path: root/src/core/SkMatrix.cpp

/*
 * 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.
 */

#include "SkMatrix.h"
#include "SkFloatBits.h"
#include "SkString.h"

#include <stddef.h>

// In a few places, we performed the following
//      a * b + c * d + e
// as
//      a * b + (c * d + e)
//
// sdot and scross are indended to capture these compound operations into a
// function, with an eye toward considering upscaling the intermediates to
// doubles for more precision (as we do in concat and invert).
//
// However, these few lines that performed the last add before the "dot", cause
// tiny image differences, so we guard that change until we see the impact on
// chrome's layouttests.
//
#define SK_LEGACY_MATRIX_MATH_ORDER

static inline float SkDoubleToFloat(double x) {
    return static_cast<float>(x);
}

/*      [scale-x    skew-x      trans-x]   [X]   [X']
        [skew-y     scale-y     trans-y] * [Y] = [Y']
        [persp-0    persp-1     persp-2]   [1]   [1 ]
*/

void SkMatrix::reset() {
    fMat[kMScaleX] = fMat[kMScaleY] = fMat[kMPersp2] = 1;
    fMat[kMSkewX]  = fMat[kMSkewY] =
    fMat[kMTransX] = fMat[kMTransY] =
    fMat[kMPersp0] = fMat[kMPersp1] = 0;

    this->setTypeMask(kIdentity_Mask | kRectStaysRect_Mask);
}

// this guy aligns with the masks, so we can compute a mask from a varaible 0/1
enum {
    kTranslate_Shift,
    kScale_Shift,
    kAffine_Shift,
    kPerspective_Shift,
    kRectStaysRect_Shift
};

static const int32_t kScalar1Int = 0x3f800000;

uint8_t SkMatrix::computePerspectiveTypeMask() const {
    // Benchmarking suggests that replacing this set of SkScalarAs2sCompliment
    // is a win, but replacing those below is not. We don't yet understand
    // that result.
    if (fMat[kMPersp0] != 0 || fMat[kMPersp1] != 0 || fMat[kMPersp2] != 1) {
        // If this is a perspective transform, we return true for all other
        // transform flags - this does not disable any optimizations, respects
        // the rule that the type mask must be conservative, and speeds up
        // type mask computation.
        return SkToU8(kORableMasks);
    }

    return SkToU8(kOnlyPerspectiveValid_Mask | kUnknown_Mask);
}

uint8_t SkMatrix::computeTypeMask() const {
    unsigned mask = 0;

    if (fMat[kMPersp0] != 0 || fMat[kMPersp1] != 0 || fMat[kMPersp2] != 1) {
        // Once it is determined that that this is a perspective transform,
        // all other flags are moot as far as optimizations are concerned.
        return SkToU8(kORableMasks);
    }

    if (fMat[kMTransX] != 0 || fMat[kMTransY] != 0) {
        mask |= kTranslate_Mask;
    }

    int m00 = SkScalarAs2sCompliment(fMat[SkMatrix::kMScaleX]);
    int m01 = SkScalarAs2sCompliment(fMat[SkMatrix::kMSkewX]);
    int m10 = SkScalarAs2sCompliment(fMat[SkMatrix::kMSkewY]);
    int m11 = SkScalarAs2sCompliment(fMat[SkMatrix::kMScaleY]);

    if (m01 | m10) {
        // The skew components may be scale-inducing, unless we are dealing
        // with a pure rotation.  Testing for a pure rotation is expensive,
        // so we opt for being conservative by always setting the scale bit.
        // along with affine.
        // By doing this, we are also ensuring that matrices have the same
        // type masks as their inverses.
        mask |= kAffine_Mask | kScale_Mask;

        // For rectStaysRect, in the affine case, we only need check that
        // the primary diagonal is all zeros and that the secondary diagonal
        // is all non-zero.

        // map non-zero to 1
        m01 = m01 != 0;
        m10 = m10 != 0;

        int dp0 = 0 == (m00 | m11) ;  // true if both are 0
        int ds1 = m01 & m10;        // true if both are 1

        mask |= (dp0 & ds1) << kRectStaysRect_Shift;
    } else {
        // Only test for scale explicitly if not affine, since affine sets the
        // scale bit.
        if ((m00 - kScalar1Int) | (m11 - kScalar1Int)) {
            mask |= kScale_Mask;
        }

        // Not affine, therefore we already know secondary diagonal is
        // all zeros, so we just need to check that primary diagonal is
        // all non-zero.

        // map non-zero to 1
        m00 = m00 != 0;
        m11 = m11 != 0;

        // record if the (p)rimary diagonal is all non-zero
        mask |= (m00 & m11) << kRectStaysRect_Shift;
    }

    return SkToU8(mask);
}

///////////////////////////////////////////////////////////////////////////////

bool operator==(const SkMatrix& a, const SkMatrix& b) {
    const SkScalar* SK_RESTRICT ma = a.fMat;
    const SkScalar* SK_RESTRICT mb = b.fMat;

    return  ma[0] == mb[0] && ma[1] == mb[1] && ma[2] == mb[2] &&
            ma[3] == mb[3] && ma[4] == mb[4] && ma[5] == mb[5] &&
            ma[6] == mb[6] && ma[7] == mb[7] && ma[8] == mb[8];
}

///////////////////////////////////////////////////////////////////////////////

// helper function to determine if upper-left 2x2 of matrix is degenerate
static inline bool is_degenerate_2x2(SkScalar scaleX, SkScalar skewX,
                                     SkScalar skewY,  SkScalar scaleY) {
    SkScalar perp_dot = scaleX*scaleY - skewX*skewY;
    return SkScalarNearlyZero(perp_dot, SK_ScalarNearlyZero*SK_ScalarNearlyZero);
}

///////////////////////////////////////////////////////////////////////////////

bool SkMatrix::isSimilarity(SkScalar tol) const {
    // if identity or translate matrix
    TypeMask mask = this->getType();
    if (mask <= kTranslate_Mask) {
        return true;
    }
    if (mask & kPerspective_Mask) {
        return false;
    }

    SkScalar mx = fMat[kMScaleX];
    SkScalar my = fMat[kMScaleY];
    // if no skew, can just compare scale factors
    if (!(mask & kAffine_Mask)) {
        return !SkScalarNearlyZero(mx) && SkScalarNearlyEqual(SkScalarAbs(mx), SkScalarAbs(my));
    }
    SkScalar sx = fMat[kMSkewX];
    SkScalar sy = fMat[kMSkewY];

    if (is_degenerate_2x2(mx, sx, sy, my)) {
        return false;
    }

    // upper 2x2 is rotation/reflection + uniform scale if basis vectors
    // are 90 degree rotations of each other
    return (SkScalarNearlyEqual(mx, my, tol) && SkScalarNearlyEqual(sx, -sy, tol))
        || (SkScalarNearlyEqual(mx, -my, tol) && SkScalarNearlyEqual(sx, sy, tol));
}

bool SkMatrix::preservesRightAngles(SkScalar tol) const {
    TypeMask mask = this->getType();

    if (mask <= kTranslate_Mask) {
        // identity, translate and/or scale
        return true;
    }
    if (mask & kPerspective_Mask) {
        return false;
    }

    SkASSERT(mask & (kAffine_Mask | kScale_Mask));

