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gerrit-public.fairphone.software / platform / external / skia / 58a1605d2b9bab077f53b6a223f9e7ce1891d3ea / . / src / gpu / GrDistanceFieldGenFromVector.cpp
blob: efea0fca8c11e7f5d998799e63ebdf59b092aeef [file] [log] [blame]
/*
* Copyright 2017 ARM Ltd.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkDistanceFieldGen.h"
#include "GrDistanceFieldGenFromVector.h"
#include "GrConfig.h"
#include "GrPathUtils.h"
#include "SkAutoMalloc.h"
#include "SkGeometry.h"
#include "SkMatrix.h"
#include "SkPathOps.h"
#include "SkPointPriv.h"
#include "SkRectPriv.h"
/**
* If a scanline (a row of texel) cross from the kRight_SegSide
* of a segment to the kLeft_SegSide, the winding score should
* add 1.
* And winding score should subtract 1 if the scanline cross
* from kLeft_SegSide to kRight_SegSide.
* Always return kNA_SegSide if the scanline does not cross over
* the segment. Winding score should be zero in this case.
* You can get the winding number for each texel of the scanline
* by adding the winding score from left to right.
* Assuming we always start from outside, so the winding number
* should always start from zero.
* ________ ________
* | | | |
* ...R|L......L|R.....L|R......R|L..... <= Scanline & side of segment
* |+1 |-1 |-1 |+1 <= Winding score
* 0 | 1 ^ 0 ^ -1 |0 <= Winding number
* |________| |________|
*
* .......NA................NA..........
* 0 0
*/
enum SegSide {
kLeft_SegSide = -1,
kOn_SegSide = 0,
kRight_SegSide = 1,
kNA_SegSide = 2,
};
struct DFData {
float fDistSq; // distance squared to nearest (so far) edge
int fDeltaWindingScore; // +1 or -1 whenever a scanline cross over a segment
};
///////////////////////////////////////////////////////////////////////////////
/*
* Type definition for double precision DPoint and DAffineMatrix
*/
// Point with double precision
struct DPoint {
double fX, fY;
static DPoint Make(double x, double y) {
DPoint pt;
pt.set(x, y);
return pt;
}
double x() const { return fX; }
double y() const { return fY; }
void set(double x, double y) { fX = x; fY = y; }
/** Returns the euclidian distance from (0,0) to (x,y)
*/
static double Length(double x, double y) {
return sqrt(x * x + y * y);
}
/** Returns the euclidian distance between a and b
*/
static double Distance(const DPoint& a, const DPoint& b) {
return Length(a.fX - b.fX, a.fY - b.fY);
}
double distanceToSqd(const DPoint& pt) const {
double dx = fX - pt.fX;
double dy = fY - pt.fY;
return dx * dx + dy * dy;
}
};
// Matrix with double precision for affine transformation.
// We don't store row 3 because its always (0, 0, 1).
class DAffineMatrix {
public:
double operator[](int index) const {
SkASSERT((unsigned)index < 6);
return fMat[index];
}
double& operator[](int index) {
SkASSERT((unsigned)index < 6);
return fMat[index];
}
void setAffine(double m11, double m12, double m13,
double m21, double m22, double m23) {
fMat[0] = m11;
fMat[1] = m12;
fMat[2] = m13;
fMat[3] = m21;
fMat[4] = m22;
fMat[5] = m23;
}
/** Set the matrix to identity
*/
void reset() {
fMat[0] = fMat[4] = 1.0;
fMat[1] = fMat[3] =
fMat[2] = fMat[5] = 0.0;
}
// alias for reset()
void setIdentity() { this->reset(); }
DPoint mapPoint(const SkPoint& src) const {
DPoint pt = DPoint::Make(src.x(), src.y());
return this->mapPoint(pt);
}
DPoint mapPoint(const DPoint& src) const {
return DPoint::Make(fMat[0] * src.x() + fMat[1] * src.y() + fMat[2],
fMat[3] * src.x() + fMat[4] * src.y() + fMat[5]);
}
private:
double fMat[6];
};
///////////////////////////////////////////////////////////////////////////////
static const double kClose = (SK_Scalar1 / 16.0);
static const double kCloseSqd = kClose * kClose;
static const double kNearlyZero = (SK_Scalar1 / (1 << 18));
static const double kTangentTolerance = (SK_Scalar1 / (1 << 11));
static const float kConicTolerance = 0.25f;
static inline bool between_closed_open(double a, double b, double c,
double tolerance = 0.0,
bool xformToleranceToX = false) {
SkASSERT(tolerance >= 0.0);
double tolB = tolerance;
double tolC = tolerance;
if (xformToleranceToX) {
// Canonical space is y = x^2 and the derivative of x^2 is 2x.
