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

23 files changed, 296 insertions, 214 deletions

diff --git a/layout/base/nsCSSRendering.cpp b/layout/base/nsCSSRendering.cpp
index 9a827546f..e6e3b5f6f 100644
--- a/layout/base/nsCSSRendering.cpp
+++ b/layout/base/nsCSSRendering.cpp
@@ -3546,10 +3546,10 @@ ComputeDrawnSizeForBackground(const CSSSizeOrRatio& aIntrinsicSize,
     imageSize.width = ComputeRoundedSize(imageSize.width, aBgPositioningArea.width);
     if (!isRepeatRoundInBothDimensions &&
         aLayerSize.mHeightType == nsStyleImageLayers::Size::DimensionType::eAuto) {
-      // Restore intrinsic rato
-      if (aIntrinsicSize.mRatio.width) {
-        float scale = float(aIntrinsicSize.mRatio.height) / aIntrinsicSize.mRatio.width;
-        imageSize.height = NSCoordSaturatingNonnegativeMultiply(imageSize.width, scale);
+      // Restore intrinsic ratio
+      if (aIntrinsicSize.mRatio) {
+        imageSize.height =
+            aIntrinsicSize.mRatio.Inverted().ApplyTo(imageSize.width);
       }
     }
   }
@@ -3560,10 +3560,9 @@ ComputeDrawnSizeForBackground(const CSSSizeOrRatio& aIntrinsicSize,
     imageSize.height = ComputeRoundedSize(imageSize.height, aBgPositioningArea.height);
     if (!isRepeatRoundInBothDimensions &&
         aLayerSize.mWidthType == nsStyleImageLayers::Size::DimensionType::eAuto) {
-      // Restore intrinsic rato
-      if (aIntrinsicSize.mRatio.height) {
-        float scale = float(aIntrinsicSize.mRatio.width) / aIntrinsicSize.mRatio.height;
-        imageSize.width = NSCoordSaturatingNonnegativeMultiply(imageSize.height, scale);
+      // Restore intrinsic ratio
+      if (aIntrinsicSize.mRatio) {
+        imageSize.width = aIntrinsicSize.mRatio.ApplyTo(imageSize.height);
       }
     }
   }
@@ -5264,17 +5263,11 @@ CSSSizeOrRatio::ComputeConcreteSize() const
     return nsSize(mWidth, mHeight);
   }
   if (mHasWidth) {
-    nscoord height = NSCoordSaturatingNonnegativeMultiply(
-      mWidth,
-      double(mRatio.height) / mRatio.width);
-    return nsSize(mWidth, height);
+    return nsSize(mWidth, mRatio.Inverted().ApplyTo(mWidth));
   }
 
   MOZ_ASSERT(mHasHeight);
-  nscoord width = NSCoordSaturatingNonnegativeMultiply(
-    mHeight,
-    double(mRatio.width) / mRatio.height);
-  return nsSize(width, mHeight);
+  return nsSize(mRatio.ApplyTo(mHeight), mHeight);
 }
 
 CSSSizeOrRatio
@@ -5379,9 +5372,7 @@ nsImageRenderer::ComputeConcreteSize(const CSSSizeOrRatio& aSpecifiedSize,
   if (aSpecifiedSize.mHasWidth) {
     nscoord height;
     if (aIntrinsicSize.HasRatio()) {
-      height = NSCoordSaturatingNonnegativeMultiply(
-        aSpecifiedSize.mWidth,
-        double(aIntrinsicSize.mRatio.height) / aIntrinsicSize.mRatio.width);
+      height = aIntrinsicSize.mRatio.Inverted().ApplyTo(aSpecifiedSize.mWidth);
     } else if (aIntrinsicSize.mHasHeight) {
       height = aIntrinsicSize.mHeight;
     } else {
@@ -5393,9 +5384,7 @@ nsImageRenderer::ComputeConcreteSize(const CSSSizeOrRatio& aSpecifiedSize,
   MOZ_ASSERT(aSpecifiedSize.mHasHeight);
   nscoord width;
   if (aIntrinsicSize.HasRatio()) {
-    width = NSCoordSaturatingNonnegativeMultiply(
-      aSpecifiedSize.mHeight,
-      double(aIntrinsicSize.mRatio.width) / aIntrinsicSize.mRatio.height);
+    width = aIntrinsicSize.mRatio.ApplyTo(aSpecifiedSize.mHeight);
   } else if (aIntrinsicSize.mHasWidth) {
     width = aIntrinsicSize.mWidth;
   } else {
@@ -5406,32 +5395,57 @@ nsImageRenderer::ComputeConcreteSize(const CSSSizeOrRatio& aSpecifiedSize,
 
