gecko-dev/gfx/2d/PathHelpers.h

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/* -*- 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/. */
#ifndef MOZILLA_GFX_PATHHELPERS_H_
#define MOZILLA_GFX_PATHHELPERS_H_
#include "2D.h"
#include "mozilla/Constants.h"
namespace mozilla {
namespace gfx {
template <typename T>
void ArcToBezier(T* aSink, const Point &aOrigin, float aRadius, float aStartAngle,
float aEndAngle, bool aAntiClockwise)
{
Point startPoint(aOrigin.x + cos(aStartAngle) * aRadius,
aOrigin.y + sin(aStartAngle) * aRadius);
aSink->LineTo(startPoint);
// Clockwise we always sweep from the smaller to the larger angle, ccw
// it's vice versa.
if (!aAntiClockwise && (aEndAngle < aStartAngle)) {
Float correction = Float(ceil((aStartAngle - aEndAngle) / (2.0f * M_PI)));
aEndAngle += float(correction * 2.0f * M_PI);
} else if (aAntiClockwise && (aStartAngle < aEndAngle)) {
Float correction = (Float)ceil((aEndAngle - aStartAngle) / (2.0f * M_PI));
aStartAngle += float(correction * 2.0f * M_PI);
}
// Sweeping more than 2 * pi is a full circle.
if (!aAntiClockwise && (aEndAngle - aStartAngle > 2 * M_PI)) {
aEndAngle = float(aStartAngle + 2.0f * M_PI);
} else if (aAntiClockwise && (aStartAngle - aEndAngle > 2.0f * M_PI)) {
aEndAngle = float(aStartAngle - 2.0f * M_PI);
}
// Calculate the total arc we're going to sweep.
Float arcSweepLeft = fabs(aEndAngle - aStartAngle);
Float sweepDirection = aAntiClockwise ? -1.0f : 1.0f;
Float currentStartAngle = aStartAngle;
while (arcSweepLeft > 0) {
// We guarantee here the current point is the start point of the next
// curve segment.
Float currentEndAngle;
if (arcSweepLeft > M_PI / 2.0f) {
currentEndAngle = Float(currentStartAngle + M_PI / 2.0f * sweepDirection);
} else {
currentEndAngle = currentStartAngle + arcSweepLeft * sweepDirection;
}
Point currentStartPoint(aOrigin.x + cos(currentStartAngle) * aRadius,
aOrigin.y + sin(currentStartAngle) * aRadius);
Point currentEndPoint(aOrigin.x + cos(currentEndAngle) * aRadius,
aOrigin.y + sin(currentEndAngle) * aRadius);
// Calculate kappa constant for partial curve. The sign of angle in the
// tangent will actually ensure this is negative for a counter clockwise
// sweep, so changing signs later isn't needed.
Float kappa = (4.0f / 3.0f) * tan((currentEndAngle - currentStartAngle) / 4.0f) * aRadius;
Point tangentStart(-sin(currentStartAngle), cos(currentStartAngle));
Point cp1 = currentStartPoint;
cp1 += tangentStart * kappa;
Point revTangentEnd(sin(currentEndAngle), -cos(currentEndAngle));
Point cp2 = currentEndPoint;
cp2 += revTangentEnd * kappa;
aSink->BezierTo(cp1, cp2, currentEndPoint);
arcSweepLeft -= Float(M_PI / 2.0f);
currentStartAngle = currentEndAngle;
}
}
}
}
#endif /* MOZILLA_GFX_PATHHELPERS_H_ */