    SkScalar mx = fMat[kMScaleX];
    SkScalar my = fMat[kMScaleY];
    SkScalar sx = fMat[kMSkewX];
    SkScalar sy = fMat[kMSkewY];

    if (is_degenerate_2x2(mx, sx, sy, my)) {
        return false;
    }

    // upper 2x2 is scale + rotation/reflection if basis vectors are orthogonal
    SkVector vec[2];
    vec[0].set(mx, sy);
    vec[1].set(sx, my);

    return SkScalarNearlyZero(vec[0].dot(vec[1]), SkScalarSquare(tol));
}

///////////////////////////////////////////////////////////////////////////////

static inline SkScalar sdot(SkScalar a, SkScalar b, SkScalar c, SkScalar d) {
    return a * b + c * d;
}

static inline SkScalar sdot(SkScalar a, SkScalar b, SkScalar c, SkScalar d,
                             SkScalar e, SkScalar f) {
    return a * b + c * d + e * f;
}

static inline SkScalar scross(SkScalar a, SkScalar b, SkScalar c, SkScalar d) {
    return a * b - c * d;
}

void SkMatrix::setTranslate(SkScalar dx, SkScalar dy) {
    if (dx || dy) {
        fMat[kMTransX] = dx;
        fMat[kMTransY] = dy;

        fMat[kMScaleX] = fMat[kMScaleY] = fMat[kMPersp2] = 1;
        fMat[kMSkewX]  = fMat[kMSkewY] =
        fMat[kMPersp0] = fMat[kMPersp1] = 0;

        this->setTypeMask(kTranslate_Mask | kRectStaysRect_Mask);
    } else {
        this->reset();
    }
}

void SkMatrix::preTranslate(SkScalar dx, SkScalar dy) {
    if (!dx && !dy) {
        return;
    }

    if (this->hasPerspective()) {
        SkMatrix    m;
        m.setTranslate(dx, dy);
        this->preConcat(m);
    } else {
        fMat[kMTransX] += sdot(fMat[kMScaleX], dx, fMat[kMSkewX], dy);
        fMat[kMTransY] += sdot(fMat[kMSkewY], dx, fMat[kMScaleY], dy);
        this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
    }
}

void SkMatrix::postTranslate(SkScalar dx, SkScalar dy) {
    if (!dx && !dy) {
        return;
    }

    if (this->hasPerspective()) {
        SkMatrix    m;
        m.setTranslate(dx, dy);
        this->postConcat(m);
    } else {
        fMat[kMTransX] += dx;
        fMat[kMTransY] += dy;
        this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
    }
}

///////////////////////////////////////////////////////////////////////////////

void SkMatrix::setScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    if (1 == sx && 1 == sy) {
        this->reset();
    } else {
        this->setScaleTranslate(sx, sy, px - sx * px, py - sy * py);
    }
}

void SkMatrix::setScale(SkScalar sx, SkScalar sy) {
    if (1 == sx && 1 == sy) {
        this->reset();
    } else {
        fMat[kMScaleX] = sx;
        fMat[kMScaleY] = sy;
        fMat[kMPersp2] = 1;

        fMat[kMTransX] = fMat[kMTransY] =
        fMat[kMSkewX]  = fMat[kMSkewY] =
        fMat[kMPersp0] = fMat[kMPersp1] = 0;

        this->setTypeMask(kScale_Mask | kRectStaysRect_Mask);
    }
}

bool SkMatrix::setIDiv(int divx, int divy) {
    if (!divx || !divy) {
        return false;
    }
    this->setScale(SkScalarInvert(divx), SkScalarInvert(divy));
    return true;
}

void SkMatrix::preScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    if (1 == sx && 1 == sy) {
        return;
    }

    SkMatrix    m;
    m.setScale(sx, sy, px, py);
    this->preConcat(m);
}

void SkMatrix::preScale(SkScalar sx, SkScalar sy) {
    if (1 == sx && 1 == sy) {
        return;
    }

    // the assumption is that these multiplies are very cheap, and that
    // a full concat and/or just computing the matrix type is more expensive.
    // Also, the fixed-point case checks for overflow, but the float doesn't,
    // so we can get away with these blind multiplies.

    fMat[kMScaleX] *= sx;
    fMat[kMSkewY]  *= sx;
    fMat[kMPersp0] *= sx;

    fMat[kMSkewX]  *= sy;
    fMat[kMScaleY] *= sy;
    fMat[kMPersp1] *= sy;

    this->orTypeMask(kScale_Mask);
}

void SkMatrix::postScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    if (1 == sx && 1 == sy) {
        return;
    }
    SkMatrix    m;
    m.setScale(sx, sy, px, py);
    this->postConcat(m);
}

void SkMatrix::postScale(SkScalar sx, SkScalar sy) {
    if (1 == sx && 1 == sy) {
        return;
    }
    SkMatrix    m;
    m.setScale(sx, sy);
    this->postConcat(m);
}

// this guy perhaps can go away, if we have a fract/high-precision way to
// scale matrices
bool SkMatrix::postIDiv(int divx, int divy) {
    if (divx == 0 || divy == 0) {
        return false;
    }

    const float invX = 1.f / divx;
    const float invY = 1.f / divy;

    fMat[kMScaleX] *= invX;
    fMat[kMSkewX]  *= invX;
    fMat[kMTransX] *= invX;

    fMat[kMScaleY] *= invY;
    fMat[kMSkewY]  *= invY;
    fMat[kMTransY] *= invY;

    this->setTypeMask(kUnknown_Mask);
    return true;
}

////////////////////////////////////////////////////////////////////////////////////

void SkMatrix::setSinCos(SkScalar sinV, SkScalar cosV, SkScalar px, SkScalar py) {
    const SkScalar oneMinusCosV = 1 - cosV;

    fMat[kMScaleX]  = cosV;
    fMat[kMSkewX]   = -sinV;
    fMat[kMTransX]  = sdot(sinV, py, oneMinusCosV, px);

    fMat[kMSkewY]   = sinV;
    fMat[kMScaleY]  = cosV;
    fMat[kMTransY]  = sdot(-sinV, px, oneMinusCosV, py);

    fMat[kMPersp0] = fMat[kMPersp1] = 0;
    fMat[kMPersp2] = 1;

    this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
}

void SkMatrix::setSinCos(SkScalar sinV, SkScalar cosV) {
    fMat[kMScaleX]  = cosV;
    fMat[kMSkewX]   = -sinV;
    fMat[kMTransX]  = 0;

    fMat[kMSkewY]   = sinV;
    fMat[kMScaleY]  = cosV;
    fMat[kMTransY]  = 0;

    fMat[kMPersp0] = fMat[kMPersp1] = 0;
    fMat[kMPersp2] = 1;

    this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
}

void SkMatrix::setRotate(SkScalar degrees, SkScalar px, SkScalar py) {
    SkScalar sinV, cosV;
    sinV = SkScalarSinCos(SkDegreesToRadians(degrees), &cosV);
    this->setSinCos(sinV, cosV, px, py);
}

void SkMatrix::setRotate(SkScalar degrees) {
    SkScalar sinV, cosV;
    sinV = SkScalarSinCos(SkDegreesToRadians(degrees), &cosV);
    this->setSinCos(sinV, cosV);
}

void SkMatrix::preRotate(SkScalar degrees, SkScalar px, SkScalar py) {
    SkMatrix    m;
    m.setRotate(degrees, px, py);
    this->preConcat(m);
}

void SkMatrix::preRotate(SkScalar degrees) {
    SkMatrix    m;
    m.setRotate(degrees);
    this->preConcat(m);
}

void SkMatrix::postRotate(SkScalar degrees, SkScalar px, SkScalar py) {
    SkMatrix    m;
    m.setRotate(degrees, px, py);
    this->postConcat(m);
}

void SkMatrix::postRotate(SkScalar degrees) {
    SkMatrix    m;
    m.setRotate(degrees);
    this->postConcat(m);
}

////////////////////////////////////////////////////////////////////////////////////

void SkMatrix::setSkew(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    fMat[kMScaleX]  = 1;
    fMat[kMSkewX]   = sx;
    fMat[kMTransX]  = -sx * py;

    fMat[kMSkewY]   = sy;
    fMat[kMScaleY]  = 1;
    fMat[kMTransY]  = -sy * px;

    fMat[kMPersp0] = fMat[kMPersp1] = 0;
    fMat[kMPersp2] = 1;

    this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
}

void SkMatrix::setSkew(SkScalar sx, SkScalar sy) {
    fMat[kMScaleX]  = 1;
    fMat[kMSkewX]   = sx;
    fMat[kMTransX]  = 0;

    fMat[kMSkewY]   = sy;
    fMat[kMScaleY]  = 1;
    fMat[kMTransY]  = 0;

    fMat[kMPersp0] = fMat[kMPersp1] = 0;
    fMat[kMPersp2] = 1;

    this->setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
}

void SkMatrix::preSkew(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    SkMatrix    m;
    m.setSkew(sx, sy, px, py);
    this->preConcat(m);
}

void SkMatrix::preSkew(SkScalar sx, SkScalar sy) {
    SkMatrix    m;
    m.setSkew(sx, sy);
    this->preConcat(m);
}

void SkMatrix::postSkew(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py) {
    SkMatrix    m;
    m.setSkew(sx, sy, px, py);
    this->postConcat(m);
}

void SkMatrix::postSkew(SkScalar sx, SkScalar sy) {
    SkMatrix    m;
    m.setSkew(sx, sy);
    this->postConcat(m);
}