 /* static */ nsSize
 nsImageRenderer::ComputeConstrainedSize(const nsSize& aConstrainingSize,
-                                        const nsSize& aIntrinsicRatio,
+                                        const AspectRatio& aIntrinsicRatio,
                                         FitType aFitType)
 {
-  if (aIntrinsicRatio.width <= 0 && aIntrinsicRatio.height <= 0) {
+  if (!aIntrinsicRatio) {
     return aConstrainingSize;
   }
 
-  float scaleX = double(aConstrainingSize.width) / aIntrinsicRatio.width;
-  float scaleY = double(aConstrainingSize.height) / aIntrinsicRatio.height;
+  // Suppose we're doing a "contain" fit. If the image's aspect ratio has a
+  // "fatter" shape than the constraint area, then we need to use the
+  // constraint area's full width, and we need to use the aspect ratio to
+  // produce a height. ON the other hand, if the aspect ratio is "skinnier", we
+  // use the constraint area's full height, and we use the aspect ratio to
+  // produce a width. (If instead we're doing a "cover" fit, then it can easily
+  // be seen that we should do precisely the opposite.)
+  //
+  // This is equivalent to the more descriptive alternative:
+  //
+  //   AspectRatio::FromSize(aConstrainingSize) < aIntrinsicRatio
+  //
+  // But gracefully handling the case where one of the two dimensions from
+  // aConstrainingSize is zero. This is easy to prove since:
+  //
+  //   aConstrainingSize.width / aConstrainingSize.height < aIntrinsicRatio
+  //
+  // Is trivially equivalent to:
+  //
+  //   aIntrinsicRatio.width < aIntrinsicRatio * aConstrainingSize.height
+  //
+  // For the cases where height is not zero.
+  //
+  // We use float math here to avoid losing precision for very lareg backgrounds
+  // since we use saturating nscoord math otherwise.
+  const float constraintWidth = float(aConstrainingSize.width);
+  const float hypotheticalWidth =
+      aIntrinsicRatio.ApplyToFloat(aConstrainingSize.height);
+
   nsSize size;
-  if ((aFitType == CONTAIN) == (scaleX < scaleY)) {
+  if ((aFitType == CONTAIN) == (constraintWidth < hypotheticalWidth)) {
     size.width = aConstrainingSize.width;
-    size.height = NSCoordSaturatingNonnegativeMultiply(
-                    aIntrinsicRatio.height, scaleX);
+    size.height = aIntrinsicRatio.Inverted().ApplyTo(aConstrainingSize.width);
     // If we're reducing the size by less than one css pixel, then just use the
     // constraining size.
     if (aFitType == CONTAIN && aConstrainingSize.height - size.height < nsPresContext::AppUnitsPerCSSPixel()) {
       size.height = aConstrainingSize.height;
     }
   } else {
-    size.width = NSCoordSaturatingNonnegativeMultiply(
-                   aIntrinsicRatio.width, scaleY);
+    size.height = aConstrainingSize.height;
+    size.width = aIntrinsicRatio.ApplyTo(aConstrainingSize.height);
     if (aFitType == CONTAIN && aConstrainingSize.width - size.width < nsPresContext::AppUnitsPerCSSPixel()) {
       size.width = aConstrainingSize.width;
     }
-    size.height = aConstrainingSize.height;
   }
   return size;
 }
diff --git a/layout/base/nsCSSRendering.h b/layout/base/nsCSSRendering.h
index 791e9656e..8ebeb7537 100644
--- a/layout/base/nsCSSRendering.h
+++ b/layout/base/nsCSSRendering.h
@@ -17,6 +17,7 @@
 #include "nsLayoutUtils.h"
 #include "nsStyleStruct.h"
 #include "nsIFrame.h"
+#include "mozilla/AspectRatio.h"
 