// So the slope of the tangent line at point (x, x^2) is 2x.
//
// /|
// sqrt(2x * 2x + 1 * 1) / | 2x
// /__|
// 1
tolB = tolerance / sqrt(4.0 * b * b + 1.0);
tolC = tolerance / sqrt(4.0 * c * c + 1.0);
}
return b < c ? (a >= b - tolB && a < c - tolC) :
(a >= c - tolC && a < b - tolB);
}
static inline bool between_closed(double a, double b, double c,
double tolerance = 0.0,
bool xformToleranceToX = false) {
SkASSERT(tolerance >= 0.0);
double tolB = tolerance;
double tolC = tolerance;
if (xformToleranceToX) {
tolB = tolerance / sqrt(4.0 * b * b + 1.0);
tolC = tolerance / sqrt(4.0 * c * c + 1.0);
}
return b < c ? (a >= b - tolB && a <= c + tolC) :
(a >= c - tolC && a <= b + tolB);
}
static inline bool nearly_zero(double x, double tolerance = kNearlyZero) {
SkASSERT(tolerance >= 0.0);
return fabs(x) <= tolerance;
}
static inline bool nearly_equal(double x, double y,
double tolerance = kNearlyZero,
bool xformToleranceToX = false) {
SkASSERT(tolerance >= 0.0);
if (xformToleranceToX) {
tolerance = tolerance / sqrt(4.0 * y * y + 1.0);
}
return fabs(x - y) <= tolerance;
}
static inline double sign_of(const double &val) {
return (val < 0.0) ? -1.0 : 1.0;
}
static bool is_colinear(const SkPoint pts[3]) {
return nearly_zero((pts[1].y() - pts[0].y()) * (pts[1].x() - pts[2].x()) -
(pts[1].y() - pts[2].y()) * (pts[1].x() - pts[0].x()), kCloseSqd);
}
class PathSegment {
public:
enum {
// These enum values are assumed in member functions below.
kLine = 0,
kQuad = 1,
} fType;
// line uses 2 pts, quad uses 3 pts
SkPoint fPts[3];
DPoint fP0T, fP2T;
DAffineMatrix fXformMatrix;
double fScalingFactor;
double fScalingFactorSqd;
double fNearlyZeroScaled;
double fTangentTolScaledSqd;
SkRect fBoundingBox;
void init();
int countPoints() {
GR_STATIC_ASSERT(0 == kLine && 1 == kQuad);
return fType + 2;
}
const SkPoint& endPt() const {
GR_STATIC_ASSERT(0 == kLine && 1 == kQuad);
return fPts[fType + 1];
}
};
typedef SkTArray<PathSegment, true> PathSegmentArray;
void PathSegment::init() {
const DPoint p0 = DPoint::Make(fPts[0].x(), fPts[0].y());
const DPoint p2 = DPoint::Make(this->endPt().x(), this->endPt().y());
const double p0x = p0.x();
const double p0y = p0.y();
const double p2x = p2.x();
const double p2y = p2.y();
fBoundingBox.set(fPts[0], this->endPt());
if (fType == PathSegment::kLine) {
fScalingFactorSqd = fScalingFactor = 1.0;
double hypotenuse = DPoint::Distance(p0, p2);
const double cosTheta = (p2x - p0x) / hypotenuse;
const double sinTheta = (p2y - p0y) / hypotenuse;
fXformMatrix.setAffine(
cosTheta, sinTheta, -(cosTheta * p0x) - (sinTheta * p0y),
-sinTheta, cosTheta, (sinTheta * p0x) - (cosTheta * p0y)
);
} else {
SkASSERT(fType == PathSegment::kQuad);
// Calculate bounding box
const SkPoint _P1mP0 = fPts[1] - fPts[0];
SkPoint t = _P1mP0 - fPts[2] + fPts[1];
t.fX = _P1mP0.x() / t.x();