///////////////////////////////////////////////////////////////////////////////

bool SkMatrix::setRectToRect(const SkRect& src, const SkRect& dst, ScaleToFit align) {
    if (src.isEmpty()) {
        this->reset();
        return false;
    }

    if (dst.isEmpty()) {
        sk_bzero(fMat, 8 * sizeof(SkScalar));
        fMat[kMPersp2] = 1;
        this->setTypeMask(kScale_Mask | kRectStaysRect_Mask);
    } else {
        SkScalar    tx, sx = dst.width() / src.width();
        SkScalar    ty, sy = dst.height() / src.height();
        bool        xLarger = false;

        if (align != kFill_ScaleToFit) {
            if (sx > sy) {
                xLarger = true;
                sx = sy;
            } else {
                sy = sx;
            }
        }

        tx = dst.fLeft - src.fLeft * sx;
        ty = dst.fTop - src.fTop * sy;
        if (align == kCenter_ScaleToFit || align == kEnd_ScaleToFit) {
            SkScalar diff;

            if (xLarger) {
                diff = dst.width() - src.width() * sy;
            } else {
                diff = dst.height() - src.height() * sy;
            }

            if (align == kCenter_ScaleToFit) {
                diff = SkScalarHalf(diff);
            }

            if (xLarger) {
                tx += diff;
            } else {
                ty += diff;
            }
        }

        this->setScaleTranslate(sx, sy, tx, ty);
    }
    return true;
}

///////////////////////////////////////////////////////////////////////////////

static inline float muladdmul(float a, float b, float c, float d) {
    return SkDoubleToFloat((double)a * b + (double)c * d);
}

static inline float rowcol3(const float row[], const float col[]) {
    return row[0] * col[0] + row[1] * col[3] + row[2] * col[6];
}

static void normalize_perspective(SkScalar mat[9]) {
    // If it was interesting to never store the last element, we could divide all 8 other
    // elements here by the 9th, making it 1.0...
    //
    // When SkScalar was SkFixed, we would sometimes rescale the entire matrix to keep its
    // component values from getting too large. This is not a concern when using floats/doubles,
    // so we do nothing now.
}

static bool only_scale_and_translate(unsigned mask) {
    return 0 == (mask & (SkMatrix::kAffine_Mask | SkMatrix::kPerspective_Mask));
}

void SkMatrix::setConcat(const SkMatrix& a, const SkMatrix& b) {
    TypeMask aType = a.getType();
    TypeMask bType = b.getType();

    if (a.isTriviallyIdentity()) {
        *this = b;
    } else if (b.isTriviallyIdentity()) {
        *this = a;
    } else if (only_scale_and_translate(aType | bType)) {
        this->setScaleTranslate(a.fMat[kMScaleX] * b.fMat[kMScaleX],
                                a.fMat[kMScaleY] * b.fMat[kMScaleY],
                                a.fMat[kMScaleX] * b.fMat[kMTransX] + a.fMat[kMTransX],
                                a.fMat[kMScaleY] * b.fMat[kMTransY] + a.fMat[kMTransY]);
    } else {
        SkMatrix tmp;

        if ((aType | bType) & kPerspective_Mask) {
            tmp.fMat[kMScaleX] = rowcol3(&a.fMat[0], &b.fMat[0]);
            tmp.fMat[kMSkewX]  = rowcol3(&a.fMat[0], &b.fMat[1]);
            tmp.fMat[kMTransX] = rowcol3(&a.fMat[0], &b.fMat[2]);
            tmp.fMat[kMSkewY]  = rowcol3(&a.fMat[3], &b.fMat[0]);
            tmp.fMat[kMScaleY] = rowcol3(&a.fMat[3], &b.fMat[1]);
            tmp.fMat[kMTransY] = rowcol3(&a.fMat[3], &b.fMat[2]);
            tmp.fMat[kMPersp0] = rowcol3(&a.fMat[6], &b.fMat[0]);
            tmp.fMat[kMPersp1] = rowcol3(&a.fMat[6], &b.fMat[1]);
            tmp.fMat[kMPersp2] = rowcol3(&a.fMat[6], &b.fMat[2]);

            normalize_perspective(tmp.fMat);
            tmp.setTypeMask(kUnknown_Mask);
        } else {
            tmp.fMat[kMScaleX] = muladdmul(a.fMat[kMScaleX],
                                           b.fMat[kMScaleX],
                                           a.fMat[kMSkewX],
                                           b.fMat[kMSkewY]);

            tmp.fMat[kMSkewX]  = muladdmul(a.fMat[kMScaleX],
                                           b.fMat[kMSkewX],
                                           a.fMat[kMSkewX],
                                           b.fMat[kMScaleY]);

            tmp.fMat[kMTransX] = muladdmul(a.fMat[kMScaleX],
                                           b.fMat[kMTransX],
                                           a.fMat[kMSkewX],
                                           b.fMat[kMTransY]) + a.fMat[kMTransX];

            tmp.fMat[kMSkewY]  = muladdmul(a.fMat[kMSkewY],
                                           b.fMat[kMScaleX],
                                           a.fMat[kMScaleY],
                                           b.fMat[kMSkewY]);

            tmp.fMat[kMScaleY] = muladdmul(a.fMat[kMSkewY],
                                           b.fMat[kMSkewX],
                                           a.fMat[kMScaleY],
                                           b.fMat[kMScaleY]);

            tmp.fMat[kMTransY] = muladdmul(a.fMat[kMSkewY],
                                           b.fMat[kMTransX],
                                           a.fMat[kMScaleY],
                                           b.fMat[kMTransY]) + a.fMat[kMTransY];

            tmp.fMat[kMPersp0] = 0;
            tmp.fMat[kMPersp1] = 0;
            tmp.fMat[kMPersp2] = 1;
            //SkDebugf("Concat mat non-persp type: %d\n", tmp.getType());
            //SkASSERT(!(tmp.getType() & kPerspective_Mask));
            tmp.setTypeMask(kUnknown_Mask | kOnlyPerspectiveValid_Mask);
        }
        *this = tmp;
    }
}

void SkMatrix::preConcat(const SkMatrix& mat) {
    // check for identity first, so we don't do a needless copy of ourselves
    // to ourselves inside setConcat()
    if(!mat.isIdentity()) {
        this->setConcat(*this, mat);
    }
}

void SkMatrix::postConcat(const SkMatrix& mat) {
    // check for identity first, so we don't do a needless copy of ourselves
    // to ourselves inside setConcat()
    if (!mat.isIdentity()) {
        this->setConcat(mat, *this);
    }
}

///////////////////////////////////////////////////////////////////////////////

/*  Matrix inversion is very expensive, but also the place where keeping
    precision may be most important (here and matrix concat). Hence to avoid
    bitmap blitting artifacts when walking the inverse, we use doubles for
    the intermediate math, even though we know that is more expensive.
 */

static inline SkScalar scross_dscale(SkScalar a, SkScalar b,
                                     SkScalar c, SkScalar d, double scale) {
    return SkDoubleToScalar(scross(a, b, c, d) * scale);
}

static inline double dcross(double a, double b, double c, double d) {
    return a * b - c * d;
}

static inline SkScalar dcross_dscale(double a, double b,
                                     double c, double d, double scale) {
    return SkDoubleToScalar(dcross(a, b, c, d) * scale);
}

static double sk_inv_determinant(const float mat[9], int isPerspective) {
    double det;

    if (isPerspective) {
        det = mat[SkMatrix::kMScaleX] *
              dcross(mat[SkMatrix::kMScaleY], mat[SkMatrix::kMPersp2],
                     mat[SkMatrix::kMTransY], mat[SkMatrix::kMPersp1])
              +
              mat[SkMatrix::kMSkewX]  *
              dcross(mat[SkMatrix::kMTransY], mat[SkMatrix::kMPersp0],
                     mat[SkMatrix::kMSkewY],  mat[SkMatrix::kMPersp2])
              +
              mat[SkMatrix::kMTransX] *
              dcross(mat[SkMatrix::kMSkewY],  mat[SkMatrix::kMPersp1],
                     mat[SkMatrix::kMScaleY], mat[SkMatrix::kMPersp0]);
    } else {
        det = dcross(mat[SkMatrix::kMScaleX], mat[SkMatrix::kMScaleY],
                     mat[SkMatrix::kMSkewX], mat[SkMatrix::kMSkewY]);
    }