 class gfxDrawable;
 class nsStyleContext;
@@ -41,8 +42,7 @@ class ImageContainer;
 struct CSSSizeOrRatio
 {
   CSSSizeOrRatio()
-    : mRatio(0, 0)
-    , mHasWidth(false)
+    : mHasWidth(false)
     , mHasHeight(false) {}
 
   bool CanComputeConcreteSize() const
@@ -50,12 +50,12 @@ struct CSSSizeOrRatio
     return mHasWidth + mHasHeight + HasRatio() >= 2;
   }
   bool IsConcrete() const { return mHasWidth && mHasHeight; }
-  bool HasRatio() const { return mRatio.width > 0 && mRatio.height > 0; }
+  bool HasRatio() const { return !!mRatio; }
   bool IsEmpty() const
   {
     return (mHasWidth && mWidth <= 0) ||
            (mHasHeight && mHeight <= 0) ||
-           mRatio.width <= 0 || mRatio.height <= 0; 
+           !mRatio; 
   }
 
   // CanComputeConcreteSize must return true when ComputeConcreteSize is
@@ -67,7 +67,7 @@ struct CSSSizeOrRatio
     mWidth = aWidth;
     mHasWidth = true;
     if (mHasHeight) {
-      mRatio = nsSize(mWidth, mHeight);
+      mRatio = AspectRatio::FromSize(mWidth, mHeight);
     }
   }
   void SetHeight(nscoord aHeight)
@@ -75,7 +75,7 @@ struct CSSSizeOrRatio
     mHeight = aHeight;
     mHasHeight = true;
     if (mHasWidth) {
-      mRatio = nsSize(mWidth, mHeight);
+      mRatio = AspectRatio::FromSize(mWidth, mHeight);
     }
   }
   void SetSize(const nsSize& aSize)
@@ -84,16 +84,16 @@ struct CSSSizeOrRatio
     mHeight = aSize.height;
     mHasWidth = true;
     mHasHeight = true;
-    mRatio = aSize;    
+    mRatio = AspectRatio::FromSize(mWidth, mHeight);    
   }
-  void SetRatio(const nsSize& aRatio)
+  void SetRatio(const AspectRatio& aRatio)
   {
     MOZ_ASSERT(!mHasWidth || !mHasHeight,
                "Probably shouldn't be setting a ratio if we have a concrete size");
     mRatio = aRatio;
   }
 
-  nsSize mRatio;
+  AspectRatio mRatio;
   nscoord mWidth;
   nscoord mHeight;
   bool mHasWidth;
@@ -184,11 +184,9 @@ public:
   /**
    * Compute the size of the rendered image using either the 'cover' or
    * 'contain' constraints (aFitType).
-   * aIntrinsicRatio may be an invalid ratio, that is one or both of its
-   * dimensions can be less than or equal to zero.
    */
   static nsSize ComputeConstrainedSize(const nsSize& aConstrainingSize,
-                                       const nsSize& aIntrinsicRatio,
+                                       const mozilla::AspectRatio& aIntrinsicRatio,
                                        FitType aFitType);
   /**
    * Compute the size of the rendered image (the concrete size) where no cover/
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index fb0b42a6c..5de6f2013 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -4045,7 +4045,7 @@ nsLayoutUtils::GetTextShadowRectsUnion(const nsRect& aTextAndDecorationsRect,
 enum ObjectDimensionType { eWidth, eHeight };
 static nscoord
 ComputeMissingDimension(const nsSize& aDefaultObjectSize,
-                        const nsSize& aIntrinsicRatio,
+                        const AspectRatio& aIntrinsicRatio,
                         const Maybe<nscoord>& aSpecifiedWidth,
                         const Maybe<nscoord>& aSpecifiedHeight,
                         ObjectDimensionType aDimensionToCompute)
@@ -4056,21 +4056,15 @@ ComputeMissingDimension(const nsSize& aDefaultObjectSize,
   // 1. "If the object has an intrinsic aspect ratio, the missing dimension of
   //     the concrete object size is calculated using the intrinsic aspect
   //     ratio and the present dimension."
-  if (aIntrinsicRatio.width > 0 && aIntrinsicRatio.height > 0) {
+  if (aIntrinsicRatio) {
     // Fill in the missing dimension using the intrinsic aspect ratio.
-    nscoord knownDimensionSize;
-    float ratio;
     if (aDimensionToCompute == eWidth) {
-      knownDimensionSize = *aSpecifiedHeight;
-      ratio = aIntrinsicRatio.width / aIntrinsicRatio.height;
-    } else {
-      knownDimensionSize = *aSpecifiedWidth;
-      ratio = aIntrinsicRatio.height / aIntrinsicRatio.width;
+      return aIntrinsicRatio.ApplyTo(*aSpecifiedHeight);
     }
-    return NSCoordSaturatingNonnegativeMultiply(knownDimensionSize, ratio);
+    return aIntrinsicRatio.Inverted().ApplyTo(*aSpecifiedWidth);
   }
 