t.fY = _P1mP0.y() / t.y();
t.fX = SkScalarClampMax(t.x(), 1.0);
t.fY = SkScalarClampMax(t.y(), 1.0);
t.fX = _P1mP0.x() * t.x();
t.fY = _P1mP0.y() * t.y();
const SkPoint m = fPts[0] + t;
SkRectPriv::GrowToInclude(&fBoundingBox, m);
const double p1x = fPts[1].x();
const double p1y = fPts[1].y();
const double p0xSqd = p0x * p0x;
const double p0ySqd = p0y * p0y;
const double p2xSqd = p2x * p2x;
const double p2ySqd = p2y * p2y;
const double p1xSqd = p1x * p1x;
const double p1ySqd = p1y * p1y;
const double p01xProd = p0x * p1x;
const double p02xProd = p0x * p2x;
const double b12xProd = p1x * p2x;
const double p01yProd = p0y * p1y;
const double p02yProd = p0y * p2y;
const double b12yProd = p1y * p2y;
const double sqrtA = p0y - (2.0 * p1y) + p2y;
const double a = sqrtA * sqrtA;
const double h = -1.0 * (p0y - (2.0 * p1y) + p2y) * (p0x - (2.0 * p1x) + p2x);
const double sqrtB = p0x - (2.0 * p1x) + p2x;
const double b = sqrtB * sqrtB;
const double c = (p0xSqd * p2ySqd) - (4.0 * p01xProd * b12yProd)
- (2.0 * p02xProd * p02yProd) + (4.0 * p02xProd * p1ySqd)
+ (4.0 * p1xSqd * p02yProd) - (4.0 * b12xProd * p01yProd)
+ (p2xSqd * p0ySqd);
const double g = (p0x * p02yProd) - (2.0 * p0x * p1ySqd)
+ (2.0 * p0x * b12yProd) - (p0x * p2ySqd)
+ (2.0 * p1x * p01yProd) - (4.0 * p1x * p02yProd)
+ (2.0 * p1x * b12yProd) - (p2x * p0ySqd)
+ (2.0 * p2x * p01yProd) + (p2x * p02yProd)
- (2.0 * p2x * p1ySqd);
const double f = -((p0xSqd * p2y) - (2.0 * p01xProd * p1y)
- (2.0 * p01xProd * p2y) - (p02xProd * p0y)
+ (4.0 * p02xProd * p1y) - (p02xProd * p2y)
+ (2.0 * p1xSqd * p0y) + (2.0 * p1xSqd * p2y)
- (2.0 * b12xProd * p0y) - (2.0 * b12xProd * p1y)
+ (p2xSqd * p0y));
const double cosTheta = sqrt(a / (a + b));
const double sinTheta = -1.0 * sign_of((a + b) * h) * sqrt(b / (a + b));
const double gDef = cosTheta * g - sinTheta * f;
const double fDef = sinTheta * g + cosTheta * f;
const double x0 = gDef / (a + b);
const double y0 = (1.0 / (2.0 * fDef)) * (c - (gDef * gDef / (a + b)));
const double lambda = -1.0 * ((a + b) / (2.0 * fDef));
fScalingFactor = fabs(1.0 / lambda);
fScalingFactorSqd = fScalingFactor * fScalingFactor;
const double lambda_cosTheta = lambda * cosTheta;
const double lambda_sinTheta = lambda * sinTheta;
fXformMatrix.setAffine(
lambda_cosTheta, -lambda_sinTheta, lambda * x0,
lambda_sinTheta, lambda_cosTheta, lambda * y0
);
}
fNearlyZeroScaled = kNearlyZero / fScalingFactor;
fTangentTolScaledSqd = kTangentTolerance * kTangentTolerance / fScalingFactorSqd;
fP0T = fXformMatrix.mapPoint(p0);
fP2T = fXformMatrix.mapPoint(p2);
}
static void init_distances(DFData* data, int size) {
DFData* currData = data;
for (int i = 0; i < size; ++i) {
// init distance to "far away"
currData->fDistSq = SK_DistanceFieldMagnitude * SK_DistanceFieldMagnitude;
currData->fDeltaWindingScore = 0;
++currData;
}
}
