4e05fd25c8
git-svn-id: http://skia.googlecode.com/svn/trunk@9493 2bbb7eff-a529-9590-31e7-b0007b416f81
302 lines
11 KiB
C++
302 lines
11 KiB
C++
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/*
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* Copyright 2006 The Android Open Source Project
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef SkGeometry_DEFINED
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#define SkGeometry_DEFINED
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#include "SkMatrix.h"
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/** An XRay is a half-line that runs from the specific point/origin to
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+infinity in the X direction. e.g. XRay(3,5) is the half-line
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(3,5)....(infinity, 5)
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*/
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typedef SkPoint SkXRay;
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/** Given a line segment from pts[0] to pts[1], and an xray, return true if
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they intersect. Optional outgoing "ambiguous" argument indicates
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whether the answer is ambiguous because the query occurred exactly at
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one of the endpoints' y coordinates, indicating that another query y
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coordinate is preferred for robustness.
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*/
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bool SkXRayCrossesLine(const SkXRay& pt, const SkPoint pts[2],
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bool* ambiguous = NULL);
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/** Given a quadratic equation Ax^2 + Bx + C = 0, return 0, 1, 2 roots for the
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equation.
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*/
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int SkFindUnitQuadRoots(SkScalar A, SkScalar B, SkScalar C, SkScalar roots[2]);
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///////////////////////////////////////////////////////////////////////////////
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/** Set pt to the point on the src quadratic specified by t. t must be
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0 <= t <= 1.0
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*/
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void SkEvalQuadAt(const SkPoint src[3], SkScalar t, SkPoint* pt,
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SkVector* tangent = NULL);
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void SkEvalQuadAtHalf(const SkPoint src[3], SkPoint* pt,
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SkVector* tangent = NULL);
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/** Given a src quadratic bezier, chop it at the specified t value,
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where 0 < t < 1, and return the two new quadratics in dst:
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dst[0..2] and dst[2..4]
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*/
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void SkChopQuadAt(const SkPoint src[3], SkPoint dst[5], SkScalar t);
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/** Given a src quadratic bezier, chop it at the specified t == 1/2,
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The new quads are returned in dst[0..2] and dst[2..4]
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*/
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void SkChopQuadAtHalf(const SkPoint src[3], SkPoint dst[5]);
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/** Given the 3 coefficients for a quadratic bezier (either X or Y values), look
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for extrema, and return the number of t-values that are found that represent
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these extrema. If the quadratic has no extrema betwee (0..1) exclusive, the
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function returns 0.
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Returned count tValues[]
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0 ignored
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1 0 < tValues[0] < 1
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*/
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int SkFindQuadExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar tValues[1]);
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/** Given 3 points on a quadratic bezier, chop it into 1, 2 beziers such that
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the resulting beziers are monotonic in Y. This is called by the scan converter.
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Depending on what is returned, dst[] is treated as follows
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0 dst[0..2] is the original quad
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1 dst[0..2] and dst[2..4] are the two new quads
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*/
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int SkChopQuadAtYExtrema(const SkPoint src[3], SkPoint dst[5]);
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int SkChopQuadAtXExtrema(const SkPoint src[3], SkPoint dst[5]);
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/** Given 3 points on a quadratic bezier, divide it into 2 quadratics
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if the point of maximum curvature exists on the quad segment.
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Depending on what is returned, dst[] is treated as follows
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1 dst[0..2] is the original quad
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2 dst[0..2] and dst[2..4] are the two new quads
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If dst == null, it is ignored and only the count is returned.
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*/
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int SkChopQuadAtMaxCurvature(const SkPoint src[3], SkPoint dst[5]);
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/** Given 3 points on a quadratic bezier, use degree elevation to
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convert it into the cubic fitting the same curve. The new cubic
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curve is returned in dst[0..3].