    // Since the determinant is on the order of the cube of the matrix members,
    // compare to the cube of the default nearly-zero constant (although an
    // estimate of the condition number would be better if it wasn't so expensive).
    if (SkScalarNearlyZero((float)det, SK_ScalarNearlyZero * SK_ScalarNearlyZero * SK_ScalarNearlyZero)) {
        return 0;
    }
    return 1.0 / det;
}

void SkMatrix::SetAffineIdentity(SkScalar affine[6]) {
    affine[kAScaleX] = 1;
    affine[kASkewY] = 0;
    affine[kASkewX] = 0;
    affine[kAScaleY] = 1;
    affine[kATransX] = 0;
    affine[kATransY] = 0;
}

bool SkMatrix::asAffine(SkScalar affine[6]) const {
    if (this->hasPerspective()) {
        return false;
    }
    if (affine) {
        affine[kAScaleX] = this->fMat[kMScaleX];
        affine[kASkewY] = this->fMat[kMSkewY];
        affine[kASkewX] = this->fMat[kMSkewX];
        affine[kAScaleY] = this->fMat[kMScaleY];
        affine[kATransX] = this->fMat[kMTransX];
        affine[kATransY] = this->fMat[kMTransY];
    }
    return true;
}

bool SkMatrix::invertNonIdentity(SkMatrix* inv) const {
    SkASSERT(!this->isIdentity());

    TypeMask mask = this->getType();

    if (0 == (mask & ~(kScale_Mask | kTranslate_Mask))) {
        bool invertible = true;
        if (inv) {
            if (mask & kScale_Mask) {
                SkScalar invX = fMat[kMScaleX];
                SkScalar invY = fMat[kMScaleY];
                if (0 == invX || 0 == invY) {
                    return false;
                }
                invX = SkScalarInvert(invX);
                invY = SkScalarInvert(invY);

                // Must be careful when writing to inv, since it may be the
                // same memory as this.

                inv->fMat[kMSkewX] = inv->fMat[kMSkewY] =
                inv->fMat[kMPersp0] = inv->fMat[kMPersp1] = 0;

                inv->fMat[kMScaleX] = invX;
                inv->fMat[kMScaleY] = invY;
                inv->fMat[kMPersp2] = 1;
                inv->fMat[kMTransX] = -fMat[kMTransX] * invX;
                inv->fMat[kMTransY] = -fMat[kMTransY] * invY;

                inv->setTypeMask(mask | kRectStaysRect_Mask);
            } else {
                // translate only
                inv->setTranslate(-fMat[kMTransX], -fMat[kMTransY]);
            }
        } else {    // inv is NULL, just check if we're invertible
            if (!fMat[kMScaleX] || !fMat[kMScaleY]) {
                invertible = false;
            }
        }
        return invertible;
    }

    int    isPersp = mask & kPerspective_Mask;
    double scale = sk_inv_determinant(fMat, isPersp);

    if (scale == 0) { // underflow
        return false;
    }

    if (inv) {
        SkMatrix tmp;
        if (inv == this) {
            inv = &tmp;
        }

        if (isPersp) {
            inv->fMat[kMScaleX] = scross_dscale(fMat[kMScaleY], fMat[kMPersp2], fMat[kMTransY], fMat[kMPersp1], scale);
            inv->fMat[kMSkewX]  = scross_dscale(fMat[kMTransX], fMat[kMPersp1], fMat[kMSkewX],  fMat[kMPersp2], scale);
            inv->fMat[kMTransX] = scross_dscale(fMat[kMSkewX],  fMat[kMTransY], fMat[kMTransX], fMat[kMScaleY], scale);

            inv->fMat[kMSkewY]  = scross_dscale(fMat[kMTransY], fMat[kMPersp0], fMat[kMSkewY],  fMat[kMPersp2], scale);
            inv->fMat[kMScaleY] = scross_dscale(fMat[kMScaleX], fMat[kMPersp2], fMat[kMTransX], fMat[kMPersp0], scale);
            inv->fMat[kMTransY] = scross_dscale(fMat[kMTransX], fMat[kMSkewY],  fMat[kMScaleX], fMat[kMTransY], scale);

            inv->fMat[kMPersp0] = scross_dscale(fMat[kMSkewY],  fMat[kMPersp1], fMat[kMScaleY], fMat[kMPersp0], scale);
            inv->fMat[kMPersp1] = scross_dscale(fMat[kMSkewX],  fMat[kMPersp0], fMat[kMScaleX], fMat[kMPersp1], scale);
            inv->fMat[kMPersp2] = scross_dscale(fMat[kMScaleX], fMat[kMScaleY], fMat[kMSkewX],  fMat[kMSkewY],  scale);
        } else {   // not perspective
            inv->fMat[kMScaleX] = SkDoubleToScalar(fMat[kMScaleY] * scale);
            inv->fMat[kMSkewX]  = SkDoubleToScalar(-fMat[kMSkewX] * scale);
            inv->fMat[kMTransX] = dcross_dscale(fMat[kMSkewX], fMat[kMTransY], fMat[kMScaleY], fMat[kMTransX], scale);

            inv->fMat[kMSkewY]  = SkDoubleToScalar(-fMat[kMSkewY] * scale);
            inv->fMat[kMScaleY] = SkDoubleToScalar(fMat[kMScaleX] * scale);
            inv->fMat[kMTransY] = dcross_dscale(fMat[kMSkewY], fMat[kMTransX], fMat[kMScaleX], fMat[kMTransY], scale);

            inv->fMat[kMPersp0] = 0;
            inv->fMat[kMPersp1] = 0;
            inv->fMat[kMPersp2] = 1;
        }

        inv->setTypeMask(fTypeMask);

        if (inv == &tmp) {
            *(SkMatrix*)this = tmp;
        }
    }
    return true;
}

///////////////////////////////////////////////////////////////////////////////

void SkMatrix::Identity_pts(const SkMatrix& m, SkPoint dst[],
                            const SkPoint src[], int count) {
    SkASSERT(m.getType() == 0);

    if (dst != src && count > 0)
        memcpy(dst, src, count * sizeof(SkPoint));
}

void SkMatrix::Trans_pts(const SkMatrix& m, SkPoint dst[],
                         const SkPoint src[], int count) {
    SkASSERT(m.getType() == kTranslate_Mask);

    if (count > 0) {
        SkScalar tx = m.fMat[kMTransX];
        SkScalar ty = m.fMat[kMTransY];
        do {
            dst->fY = src->fY + ty;
            dst->fX = src->fX + tx;
            src += 1;
            dst += 1;
        } while (--count);
    }
}

void SkMatrix::Scale_pts(const SkMatrix& m, SkPoint dst[],
                         const SkPoint src[], int count) {
    SkASSERT(m.getType() == kScale_Mask);

    if (count > 0) {
        SkScalar mx = m.fMat[kMScaleX];
        SkScalar my = m.fMat[kMScaleY];
        do {
            dst->fY = src->fY * my;
            dst->fX = src->fX * mx;
            src += 1;
            dst += 1;
        } while (--count);
    }
}

void SkMatrix::ScaleTrans_pts(const SkMatrix& m, SkPoint dst[],
                              const SkPoint src[], int count) {
    SkASSERT(m.getType() == (kScale_Mask | kTranslate_Mask));

    if (count > 0) {
        SkScalar mx = m.fMat[kMScaleX];
        SkScalar my = m.fMat[kMScaleY];
        SkScalar tx = m.fMat[kMTransX];
        SkScalar ty = m.fMat[kMTransY];
        do {
            dst->fY = src->fY * my + ty;
            dst->fX = src->fX * mx + tx;
            src += 1;
            dst += 1;
        } while (--count);
    }
}

void SkMatrix::Rot_pts(const SkMatrix& m, SkPoint dst[],
                       const SkPoint src[], int count) {
    SkASSERT((m.getType() & (kPerspective_Mask | kTranslate_Mask)) == 0);

    if (count > 0) {
        SkScalar mx = m.fMat[kMScaleX];
        SkScalar my = m.fMat[kMScaleY];
        SkScalar kx = m.fMat[kMSkewX];
        SkScalar ky = m.fMat[kMSkewY];
        do {
            SkScalar sy = src->fY;
            SkScalar sx = src->fX;
            src += 1;
            dst->fY = sdot(sx, ky, sy, my);
            dst->fX = sdot(sx, mx, sy, kx);
            dst += 1;
        } while (--count);
    }
}

