Move Dashing filterPath to a dashing utils file

src/utils/SkDashPath.cpp

+/*
+ * 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"
+
+static inline int is_even(int x) {
+    return (~x) << 31;
+}
+
+static SkScalar find_first_interval(const SkScalar intervals[], SkScalar phase,
+                                    int32_t* index, int count) {
+    for (int i = 0; i < count; ++i) {
+        if (phase > intervals[i]) {
+            phase -= intervals[i];
+        } else {
+            *index = i;
+            return intervals[i] - 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;
+
+    // watch out for values that might make us go out of bounds
+    if ((len > 0) && SkScalarIsFinite(phase) && SkScalarIsFinite(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);
+    } else {
+        *initialDashLength = -1;    // signal bad dash intervals
+    }
+}
+
+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 = SkScalarMul(radius, rec.getMiter());
+    }
+    rect->outset(radius, radius);
+}
+
+// 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) {
+    if (NULL == cullRect) {
+        return false;
+    }
+
+    SkPoint pts[2];
+    if (!srcPath.isLine(pts)) {
+        return false;
+    }
+
+    SkRect bounds = *cullRect;
+    outset_for_stroke(&bounds, rec);
+
+    SkScalar dx = pts[1].x() - pts[0].x();
+    SkScalar dy = pts[1].y() - pts[0].y();
+
+    // just do horizontal lines for now (lazy)
+    if (dy) {
+        return false;
+    }
+
+    SkScalar minX = pts[0].fX;
+    SkScalar maxX = pts[1].fX;
+
+    if (maxX < bounds.fLeft || minX > bounds.fRight) {
+        return false;
+    }
+
+    if (dx < 0) {
+        SkTSwap(minX, maxX);
+    }
+
+    // Now we actually perform the chop, removing the excess to the left and
+    // right of the bounds (keeping our new line "in phase" with the dash,
+    // hence the (mod intervalLength).
+
+    if (minX < bounds.fLeft) {
+        minX = bounds.fLeft - SkScalarMod(bounds.fLeft - minX,
+                                          intervalLength);
+    }
+    if (maxX > bounds.fRight) {
+        maxX = bounds.fRight + SkScalarMod(maxX - bounds.fRight,
+                                           intervalLength);
+    }
+
+    SkASSERT(maxX >= minX);
+    if (dx < 0) {
+        SkTSwap(minX, maxX);
+    }
+    pts[0].fX = minX;
+    pts[1].fX = maxX;
+
+    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));
+        fTangent.rotateCCW(&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 = SkScalarMulDiv(pathLength,
+                                          SkIntToScalar(intervalCount),
+                                          intervalLength);
+        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 + SkScalarMul(fTangent.fX, d0);
+        SkScalar x1 = fPts[0].fX + SkScalarMul(fTangent.fX, d1);
+        SkScalar y0 = fPts[0].fY + SkScalarMul(fTangent.fY, d0);
+        SkScalar y1 = fPts[0].fY + SkScalarMul(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::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
+                                const SkRect* cullRect, const SkScalar aIntervals[],
+                                int32_t count, SkScalar initialDashLength, int32_t initialDashIndex,
+                                SkScalar intervalLength) {
+
+    // we do nothing if the src wants to be filled, or if our dashlength is 0
+    if (rec->isFillStyle() || initialDashLength < 0) {
+        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)) {
+        srcPtr = &cullPathStorage;
+    }
+
+    SpecialLineRec lineRec;
+    bool specialLine = lineRec.init(*srcPtr, dst, rec, count >> 1, intervalLength);
+
+    SkPathMeasure   meas(*srcPtr, false);
+
+    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.
+        static const SkScalar kMaxDashCount = 1000000;
+        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) && dlen > 0 && !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) {
+    SkScalar initialDashLength = 0;
+    int32_t initialDashIndex = 0;
+    SkScalar intervalLength = 0;
+    CalcDashParameters(info.fPhase, info.fIntervals, info.fCount,
+                       &initialDashLength, &initialDashIndex, &intervalLength);
+    return FilterDashPath(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
+                          initialDashIndex, intervalLength);
+}