static inline void add_line_to_segment(const SkPoint pts[2],
PathSegmentArray* segments) {
segments->push_back();
segments->back().fType = PathSegment::kLine;
segments->back().fPts[0] = pts[0];
segments->back().fPts[1] = pts[1];
segments->back().init();
}
static inline void add_quad_segment(const SkPoint pts[3],
PathSegmentArray* segments) {
if (SkPointPriv::DistanceToSqd(pts[0], pts[1]) < kCloseSqd ||
SkPointPriv::DistanceToSqd(pts[1], pts[2]) < kCloseSqd ||
is_colinear(pts)) {
if (pts[0] != pts[2]) {
SkPoint line_pts[2];
line_pts[0] = pts[0];
line_pts[1] = pts[2];
add_line_to_segment(line_pts, segments);
}
} else {
segments->push_back();
segments->back().fType = PathSegment::kQuad;
segments->back().fPts[0] = pts[0];
segments->back().fPts[1] = pts[1];
segments->back().fPts[2] = pts[2];
segments->back().init();
}
}
static inline void add_cubic_segments(const SkPoint pts[4],
PathSegmentArray* segments) {
SkSTArray<15, SkPoint, true> quads;
GrPathUtils::convertCubicToQuads(pts, SK_Scalar1, &quads);
int count = quads.count();
for (int q = 0; q < count; q += 3) {
add_quad_segment(&quads[q], segments);
}
}
static float calculate_nearest_point_for_quad(
const PathSegment& segment,
const DPoint &xFormPt) {
static const float kThird = 0.33333333333f;
static const float kTwentySeventh = 0.037037037f;
const float a = 0.5f - (float)xFormPt.y();
const float b = -0.5f * (float)xFormPt.x();
const float a3 = a * a * a;
const float b2 = b * b;
const float c = (b2 * 0.25f) + (a3 * kTwentySeventh);
if (c >= 0.f) {
const float sqrtC = sqrt(c);
const float result = (float)cbrt((-b * 0.5f) + sqrtC) + (float)cbrt((-b * 0.5f) - sqrtC);
return result;
} else {
const float cosPhi = (float)sqrt((b2 * 0.25f) * (-27.f / a3)) * ((b > 0) ? -1.f : 1.f);
const float phi = (float)acos(cosPhi);
float result;
if (xFormPt.x() > 0.f) {
result = 2.f * (float)sqrt(-a * kThird) * (float)cos(phi * kThird);
if (!between_closed(result, segment.fP0T.x(), segment.fP2T.x())) {
result = 2.f * (float)sqrt(-a * kThird) * (float)cos((phi * kThird) + (SK_ScalarPI * 2.f * kThird));
}
} else {
result = 2.f * (float)sqrt(-a * kThird) * (float)cos((phi * kThird) + (SK_ScalarPI * 2.f * kThird));
if (!between_closed(result, segment.fP0T.x(), segment.fP2T.x())) {
result = 2.f * (float)sqrt(-a * kThird) * (float)cos(phi * kThird);
}
}
return result;
}
}
// This structure contains some intermediate values shared by the same row.
// It is used to calculate segment side of a quadratic bezier.
struct RowData {
// The intersection type of a scanline and y = x * x parabola in canonical space.
enum IntersectionType {
kNoIntersection,
kVerticalLine,
kTangentLine,
kTwoPointsIntersect
} fIntersectionType;
// The direction of the quadratic segment/scanline in the canonical space.
// 1: The quadratic segment/scanline going from negative x-axis to positive x-axis.