void SkMatrix::RotTrans_pts(const SkMatrix& m, SkPoint dst[],
                            const SkPoint src[], int count) {
    SkASSERT(!m.hasPerspective());

    if (count > 0) {
        SkScalar mx = m.fMat[kMScaleX];
        SkScalar my = m.fMat[kMScaleY];
        SkScalar kx = m.fMat[kMSkewX];
        SkScalar ky = m.fMat[kMSkewY];
        SkScalar tx = m.fMat[kMTransX];
        SkScalar ty = m.fMat[kMTransY];
        do {
            SkScalar sy = src->fY;
            SkScalar sx = src->fX;
            src += 1;
#ifdef SK_LEGACY_MATRIX_MATH_ORDER
            dst->fY = sx * ky + (sy * my + ty);
            dst->fX = sx * mx + (sy * kx + tx);
#else
            dst->fY = sdot(sx, ky, sy, my) + ty;
            dst->fX = sdot(sx, mx, sy, kx) + tx;
#endif
            dst += 1;
        } while (--count);
    }
}

void SkMatrix::Persp_pts(const SkMatrix& m, SkPoint dst[],
                         const SkPoint src[], int count) {
    SkASSERT(m.hasPerspective());

    if (count > 0) {
        do {
            SkScalar sy = src->fY;
            SkScalar sx = src->fX;
            src += 1;

            SkScalar x = sdot(sx, m.fMat[kMScaleX], sy, m.fMat[kMSkewX])  + m.fMat[kMTransX];
            SkScalar y = sdot(sx, m.fMat[kMSkewY],  sy, m.fMat[kMScaleY]) + m.fMat[kMTransY];
#ifdef SK_LEGACY_MATRIX_MATH_ORDER
            SkScalar z = sx * m.fMat[kMPersp0] + (sy * m.fMat[kMPersp1] + m.fMat[kMPersp2]);
#else
            SkScalar z = sdot(sx, m.fMat[kMPersp0], sy, m.fMat[kMPersp1]) + m.fMat[kMPersp2];
#endif
            if (z) {
                z = SkScalarFastInvert(z);
            }

            dst->fY = y * z;
            dst->fX = x * z;
            dst += 1;
        } while (--count);
    }
}

const SkMatrix::MapPtsProc SkMatrix::gMapPtsProcs[] = {
    SkMatrix::Identity_pts, SkMatrix::Trans_pts,
    SkMatrix::Scale_pts,    SkMatrix::ScaleTrans_pts,
    SkMatrix::Rot_pts,      SkMatrix::RotTrans_pts,
    SkMatrix::Rot_pts,      SkMatrix::RotTrans_pts,
    // repeat the persp proc 8 times
    SkMatrix::Persp_pts,    SkMatrix::Persp_pts,
    SkMatrix::Persp_pts,    SkMatrix::Persp_pts,
    SkMatrix::Persp_pts,    SkMatrix::Persp_pts,
    SkMatrix::Persp_pts,    SkMatrix::Persp_pts
};

void SkMatrix::mapPoints(SkPoint dst[], const SkPoint src[], int count) const {
    SkASSERT((dst && src && count > 0) || 0 == count);
    // no partial overlap
    SkASSERT(src == dst || &dst[count] <= &src[0] || &src[count] <= &dst[0]);

    this->getMapPtsProc()(*this, dst, src, count);
}

///////////////////////////////////////////////////////////////////////////////

void SkMatrix::mapHomogeneousPoints(SkScalar dst[], const SkScalar src[], int count) const {
    SkASSERT((dst && src && count > 0) || 0 == count);
    // no partial overlap
    SkASSERT(src == dst || SkAbs32((int32_t)(src - dst)) >= 3*count);

    if (count > 0) {
        if (this->isIdentity()) {
            memcpy(dst, src, 3*count*sizeof(SkScalar));
            return;
        }
        do {
            SkScalar sx = src[0];
            SkScalar sy = src[1];
            SkScalar sw = src[2];
            src += 3;

            SkScalar x = sdot(sx, fMat[kMScaleX], sy, fMat[kMSkewX],  sw, fMat[kMTransX]);
            SkScalar y = sdot(sx, fMat[kMSkewY],  sy, fMat[kMScaleY], sw, fMat[kMTransY]);
            SkScalar w = sdot(sx, fMat[kMPersp0], sy, fMat[kMPersp1], sw, fMat[kMPersp2]);

            dst[0] = x;
            dst[1] = y;
            dst[2] = w;
            dst += 3;
        } while (--count);
    }
}

///////////////////////////////////////////////////////////////////////////////

void SkMatrix::mapVectors(SkPoint dst[], const SkPoint src[], int count) const {
    if (this->hasPerspective()) {
        SkPoint origin;

        MapXYProc proc = this->getMapXYProc();
        proc(*this, 0, 0, &origin);

        for (int i = count - 1; i >= 0; --i) {
            SkPoint tmp;

            proc(*this, src[i].fX, src[i].fY, &tmp);
            dst[i].set(tmp.fX - origin.fX, tmp.fY - origin.fY);
        }
    } else {
        SkMatrix tmp = *this;

        tmp.fMat[kMTransX] = tmp.fMat[kMTransY] = 0;
        tmp.clearTypeMask(kTranslate_Mask);
        tmp.mapPoints(dst, src, count);
    }
}

bool SkMatrix::mapRect(SkRect* dst, const SkRect& src) const {
    SkASSERT(dst);

    if (this->rectStaysRect()) {
        this->mapPoints((SkPoint*)dst, (const SkPoint*)&src, 2);
        dst->sort();
        return true;
    } else {
        SkPoint quad[4];

        src.toQuad(quad);
        this->mapPoints(quad, quad, 4);
        dst->set(quad, 4);
        return false;
    }
}

SkScalar SkMatrix::mapRadius(SkScalar radius) const {
    SkVector    vec[2];

    vec[0].set(radius, 0);
    vec[1].set(0, radius);
    this->mapVectors(vec, 2);

    SkScalar d0 = vec[0].length();
    SkScalar d1 = vec[1].length();

    // return geometric mean
    return SkScalarSqrt(d0 * d1);
}

///////////////////////////////////////////////////////////////////////////////

void SkMatrix::Persp_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                        SkPoint* pt) {
    SkASSERT(m.hasPerspective());

    SkScalar x = sdot(sx, m.fMat[kMScaleX], sy, m.fMat[kMSkewX])  + m.fMat[kMTransX];
    SkScalar y = sdot(sx, m.fMat[kMSkewY],  sy, m.fMat[kMScaleY]) + m.fMat[kMTransY];
    SkScalar z = sdot(sx, m.fMat[kMPersp0], sy, m.fMat[kMPersp1]) + m.fMat[kMPersp2];
    if (z) {
        z = SkScalarFastInvert(z);
    }
    pt->fX = x * z;
    pt->fY = y * z;
}

void SkMatrix::RotTrans_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                           SkPoint* pt) {
    SkASSERT((m.getType() & (kAffine_Mask | kPerspective_Mask)) == kAffine_Mask);

#ifdef SK_LEGACY_MATRIX_MATH_ORDER
    pt->fX = sx * m.fMat[kMScaleX] + (sy * m.fMat[kMSkewX]  +  m.fMat[kMTransX]);
    pt->fY = sx * m.fMat[kMSkewY]  + (sy * m.fMat[kMScaleY] + m.fMat[kMTransY]);
#else
    pt->fX = sdot(sx, m.fMat[kMScaleX], sy, m.fMat[kMSkewX])  + m.fMat[kMTransX];
    pt->fY = sdot(sx, m.fMat[kMSkewY],  sy, m.fMat[kMScaleY]) + m.fMat[kMTransY];
#endif
}

void SkMatrix::Rot_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                      SkPoint* pt) {
    SkASSERT((m.getType() & (kAffine_Mask | kPerspective_Mask))== kAffine_Mask);
    SkASSERT(0 == m.fMat[kMTransX]);
    SkASSERT(0 == m.fMat[kMTransY]);