-  // 2. "Otherwise, if the missing dimension is present in the object’s
+  // 2. "Otherwise, if the missing dimension is present in the object's
   //     intrinsic dimensions, [...]"
   // NOTE: *Skipping* this case, because we already know it's not true -- we're
   // in this function because the missing dimension is *not* present in
@@ -4108,7 +4102,7 @@ ComputeMissingDimension(const nsSize& aDefaultObjectSize,
 static Maybe<nsSize>
 MaybeComputeObjectFitNoneSize(const nsSize& aDefaultObjectSize,
                               const IntrinsicSize& aIntrinsicSize,
-                              const nsSize& aIntrinsicRatio)
+                              const AspectRatio& aIntrinsicRatio)
 {
   // "If the object has an intrinsic height or width, its size is resolved as
   // if its intrinsic dimensions were given as the specified size."
@@ -4155,15 +4149,13 @@ MaybeComputeObjectFitNoneSize(const nsSize& aDefaultObjectSize,
 static nsSize
 ComputeConcreteObjectSize(const nsSize& aConstraintSize,
                           const IntrinsicSize& aIntrinsicSize,
-                          const nsSize& aIntrinsicRatio,
+                          const AspectRatio& aIntrinsicRatio,
                           uint8_t aObjectFit)
 {
   // Handle default behavior (filling the container) w/ fast early return.
   // (Also: if there's no valid intrinsic ratio, then we have the "fill"
   // behavior & just use the constraint size.)
-  if (MOZ_LIKELY(aObjectFit == NS_STYLE_OBJECT_FIT_FILL) ||
-      aIntrinsicRatio.width == 0 ||
-      aIntrinsicRatio.height == 0) {
+  if (MOZ_LIKELY(aObjectFit == NS_STYLE_OBJECT_FIT_FILL) || !aIntrinsicRatio) {
     return aConstraintSize;
   }
 
@@ -4250,7 +4242,7 @@ HasInitialObjectFitAndPosition(const nsStylePosition* aStylePos)
 /* static */ nsRect
 nsLayoutUtils::ComputeObjectDestRect(const nsRect& aConstraintRect,
                                      const IntrinsicSize& aIntrinsicSize,
-                                     const nsSize& aIntrinsicRatio,
+                                     const AspectRatio& aIntrinsicRatio,
                                      const nsStylePosition* aStylePos,
                                      nsPoint* aAnchorPoint)
 {
@@ -5172,10 +5164,12 @@ nsLayoutUtils::IntrinsicForAxis(PhysicalAxis              aAxis,
            styleMinBSize.GetCoordValue() == 0)) ||
         styleMaxBSize.GetUnit() != eStyleUnit_None) {
 
-      nsSize ratio(aFrame->GetIntrinsicRatio());
-      nscoord ratioISize = (horizontalAxis ? ratio.width  : ratio.height);
-      nscoord ratioBSize = (horizontalAxis ? ratio.height : ratio.width);
-      if (ratioBSize != 0) {
+      AspectRatio ratio = aFrame->GetIntrinsicRatio();
+      if (ratio) {
+        // Convert 'ratio' if necessary, so that it's storing ISize/BSize:
+        if (!horizontalAxis) {
+          ratio = ratio.Inverted();
+        }
         AddStateBitToAncestors(aFrame,
             NS_FRAME_DESCENDANT_INTRINSIC_ISIZE_DEPENDS_ON_BSIZE);
 
