SkGeometry.h

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/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
#ifndef SkGeometry_DEFINED
#define SkGeometry_DEFINED
 
#include "include/core/SkPoint.h"
#include "include/core/SkScalar.h"
#include "include/core/SkTypes.h"
#include "include/private/base/SkFloatingPoint.h"
#include "src/base/SkVx.h"
 
#include <cstring>
 
class SkMatrix;
struct SkRect;
 
static inline skvx::float2 from_point(const SkPoint& point) {
    return skvx::float2::Load(&point);
}
 
static inline SkPoint to_point(const skvx::float2& x) {
    SkPoint point;
    x.store(&point);
    return point;
}
 
static skvx::float2 times_2(const skvx::float2& value) {
    return value + value;
}
 
/** Given a quadratic equation Ax^2 + Bx + C = 0, return 0, 1, 2 roots for the
    equation.
*/
int SkFindUnitQuadRoots(SkScalar A, SkScalar B, SkScalar C, SkScalar roots[2]);
 
/** Measures the angle between two vectors, in the range [0, pi].
*/
float SkMeasureAngleBetweenVectors(SkVector, SkVector);
 
/** Returns a new, arbitrarily scaled vector that bisects the given vectors. The returned bisector
    will always point toward the interior of the provided vectors.
*/
SkVector SkFindBisector(SkVector, SkVector);
 
///////////////////////////////////////////////////////////////////////////////
 
SkPoint SkEvalQuadAt(const SkPoint src[3], SkScalar t);
SkPoint SkEvalQuadTangentAt(const SkPoint src[3], SkScalar t);
 
/** Set pt to the point on the src quadratic specified by t. t must be
    0 <= t <= 1.0
*/
void SkEvalQuadAt(const SkPoint src[3], SkScalar t, SkPoint* pt, SkVector* tangent = nullptr);
 
/** Given a src quadratic bezier, chop it at the specified t value,
    where 0 < t < 1, and return the two new quadratics in dst:
    dst[0..2] and dst[2..4]
*/
void SkChopQuadAt(const SkPoint src[3], SkPoint dst[5], SkScalar t);
 
/** Given a src quadratic bezier, chop it at the specified t == 1/2,
    The new quads are returned in dst[0..2] and dst[2..4]
*/
void SkChopQuadAtHalf(const SkPoint src[3], SkPoint dst[5]);
 
/** Measures the rotation of the given quadratic curve in radians.
 
    Rotation is perhaps easiest described via a driving analogy: If you drive your car along the
    curve from p0 to p2, then by the time you arrive at p2, how many radians will your car have
    rotated? For a quadratic this is the same as the vector inside the tangents at the endpoints.
 
    Quadratics can have rotations in the range [0, pi].
*/
inline float SkMeasureQuadRotation(const SkPoint pts[3]) {
    return SkMeasureAngleBetweenVectors(pts[1] - pts[0], pts[2] - pts[1]);
}
 
/** Given a src quadratic bezier, returns the T value whose tangent angle is halfway between the
    tangents at p0 and p3.
*/
float SkFindQuadMidTangent(const SkPoint src[3]);
 
/** Given a src quadratic bezier, chop it at the tangent whose angle is halfway between the
    tangents at p0 and p2. The new quads are returned in dst[0..2] and dst[2..4].
*/
inline void SkChopQuadAtMidTangent(const SkPoint src[3], SkPoint dst[5]) {
    SkChopQuadAt(src, dst, SkFindQuadMidTangent(src));
}
 
/** Given the 3 coefficients for a quadratic bezier (either X or Y values), look
    for extrema, and return the number of t-values that are found that represent
    these extrema. If the quadratic has no extrema betwee (0..1) exclusive, the
    function returns 0.
    Returned count      tValues[]
    0                   ignored
    1                   0 < tValues[0] < 1
*/
int SkFindQuadExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar tValues[1]);
 
/** Given 3 points on a quadratic bezier, chop it into 1, 2 beziers such that
    the resulting beziers are monotonic in Y. This is called by the scan converter.
    Depending on what is returned, dst[] is treated as follows
    0   dst[0..2] is the original quad
    1   dst[0..2] and dst[2..4] are the two new quads
*/
int SkChopQuadAtYExtrema(const SkPoint src[3], SkPoint dst[5]);
int SkChopQuadAtXExtrema(const SkPoint src[3], SkPoint dst[5]);
 