#ifdef SK_LEGACY_MATRIX_MATH_ORDER
    pt->fX = sx * m.fMat[kMScaleX] + (sy * m.fMat[kMSkewX]  + m.fMat[kMTransX]);
    pt->fY = sx * m.fMat[kMSkewY]  + (sy * m.fMat[kMScaleY] + m.fMat[kMTransY]);
#else
    pt->fX = sdot(sx, m.fMat[kMScaleX], sy, m.fMat[kMSkewX])  + m.fMat[kMTransX];
    pt->fY = sdot(sx, m.fMat[kMSkewY],  sy, m.fMat[kMScaleY]) + m.fMat[kMTransY];
#endif
}

void SkMatrix::ScaleTrans_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                             SkPoint* pt) {
    SkASSERT((m.getType() & (kScale_Mask | kAffine_Mask | kPerspective_Mask))
             == kScale_Mask);

    pt->fX = sx * m.fMat[kMScaleX] + m.fMat[kMTransX];
    pt->fY = sy * m.fMat[kMScaleY] + m.fMat[kMTransY];
}

void SkMatrix::Scale_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                        SkPoint* pt) {
    SkASSERT((m.getType() & (kScale_Mask | kAffine_Mask | kPerspective_Mask))
             == kScale_Mask);
    SkASSERT(0 == m.fMat[kMTransX]);
    SkASSERT(0 == m.fMat[kMTransY]);

    pt->fX = sx * m.fMat[kMScaleX];
    pt->fY = sy * m.fMat[kMScaleY];
}

void SkMatrix::Trans_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                        SkPoint* pt) {
    SkASSERT(m.getType() == kTranslate_Mask);

    pt->fX = sx + m.fMat[kMTransX];
    pt->fY = sy + m.fMat[kMTransY];
}

void SkMatrix::Identity_xy(const SkMatrix& m, SkScalar sx, SkScalar sy,
                           SkPoint* pt) {
    SkASSERT(0 == m.getType());

    pt->fX = sx;
    pt->fY = sy;
}

const SkMatrix::MapXYProc SkMatrix::gMapXYProcs[] = {
    SkMatrix::Identity_xy, SkMatrix::Trans_xy,
    SkMatrix::Scale_xy,    SkMatrix::ScaleTrans_xy,
    SkMatrix::Rot_xy,      SkMatrix::RotTrans_xy,
    SkMatrix::Rot_xy,      SkMatrix::RotTrans_xy,
    // repeat the persp proc 8 times
    SkMatrix::Persp_xy,    SkMatrix::Persp_xy,
    SkMatrix::Persp_xy,    SkMatrix::Persp_xy,
    SkMatrix::Persp_xy,    SkMatrix::Persp_xy,
    SkMatrix::Persp_xy,    SkMatrix::Persp_xy
};

///////////////////////////////////////////////////////////////////////////////

// if its nearly zero (just made up 26, perhaps it should be bigger or smaller)
#define PerspNearlyZero(x)  SkScalarNearlyZero(x, (1.0f / (1 << 26)))

bool SkMatrix::fixedStepInX(SkScalar y, SkFixed* stepX, SkFixed* stepY) const {
    if (PerspNearlyZero(fMat[kMPersp0])) {
        if (stepX || stepY) {
            if (PerspNearlyZero(fMat[kMPersp1]) &&
                    PerspNearlyZero(fMat[kMPersp2] - 1)) {
                if (stepX) {
                    *stepX = SkScalarToFixed(fMat[kMScaleX]);
                }
                if (stepY) {
                    *stepY = SkScalarToFixed(fMat[kMSkewY]);
                }
            } else {
                SkScalar z = y * fMat[kMPersp1] + fMat[kMPersp2];
                if (stepX) {
                    *stepX = SkScalarToFixed(fMat[kMScaleX] / z);
                }
                if (stepY) {
                    *stepY = SkScalarToFixed(fMat[kMSkewY] / z);
                }
            }
        }
        return true;
    }
    return false;
}

///////////////////////////////////////////////////////////////////////////////

#include "SkPerspIter.h"

SkPerspIter::SkPerspIter(const SkMatrix& m, SkScalar x0, SkScalar y0, int count)
        : fMatrix(m), fSX(x0), fSY(y0), fCount(count) {
    SkPoint pt;

    SkMatrix::Persp_xy(m, x0, y0, &pt);
    fX = SkScalarToFixed(pt.fX);
    fY = SkScalarToFixed(pt.fY);
}

int SkPerspIter::next() {
    int n = fCount;

    if (0 == n) {
        return 0;
    }
    SkPoint pt;
    SkFixed x = fX;
    SkFixed y = fY;
    SkFixed dx, dy;

    if (n >= kCount) {
        n = kCount;
        fSX += SkIntToScalar(kCount);
        SkMatrix::Persp_xy(fMatrix, fSX, fSY, &pt);
        fX = SkScalarToFixed(pt.fX);
        fY = SkScalarToFixed(pt.fY);
        dx = (fX - x) >> kShift;
        dy = (fY - y) >> kShift;
    } else {
        fSX += SkIntToScalar(n);
        SkMatrix::Persp_xy(fMatrix, fSX, fSY, &pt);
        fX = SkScalarToFixed(pt.fX);
        fY = SkScalarToFixed(pt.fY);
        dx = (fX - x) / n;
        dy = (fY - y) / n;
    }

    SkFixed* p = fStorage;
    for (int i = 0; i < n; i++) {
        *p++ = x; x += dx;
        *p++ = y; y += dy;
    }

    fCount -= n;
    return n;
}

///////////////////////////////////////////////////////////////////////////////

static inline bool checkForZero(float x) {
    return x*x == 0;
}

static inline bool poly_to_point(SkPoint* pt, const SkPoint poly[], int count) {
    float   x = 1, y = 1;
    SkPoint pt1, pt2;

    if (count > 1) {
        pt1.fX = poly[1].fX - poly[0].fX;
        pt1.fY = poly[1].fY - poly[0].fY;
        y = SkPoint::Length(pt1.fX, pt1.fY);
        if (checkForZero(y)) {
            return false;
        }
        switch (count) {
            case 2:
                break;
            case 3:
                pt2.fX = poly[0].fY - poly[2].fY;
                pt2.fY = poly[2].fX - poly[0].fX;
                goto CALC_X;
            default:
                pt2.fX = poly[0].fY - poly[3].fY;
                pt2.fY = poly[3].fX - poly[0].fX;
            CALC_X:
                x = sdot(pt1.fX, pt2.fX, pt1.fY, pt2.fY) / y;
                break;
        }
    }
    pt->set(x, y);
    return true;
}

bool SkMatrix::Poly2Proc(const SkPoint srcPt[], SkMatrix* dst,
                         const SkPoint& scale) {
    float invScale = 1 / scale.fY;

    dst->fMat[kMScaleX] = (srcPt[1].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMSkewY] = (srcPt[0].fX - srcPt[1].fX) * invScale;
    dst->fMat[kMPersp0] = 0;
    dst->fMat[kMSkewX] = (srcPt[1].fX - srcPt[0].fX) * invScale;
    dst->fMat[kMScaleY] = (srcPt[1].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMPersp1] = 0;
    dst->fMat[kMTransX] = srcPt[0].fX;
    dst->fMat[kMTransY] = srcPt[0].fY;
    dst->fMat[kMPersp2] = 1;
    dst->setTypeMask(kUnknown_Mask);
    return true;
}

bool SkMatrix::Poly3Proc(const SkPoint srcPt[], SkMatrix* dst,
                         const SkPoint& scale) {
    float invScale = 1 / scale.fX;
    dst->fMat[kMScaleX] = (srcPt[2].fX - srcPt[0].fX) * invScale;
    dst->fMat[kMSkewY] = (srcPt[2].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMPersp0] = 0;

    invScale = 1 / scale.fY;
    dst->fMat[kMSkewX] = (srcPt[1].fX - srcPt[0].fX) * invScale;
    dst->fMat[kMScaleY] = (srcPt[1].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMPersp1] = 0;

    dst->fMat[kMTransX] = srcPt[0].fX;
    dst->fMat[kMTransY] = srcPt[0].fY;
    dst->fMat[kMPersp2] = 1;
    dst->setTypeMask(kUnknown_Mask);
    return true;
}

bool SkMatrix::Poly4Proc(const SkPoint srcPt[], SkMatrix* dst,
                         const SkPoint& scale) {
    float   a1, a2;
    float   x0, y0, x1, y1, x2, y2;

    x0 = srcPt[2].fX - srcPt[0].fX;
    y0 = srcPt[2].fY - srcPt[0].fY;
    x1 = srcPt[2].fX - srcPt[1].fX;
    y1 = srcPt[2].fY - srcPt[1].fY;
    x2 = srcPt[2].fX - srcPt[3].fX;
    y2 = srcPt[2].fY - srcPt[3].fY;