// 0: The scanline is a vertical line in the canonical space.
// -1: The quadratic segment/scanline going from positive x-axis to negative x-axis.
int fQuadXDirection;
int fScanlineXDirection;
// The y-value(equal to x*x) of intersection point for the kVerticalLine intersection type.
double fYAtIntersection;
// The x-value for two intersection points.
double fXAtIntersection1;
double fXAtIntersection2;
};
void precomputation_for_row(
RowData *rowData,
const PathSegment& segment,
const SkPoint& pointLeft,
const SkPoint& pointRight
) {
if (segment.fType != PathSegment::kQuad) {
return;
}
const DPoint& xFormPtLeft = segment.fXformMatrix.mapPoint(pointLeft);
const DPoint& xFormPtRight = segment.fXformMatrix.mapPoint(pointRight);;
rowData->fQuadXDirection = (int)sign_of(segment.fP2T.x() - segment.fP0T.x());
rowData->fScanlineXDirection = (int)sign_of(xFormPtRight.x() - xFormPtLeft.x());
const double x1 = xFormPtLeft.x();
const double y1 = xFormPtLeft.y();
const double x2 = xFormPtRight.x();
const double y2 = xFormPtRight.y();
if (nearly_equal(x1, x2, segment.fNearlyZeroScaled, true)) {
rowData->fIntersectionType = RowData::kVerticalLine;
rowData->fYAtIntersection = x1 * x1;
rowData->fScanlineXDirection = 0;
return;
}
// Line y = mx + b
const double m = (y2 - y1) / (x2 - x1);
const double b = -m * x1 + y1;
const double m2 = m * m;
const double c = m2 + 4.0 * b;
const double tol = 4.0 * segment.fTangentTolScaledSqd / (m2 + 1.0);
// Check if the scanline is the tangent line of the curve,
// and the curve start or end at the same y-coordinate of the scanline
if ((rowData->fScanlineXDirection == 1 &&
(segment.fPts[0].y() == pointLeft.y() ||
segment.fPts[2].y() == pointLeft.y())) &&
nearly_zero(c, tol)) {
rowData->fIntersectionType = RowData::kTangentLine;
rowData->fXAtIntersection1 = m / 2.0;
rowData->fXAtIntersection2 = m / 2.0;
} else if (c <= 0.0) {
rowData->fIntersectionType = RowData::kNoIntersection;
return;
} else {
rowData->fIntersectionType = RowData::kTwoPointsIntersect;
const double d = sqrt(c);
rowData->fXAtIntersection1 = (m + d) / 2.0;
rowData->fXAtIntersection2 = (m - d) / 2.0;
}
}
SegSide calculate_side_of_quad(
const PathSegment& segment,
const SkPoint& point,
const DPoint& xFormPt,
const RowData& rowData) {
SegSide side = kNA_SegSide;
if (RowData::kVerticalLine == rowData.fIntersectionType) {
side = (SegSide)(int)(sign_of(xFormPt.y() - rowData.fYAtIntersection) * rowData.fQuadXDirection);
}
else if (RowData::kTwoPointsIntersect == rowData.fIntersectionType) {
const double p1 = rowData.fXAtIntersection1;
const double p2 = rowData.fXAtIntersection2;
int signP1 = (int)sign_of(p1 - xFormPt.x());
bool includeP1 = true;
bool includeP2 = true;
if (rowData.fScanlineXDirection == 1) {
if ((rowData.fQuadXDirection == -1 && segment.fPts[0].y() <= point.y() &&
nearly_equal(segment.fP0T.x(), p1, segment.fNearlyZeroScaled, true)) ||
(rowData.fQuadXDirection == 1 && segment.fPts[2].y() <= point.y() &&
nearly_equal(segment.fP2T.x(), p1, segment.fNearlyZeroScaled, true))) {
includeP1 = false;
}
if ((rowData.fQuadXDirection == -1 && segment.fPts[2].y() <= point.y() &&
nearly_equal(segment.fP2T.x(), p2, segment.fNearlyZeroScaled, true)) ||
(rowData.fQuadXDirection == 1 && segment.fPts[0].y() <= point.y() &&
nearly_equal(segment.fP0T.x(), p2, segment.fNearlyZeroScaled, true))) {
includeP2 = false;
}
}
if (includeP1 && between_closed(p1, segment.fP0T.x(), segment.fP2T.x(),
segment.fNearlyZeroScaled, true)) {
side = (SegSide)(signP1 * rowData.fQuadXDirection);
}
if (includeP2 && between_closed(p2, segment.fP0T.x(), segment.fP2T.x(),
segment.fNearlyZeroScaled, true)) {
int signP2 = (int)sign_of(p2 - xFormPt.x());
if (side == kNA_SegSide || signP2 == 1) {
side = (SegSide)(-signP2 * rowData.fQuadXDirection);
}
}
} else if (RowData::kTangentLine == rowData.fIntersectionType) {
// The scanline is the tangent line of current quadratic segment.