/** Given 3 points on a quadratic bezier, if the point of maximum
    curvature exists on the segment, returns the t value for this
    point along the curve. Otherwise it will return a value of 0.
*/
SkScalar SkFindQuadMaxCurvature(const SkPoint src[3]);
 
/** Given 3 points on a quadratic bezier, divide it into 2 quadratics
    if the point of maximum curvature exists on the quad segment.
    Depending on what is returned, dst[] is treated as follows
    1   dst[0..2] is the original quad
    2   dst[0..2] and dst[2..4] are the two new quads
    If dst == null, it is ignored and only the count is returned.
*/
int SkChopQuadAtMaxCurvature(const SkPoint src[3], SkPoint dst[5]);
 
/** Given 3 points on a quadratic bezier, use degree elevation to
    convert it into the cubic fitting the same curve. The new cubic
    curve is returned in dst[0..3].
*/
void SkConvertQuadToCubic(const SkPoint src[3], SkPoint dst[4]);
 
///////////////////////////////////////////////////////////////////////////////
 
/** Set pt to the point on the src cubic specified by t. t must be
    0 <= t <= 1.0
*/
void SkEvalCubicAt(const SkPoint src[4], SkScalar t, SkPoint* locOrNull,
                   SkVector* tangentOrNull, SkVector* curvatureOrNull);
 
/** Given a src cubic bezier, chop it at the specified t value,
    where 0 <= t <= 1, and return the two new cubics in dst:
    dst[0..3] and dst[3..6]
*/
void SkChopCubicAt(const SkPoint src[4], SkPoint dst[7], SkScalar t);
 
/** Given a src cubic bezier, chop it at the specified t0 and t1 values,
    where 0 <= t0 <= t1 <= 1, and return the three new cubics in dst:
    dst[0..3], dst[3..6], and dst[6..9]
*/
void SkChopCubicAt(const SkPoint src[4], SkPoint dst[10], float t0, float t1);
 
/** Given a src cubic bezier, chop it at the specified t values,
    where 0 <= t0 <= t1 <= ... <= 1, and return the new cubics in dst:
    dst[0..3],dst[3..6],...,dst[3*t_count..3*(t_count+1)]
*/
void SkChopCubicAt(const SkPoint src[4], SkPoint dst[], const SkScalar t[],
                   int t_count);
 
/** Given a src cubic bezier, chop it at the specified t == 1/2,
    The new cubics are returned in dst[0..3] and dst[3..6]
*/
void SkChopCubicAtHalf(const SkPoint src[4], SkPoint dst[7]);
 
/** Given a cubic curve with no inflection points, this method measures the rotation in radians.
 
    Rotation is perhaps easiest described via a driving analogy: If you drive your car along the
    curve from p0 to p3, then by the time you arrive at p3, how many radians will your car have
    rotated? This is not quite the same as the vector inside the tangents at the endpoints, even
    without inflection, because the curve might rotate around the outside of the
    tangents (>= 180 degrees) or the inside (<= 180 degrees).
 
    Cubics can have rotations in the range [0, 2*pi].
 
    NOTE: The caller must either call SkChopCubicAtInflections or otherwise prove that the provided
    cubic has no inflection points prior to calling this method.
*/
float SkMeasureNonInflectCubicRotation(const SkPoint[4]);
 
/** Given a src cubic bezier, returns the T value whose tangent angle is halfway between the
    tangents at p0 and p3.
*/
float SkFindCubicMidTangent(const SkPoint src[4]);
 
/** Given a src cubic bezier, chop it at the tangent whose angle is halfway between the
    tangents at p0 and p3. The new cubics are returned in dst[0..3] and dst[3..6].
 
    NOTE: 0- and 360-degree flat lines don't have single points of midtangent.
    (tangent == midtangent at every point on these curves except the cusp points.)
    If this is the case then we simply chop at a point which guarantees neither side rotates more
    than 180 degrees.
*/
inline void SkChopCubicAtMidTangent(const SkPoint src[4], SkPoint dst[7]) {
    SkChopCubicAt(src, dst, SkFindCubicMidTangent(src));
}
 
/** Given the 4 coefficients for a cubic bezier (either X or Y values), look
    for extrema, and return the number of t-values that are found that represent
    these extrema. If the cubic has no extrema betwee (0..1) exclusive, the
    function returns 0.
    Returned count      tValues[]
    0                   ignored
    1                   0 < tValues[0] < 1
    2                   0 < tValues[0] < tValues[1] < 1
*/
int SkFindCubicExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar d,
                       SkScalar tValues[2]);
 