    /* check if abs(x2) > abs(y2) */
    if ( x2 > 0 ? y2 > 0 ? x2 > y2 : x2 > -y2 : y2 > 0 ? -x2 > y2 : x2 < y2) {
        float denom = SkScalarMulDiv(x1, y2, x2) - y1;
        if (checkForZero(denom)) {
            return false;
        }
        a1 = (SkScalarMulDiv(x0 - x1, y2, x2) - y0 + y1) / denom;
    } else {
        float denom = x1 - SkScalarMulDiv(y1, x2, y2);
        if (checkForZero(denom)) {
            return false;
        }
        a1 = (x0 - x1 - SkScalarMulDiv(y0 - y1, x2, y2)) / denom;
    }

    /* check if abs(x1) > abs(y1) */
    if ( x1 > 0 ? y1 > 0 ? x1 > y1 : x1 > -y1 : y1 > 0 ? -x1 > y1 : x1 < y1) {
        float denom = y2 - SkScalarMulDiv(x2, y1, x1);
        if (checkForZero(denom)) {
            return false;
        }
        a2 = (y0 - y2 - SkScalarMulDiv(x0 - x2, y1, x1)) / denom;
    } else {
        float denom = SkScalarMulDiv(y2, x1, y1) - x2;
        if (checkForZero(denom)) {
            return false;
        }
        a2 = (SkScalarMulDiv(y0 - y2, x1, y1) - x0 + x2) / denom;
    }

    float invScale = SkScalarInvert(scale.fX);
    dst->fMat[kMScaleX] = (a2 * srcPt[3].fX + srcPt[3].fX - srcPt[0].fX) * invScale;
    dst->fMat[kMSkewY]  = (a2 * srcPt[3].fY + srcPt[3].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMPersp0] = a2 * invScale;

    invScale = SkScalarInvert(scale.fY);
    dst->fMat[kMSkewX]  = (a1 * srcPt[1].fX + srcPt[1].fX - srcPt[0].fX) * invScale;
    dst->fMat[kMScaleY] = (a1 * srcPt[1].fY + srcPt[1].fY - srcPt[0].fY) * invScale;
    dst->fMat[kMPersp1] = a1 * invScale;

    dst->fMat[kMTransX] = srcPt[0].fX;
    dst->fMat[kMTransY] = srcPt[0].fY;
    dst->fMat[kMPersp2] = 1;
    dst->setTypeMask(kUnknown_Mask);
    return true;
}

typedef bool (*PolyMapProc)(const SkPoint[], SkMatrix*, const SkPoint&);

/*  Taken from Rob Johnson's original sample code in QuickDraw GX
*/
bool SkMatrix::setPolyToPoly(const SkPoint src[], const SkPoint dst[],
                             int count) {
    if ((unsigned)count > 4) {
        SkDebugf("--- SkMatrix::setPolyToPoly count out of range %d\n", count);
        return false;
    }

    if (0 == count) {
        this->reset();
        return true;
    }
    if (1 == count) {
        this->setTranslate(dst[0].fX - src[0].fX, dst[0].fY - src[0].fY);
        return true;
    }

    SkPoint scale;
    if (!poly_to_point(&scale, src, count) ||
            SkScalarNearlyZero(scale.fX) ||
            SkScalarNearlyZero(scale.fY)) {
        return false;
    }

    static const PolyMapProc gPolyMapProcs[] = {
        SkMatrix::Poly2Proc, SkMatrix::Poly3Proc, SkMatrix::Poly4Proc
    };
    PolyMapProc proc = gPolyMapProcs[count - 2];

    SkMatrix tempMap, result;
    tempMap.setTypeMask(kUnknown_Mask);

    if (!proc(src, &tempMap, scale)) {
        return false;
    }
    if (!tempMap.invert(&result)) {
        return false;
    }
    if (!proc(dst, &tempMap, scale)) {
        return false;
    }
    this->setConcat(tempMap, result);
    return true;
}

///////////////////////////////////////////////////////////////////////////////

enum MinMaxOrBoth {
    kMin_MinMaxOrBoth,
    kMax_MinMaxOrBoth,
    kBoth_MinMaxOrBoth
};

template <MinMaxOrBoth MIN_MAX_OR_BOTH> bool get_scale_factor(SkMatrix::TypeMask typeMask,
                                                              const SkScalar m[9],
                                                              SkScalar results[/*1 or 2*/]) {
    if (typeMask & SkMatrix::kPerspective_Mask) {
        return false;
    }
    if (SkMatrix::kIdentity_Mask == typeMask) {
        results[0] = SK_Scalar1;
        if (kBoth_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
            results[1] = SK_Scalar1;
        }
        return true;
    }
    if (!(typeMask & SkMatrix::kAffine_Mask)) {
        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
             results[0] = SkMinScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
                                      SkScalarAbs(m[SkMatrix::kMScaleY]));
        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
             results[0] = SkMaxScalar(SkScalarAbs(m[SkMatrix::kMScaleX]),
                                      SkScalarAbs(m[SkMatrix::kMScaleY]));
        } else {
            results[0] = SkScalarAbs(m[SkMatrix::kMScaleX]);
            results[1] = SkScalarAbs(m[SkMatrix::kMScaleY]);
             if (results[0] > results[1]) {
                 SkTSwap(results[0], results[1]);
             }
        }
        return true;
    }
    // ignore the translation part of the matrix, just look at 2x2 portion.
    // compute singular values, take largest or smallest abs value.
    // [a b; b c] = A^T*A
    SkScalar a = sdot(m[SkMatrix::kMScaleX], m[SkMatrix::kMScaleX],
                      m[SkMatrix::kMSkewY],  m[SkMatrix::kMSkewY]);
    SkScalar b = sdot(m[SkMatrix::kMScaleX], m[SkMatrix::kMSkewX],
                      m[SkMatrix::kMScaleY], m[SkMatrix::kMSkewY]);
    SkScalar c = sdot(m[SkMatrix::kMSkewX],  m[SkMatrix::kMSkewX],
                      m[SkMatrix::kMScaleY], m[SkMatrix::kMScaleY]);
    // eigenvalues of A^T*A are the squared singular values of A.
    // characteristic equation is det((A^T*A) - l*I) = 0
    // l^2 - (a + c)l + (ac-b^2)
    // solve using quadratic equation (divisor is non-zero since l^2 has 1 coeff
    // and roots are guaranteed to be pos and real).
    SkScalar bSqd = b * b;
    // if upper left 2x2 is orthogonal save some math
    if (bSqd <= SK_ScalarNearlyZero*SK_ScalarNearlyZero) {
        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
            results[0] = SkMinScalar(a, c);
        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
            results[0] = SkMaxScalar(a, c);
        } else {
            results[0] = a;
            results[1] = c;
            if (results[0] > results[1]) {
                SkTSwap(results[0], results[1]);
            }
        }
    } else {
        SkScalar aminusc = a - c;
        SkScalar apluscdiv2 = SkScalarHalf(a + c);
        SkScalar x = SkScalarHalf(SkScalarSqrt(aminusc * aminusc + 4 * bSqd));
        if (kMin_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
            results[0] = apluscdiv2 - x;
        } else if (kMax_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
            results[0] = apluscdiv2 + x;
        } else {
            results[0] = apluscdiv2 - x;
            results[1] = apluscdiv2 + x;
        }
    }
    SkASSERT(results[0] >= 0);
    results[0] = SkScalarSqrt(results[0]);
    if (kBoth_MinMaxOrBoth == MIN_MAX_OR_BOTH) {
        SkASSERT(results[1] >= 0);
        results[1] = SkScalarSqrt(results[1]);
    }
    return true;
}

SkScalar SkMatrix::getMinScale() const {
    SkScalar factor;
    if (get_scale_factor<kMin_MinMaxOrBoth>(this->getType(), fMat, &factor)) {
        return factor;
    } else {
        return -1;
    }
}

