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SkDashPath.cpp
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SkDashPath.cpp
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/*
* Copyright 2014 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "src/utils/SkDashPathPriv.h"
#include "include/core/SkPaint.h"
#include "include/core/SkPath.h"
#include "include/core/SkPathEffect.h"
#include "include/core/SkPathMeasure.h"
#include "include/core/SkPoint.h"
#include "include/core/SkRect.h"
#include "include/core/SkScalar.h"
#include "include/core/SkStrokeRec.h"
#include "include/core/SkTypes.h"
#include "include/private/base/SkAlign.h"
#include "include/private/base/SkFloatingPoint.h"
#include "include/private/base/SkTo.h"
#include "src/core/SkPathEnums.h"
#include "src/core/SkPathPriv.h"
#include "src/core/SkPointPriv.h"
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <iterator>
static inline int is_even(int x) {
return !(x & 1);
}
static SkScalar find_first_interval(const SkScalar intervals[], SkScalar phase,
int32_t* index, int count) {
for (int i = 0; i < count; ++i) {
SkScalar gap = intervals[i];
if (phase > gap || (phase == gap && gap)) {
phase -= gap;
} else {
*index = i;
return gap - phase;
}
}
// If we get here, phase "appears" to be larger than our length. This
// shouldn't happen with perfect precision, but we can accumulate errors
// during the initial length computation (rounding can make our sum be too
// big or too small. In that event, we just have to eat the error here.
*index = 0;
return intervals[0];
}
void SkDashPath::CalcDashParameters(SkScalar phase, const SkScalar intervals[], int32_t count,
SkScalar* initialDashLength, int32_t* initialDashIndex,
SkScalar* intervalLength, SkScalar* adjustedPhase) {
SkScalar len = 0;
for (int i = 0; i < count; i++) {
len += intervals[i];
}
*intervalLength = len;
// Adjust phase to be between 0 and len, "flipping" phase if negative.
// e.g., if len is 100, then phase of -20 (or -120) is equivalent to 80
if (adjustedPhase) {
if (phase < 0) {
phase = -phase;
if (phase > len) {
phase = SkScalarMod(phase, len);
}
phase = len - phase;
// Due to finite precision, it's possible that phase == len,
// even after the subtract (if len >>> phase), so fix that here.
// This fixes http://crbug.com/124652 .
SkASSERT(phase <= len);
if (phase == len) {
phase = 0;
}
} else if (phase >= len) {
phase = SkScalarMod(phase, len);
}
*adjustedPhase = phase;
}
SkASSERT(phase >= 0 && phase < len);
*initialDashLength = find_first_interval(intervals, phase,
initialDashIndex, count);
SkASSERT(*initialDashLength >= 0);
SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count);
}
static void outset_for_stroke(SkRect* rect, const SkStrokeRec& rec) {
SkScalar radius = SkScalarHalf(rec.getWidth());
if (0 == radius) {
radius = SK_Scalar1; // hairlines
}
if (SkPaint::kMiter_Join == rec.getJoin()) {
radius *= rec.getMiter();
}
rect->outset(radius, radius);
}
// If line is zero-length, bump out the end by a tiny amount
// to draw endcaps. The bump factor is sized so that
// SkPoint::Distance() computes a non-zero length.
// Offsets SK_ScalarNearlyZero or smaller create empty paths when Iter measures length.
// Large values are scaled by SK_ScalarNearlyZero so significant bits change.
static void adjust_zero_length_line(SkPoint pts[2]) {
SkASSERT(pts[0] == pts[1]);
pts[1].fX += std::max(1.001f, pts[1].fX) * SK_ScalarNearlyZero;
}
static bool clip_line(SkPoint pts[2], const SkRect& bounds, SkScalar intervalLength,
SkScalar priorPhase) {
SkVector dxy = pts[1] - pts[0];
// only horizontal or vertical lines
if (dxy.fX && dxy.fY) {
return false;
}
int xyOffset = SkToBool(dxy.fY); // 0 to adjust horizontal, 1 to adjust vertical
SkScalar minXY = (&pts[0].fX)[xyOffset];
SkScalar maxXY = (&pts[1].fX)[xyOffset];
bool swapped = maxXY < minXY;
if (swapped) {
using std::swap;
swap(minXY, maxXY);
}
SkASSERT(minXY <= maxXY);
SkScalar leftTop = (&bounds.fLeft)[xyOffset];
SkScalar rightBottom = (&bounds.fRight)[xyOffset];
if (maxXY < leftTop || minXY > rightBottom) {
return false;
}
// Now we actually perform the chop, removing the excess to the left/top and
// right/bottom of the bounds (keeping our new line "in phase" with the dash,
// hence the (mod intervalLength).