@@ -5191,14 +5185,14 @@ nsLayoutUtils::IntrinsicForAxis(PhysicalAxis              aAxis,
             (aPercentageBasis.isNothing() &&
              GetPercentBSize(styleBSize, aFrame, horizontalAxis, h))) {
           h = std::max(0, h - bSizeTakenByBoxSizing);
-          result = NSCoordMulDiv(h, ratioISize, ratioBSize);
+          result = ratio.ApplyTo(h);
         }
 
         if (GetDefiniteSize(styleMaxBSize, aFrame, !isInlineAxis, aPercentageBasis, &h) ||
             (aPercentageBasis.isNothing() &&
              GetPercentBSize(styleMaxBSize, aFrame, horizontalAxis, h))) {
           h = std::max(0, h - bSizeTakenByBoxSizing);
-          nscoord maxISize = NSCoordMulDiv(h, ratioISize, ratioBSize);
+          nscoord maxISize = ratio.ApplyTo(h);
           if (maxISize < result) {
             result = maxISize;
           }
@@ -5211,7 +5205,7 @@ nsLayoutUtils::IntrinsicForAxis(PhysicalAxis              aAxis,
             (aPercentageBasis.isNothing() &&
              GetPercentBSize(styleMinBSize, aFrame, horizontalAxis, h))) {
           h = std::max(0, h - bSizeTakenByBoxSizing);
-          nscoord minISize = NSCoordMulDiv(h, ratioISize, ratioBSize);
+          nscoord minISize = ratio.ApplyTo(h);
           if (minISize > result) {
             result = minISize;
           }
@@ -6674,12 +6668,12 @@ nsLayoutUtils::DrawSingleImage(gfxContext&            aContext,
 /* static */ void
 nsLayoutUtils::ComputeSizeForDrawing(imgIContainer *aImage,
                                      CSSIntSize&    aImageSize, /*outparam*/
-                                     nsSize&        aIntrinsicRatio, /*outparam*/
+                                     AspectRatio&   aIntrinsicRatio, /*outparam*/
                                      bool&          aGotWidth,  /*outparam*/
                                      bool&          aGotHeight  /*outparam*/)
 {
   aGotWidth  = NS_SUCCEEDED(aImage->GetWidth(&aImageSize.width));
-  aGotHeight = NS_SUCCEEDED(aImage->GetHeight(&aImageSize.height));
+  aGotHeight = NS_SUCCEEDED(aImage->GetHeight(&aImageSize.height)); 
   bool gotRatio = NS_SUCCEEDED(aImage->GetIntrinsicRatio(&aIntrinsicRatio));
 
   if (!(aGotWidth && aGotHeight) && !gotRatio) {
@@ -6687,7 +6681,7 @@ nsLayoutUtils::ComputeSizeForDrawing(imgIContainer *aImage,
     // decoded) and should return zero size.
     aGotWidth = aGotHeight = true;
     aImageSize = CSSIntSize(0, 0);
-    aIntrinsicRatio = nsSize(0, 0);
+    aIntrinsicRatio = AspectRatio();
   }
 }
 
@@ -6696,7 +6690,7 @@ nsLayoutUtils::ComputeSizeForDrawingWithFallback(imgIContainer* aImage,
                                                  const nsSize&  aFallbackSize)
 {
   CSSIntSize imageSize;
-  nsSize imageRatio;
+  AspectRatio imageRatio;
   bool gotHeight, gotWidth;
   ComputeSizeForDrawing(aImage, imageSize, imageRatio, gotWidth, gotHeight);
 