SkScalar SkMatrix::getMaxScale() const {
    SkScalar factor;
    if (get_scale_factor<kMax_MinMaxOrBoth>(this->getType(), fMat, &factor)) {
        return factor;
    } else {
        return -1;
    }
}

bool SkMatrix::getMinMaxScales(SkScalar scaleFactors[2]) const {
    return get_scale_factor<kBoth_MinMaxOrBoth>(this->getType(), fMat, scaleFactors);
}

namespace {

struct PODMatrix {
    SkScalar matrix[9];
    uint32_t typemask;

    const SkMatrix& asSkMatrix() const { return *reinterpret_cast<const SkMatrix*>(this); }
};
SK_COMPILE_ASSERT(sizeof(PODMatrix) == sizeof(SkMatrix), PODMatrixSizeMismatch);

}  // namespace

const SkMatrix& SkMatrix::I() {
    SK_COMPILE_ASSERT(offsetof(SkMatrix, fMat)      == offsetof(PODMatrix, matrix),   BadfMat);
    SK_COMPILE_ASSERT(offsetof(SkMatrix, fTypeMask) == offsetof(PODMatrix, typemask), BadfTypeMask);

    static const PODMatrix identity = { {SK_Scalar1, 0, 0,
                                         0, SK_Scalar1, 0,
                                         0, 0, SK_Scalar1 },
                                       kIdentity_Mask | kRectStaysRect_Mask};
    SkASSERT(identity.asSkMatrix().isIdentity());
    return identity.asSkMatrix();
}

const SkMatrix& SkMatrix::InvalidMatrix() {
    SK_COMPILE_ASSERT(offsetof(SkMatrix, fMat)      == offsetof(PODMatrix, matrix),   BadfMat);
    SK_COMPILE_ASSERT(offsetof(SkMatrix, fTypeMask) == offsetof(PODMatrix, typemask), BadfTypeMask);

    static const PODMatrix invalid =
        { {SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
           SK_ScalarMax, SK_ScalarMax, SK_ScalarMax,
           SK_ScalarMax, SK_ScalarMax, SK_ScalarMax },
         kTranslate_Mask | kScale_Mask | kAffine_Mask | kPerspective_Mask };
    return invalid.asSkMatrix();
}

///////////////////////////////////////////////////////////////////////////////

size_t SkMatrix::writeToMemory(void* buffer) const {
    // TODO write less for simple matrices
    static const size_t sizeInMemory = 9 * sizeof(SkScalar);
    if (buffer) {
        memcpy(buffer, fMat, sizeInMemory);
    }
    return sizeInMemory;
}

size_t SkMatrix::readFromMemory(const void* buffer, size_t length) {
    static const size_t sizeInMemory = 9 * sizeof(SkScalar);
    if (length < sizeInMemory) {
        return 0;
    }
    if (buffer) {
        memcpy(fMat, buffer, sizeInMemory);
        this->setTypeMask(kUnknown_Mask);
    }
    return sizeInMemory;
}

void SkMatrix::dump() const {
    SkString str;
    this->toString(&str);
    SkDebugf("%s\n", str.c_str());
}

void SkMatrix::toString(SkString* str) const {
    str->appendf("[%8.4f %8.4f %8.4f][%8.4f %8.4f %8.4f][%8.4f %8.4f %8.4f]",
             fMat[0], fMat[1], fMat[2], fMat[3], fMat[4], fMat[5],
             fMat[6], fMat[7], fMat[8]);
}

///////////////////////////////////////////////////////////////////////////////

#include "SkMatrixUtils.h"

bool SkTreatAsSprite(const SkMatrix& mat, int width, int height,
                     unsigned subpixelBits) {
    // quick reject on affine or perspective
    if (mat.getType() & ~(SkMatrix::kScale_Mask | SkMatrix::kTranslate_Mask)) {
        return false;
    }

    // quick success check
    if (!subpixelBits && !(mat.getType() & ~SkMatrix::kTranslate_Mask)) {
        return true;
    }

    // mapRect supports negative scales, so we eliminate those first
    if (mat.getScaleX() < 0 || mat.getScaleY() < 0) {
        return false;
    }

    SkRect dst;
    SkIRect isrc = { 0, 0, width, height };

    {
        SkRect src;
        src.set(isrc);
        mat.mapRect(&dst, src);
    }

    // just apply the translate to isrc
    isrc.offset(SkScalarRoundToInt(mat.getTranslateX()),
                SkScalarRoundToInt(mat.getTranslateY()));

    if (subpixelBits) {
        isrc.fLeft <<= subpixelBits;
        isrc.fTop <<= subpixelBits;
        isrc.fRight <<= subpixelBits;
        isrc.fBottom <<= subpixelBits;

        const float scale = 1 << subpixelBits;
        dst.fLeft *= scale;
        dst.fTop *= scale;
        dst.fRight *= scale;
        dst.fBottom *= scale;
    }

    SkIRect idst;
    dst.round(&idst);
    return isrc == idst;
}

// A square matrix M can be decomposed (via polar decomposition) into two matrices --
// an orthogonal matrix Q and a symmetric matrix S. In turn we can decompose S into U*W*U^T,
// where U is another orthogonal matrix and W is a scale matrix. These can be recombined
// to give M = (Q*U)*W*U^T, i.e., the product of two orthogonal matrices and a scale matrix.
//
// The one wrinkle is that traditionally Q may contain a reflection -- the
// calculation has been rejiggered to put that reflection into W.
bool SkDecomposeUpper2x2(const SkMatrix& matrix,
                         SkPoint* rotation1,
                         SkPoint* scale,
                         SkPoint* rotation2) {

    SkScalar A = matrix[SkMatrix::kMScaleX];
    SkScalar B = matrix[SkMatrix::kMSkewX];
    SkScalar C = matrix[SkMatrix::kMSkewY];
    SkScalar D = matrix[SkMatrix::kMScaleY];

    if (is_degenerate_2x2(A, B, C, D)) {
        return false;
    }

    double w1, w2;
    SkScalar cos1, sin1;
    SkScalar cos2, sin2;

    // do polar decomposition (M = Q*S)
    SkScalar cosQ, sinQ;
    double Sa, Sb, Sd;
    // if M is already symmetric (i.e., M = I*S)
    if (SkScalarNearlyEqual(B, C)) {
        cosQ = 1;
        sinQ = 0;

        Sa = A;
        Sb = B;
        Sd = D;
    } else {
        cosQ = A + D;
        sinQ = C - B;
        SkScalar reciplen = SkScalarInvert(SkScalarSqrt(cosQ*cosQ + sinQ*sinQ));
        cosQ *= reciplen;
        sinQ *= reciplen;

        // S = Q^-1*M
        // we don't calc Sc since it's symmetric
        Sa = A*cosQ + C*sinQ;
        Sb = B*cosQ + D*sinQ;
        Sd = -B*sinQ + D*cosQ;
    }

    // Now we need to compute eigenvalues of S (our scale factors)
    // and eigenvectors (bases for our rotation)
    // From this, should be able to reconstruct S as U*W*U^T
    if (SkScalarNearlyZero(SkDoubleToScalar(Sb))) {
        // already diagonalized
        cos1 = 1;
        sin1 = 0;
        w1 = Sa;
        w2 = Sd;
        cos2 = cosQ;
        sin2 = sinQ;
    } else {
        double diff = Sa - Sd;
        double discriminant = sqrt(diff*diff + 4.0*Sb*Sb);
        double trace = Sa + Sd;
        if (diff > 0) {
            w1 = 0.5*(trace + discriminant);
            w2 = 0.5*(trace - discriminant);
        } else {
            w1 = 0.5*(trace - discriminant);
            w2 = 0.5*(trace + discriminant);
        }

        cos1 = SkDoubleToScalar(Sb); sin1 = SkDoubleToScalar(w1 - Sa);
        SkScalar reciplen = SkScalarInvert(SkScalarSqrt(cos1*cos1 + sin1*sin1));
        cos1 *= reciplen;
        sin1 *= reciplen;

        // rotation 2 is composition of Q and U
        cos2 = cos1*cosQ - sin1*sinQ;
        sin2 = sin1*cosQ + cos1*sinQ;

        // rotation 1 is U^T
        sin1 = -sin1;
    }

    if (scale) {
        scale->fX = SkDoubleToScalar(w1);
        scale->fY = SkDoubleToScalar(w2);
    }
    if (rotation1) {
        rotation1->fX = cos1;
        rotation1->fY = sin1;
    }
    if (rotation2) {
        rotation2->fX = cos2;
        rotation2->fY = sin2;
    }

    return true;
}