const double p = rowData.fXAtIntersection1;
int signP = (int)sign_of(p - xFormPt.x());
if (rowData.fScanlineXDirection == 1) {
// The path start or end at the tangent point.
if (segment.fPts[0].y() == point.y()) {
side = (SegSide)(signP);
} else if (segment.fPts[2].y() == point.y()) {
side = (SegSide)(-signP);
}
}
}
return side;
}
static float distance_to_segment(const SkPoint& point,
const PathSegment& segment,
const RowData& rowData,
SegSide* side) {
SkASSERT(side);
const DPoint xformPt = segment.fXformMatrix.mapPoint(point);
if (segment.fType == PathSegment::kLine) {
float result = SK_DistanceFieldPad * SK_DistanceFieldPad;
if (between_closed(xformPt.x(), segment.fP0T.x(), segment.fP2T.x())) {
result = (float)(xformPt.y() * xformPt.y());
} else if (xformPt.x() < segment.fP0T.x()) {
result = (float)(xformPt.x() * xformPt.x() + xformPt.y() * xformPt.y());
} else {
result = (float)((xformPt.x() - segment.fP2T.x()) * (xformPt.x() - segment.fP2T.x())
+ xformPt.y() * xformPt.y());
}
if (between_closed_open(point.y(), segment.fBoundingBox.top(),
segment.fBoundingBox.bottom())) {
*side = (SegSide)(int)sign_of(xformPt.y());
} else {
*side = kNA_SegSide;
}
return result;
} else {
SkASSERT(segment.fType == PathSegment::kQuad);
const float nearestPoint = calculate_nearest_point_for_quad(segment, xformPt);
float dist;
if (between_closed(nearestPoint, segment.fP0T.x(), segment.fP2T.x())) {
DPoint x = DPoint::Make(nearestPoint, nearestPoint * nearestPoint);
dist = (float)xformPt.distanceToSqd(x);
} else {
const float distToB0T = (float)xformPt.distanceToSqd(segment.fP0T);
const float distToB2T = (float)xformPt.distanceToSqd(segment.fP2T);
if (distToB0T < distToB2T) {
dist = distToB0T;
} else {
dist = distToB2T;
}
}
if (between_closed_open(point.y(), segment.fBoundingBox.top(),
segment.fBoundingBox.bottom())) {
*side = calculate_side_of_quad(segment, point, xformPt, rowData);
} else {
*side = kNA_SegSide;
}
return (float)(dist * segment.fScalingFactorSqd);
}
}
static void calculate_distance_field_data(PathSegmentArray* segments,
DFData* dataPtr,
int width, int height) {
int count = segments->count();
for (int a = 0; a < count; ++a) {
PathSegment& segment = (*segments)[a];
const SkRect& segBB = segment.fBoundingBox.makeOutset(
SK_DistanceFieldPad, SK_DistanceFieldPad);
int startColumn = (int)segBB.left();
int endColumn = SkScalarCeilToInt(segBB.right());
int startRow = (int)segBB.top();
int endRow = SkScalarCeilToInt(segBB.bottom());