@@ -6704,19 +6698,13 @@ nsLayoutUtils::ComputeSizeForDrawingWithFallback(imgIContainer* aImage,
   // intrinsic ratio of the image.
   if (gotWidth != gotHeight) {
     if (!gotWidth) {
-      if (imageRatio.height != 0) {
-        imageSize.width =
-          NSCoordSaturatingNonnegativeMultiply(imageSize.height,
-                                               float(imageRatio.width) /
-                                               float(imageRatio.height));
+      if (imageRatio) {
+        imageSize.width = imageRatio.ApplyTo(imageSize.height);
         gotWidth = true;
       }
     } else {
-      if (imageRatio.width != 0) {
-        imageSize.height =
-          NSCoordSaturatingNonnegativeMultiply(imageSize.width,
-                                               float(imageRatio.height) /
-                                               float(imageRatio.width));
+      if (imageRatio) {
+        imageSize.height = imageRatio.Inverted().ApplyTo(imageSize.width);
         gotHeight = true;
       }
     }
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index bba1f3265..f4471ce74 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -65,6 +65,7 @@ struct nsStyleImageOrientation;
 struct nsOverflowAreas;
 
 namespace mozilla {
+struct aspectRatio;
 enum class CSSPseudoElementType : uint8_t;
 class EventListenerManager;
 class SVGImageContext;
@@ -126,6 +127,7 @@ enum class RelativeTo {
  */
 class nsLayoutUtils
 {
+  typedef mozilla::AspectRatio AspectRatio;
   typedef mozilla::dom::DOMRectList DOMRectList;
   typedef mozilla::layers::Layer Layer;
   typedef mozilla::ContainerLayerParameters ContainerLayerParameters;
@@ -1258,7 +1260,7 @@ public:
    */
   static nsRect ComputeObjectDestRect(const nsRect& aConstraintRect,
                                       const IntrinsicSize& aIntrinsicSize,
-                                      const nsSize& aIntrinsicRatio,
+                                      const AspectRatio& aIntrinsicRatio,
                                       const nsStylePosition* aStylePos,
                                       nsPoint* aAnchorPoint = nullptr);
 
@@ -1878,7 +1880,7 @@ public:
    */
   static void ComputeSizeForDrawing(imgIContainer* aImage,
                                     CSSIntSize&    aImageSize,
-                                    nsSize&        aIntrinsicRatio,
+                                    AspectRatio&        aIntrinsicRatio,
                                     bool&          aGotWidth,
                                     bool&          aGotHeight);
 
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,
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index 200f934c5..9270f2960 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -2731,7 +2731,7 @@ nsStyleImageLayers::Size::DependsOnPositioningAreaSize(const nsStyleImage& aImag
     }
     if (imgContainer) {
       CSSIntSize imageSize;
-      nsSize imageRatio;
+      AspectRatio imageRatio;
       bool hasWidth, hasHeight;
       nsLayoutUtils::ComputeSizeForDrawing(imgContainer, imageSize, imageRatio,
                                            hasWidth, hasHeight);
@@ -2744,7 +2744,7 @@ nsStyleImageLayers::Size::DependsOnPositioningAreaSize(const nsStyleImage& aImag
 
       // If the image has an intrinsic ratio, rendering will depend on frame
       // size when background-size is all auto.
-      if (imageRatio != nsSize(0, 0)) {
+      if (imageRatio) {
         return mWidthType == mHeightType;
       }
 
diff --git a/layout/svg/nsSVGOuterSVGFrame.cpp b/layout/svg/nsSVGOuterSVGFrame.cpp
index 16dfc2b37..d8cd2cb77 100644
--- a/layout/svg/nsSVGOuterSVGFrame.cpp
+++ b/layout/svg/nsSVGOuterSVGFrame.cpp
@@ -232,28 +232,38 @@ nsSVGOuterSVGFrame::GetIntrinsicSize()
   return intrinsicSize;
 }
 
-/* virtual */ nsSize
+/* virtual */ AspectRatio
 nsSVGOuterSVGFrame::GetIntrinsicRatio()
 {
+  // 2020-07-14 (RealityRipple) Firefox Uses a new IsReplacedAndContainSize(this)
+  // function call [Line 96-99 on trunk].
+/*
+  static inline bool IsReplacedAndContainSize(const nsSVGOuterSVGFrame* aFrame) {
+    return aFrame->GetContent->GetParent() &&
+           aFrame->StyleDisplay()->IsContainSize();
+  }
+ */
+  // but since contain: size doesn't exist in Pale Moon yet...
+/*
+  if (IsReplacedAndContainSize(this)) {
+    return AspectRatio();
+  }
+ */
+  
   // We only have an intrinsic size/ratio if our width and height attributes
   // are both specified and set to non-percentage values, or we have a viewBox
   // rect: http://www.w3.org/TR/SVGMobile12/coords.html#IntrinsicSizing
+  // Unfortunately we have to return the ratio as two nscoords whereas what
+  // we have are two floats. Using app units allows for some floating point
+  // values to work but really small or large numbers will fail.
 
