Add SkDashMeasure.h (name up for bikeshedding) which takes a dashinfo

experimental/curve_dash_measure/SkDashMeasure.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCurveMeasure.h"
+#include "SkDashMeasure.h"
+#include "SkPathMeasurePriv.h"
+
+void getDashedPath(const SkPath& path,
+                            const struct SkPathEffect::DashInfo& dashInfo,
+                            SkPath* dst) {
+    const SkScalar* intervals = dashInfo.fIntervals;
+
+    int32_t interval_index = 0;
+    SkScalar interval_accum = intervals[interval_index];
+
+    SkPath::Iter iter(path, false);
+    SkPath::Verb current;
+    SkPoint pts[4];
+
+    while ((current = iter.next(pts)) != SkPath::kDone_Verb) {
+        SkSegType segtype;
+        SkPoint end;
+        switch (current) {
+            case SkPath::kMove_Verb:
+                dst->moveTo(pts[0]);
+                continue;
+            case SkPath::kLine_Verb:
+                segtype = kLine_SegType;
+                end = pts[1];
+                break;
+            case SkPath::kQuad_Verb:
+                segtype = kQuad_SegType;
+                end = pts[2];
+                break;
+            case SkPath::kConic_Verb:
+                segtype = kConic_SegType;
+                end = pts[2];
+                break;
+            case SkPath::kCubic_Verb:
+                segtype = kCubic_SegType;
+                end = pts[3];
+                break;
+            case SkPath::kClose_Verb:
+                // should not appear in the iter since we're not using RawIter
+                SkASSERT(false);
+                break;
+            default:  // unreachable
+                SkASSERT(false);
+                break;
+        }
+
+        // TODO(hstern): Do heuristic check to see whether we should do
+        // pathmeasure or curvemeasure. probably do it before the outer loop
+        // by giving CurveMeasure a reset() and reusing the object inside.
+        SkCurveMeasure meas(pts, segtype);
+
+        SkScalar prevT = 0;
+
+        SkScalar current_length = meas.getLength();
+        while (interval_accum < current_length) {
+            SkScalar time;
+            SkPoint pos;
+            meas.getPosTanTime(interval_accum, &pos, nullptr, &time);
+            if (dashIsOn(interval_index)) {
+                SkPathMeasure_segTo(pts, segtype, prevT, time, dst);
+            } else {
+                dst->moveTo(pos);
+            }
+            prevT = time;
+
+            interval_accum += intervals[interval_index];
+            interval_index = (interval_index+1) % dashInfo.fCount;
+        }
+        if (dashIsOn(interval_index)) {
+            SkPathMeasure_segTo(pts, segtype, prevT, 1, dst);
+        } else {
+            dst->moveTo(end);
+        }
+
+        interval_accum = interval_accum - current_length;
+    }
+}