/*
* 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 "SkDashPathPriv.h"
#include "SkPathMeasure.h"
#include "SkPointPriv.h"
#include "SkStrokeRec.h"
#include <utility>
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 += SkTMax(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;
}
static bool contains_inclusive(const SkRect& rect, const SkPoint& pt) {
return rect.fLeft <= pt.fX && pt.fX <= rect.fRight &&
rect.fTop <= pt.fY && pt.fY <= rect.fBottom;
}
// Returns true is b is between a and c, that is: a <= b <= c, or a >= b >= c.
// Can perform this test with one branch by observing that, relative to b,
// the condition is true only if one side is positive and one side is negative.
// If the numbers are very small, the optimization may return the wrong result
// because the multiply may generate a zero where the simple compare does not.
// For this reason the assert does not fire when all three numbers are near zero.
static bool between(SkScalar a, SkScalar b, SkScalar c) {
SkASSERT(((a <= b && b <= c) || (a >= b && b >= c)) == ((a - b) * (c - b) <= 0)
|| (SkScalarNearlyZero(a) && SkScalarNearlyZero(b) && SkScalarNearlyZero(c)));
return (a - b) * (c - b) <= 0;
}
// Only handles lines for now. If returns true, dstPath is the new (smaller)
// path. If returns false, then dstPath parameter is ignored.
static bool cull_path(const SkPath& srcPath, const SkStrokeRec& rec,
const SkRect* cullRect, SkScalar intervalLength,
SkPath* dstPath) {
SkPoint pts[4];
if (nullptr == cullRect) {
if (srcPath.isLine(pts) && pts[0] == pts[1]) {
adjust_zero_length_line(pts);
} else {
return false;
}
} else {
SkRect bounds;
bool isLine = srcPath.isLine(pts);
bool isRect = !isLine && srcPath.isRect(nullptr);
if (!isLine && !isRect) {
return false;
}
bounds = *cullRect;
outset_for_stroke(&bounds, rec);
if (isRect) {
// break rect into four lines, and call each one separately
SkPath::Iter iter(srcPath, false);
SkAssertResult(SkPath::kMove_Verb == iter.next(pts));
SkScalar priorLength = 0;
while (SkPath::kLine_Verb == iter.next(pts)) {
SkVector v = pts[1] - pts[0];
// if line is entirely outside clip rect, skip it
if (v.fX ? between(bounds.fTop, pts[0].fY, bounds.fBottom) :
between(bounds.fLeft, pts[0].fX, bounds.fRight)) {
bool skipMoveTo = contains_inclusive(bounds, pts[0]);
if (clip_line(pts, bounds, intervalLength,
SkScalarMod(priorLength, intervalLength))) {
if (0 == priorLength || !skipMoveTo) {
dstPath->moveTo(pts[0]);
}
dstPath->lineTo(pts[1]);
}
}
// keep track of all prior lengths to set phase of next line
priorLength += SkScalarAbs(v.fX ? v.fX : v.fY);
}
return !dstPath->isEmpty();
}
SkASSERT(isLine);
if (!clip_line(pts, bounds, intervalLength, 0)) {
return false;
}
}
dstPath->moveTo(pts[0]);
dstPath->lineTo(pts[1]);
return true;
}
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(SkScalarInvert(pathLength));
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 = SkTMin(ptCount, SkDashPath::kMaxDashCount);
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, SK_ARRAY_COUNT(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,
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();
SkScalar endPhase = SkScalarMod(pathLength + initialDashLength, intervalLength);
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());
if (segCount > 1) {
dst->setConvexity(SkPath::kConcave_Convexity);
}
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);
}
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);
}