if (minXY < leftTop) {
minXY = leftTop - SkScalarMod(leftTop - minXY, intervalLength);
if (!swapped) {
minXY -= priorPhase; // for rectangles, adjust by prior phase
}
}
if (maxXY > rightBottom) {
maxXY = rightBottom + SkScalarMod(maxXY - rightBottom, intervalLength);
if (swapped) {
maxXY += priorPhase; // for rectangles, adjust by prior phase
}
}
SkASSERT(maxXY >= minXY);
if (swapped) {
using std::swap;
swap(minXY, maxXY);
}
(&pts[0].fX)[xyOffset] = minXY;
(&pts[1].fX)[xyOffset] = maxXY;
if (minXY == maxXY) {
adjust_zero_length_line(pts);
}
return true;
}
// Handles only lines and rects.
// If cull_path() returns true, dstPath is the new smaller path,
// otherwise dstPath may have been changed but you should ignore it.
static bool cull_path(const SkPath& srcPath, const SkStrokeRec& rec,
const SkRect* cullRect, SkScalar intervalLength, SkPath* dstPath) {
if (!cullRect) {
SkPoint pts[2];
if (srcPath.isLine(pts) && pts[0] == pts[1]) {
adjust_zero_length_line(pts);
dstPath->moveTo(pts[0]);
dstPath->lineTo(pts[1]);
return true;
}
return false;
}
SkRect bounds;
bounds = *cullRect;
outset_for_stroke(&bounds, rec);
{
SkPoint pts[2];
if (srcPath.isLine(pts)) {
if (clip_line(pts, bounds, intervalLength, 0)) {
dstPath->moveTo(pts[0]);
dstPath->lineTo(pts[1]);
return true;
}
return false;
}
}
if (srcPath.isRect(nullptr)) {
// We'll break the rect into four lines, culling each separately.
SkPath::Iter iter(srcPath, false);
SkPoint pts[4]; // Rects are all moveTo and lineTo, so we'll only use pts[0] and pts[1].
SkAssertResult(SkPath::kMove_Verb == iter.next(pts));
double accum = 0; // Sum of unculled edge lengths to keep the phase correct.
// Intentionally a double to minimize the risk of overflow and drift.
while (iter.next(pts) == SkPath::kLine_Verb) {
// Notice this vector v and accum work with the original unclipped length.
SkVector v = pts[1] - pts[0];
if (clip_line(pts, bounds, intervalLength, std::fmod(accum, intervalLength))) {
// pts[0] may have just been changed by clip_line().
// If that's not where we ended the previous lineTo(), we need to moveTo() there.
SkPoint last;
if (!dstPath->getLastPt(&last) || last != pts[0]) {
dstPath->moveTo(pts[0]);
}
dstPath->lineTo(pts[1]);
}
// We either just traveled v.fX horizontally or v.fY vertically.
