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diff --git a/layout/base/ShapeUtils.h b/layout/base/ShapeUtils.h
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+++ b/layout/base/ShapeUtils.h
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+/* -*- 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_ShapeUtils_h
+#define mozilla_ShapeUtils_h
+
+#include "nsCoord.h"
+#include "nsSize.h"
+#include "nsStyleConsts.h"
+#include "nsTArray.h"
+
+struct nsPoint;
+struct nsRect;
+
+namespace mozilla {
+// ShapeUtils is a namespace class containing utility functions related to
+// processing basic shapes in the CSS Shapes Module.
+// https://drafts.csswg.org/css-shapes/#basic-shape-functions
+//
+struct ShapeUtils final {
+  // Compute the length of a keyword <shape-radius>, i.e. closest-side or
+  // farthest-side, for a circle or an ellipse on a single dimension. The
+  // caller needs to call for both dimensions and combine the result.
+  // https://drafts.csswg.org/css-shapes/#typedef-shape-radius.
+  // @return The length of the radius in app units.
+  static nscoord ComputeShapeRadius(const StyleShapeRadius& aType,
+                                    const nscoord aCenter,
+                                    const nscoord aPosMin,
+                                    const nscoord aPosMax);
+
+  // Compute the center of a circle or an ellipse.
+  // @param aRefBox The reference box of the basic shape.
+  // @return The point of the center.
+  static nsPoint ComputeCircleOrEllipseCenter(const StyleBasicShape&,
+                                              const nsRect& aRefBox);
+
+  // Compute the radius for a circle.
+  // @param aCenter the center of the circle.
+  // @param aRefBox the reference box of the circle.
+  // @return The length of the radius in app units.
+  static nscoord ComputeCircleRadius(const StyleBasicShape&,
+                                     const nsPoint& aCenter,
+                                     const nsRect& aRefBox);
+
+  // Compute the radii for an ellipse.
+  // @param aCenter the center of the ellipse.
+  // @param aRefBox the reference box of the ellipse.
+  // @return The radii of the ellipse in app units. The width and height
+  // represent the x-axis and y-axis radii of the ellipse.
+  static nsSize ComputeEllipseRadii(const StyleBasicShape&,
+                                    const nsPoint& aCenter,
+                                    const nsRect& aRefBox);
+
+  // Compute the rect for an inset. If the inset amount is larger than
+  // aRefBox itself, this will return a rect the same shape as the inverse
+  // rect that would be created by insetting aRefBox by the inset amount.
+  // This process is *not* what is called for by the current spec at
+  // https://drafts.csswg.org/css-shapes-1/#supported-basic-shapes.
+  // The spec currently treats empty shapes, including overly-inset rects, as
+  // defining 'empty float areas' that don't affect layout. However, it is
+  // practically useful to treat empty shapes as having edges for purposes of
+  // affecting layout, and there is growing momentum for the approach we
+  // are taking here.
+  // @param aRefBox the reference box of the inset.
+  // @return The inset rect in app units.
+  static nsRect ComputeInsetRect(const StyleBasicShape&, const nsRect& aRefBox);
+
+  // Compute the radii for an inset.
+  // @param aRefBox the reference box of the inset.
+  // @param aInsetRect the inset rect computed by ComputeInsetRect().
+  // @param aRadii the returned radii in app units.
+  // @return true if any of the radii is nonzero; false otherwise.
+  static bool ComputeInsetRadii(const StyleBasicShape&,
+                                const nsRect& aInsetRect, const nsRect& aRefBox,
+                                nscoord aRadii[8]);
+
+  // Compute the vertices for a polygon.
+  // @param aRefBox the reference box of the polygon.
+  // @return The vertices in app units; the coordinate space is the same
+  //         as aRefBox.
+  static nsTArray<nsPoint> ComputePolygonVertices(const StyleBasicShape&,
+                                                  const nsRect& aRefBox);
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_ShapeUtils_h