   SVGSVGElement *content = static_cast<SVGSVGElement*>(mContent);
   nsSVGLength2 &width  = content->mLengthAttributes[SVGSVGElement::ATTR_WIDTH];
   nsSVGLength2 &height = content->mLengthAttributes[SVGSVGElement::ATTR_HEIGHT];
 
   if (!width.IsPercentage() && !height.IsPercentage()) {
-    nsSize ratio(
-      nsPresContext::CSSPixelsToAppUnits(width.GetAnimValue(content)),
-      nsPresContext::CSSPixelsToAppUnits(height.GetAnimValue(content)));
-    if (ratio.width < 0) {
-      ratio.width = 0;
-    }
-    if (ratio.height < 0) {
-      ratio.height = 0;
-    }
-    return ratio;
+    return AspectRatio::FromSize(width.GetAnimValue(content),
+                                 height.GetAnimValue(content));
   }
 
   SVGViewElement* viewElement = content->GetCurrentViewElement();
@@ -267,17 +277,7 @@ nsSVGOuterSVGFrame::GetIntrinsicRatio()
   }
 
   if (viewbox) {
-    float viewBoxWidth = viewbox->width;
-    float viewBoxHeight = viewbox->height;
-
-    if (viewBoxWidth < 0.0f) {
-      viewBoxWidth = 0.0f;
-    }
-    if (viewBoxHeight < 0.0f) {
-      viewBoxHeight = 0.0f;
-    }
-    return nsSize(nsPresContext::CSSPixelsToAppUnits(viewBoxWidth),
-                  nsPresContext::CSSPixelsToAppUnits(viewBoxHeight));
+    return AspectRatio::FromSize(viewbox->width, viewbox->height);
   }
 
   return nsSVGDisplayContainerFrame::GetIntrinsicRatio();
diff --git a/layout/svg/nsSVGOuterSVGFrame.h b/layout/svg/nsSVGOuterSVGFrame.h
index ee59b7d1c..4705b6ebe 100644
--- a/layout/svg/nsSVGOuterSVGFrame.h
+++ b/layout/svg/nsSVGOuterSVGFrame.h
@@ -42,7 +42,7 @@ public:
   virtual nscoord GetPrefISize(nsRenderingContext *aRenderingContext) override;
 
   virtual mozilla::IntrinsicSize GetIntrinsicSize() override;
-  virtual nsSize  GetIntrinsicRatio() override;
+  virtual mozilla::AspectRatio GetIntrinsicRatio() override;
 
   virtual mozilla::LogicalSize
   ComputeSize(nsRenderingContext *aRenderingContext,
diff --git a/layout/xul/nsImageBoxFrame.cpp b/layout/xul/nsImageBoxFrame.cpp
index e88b502ab..5286b6d88 100644
--- a/layout/xul/nsImageBoxFrame.cpp
+++ b/layout/xul/nsImageBoxFrame.cpp
@@ -402,12 +402,13 @@ nsImageBoxFrame::PaintImage(nsRenderingContext& aRenderingContext,
     // Determine dest rect based on intrinsic size & ratio, along with
     // 'object-fit' & 'object-position' properties:
     IntrinsicSize intrinsicSize;
-    nsSize intrinsicRatio;
+    AspectRatio intrinsicRatio;
     if (mIntrinsicSize.width > 0 && mIntrinsicSize.height > 0) {
       // Image has a valid size; use it as intrinsic size & ratio.
       intrinsicSize.width.SetCoordValue(mIntrinsicSize.width);
       intrinsicSize.height.SetCoordValue(mIntrinsicSize.height);
-      intrinsicRatio = mIntrinsicSize;
+      intrinsicRatio =
+          AspectRatio::FromSize(mIntrinsicSize);
     } else {
       // Image doesn't have a (valid) intrinsic size.
       // Try to look up intrinsic ratio and use that at least.