Simple iterator for textblobs

bug: skia:9503

Change-Id: I5b4e2434c6085d048d6d0fc42b2b928439b1066b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/246296
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>

RELEASE_NOTES.txt

@@ -4,6 +4,9 @@ This file includes a list of high level updates for each milestone release.
 
 * * *
 
+  * SkTextBlob::Iter to discover the glyph indices and typefaces in each run
+    https://skia-review.googlesource.com/246296
+
 Milestone 79
 
 [Insert new notes here.]

include/core/SkTextBlob.h

@@ -26,6 +26,9 @@ struct SkDeserialProcs;
     fonts and text rendering are used by run.
 */
 class SK_API SkTextBlob final : public SkNVRefCnt<SkTextBlob> {
+private:
+    class RunRecord;
+
 public:
 
     /** Returns conservative bounding box. Uses SkPaint associated with each glyph to
@@ -186,9 +189,28 @@ public:
     static sk_sp<SkTextBlob> Deserialize(const void* data, size_t size,
                                          const SkDeserialProcs& procs);
 
+    class Iter {
+    public:
+        struct Run {
+            SkTypeface*     fTypeface;
+            int             fGlyphCount;
+            const uint16_t* fGlyphIndices;
+        };
+
+        Iter(const SkTextBlob&);
+
+        /**
+         * Returns true for each "run" inside the textblob, setting the Run fields (if not null).
+         * If this returns false, there are no more runs, and the Run parameter will be ignored.
+         */
+        bool next(Run*);
+
+    private:
+        const RunRecord* fRunRecord;
+    };
+
 private:
     friend class SkNVRefCnt<SkTextBlob>;
-    class RunRecord;
 
     enum GlyphPositioning : uint8_t;
 

src/core/SkTextBlob.cpp

@@ -919,3 +919,26 @@ int SkTextBlob::getIntercepts(const SkScalar bounds[2], SkScalar intervals[],
 
     return intervalCount;
 }
+
+////////
+
+SkTextBlob::Iter::Iter(const SkTextBlob& blob) {
+    fRunRecord = RunRecord::First(&blob);
+}
+
+bool SkTextBlob::Iter::next(Run* rec) {
+    if (fRunRecord) {
+        if (rec) {
+            rec->fTypeface = fRunRecord->font().getTypeface();
+            rec->fGlyphCount = fRunRecord->glyphCount();
+            rec->fGlyphIndices = fRunRecord->glyphBuffer();
+        }
+        if (fRunRecord->isLastRun()) {
+            fRunRecord = nullptr;
+        } else {
+            fRunRecord = RunRecord::Next(fRunRecord);
+        }
+        return true;
+    }
+    return false;
+}

src/core/SkTextBlobPriv.h

@@ -150,6 +150,8 @@ public:
                : nullptr;
     }
 
+    bool isLastRun() const { return SkToBool(fFlags & kLast_Flag); }
+
     static size_t StorageSize(uint32_t glyphCount, uint32_t textSize,
                               SkTextBlob::GlyphPositioning positioning,
                               SkSafeMath* safe);

tests/TextBlobTest.cpp

@@ -449,3 +449,34 @@ DEF_TEST(TextBlob_MakeAsDrawText, reporter) {
     REPORTER_ASSERT(reporter, runs == 1);
 
 }
+
+DEF_TEST(TextBlob_iter, reporter) {
+    sk_sp<SkTypeface> tf = SkTypeface::MakeFromName(nullptr, SkFontStyle::BoldItalic());
+
+    SkTextBlobBuilder builder;
+    add_run(&builder, "Hello", 10, 20, nullptr);
+    add_run(&builder, "World", 10, 40, tf);
+    auto blob = builder.make();
+
+    SkTextBlob::Iter::Run expected[] = {
+        { nullptr, 5, nullptr },
+        { tf.get(), 5, nullptr },
+    };
+
+    SkTextBlob::Iter iter(*blob);
+    SkTextBlob::Iter::Run run;
+    for (auto exp : expected) {
+        REPORTER_ASSERT(reporter, iter.next(&run));
+        REPORTER_ASSERT(reporter, run.fTypeface == exp.fTypeface);
+        REPORTER_ASSERT(reporter, run.fGlyphCount == exp.fGlyphCount);
+        for (int i = 0; i < run.fGlyphCount; ++i) {
+            REPORTER_ASSERT(reporter, run.fGlyphIndices[i] != 0);
+        }
+    }
+    REPORTER_ASSERT(reporter, !iter.next(&run));    // we're done
+
+    SkTextBlob::Iter iter2(*blob);
+    REPORTER_ASSERT(reporter, iter2.next(&run));
+    // Hello should have the same glyph repeated for the 'l'
+    REPORTER_ASSERT(reporter, run.fGlyphIndices[2] == run.fGlyphIndices[3]);
+}