SkASSERT(v.fX == 0 || v.fY == 0);
accum += SkScalarAbs(v.fX + v.fY);
}
return !dstPath->isEmpty();
}
return false;
}
class SpecialLineRec {
public:
bool init(const SkPath& src, SkPath* dst, SkStrokeRec* rec,
int intervalCount, SkScalar intervalLength) {
if (rec->isHairlineStyle() || !src.isLine(fPts)) {
return false;
}
// can relax this in the future, if we handle square and round caps
if (SkPaint::kButt_Cap != rec->getCap()) {
return false;
}
SkScalar pathLength = SkPoint::Distance(fPts[0], fPts[1]);
fTangent = fPts[1] - fPts[0];
if (fTangent.isZero()) {
return false;
}
fPathLength = pathLength;
fTangent.scale(sk_ieee_float_divide(1.0f, pathLength));
if (!SkScalarsAreFinite(fTangent.fX, fTangent.fY)) {
return false;
}
SkPointPriv::RotateCCW(fTangent, &fNormal);
fNormal.scale(SkScalarHalf(rec->getWidth()));
// now estimate how many quads will be added to the path
// resulting segments = pathLen * intervalCount / intervalLen
// resulting points = 4 * segments
SkScalar ptCount = pathLength * intervalCount / (float)intervalLength;
ptCount = std::min(ptCount, SkDashPath::kMaxDashCount);
if (SkScalarIsNaN(ptCount)) {
return false;
}
int n = SkScalarCeilToInt(ptCount) << 2;
dst->incReserve(n);
// we will take care of the stroking
rec->setFillStyle();
return true;
}
void addSegment(SkScalar d0, SkScalar d1, SkPath* path) const {
SkASSERT(d0 <= fPathLength);
// clamp the segment to our length
if (d1 > fPathLength) {
d1 = fPathLength;
}
SkScalar x0 = fPts[0].fX + fTangent.fX * d0;
SkScalar x1 = fPts[0].fX + fTangent.fX * d1;
SkScalar y0 = fPts[0].fY + fTangent.fY * d0;
SkScalar y1 = fPts[0].fY + fTangent.fY * d1;
SkPoint pts[4];
pts[0].set(x0 + fNormal.fX, y0 + fNormal.fY); // moveTo
pts[1].set(x1 + fNormal.fX, y1 + fNormal.fY); // lineTo
pts[2].set(x1 - fNormal.fX, y1 - fNormal.fY); // lineTo
pts[3].set(x0 - fNormal.fX, y0 - fNormal.fY); // lineTo
path->addPoly(pts, std::size(pts), false);
}
private:
SkPoint fPts[2];
SkVector fTangent;
SkVector fNormal;
SkScalar fPathLength;
};
bool SkDashPath::InternalFilter(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
const SkRect* cullRect, const SkScalar aIntervals[],
int32_t count, SkScalar initialDashLength, int32_t initialDashIndex,
SkScalar intervalLength, SkScalar startPhase,
StrokeRecApplication strokeRecApplication) {
// we must always have an even number of intervals
SkASSERT(is_even(count));
// we do nothing if the src wants to be filled
SkStrokeRec::Style style = rec->getStyle();
if (SkStrokeRec::kFill_Style == style || SkStrokeRec::kStrokeAndFill_Style == style) {
return false;
}
const SkScalar* intervals = aIntervals;
SkScalar dashCount = 0;
int segCount = 0;
SkPath cullPathStorage;
const SkPath* srcPtr = &src;
if (cull_path(src, *rec, cullRect, intervalLength, &cullPathStorage)) {
// if rect is closed, starts in a dash, and ends in a dash, add the initial join
// potentially a better fix is described here: bug.skia.org/7445
if (src.isRect(nullptr) && src.isLastContourClosed() && is_even(initialDashIndex)) {
SkScalar pathLength = SkPathMeasure(src, false, rec->getResScale()).getLength();
#if defined(SK_LEGACY_RECT_DASHING_BUG)
SkScalar endPhase = SkScalarMod(pathLength + initialDashLength, intervalLength);
#else
SkScalar endPhase = SkScalarMod(pathLength + startPhase, intervalLength);
#endif
int index = 0;
while (endPhase > intervals[index]) {
endPhase -= intervals[index++];
SkASSERT(index <= count);
if (index == count) {
// We have run out of intervals. endPhase "should" never get to this point,
// but it could if the subtracts underflowed. Hence we will pin it as if it
// perfectly ran through the intervals.