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*/
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SK_API void SkConvertQuadToCubic(const SkPoint src[3], SkPoint dst[4]);
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///////////////////////////////////////////////////////////////////////////////
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/** Convert from parametric from (pts) to polynomial coefficients
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coeff[0]*T^3 + coeff[1]*T^2 + coeff[2]*T + coeff[3]
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*/
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void SkGetCubicCoeff(const SkPoint pts[4], SkScalar cx[4], SkScalar cy[4]);
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/** Set pt to the point on the src cubic specified by t. t must be
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0 <= t <= 1.0
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*/
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void SkEvalCubicAt(const SkPoint src[4], SkScalar t, SkPoint* locOrNull,
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SkVector* tangentOrNull, SkVector* curvatureOrNull);
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/** Given a src cubic bezier, chop it at the specified t value,
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where 0 < t < 1, and return the two new cubics in dst:
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dst[0..3] and dst[3..6]
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*/
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void SkChopCubicAt(const SkPoint src[4], SkPoint dst[7], SkScalar t);
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/** Given a src cubic bezier, chop it at the specified t values,
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where 0 < t < 1, and return the new cubics in dst:
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dst[0..3],dst[3..6],...,dst[3*t_count..3*(t_count+1)]
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*/
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void SkChopCubicAt(const SkPoint src[4], SkPoint dst[], const SkScalar t[],
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int t_count);
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/** Given a src cubic bezier, chop it at the specified t == 1/2,
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The new cubics are returned in dst[0..3] and dst[3..6]
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*/
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void SkChopCubicAtHalf(const SkPoint src[4], SkPoint dst[7]);
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/** Given the 4 coefficients for a cubic bezier (either X or Y values), look
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for extrema, and return the number of t-values that are found that represent
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these extrema. If the cubic has no extrema betwee (0..1) exclusive, the
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function returns 0.
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Returned count tValues[]
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0 ignored
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1 0 < tValues[0] < 1
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2 0 < tValues[0] < tValues[1] < 1
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*/
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int SkFindCubicExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar d,
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SkScalar tValues[2]);
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/** Given 4 points on a cubic bezier, chop it into 1, 2, 3 beziers such that
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the resulting beziers are monotonic in Y. This is called by the scan converter.
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Depending on what is returned, dst[] is treated as follows
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0 dst[0..3] is the original cubic
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1 dst[0..3] and dst[3..6] are the two new cubics
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2 dst[0..3], dst[3..6], dst[6..9] are the three new cubics
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If dst == null, it is ignored and only the count is returned.
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*/
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int SkChopCubicAtYExtrema(const SkPoint src[4], SkPoint dst[10]);
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int SkChopCubicAtXExtrema(const SkPoint src[4], SkPoint dst[10]);
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/** Given a cubic bezier, return 0, 1, or 2 t-values that represent the
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inflection points.
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*/
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int SkFindCubicInflections(const SkPoint src[4], SkScalar tValues[2]);
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/** Return 1 for no chop, 2 for having chopped the cubic at a single
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inflection point, 3 for having chopped at 2 inflection points.
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dst will hold the resulting 1, 2, or 3 cubics.
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*/
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int SkChopCubicAtInflections(const SkPoint src[4], SkPoint dst[10]);
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int SkFindCubicMaxCurvature(const SkPoint src[4], SkScalar tValues[3]);
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int SkChopCubicAtMaxCurvature(const SkPoint src[4], SkPoint dst[13],
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SkScalar tValues[3] = NULL);
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/** Given a monotonic cubic bezier, determine whether an xray intersects the
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cubic.
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By definition the cubic is open at the starting point; in other
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words, if pt.fY is equivalent to cubic[0].fY, and pt.fX is to the
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left of the curve, the line is not considered to cross the curve,
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but if it is equal to cubic[3].fY then it is considered to
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cross.
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Optional outgoing "ambiguous" argument indicates whether the answer is
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ambiguous because the query occurred exactly at one of the endpoints' y
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coordinates, indicating that another query y coordinate is preferred
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for robustness.
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*/
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bool SkXRayCrossesMonotonicCubic(const SkXRay& pt, const SkPoint cubic[4],
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bool* ambiguous = NULL);
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/** Given an arbitrary cubic bezier, return the number of times an xray crosses
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the cubic. Valid return values are [0..3]
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By definition the cubic is open at the starting point; in other
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words, if pt.fY is equivalent to cubic[0].fY, and pt.fX is to the
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left of the curve, the line is not considered to cross the curve,
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but if it is equal to cubic[3].fY then it is considered to
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cross.
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Optional outgoing "ambiguous" argument indicates whether the answer is
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ambiguous because the query occurred exactly at one of the endpoints' y
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coordinates or at a tangent point, indicating that another query y
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coordinate is preferred for robustness.
