The Tor Browser: gfx/2d/PathHelpers.cpp@97036ab72558 (annotated)

gfx/2d/PathHelpers.cpp@97036ab72558 (annotated)

gfx/2d/PathHelpers.cpp

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
  * 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/. */
 #include "PathHelpers.h"
 namespace mozilla {
 namespace gfx {
 void
 AppendRoundedRectToPath(PathBuilder* aPathBuilder,
                         const Rect& aRect,
                         // paren's needed due to operator precedence:
                         const Size(& aCornerRadii)[4],
                         bool aDrawClockwise)
 {
   // For CW drawing, this looks like:
   //
   //  ...******0**      1    C
   //              ****
   //                  ***    2
   //                     **
   //                       *
   //                        *
   //                         3
   //                         *
   //                         *
   //
   // Where 0, 1, 2, 3 are the control points of the Bezier curve for
   // the corner, and C is the actual corner point.
   //
   // At the start of the loop, the current point is assumed to be
   // the point adjacent to the top left corner on the top
   // horizontal.  Note that corner indices start at the top left and
   // continue clockwise, whereas in our loop i = 0 refers to the top
   // right corner.
   //
   // When going CCW, the control points are swapped, and the first
   // corner that's drawn is the top left (along with the top segment).
   //
   // There is considerable latitude in how one chooses the four
   // control points for a Bezier curve approximation to an ellipse.
   // For the overall path to be continuous and show no corner at the
   // endpoints of the arc, points 0 and 3 must be at the ends of the
   // straight segments of the rectangle; points 0, 1, and C must be
   // collinear; and points 3, 2, and C must also be collinear.  This
   // leaves only two free parameters: the ratio of the line segments
   // 01 and 0C, and the ratio of the line segments 32 and 3C.  See
   // the following papers for extensive discussion of how to choose
   // these ratios:
   //
   //   Dokken, Tor, et al. "Good approximation of circles by
   //      curvature-continuous Bezier curves."  Computer-Aided
   //      Geometric Design 7(1990) 33--41.
   //   Goldapp, Michael. "Approximation of circular arcs by cubic
   //      polynomials." Computer-Aided Geometric Design 8(1991) 227--238.
   //   Maisonobe, Luc. "Drawing an elliptical arc using polylines,
   //      quadratic, or cubic Bezier curves."
   //      http://www.spaceroots.org/documents/ellipse/elliptical-arc.pdf
   //
   // We follow the approach in section 2 of Goldapp (least-error,
   // Hermite-type approximation) and make both ratios equal to
   //
   //          2   2 + n - sqrt(2n + 28)
   //  alpha = - * ---------------------
   //          3           n - 4
   //
   // where n = 3( cbrt(sqrt(2)+1) - cbrt(sqrt(2)-1) ).
   //
   // This is the result of Goldapp's equation (10b) when the angle
   // swept out by the arc is pi/2, and the parameter "a-bar" is the
   // expression given immediately below equation (21).
   //
   // Using this value, the maximum radial error for a circle, as a
   // fraction of the radius, is on the order of 0.2 x 10^-3.
   // Neither Dokken nor Goldapp discusses error for a general
   // ellipse; Maisonobe does, but his choice of control points
   // follows different constraints, and Goldapp's expression for
   // 'alpha' gives much smaller radial error, even for very flat
   // ellipses, than Maisonobe's equivalent.
   //
   // For the various corners and for each axis, the sign of this
   // constant changes, or it might be 0 -- it's multiplied by the
   // appropriate multiplier from the list before using.
   const Float alpha = Float(0.55191497064665766025);
   typedef struct { Float a, b; } twoFloats;
   twoFloats cwCornerMults[4] = { { -1,  0 },    // cc == clockwise
                                  {  0, -1 },
                                  { +1,  0 },
                                  {  0, +1 } };
   twoFloats ccwCornerMults[4] = { { +1,  0 },   // ccw == counter-clockwise
                                   {  0, -1 },
                                   { -1,  0 },
                                   {  0, +1 } };
   twoFloats *cornerMults = aDrawClockwise ? cwCornerMults : ccwCornerMults;
   Point cornerCoords[] = { aRect.TopLeft(), aRect.TopRight(),
                            aRect.BottomRight(), aRect.BottomLeft() };
   Point pc, p0, p1, p2, p3;
   // The indexes of the corners:
   const int kTopLeft = 0, kTopRight = 1;
   if (aDrawClockwise) {
     aPathBuilder->MoveTo(Point(aRect.X() + aCornerRadii[kTopLeft].width,
                                aRect.Y()));
   } else {
     aPathBuilder->MoveTo(Point(aRect.X() + aRect.Width() - aCornerRadii[kTopRight].width,
                                aRect.Y()));
   }
   for (int i = 0; i < 4; ++i) {
     // the corner index -- either 1 2 3 0 (cw) or 0 3 2 1 (ccw)
     int c = aDrawClockwise ? ((i+1) % 4) : ((4-i) % 4);
     // i+2 and i+3 respectively.  These are used to index into the corner
     // multiplier table, and were deduced by calculating out the long form
     // of each corner and finding a pattern in the signs and values.
     int i2 = (i+2) % 4;
     int i3 = (i+3) % 4;
     pc = cornerCoords[c];
     if (aCornerRadii[c].width > 0.0 && aCornerRadii[c].height > 0.0) {
       p0.x = pc.x + cornerMults[i].a * aCornerRadii[c].width;
       p0.y = pc.y + cornerMults[i].b * aCornerRadii[c].height;
       p3.x = pc.x + cornerMults[i3].a * aCornerRadii[c].width;
       p3.y = pc.y + cornerMults[i3].b * aCornerRadii[c].height;
       p1.x = p0.x + alpha * cornerMults[i2].a * aCornerRadii[c].width;
       p1.y = p0.y + alpha * cornerMults[i2].b * aCornerRadii[c].height;
       p2.x = p3.x - alpha * cornerMults[i3].a * aCornerRadii[c].width;
       p2.y = p3.y - alpha * cornerMults[i3].b * aCornerRadii[c].height;
       aPathBuilder->LineTo(p0);
       aPathBuilder->BezierTo(p1, p2, p3);
     } else {
       aPathBuilder->LineTo(pc);
     }
   }
   aPathBuilder->Close();
 }
 void
 AppendEllipseToPath(PathBuilder* aPathBuilder,
                     const Point& aCenter,
                     const Size& aDimensions)
 {
   Size halfDim = aDimensions / 2.0;
   Rect rect(aCenter - Point(halfDim.width, halfDim.height), aDimensions);
   Size radii[] = { halfDim, halfDim, halfDim, halfDim };
   AppendRoundedRectToPath(aPathBuilder, rect, radii);
 }
 } // namespace gfx
 } // namespace mozilla

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gfx/2d/PathHelpers.cpp@97036ab72558 (annotated)

gfx/2d/PathHelpers.cpp