// See crbug.com/875494 (and skbug.com/8274)
endPhase = 0;
break;
}
}
// if dash ends inside "on", or ends at beginning of "off"
if (is_even(index) == (endPhase > 0)) {
SkPoint midPoint = src.getPoint(0);
// get vector at end of rect
int last = src.countPoints() - 1;
while (midPoint == src.getPoint(last)) {
--last;
SkASSERT(last >= 0);
}
// get vector at start of rect
int next = 1;
while (midPoint == src.getPoint(next)) {
++next;
SkASSERT(next < last);
}
SkVector v = midPoint - src.getPoint(last);
const SkScalar kTinyOffset = SK_ScalarNearlyZero;
// scale vector to make start of tiny right angle
v *= kTinyOffset;
cullPathStorage.moveTo(midPoint - v);
cullPathStorage.lineTo(midPoint);
v = midPoint - src.getPoint(next);
// scale vector to make end of tiny right angle
v *= kTinyOffset;
cullPathStorage.lineTo(midPoint - v);
}
}
srcPtr = &cullPathStorage;
}
SpecialLineRec lineRec;
bool specialLine = (StrokeRecApplication::kAllow == strokeRecApplication) &&
lineRec.init(*srcPtr, dst, rec, count >> 1, intervalLength);
SkPathMeasure meas(*srcPtr, false, rec->getResScale());
do {
bool skipFirstSegment = meas.isClosed();
bool addedSegment = false;
SkScalar length = meas.getLength();
int index = initialDashIndex;
// Since the path length / dash length ratio may be arbitrarily large, we can exert
// significant memory pressure while attempting to build the filtered path. To avoid this,
// we simply give up dashing beyond a certain threshold.
//
// The original bug report (http://crbug.com/165432) is based on a path yielding more than
// 90 million dash segments and crashing the memory allocator. A limit of 1 million
// segments seems reasonable: at 2 verbs per segment * 9 bytes per verb, this caps the
// maximum dash memory overhead at roughly 17MB per path.
dashCount += length * (count >> 1) / intervalLength;
if (dashCount > kMaxDashCount) {
dst->reset();
return false;
}
// Using double precision to avoid looping indefinitely due to single precision rounding
// (for extreme path_length/dash_length ratios). See test_infinite_dash() unittest.
double distance = 0;
double dlen = initialDashLength;
while (distance < length) {
SkASSERT(dlen >= 0);
addedSegment = false;
if (is_even(index) && !skipFirstSegment) {
addedSegment = true;
++segCount;
if (specialLine) {
lineRec.addSegment(SkDoubleToScalar(distance),
SkDoubleToScalar(distance + dlen),
dst);
} else {
meas.getSegment(SkDoubleToScalar(distance),
SkDoubleToScalar(distance + dlen),
dst, true);
}
}
distance += dlen;
// clear this so we only respect it the first time around
skipFirstSegment = false;
// wrap around our intervals array if necessary
index += 1;
SkASSERT(index <= count);
if (index == count) {
index = 0;
}
// fetch our next dlen
dlen = intervals[index];
}
// extend if we ended on a segment and we need to join up with the (skipped) initial segment
if (meas.isClosed() && is_even(initialDashIndex) &&
initialDashLength >= 0) {
meas.getSegment(0, initialDashLength, dst, !addedSegment);
++segCount;
}
} while (meas.nextContour());
// TODO: do we still need this?
if (segCount > 1) {
SkPathPriv::SetConvexity(*dst, SkPathConvexity::kConcave);
}
return true;
}
bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
const SkRect* cullRect, const SkPathEffect::DashInfo& info) {
if (!ValidDashPath(info.fPhase, info.fIntervals, info.fCount)) {
return false;
}
SkScalar initialDashLength = 0;
int32_t initialDashIndex = 0;
SkScalar intervalLength = 0;
CalcDashParameters(info.fPhase, info.fIntervals, info.fCount,
&initialDashLength, &initialDashIndex, &intervalLength);
return InternalFilter(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
initialDashIndex, intervalLength, info.fPhase);
}
bool SkDashPath::ValidDashPath(SkScalar phase, const SkScalar intervals[], int32_t count) {
if (count < 2 || !SkIsAlign2(count)) {
return false;
}
SkScalar length = 0;
for (int i = 0; i < count; i++) {
if (intervals[i] < 0) {
return false;
}
length += intervals[i];
}
// watch out for values that might make us go out of bounds
return length > 0 && SkScalarIsFinite(phase) && SkScalarIsFinite(length);
}