SkASSERT((startColumn >= 0) && "StartColumn < 0!");
SkASSERT((endColumn <= width) && "endColumn > width!");
SkASSERT((startRow >= 0) && "StartRow < 0!");
SkASSERT((endRow <= height) && "EndRow > height!");
// Clip inside the distance field to avoid overflow
startColumn = SkTMax(startColumn, 0);
endColumn = SkTMin(endColumn, width);
startRow = SkTMax(startRow, 0);
endRow = SkTMin(endRow, height);
for (int row = startRow; row < endRow; ++row) {
SegSide prevSide = kNA_SegSide;
const float pY = row + 0.5f;
RowData rowData;
const SkPoint pointLeft = SkPoint::Make((SkScalar)startColumn, pY);
const SkPoint pointRight = SkPoint::Make((SkScalar)endColumn, pY);
if (between_closed_open(pY, segment.fBoundingBox.top(),
segment.fBoundingBox.bottom())) {
precomputation_for_row(&rowData, segment, pointLeft, pointRight);
}
for (int col = startColumn; col < endColumn; ++col) {
int idx = (row * width) + col;
const float pX = col + 0.5f;
const SkPoint point = SkPoint::Make(pX, pY);
const float distSq = dataPtr[idx].fDistSq;
int dilation = distSq < 1.5 * 1.5 ? 1 :
distSq < 2.5 * 2.5 ? 2 :
distSq < 3.5 * 3.5 ? 3 : SK_DistanceFieldPad;
if (dilation > SK_DistanceFieldPad) {
dilation = SK_DistanceFieldPad;
}
// Optimisation for not calculating some points.
if (dilation != SK_DistanceFieldPad && !segment.fBoundingBox.roundOut()
.makeOutset(dilation, dilation).contains(col, row)) {
continue;
}
SegSide side = kNA_SegSide;
int deltaWindingScore = 0;
float currDistSq = distance_to_segment(point, segment, rowData, &side);
if (prevSide == kLeft_SegSide && side == kRight_SegSide) {
deltaWindingScore = -1;
} else if (prevSide == kRight_SegSide && side == kLeft_SegSide) {
deltaWindingScore = 1;
}
prevSide = side;
if (currDistSq < distSq) {
dataPtr[idx].fDistSq = currDistSq;
}
dataPtr[idx].fDeltaWindingScore += deltaWindingScore;
}
}
}
}
template <int distanceMagnitude>
static unsigned char pack_distance_field_val(float dist) {
// The distance field is constructed as unsigned char values, so that the zero value is at 128,
// Beside 128, we have 128 values in range [0, 128), but only 127 values in range (128, 255].
// So we multiply distanceMagnitude by 127/128 at the latter range to avoid overflow.
dist = SkScalarPin(-dist, -distanceMagnitude, distanceMagnitude * 127.0f / 128.0f);
// Scale into the positive range for unsigned distance.
dist += distanceMagnitude;
// Scale into unsigned char range.
// Round to place negative and positive values as equally as possible around 128
// (which represents zero).