/** Given 4 points on a cubic bezier, chop it into 1, 2, 3 beziers such that
    the resulting beziers are monotonic in Y. This is called by the scan converter.
    Depending on what is returned, dst[] is treated as follows
    0   dst[0..3] is the original cubic
    1   dst[0..3] and dst[3..6] are the two new cubics
    2   dst[0..3], dst[3..6], dst[6..9] are the three new cubics
    If dst == null, it is ignored and only the count is returned.
*/
int SkChopCubicAtYExtrema(const SkPoint src[4], SkPoint dst[10]);
int SkChopCubicAtXExtrema(const SkPoint src[4], SkPoint dst[10]);
 
/** Given a cubic bezier, return 0, 1, or 2 t-values that represent the
    inflection points.
*/
int SkFindCubicInflections(const SkPoint src[4], SkScalar tValues[2]);
 
/** Return 1 for no chop, 2 for having chopped the cubic at a single
    inflection point, 3 for having chopped at 2 inflection points.
    dst will hold the resulting 1, 2, or 3 cubics.
*/
int SkChopCubicAtInflections(const SkPoint src[4], SkPoint dst[10]);
 
int SkFindCubicMaxCurvature(const SkPoint src[4], SkScalar tValues[3]);
int SkChopCubicAtMaxCurvature(const SkPoint src[4], SkPoint dst[13],
                              SkScalar tValues[3] = nullptr);
/** Returns t value of cusp if cubic has one; returns -1 otherwise.
 */
SkScalar SkFindCubicCusp(const SkPoint src[4]);
 
/** Given a monotonically increasing or decreasing cubic bezier src, chop it
 *  where the X value is the specified value. The returned cubics will be in
 *  dst, sharing the middle point. That is, the first cubic is dst[0..3] and
 *  the second dst[3..6].
 *
 *  If the cubic provided is *not* monotone, it will be chopped at the first
 *  time the curve has the specified X value.
 *
 *  If the cubic never reaches the specified value, the function returns false.
*/
bool SkChopMonoCubicAtX(const SkPoint src[4], SkScalar x, SkPoint dst[7]);
 
/** Given a monotonically increasing or decreasing cubic bezier src, chop it
 *  where the Y value is the specified value. The returned cubics will be in
 *  dst, sharing the middle point. That is, the first cubic is dst[0..3] and
 *  the second dst[3..6].
 *
 *  If the cubic provided is *not* monotone, it will be chopped at the first
 *  time the curve has the specified Y value.
 *
 *  If the cubic never reaches the specified value, the function returns false.
*/
bool SkChopMonoCubicAtY(const SkPoint src[4], SkScalar y, SkPoint dst[7]);
 
enum class SkCubicType {
    kSerpentine,
    kLoop,
    kLocalCusp,       // Cusp at a non-infinite parameter value with an inflection at t=infinity.
    kCuspAtInfinity,  // Cusp with a cusp at t=infinity and a local inflection.
    kQuadratic,
    kLineOrPoint
};
 
static inline bool SkCubicIsDegenerate(SkCubicType type) {
    switch (type) {
        case SkCubicType::kSerpentine:
        case SkCubicType::kLoop:
        case SkCubicType::kLocalCusp:
        case SkCubicType::kCuspAtInfinity:
            return false;
        case SkCubicType::kQuadratic:
        case SkCubicType::kLineOrPoint:
            return true;
    }
    SK_ABORT("Invalid SkCubicType");
}
 
static inline const char* SkCubicTypeName(SkCubicType type) {
    switch (type) {
        case SkCubicType::kSerpentine: return "kSerpentine";
        case SkCubicType::kLoop: return "kLoop";
        case SkCubicType::kLocalCusp: return "kLocalCusp";
        case SkCubicType::kCuspAtInfinity: return "kCuspAtInfinity";
        case SkCubicType::kQuadratic: return "kQuadratic";
        case SkCubicType::kLineOrPoint: return "kLineOrPoint";
    }
    SK_ABORT("Invalid SkCubicType");
}
 
/** Returns the cubic classification.
 
    t[],s[] are set to the two homogeneous parameter values at which points the lines L & M
    intersect with K, sorted from smallest to largest and oriented so positive values of the
    implicit are on the "left" side. For a serpentine curve they are the inflection points. For a
    loop they are the double point. For a local cusp, they are both equal and denote the cusp point.
    For a cusp at an infinite parameter value, one will be the local inflection point and the other
    +inf (t,s = 1,0). If the curve is degenerate (i.e. quadratic or linear) they are both set to a
    parameter value of +inf (t,s = 1,0).
 