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*/
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int SkNumXRayCrossingsForCubic(const SkXRay& pt, const SkPoint cubic[4],
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bool* ambiguous = NULL);
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///////////////////////////////////////////////////////////////////////////////
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enum SkRotationDirection {
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kCW_SkRotationDirection,
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kCCW_SkRotationDirection
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};
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/** Maximum number of points needed in the quadPoints[] parameter for
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SkBuildQuadArc()
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*/
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#define kSkBuildQuadArcStorage 17
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/** Given 2 unit vectors and a rotation direction, fill out the specified
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array of points with quadratic segments. Return is the number of points
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written to, which will be { 0, 3, 5, 7, ... kSkBuildQuadArcStorage }
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matrix, if not null, is appled to the points before they are returned.
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*/
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int SkBuildQuadArc(const SkVector& unitStart, const SkVector& unitStop,
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SkRotationDirection, const SkMatrix*, SkPoint quadPoints[]);
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// experimental
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struct SkConic {
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SkPoint fPts[3];
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SkScalar fW;
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void set(const SkPoint pts[3], SkScalar w) {
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memcpy(fPts, pts, 3 * sizeof(SkPoint));
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fW = w;
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}
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/**
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* Given a t-value [0...1] return its position and/or tangent.
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* If pos is not null, return its position at the t-value.
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* If tangent is not null, return its tangent at the t-value. NOTE the
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* tangent value's length is arbitrary, and only its direction should
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* be used.
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*/
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void evalAt(SkScalar t, SkPoint* pos, SkVector* tangent = NULL) const;
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void chopAt(SkScalar t, SkConic dst[2]) const;
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void chop(SkConic dst[2]) const;
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void computeAsQuadError(SkVector* err) const;
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bool asQuadTol(SkScalar tol) const;
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/**
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* return the power-of-2 number of quads needed to approximate this conic
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* with a sequence of quads. Will be >= 0.
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*/
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int computeQuadPOW2(SkScalar tol) const;
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/**
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* Chop this conic into N quads, stored continguously in pts[], where
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* N = 1 << pow2. The amount of storage needed is (1 + 2 * N)
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*/
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int chopIntoQuadsPOW2(SkPoint pts[], int pow2) const;
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bool findXExtrema(SkScalar* t) const;
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bool findYExtrema(SkScalar* t) const;
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bool chopAtXExtrema(SkConic dst[2]) const;
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bool chopAtYExtrema(SkConic dst[2]) const;
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void computeTightBounds(SkRect* bounds) const;
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void computeFastBounds(SkRect* bounds) const;
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};
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#include "SkTemplates.h"
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/**
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* Help class to allocate storage for approximating a conic with N quads.
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*/
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class SkAutoConicToQuads {
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public:
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SkAutoConicToQuads() : fQuadCount(0) {}
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/**
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* Given a conic and a tolerance, return the array of points for the
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* approximating quad(s). Call countQuads() to know the number of quads
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* represented in these points.
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*
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* The quads are allocated to share end-points. e.g. if there are 4 quads,
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* there will be 9 points allocated as follows
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* quad[0] == pts[0..2]
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* quad[1] == pts[2..4]
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* quad[2] == pts[4..6]
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* quad[3] == pts[6..8]
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*/
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const SkPoint* computeQuads(const SkConic& conic, SkScalar tol) {
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int pow2 = conic.computeQuadPOW2(tol);
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fQuadCount = 1 << pow2;
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SkPoint* pts = fStorage.reset(1 + 2 * fQuadCount);
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conic.chopIntoQuadsPOW2(pts, pow2);
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return pts;
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}
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const SkPoint* computeQuads(const SkPoint pts[3], SkScalar weight,
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SkScalar tol) {
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SkConic conic;
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conic.set(pts, weight);
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return computeQuads(conic, tol);
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}
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int countQuads() const { return fQuadCount; }
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private:
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enum {
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kQuadCount = 8, // should handle most conics
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kPointCount = 1 + 2 * kQuadCount,
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};
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SkAutoSTMalloc<kPointCount, SkPoint> fStorage;
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int fQuadCount; // #quads for current usage
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};
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#endif
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