return (unsigned char)SkScalarRoundToInt(dist / (2 * distanceMagnitude) * 256.0f);
}
bool GrGenerateDistanceFieldFromPath(unsigned char* distanceField,
const SkPath& path, const SkMatrix& drawMatrix,
int width, int height, size_t rowBytes) {
SkASSERT(distanceField);
SkDEBUGCODE(SkPath xformPath;);
SkDEBUGCODE(path.transform(drawMatrix, &xformPath));
SkDEBUGCODE(SkIRect pathBounds = xformPath.getBounds().roundOut());
SkDEBUGCODE(SkIRect expectPathBounds = SkIRect::MakeWH(width - 2 * SK_DistanceFieldPad,
height - 2 * SK_DistanceFieldPad));
SkASSERT(expectPathBounds.isEmpty() ||
expectPathBounds.contains(pathBounds.x(), pathBounds.y()));
SkASSERT(expectPathBounds.isEmpty() || pathBounds.isEmpty() ||
expectPathBounds.contains(pathBounds));
SkPath simplifiedPath;
SkPath workingPath;
if (Simplify(path, &simplifiedPath)) {
workingPath = simplifiedPath;
} else {
workingPath = path;
}
if (!IsDistanceFieldSupportedFillType(workingPath.getFillType())) {
return false;
}
workingPath.transform(drawMatrix);
SkDEBUGCODE(pathBounds = workingPath.getBounds().roundOut());
SkASSERT(expectPathBounds.isEmpty() ||
expectPathBounds.contains(pathBounds.x(), pathBounds.y()));
SkASSERT(expectPathBounds.isEmpty() || pathBounds.isEmpty() ||
expectPathBounds.contains(pathBounds));
// translate path to offset (SK_DistanceFieldPad, SK_DistanceFieldPad)
SkMatrix dfMatrix;
dfMatrix.setTranslate(SK_DistanceFieldPad, SK_DistanceFieldPad);
workingPath.transform(dfMatrix);
// create temp data
size_t dataSize = width * height * sizeof(DFData);
SkAutoSMalloc<1024> dfStorage(dataSize);
DFData* dataPtr = (DFData*) dfStorage.get();
// create initial distance data
init_distances(dataPtr, width * height);
SkPath::Iter iter(workingPath, true);
SkSTArray<15, PathSegment, true> segments;
for (;;) {
SkPoint pts[4];
SkPath::Verb verb = iter.next(pts);
switch (verb) {
case SkPath::kMove_Verb:
break;
case SkPath::kLine_Verb: {
add_line_to_segment(pts, &segments);
break;
}
case SkPath::kQuad_Verb:
add_quad_segment(pts, &segments);
break;
case SkPath::kConic_Verb: {
SkScalar weight = iter.conicWeight();
SkAutoConicToQuads converter;
const SkPoint* quadPts = converter.computeQuads(pts, weight, kConicTolerance);
for (int i = 0; i < converter.countQuads(); ++i) {
add_quad_segment(quadPts + 2*i, &segments);
}
break;
}
case SkPath::kCubic_Verb: {
add_cubic_segments(pts, &segments);
break;
};
default:
break;
}
if (verb == SkPath::kDone_Verb) {
break;
}
}
calculate_distance_field_data(&segments, dataPtr, width, height);
for (int row = 0; row < height; ++row) {
int windingNumber = 0; // Winding number start from zero for each scanline
for (int col = 0; col < width; ++col) {
int idx = (row * width) + col;
windingNumber += dataPtr[idx].fDeltaWindingScore;
enum DFSign {
kInside = -1,
kOutside = 1
} dfSign;
if (workingPath.getFillType() == SkPath::kWinding_FillType) {
dfSign = windingNumber ? kInside : kOutside;
} else if (workingPath.getFillType() == SkPath::kInverseWinding_FillType) {
dfSign = windingNumber ? kOutside : kInside;
} else if (workingPath.getFillType() == SkPath::kEvenOdd_FillType) {
dfSign = (windingNumber % 2) ? kInside : kOutside;
} else {
SkASSERT(workingPath.getFillType() == SkPath::kInverseEvenOdd_FillType);
dfSign = (windingNumber % 2) ? kOutside : kInside;
}
// The winding number at the end of a scanline should be zero.
SkASSERT(((col != width - 1) || (windingNumber == 0)) &&
"Winding number should be zero at the end of a scan line.");
// Fallback to use SkPath::contains to determine the sign of pixel in release build.
if (col == width - 1 && windingNumber != 0) {
for (int col = 0; col < width; ++col) {
int idx = (row * width) + col;
dfSign = workingPath.contains(col + 0.5, row + 0.5) ? kInside : kOutside;
const float miniDist = sqrt(dataPtr[idx].fDistSq);
const float dist = dfSign * miniDist;
unsigned char pixelVal = pack_distance_field_val<SK_DistanceFieldMagnitude>(dist);
distanceField[(row * rowBytes) + col] = pixelVal;
}
continue;
}
const float miniDist = sqrt(dataPtr[idx].fDistSq);
const float dist = dfSign * miniDist;
unsigned char pixelVal = pack_distance_field_val<SK_DistanceFieldMagnitude>(dist);
distanceField[(row * rowBytes) + col] = pixelVal;
}
}
return true;
}