    d[] is filled with the cubic inflection function coefficients. See "Resolution Independent
    Curve Rendering using Programmable Graphics Hardware", 4.2 Curve Categorization:
 
    If the input points contain infinities or NaN, the return values are undefined.
 
    https://www.microsoft.com/en-us/research/wp-content/uploads/2005/01/p1000-loop.pdf
*/
SkCubicType SkClassifyCubic(const SkPoint p[4], double t[2] = nullptr, double s[2] = nullptr,
                            double d[4] = nullptr);
 
///////////////////////////////////////////////////////////////////////////////
 
enum SkRotationDirection {
    kCW_SkRotationDirection,
    kCCW_SkRotationDirection
};
 
struct SkConic {
    SkConic() {}
    SkConic(const SkPoint& p0, const SkPoint& p1, const SkPoint& p2, SkScalar w) {
        this->set(p0, p1, p2, w);
    }
 
    SkConic(const SkPoint pts[3], SkScalar w) {
        this->set(pts, w);
    }
 
    SkPoint  fPts[3];
    SkScalar fW;
 
    void set(const SkPoint pts[3], SkScalar w) {
        memcpy(fPts, pts, 3 * sizeof(SkPoint));
        this->setW(w);
    }
 
    void set(const SkPoint& p0, const SkPoint& p1, const SkPoint& p2, SkScalar w) {
        fPts[0] = p0;
        fPts[1] = p1;
        fPts[2] = p2;
        this->setW(w);
    }
 
    void setW(SkScalar w) {
        if (SkIsFinite(w)) {
            SkASSERT(w > 0);
        }
 
        // Guard against bad weights by forcing them to 1.
        fW = w > 0 && SkIsFinite(w) ? w : 1;
    }
 
    /**
     *  Given a t-value [0...1] return its position and/or tangent.
     *  If pos is not null, return its position at the t-value.
     *  If tangent is not null, return its tangent at the t-value. NOTE the
     *  tangent value's length is arbitrary, and only its direction should
     *  be used.
     */
    void evalAt(SkScalar t, SkPoint* pos, SkVector* tangent = nullptr) const;
    [[nodiscard]] bool chopAt(SkScalar t, SkConic dst[2]) const;
    void chopAt(SkScalar t1, SkScalar t2, SkConic* dst) const;
    void chop(SkConic dst[2]) const;
 
    SkPoint evalAt(SkScalar t) const;
    SkVector evalTangentAt(SkScalar t) const;
 
    void computeAsQuadError(SkVector* err) const;
    bool asQuadTol(SkScalar tol) const;
 
    /**
     *  return the power-of-2 number of quads needed to approximate this conic
     *  with a sequence of quads. Will be >= 0.
     */
    int SK_SPI computeQuadPOW2(SkScalar tol) const;
 
    /**
     *  Chop this conic into N quads, stored continguously in pts[], where
     *  N = 1 << pow2. The amount of storage needed is (1 + 2 * N)
     */
    [[nodiscard]] int SK_SPI chopIntoQuadsPOW2(SkPoint pts[], int pow2) const;
 
    float findMidTangent() const;
    bool findXExtrema(SkScalar* t) const;
    bool findYExtrema(SkScalar* t) const;
    bool chopAtXExtrema(SkConic dst[2]) const;
    bool chopAtYExtrema(SkConic dst[2]) const;
 
    void computeTightBounds(SkRect* bounds) const;
    void computeFastBounds(SkRect* bounds) const;
 
    /** Find the parameter value where the conic takes on its maximum curvature.
     *
     *  @param t   output scalar for max curvature.  Will be unchanged if
     *             max curvature outside 0..1 range.
     *
     *  @return  true if max curvature found inside 0..1 range, false otherwise
     */
//    bool findMaxCurvature(SkScalar* t) const;  // unimplemented
 
    static SkScalar TransformW(const SkPoint[3], SkScalar w, const SkMatrix&);
 
    enum {
        kMaxConicsForArc = 5
    };
    static int BuildUnitArc(const SkVector& start, const SkVector& stop, SkRotationDirection,
                            const SkMatrix*, SkConic conics[kMaxConicsForArc]);
};
 
