allow one zero length dash

src/utils/SkDashPath.cpp

Index: src/utils/SkDashPath.cpp
diff --git a/src/utils/SkDashPath.cpp b/src/utils/SkDashPath.cpp
index cd01a9972b94695e1a4b27e1e819bb675fcb56e0..9a607c47eb56cbd875bcaf79eda631d34884bc94 100644
--- a/src/utils/SkDashPath.cpp
+++ b/src/utils/SkDashPath.cpp
@@ -39,42 +39,35 @@ void SkDashPath::CalcDashParameters(SkScalar phase, const SkScalar intervals[],
         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) {
+    // 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);
             }
-            *adjustedPhase = phase;
+            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);
         }
-        SkASSERT(phase >= 0 && phase < len);
+        *adjustedPhase = phase;
+    }
+    SkASSERT(phase >= 0 && phase < len);
 
-        *initialDashLength = find_first_interval(intervals, phase,
-                                                initialDashIndex, count);
+    *initialDashLength = find_first_interval(intervals, phase,
+                                            initialDashIndex, count);
 
-        SkASSERT(*initialDashLength >= 0);
-        SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count);
-    } else {
-        *initialDashLength = -1;    // signal bad dash intervals
-    }
+    SkASSERT(*initialDashLength >= 0);
+    SkASSERT(*initialDashIndex >= 0 && *initialDashIndex < count);
 }
 
 static void outset_for_stroke(SkRect* rect, const SkStrokeRec& rec) {
@@ -219,13 +212,13 @@ private:
 };
 
 
-bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
+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) {
 
-    // we do nothing if the src wants to be filled, or if our dashlength is 0
-    if (rec->isFillStyle() || initialDashLength < 0) {
+    // we do nothing if the src wants to be filled
+    if (rec->isFillStyle()) {
         return false;
     }
 
@@ -305,7 +298,7 @@ bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec
 
         // 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) {
+            initialDashLength >= 0) {
             meas.getSegment(0, initialDashLength, dst, !addedSegment);
             ++segCount;
         }
@@ -320,11 +313,29 @@ bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec
 
 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 FilterDashPath(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
+    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);
+}