,7 @@ public:
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
 
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
-  virtual nsSize  GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
 
   virtual mozilla::LogicalSize
   ComputeAutoSize(nsRenderingContext*         aRenderingContext,
diff --git a/layout/generic/nsVideoFrame.cpp b/layout/generic/nsVideoFrame.cpp
index cea209cb5..6bd6395a3 100644
--- a/layout/generic/nsVideoFrame.cpp
+++ b/layout/generic/nsVideoFrame.cpp
@@ -217,12 +217,10 @@ nsVideoFrame::BuildLayer(nsDisplayListBuilder* aBuilder,
   // Convert video size from pixel units into app units, to get an aspect-ratio
   // (which has to be represented as a nsSize) and an IntrinsicSize that we
   // can pass to ComputeObjectRenderRect.
-  nsSize aspectRatio(nsPresContext::CSSPixelsToAppUnits(videoSizeInPx.width),
-                     nsPresContext::CSSPixelsToAppUnits(videoSizeInPx.height));
+  auto aspectRatio = AspectRatio::FromSize(videoSizeInPx);
   IntrinsicSize intrinsicSize;
-  intrinsicSize.width.SetCoordValue(aspectRatio.width);
-  intrinsicSize.height.SetCoordValue(aspectRatio.height);
-
+  intrinsicSize.width.SetCoordValue(nsPresContext::CSSPixelsToAppUnits(videoSizeInPx.width));
+  intrinsicSize.height.SetCoordValue(nsPresContext::CSSPixelsToAppUnits(videoSizeInPx.height));
   nsRect dest = nsLayoutUtils::ComputeObjectDestRect(area,
                                                      intrinsicSize,
                                                      aspectRatio,
@@ -533,7 +531,9 @@ nsVideoFrame::ComputeSize(nsRenderingContext *aRenderingContext,
   intrinsicSize.height.SetCoordValue(size.height);
 
   // Only video elements have an intrinsic ratio.
-  nsSize intrinsicRatio = HasVideoElement() ? size : nsSize(0, 0);
+  auto intrinsicRatio = HasVideoElement()
+                            ? AspectRatio::FromSize(size)
+                            : AspectRatio();
 
   return ComputeSizeWithIntrinsicDimensions(aRenderingContext, aWM,
                                             intrinsicSize, intrinsicRatio,
@@ -557,14 +557,14 @@ nscoord nsVideoFrame::GetPrefISize(nsRenderingContext *aRenderingContext)
   return result;
 }
 
-nsSize nsVideoFrame::GetIntrinsicRatio()
+AspectRatio nsVideoFrame::GetIntrinsicRatio()
 {
   if (!HasVideoElement()) {
     // Audio elements have no intrinsic ratio.
-    return nsSize(0, 0);
+    return AspectRatio();
   }
 
-  return GetVideoIntrinsicSize(nullptr);
+  return AspectRatio::FromSize(GetVideoIntrinsicSize(nullptr));
 }
 
 bool nsVideoFrame::ShouldDisplayPoster()
diff --git a/layout/generic/nsVideoFrame.h b/layout/generic/nsVideoFrame.h
index d624ae6b9..f52cd8277 100644
--- a/layout/generic/nsVideoFrame.h
+++ b/layout/generic/nsVideoFrame.h
@@ -56,7 +56,7 @@ public:
 
   /* get the size of the video's display */
   nsSize GetVideoIntrinsicSize(nsRenderingContext *aRenderingContext);
-  virtual nsSize GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext *aRenderingContext,
               mozilla::WritingMode aWritingMode,