// inline helpers are contained in a namespace to avoid external leakage to fragile SkVx members
namespace {  // NOLINT(google-build-namespaces)
 
/**
 *  use for : eval(t) == A * t^2 + B * t + C
 */
struct SkQuadCoeff {
    SkQuadCoeff() {}
 
    SkQuadCoeff(const skvx::float2& A, const skvx::float2& B, const skvx::float2& C)
        : fA(A)
        , fB(B)
        , fC(C)
    {
    }
 
    SkQuadCoeff(const SkPoint src[3]) {
        fC = from_point(src[0]);
        auto P1 = from_point(src[1]);
        auto P2 = from_point(src[2]);
        fB = times_2(P1 - fC);
        fA = P2 - times_2(P1) + fC;
    }
 
    skvx::float2 eval(const skvx::float2& tt) {
        return (fA * tt + fB) * tt + fC;
    }
 
    skvx::float2 fA;
    skvx::float2 fB;
    skvx::float2 fC;
};
 
struct SkConicCoeff {
    SkConicCoeff(const SkConic& conic) {
        skvx::float2 p0 = from_point(conic.fPts[0]);
        skvx::float2 p1 = from_point(conic.fPts[1]);
        skvx::float2 p2 = from_point(conic.fPts[2]);
        skvx::float2 ww(conic.fW);
 
        auto p1w = p1 * ww;
        fNumer.fC = p0;
        fNumer.fA = p2 - times_2(p1w) + p0;
        fNumer.fB = times_2(p1w - p0);
 
        fDenom.fC = 1;
        fDenom.fB = times_2(ww - fDenom.fC);
        fDenom.fA = 0 - fDenom.fB;
    }
 
    skvx::float2 eval(SkScalar t) {
        skvx::float2 tt(t);
        skvx::float2 numer = fNumer.eval(tt);
        skvx::float2 denom = fDenom.eval(tt);
        return numer / denom;
    }
 
    SkQuadCoeff fNumer;
    SkQuadCoeff fDenom;
};
 
struct SkCubicCoeff {
    SkCubicCoeff(const SkPoint src[4]) {
        skvx::float2 P0 = from_point(src[0]);
        skvx::float2 P1 = from_point(src[1]);
        skvx::float2 P2 = from_point(src[2]);
        skvx::float2 P3 = from_point(src[3]);
        skvx::float2 three(3);
        fA = P3 + three * (P1 - P2) - P0;
        fB = three * (P2 - times_2(P1) + P0);
        fC = three * (P1 - P0);
        fD = P0;
    }
 
    skvx::float2 eval(const skvx::float2& t) {
        return ((fA * t + fB) * t + fC) * t + fD;
    }
 
    skvx::float2 fA;
    skvx::float2 fB;
    skvx::float2 fC;
    skvx::float2 fD;
};
 
}  // namespace
 
#include "include/private/base/SkTemplates.h"
 
/**
 *  Help class to allocate storage for approximating a conic with N quads.
 */
class SkAutoConicToQuads {
public:
    SkAutoConicToQuads() : fQuadCount(0) {}
 
    /**
     *  Given a conic and a tolerance, return the array of points for the
     *  approximating quad(s). Call countQuads() to know the number of quads
     *  represented in these points.
     *
     *  The quads are allocated to share end-points. e.g. if there are 4 quads,
     *  there will be 9 points allocated as follows
     *      quad[0] == pts[0..2]
     *      quad[1] == pts[2..4]
     *      quad[2] == pts[4..6]
     *      quad[3] == pts[6..8]
     */
    const SkPoint* computeQuads(const SkConic& conic, SkScalar tol) {
        int pow2 = conic.computeQuadPOW2(tol);
        fQuadCount = 1 << pow2;
        SkPoint* pts = fStorage.reset(1 + 2 * fQuadCount);
        fQuadCount = conic.chopIntoQuadsPOW2(pts, pow2);
        return pts;
    }
 
    const SkPoint* computeQuads(const SkPoint pts[3], SkScalar weight,
                                SkScalar tol) {
        SkConic conic;
        conic.set(pts, weight);
        return computeQuads(conic, tol);
    }
 
    int countQuads() const { return fQuadCount; }
 
private:
    enum {
        kQuadCount = 8, // should handle most conics
        kPointCount = 1 + 2 * kQuadCount,
    };
    skia_private::AutoSTMalloc<kPointCount, SkPoint> fStorage;
    int fQuadCount; // #quads for current usage
};
 
#endif