Souped-up SkTextBlob (reland)

src/core/SkTextBlob.cpp

Index: src/core/SkTextBlob.cpp
diff --git a/src/core/SkTextBlob.cpp b/src/core/SkTextBlob.cpp
index ee110c7d07b9737bf992b8a72ec5124da767a34e..af62b72b6ae85296a421fbdcf71b8eb68b003378 100644
--- a/src/core/SkTextBlob.cpp
+++ b/src/core/SkTextBlob.cpp
@@ -10,14 +10,128 @@
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
-SkTextBlob::SkTextBlob(uint16_t *glyphs, SkScalar *pos, const SkTArray<Run> *runs,
-                       const SkRect& bounds)
-    : fGlyphBuffer(glyphs)
-    , fPosBuffer(pos)
-    , fRuns(runs)
+//
+// Textblob data is laid out into externally-managed storage as follows:
+//
+//    -----------------------------------------------------------------------------
+//   | SkTextBlob | RunRecord | Glyphs[] | Pos[] | RunRecord | Glyphs[] | Pos[] | ...
+//    -----------------------------------------------------------------------------
+//
+//  Each run record describes a text blob run, and can be used to determine the (implicit)
+//  location of the following record.
+
+SkDEBUGCODE(static const unsigned kRunRecordMagic = 0xb10bcafe;)
+
+class SkTextBlob::RunRecord {
+public:
+    RunRecord(uint32_t count, const SkPoint& offset, const SkPaint& font, GlyphPositioning pos)
+        : fCount(count)
+        , fOffset(offset)
+        , fFont(font)
+        , fPositioning(pos) {
+        SkDEBUGCODE(fMagic = kRunRecordMagic);
+    }
+
+    uint32_t glyphCount() const {
+        return fCount;
+    }
+
+    const SkPoint& offset() const {
+        return fOffset;
+    }
+
+    const SkPaint& font() const {
+        return fFont;
+    }
+
+    GlyphPositioning positioning() const {
+        return fPositioning;
+    }
+
+    uint16_t* glyphBuffer() const {
+        // Glyph are stored immediately following the record.
+        return reinterpret_cast<uint16_t*>(const_cast<RunRecord*>(this) + 1);
+    }
+
+    SkScalar* posBuffer() const {
+        // Position scalars follow the (aligned) glyph buffer.
+        return reinterpret_cast<SkScalar*>(reinterpret_cast<uint8_t*>(this->glyphBuffer()) +
+                                           SkAlign4(fCount * sizeof(uint16_t)));
+    }
+
+    static size_t StorageSize(int glyphCount, SkTextBlob::GlyphPositioning positioning) {

[mtklein, 2014/09/19 14:33:02]

Let's use SkAlignPtr.  RunRecord contains pointers, so SkAlign4 might only be
half-aligned.  This is usually fine, but chrome's LSAN setup checks for leaks
before we're destroyed, and it won't see the pointers as live pointers.

[f(malita), 2014/09/19 15:42:36]

Done.

+        // RunRecord object + (aligned) glyph buffer + position buffer
+        size_t size = sizeof(SkTextBlob::RunRecord)
+                    + SkAlign4(glyphCount* sizeof(uint16_t))
+                    + glyphCount * sizeof(SkScalar) * ScalarsPerGlyph(positioning);
+
+        SkASSERT(SkIsAlign4(size));
+        return size;
+    }
+
+    static const RunRecord* First(const SkTextBlob* blob) {
+        // The first record (if present) is stored following the blob object.
+        return reinterpret_cast<const RunRecord*>(blob + 1);
+    }
+
+    static const RunRecord* Next(const RunRecord* run) {
+        return reinterpret_cast<const RunRecord*>(reinterpret_cast<const uint8_t*>(run)
+            + StorageSize(run->glyphCount(), run->positioning()));
+    }
+
+    void validate(uint8_t* storageTop) const {
+        SkASSERT(kRunRecordMagic == fMagic);
+        SkASSERT((uint8_t*)Next(this) <= storageTop);
+        SkASSERT(glyphBuffer() + fCount <= (uint16_t*)posBuffer());
+        SkASSERT(posBuffer() + fCount * ScalarsPerGlyph(fPositioning) == (SkScalar*)Next(this));
+    }
+
+private:
+    friend class SkTextBlobBuilder;
+
+    void grow(uint32_t count) {
+        SkScalar* initialPosBuffer = posBuffer();
+        uint32_t initialCount = fCount;
+        fCount += count;
+
+        // Move the initial pos scalars to their new location.
+        size_t copySize = initialCount * sizeof(SkScalar) * ScalarsPerGlyph(fPositioning);
+        SkASSERT((uint8_t*)posBuffer() + copySize <= (uint8_t*)Next(this));
+
+        // memmove, as the buffers may overlap
+        memmove(posBuffer(), initialPosBuffer, copySize);
+    }
+
+    uint32_t         fCount;
+    SkPoint          fOffset;
+    SkPaint          fFont;
+    GlyphPositioning fPositioning;
+
+    SkDEBUGCODE(unsigned fMagic;)
+};
+
+SkTextBlob::SkTextBlob(int runCount, const SkRect& bounds)
+    : fRunCount(runCount)
     , fBounds(bounds) {
 }
 
+SkTextBlob::~SkTextBlob() {
+    const RunRecord* run = RunRecord::First(this);
+    for (int i = 0; i < fRunCount; ++i) {
+        const RunRecord* nextRun = RunRecord::Next(run);
+        SkDEBUGCODE(run->validate((uint8_t*)this + fStorageSize);)
+        run->~RunRecord();
+        run = nextRun;
+    }
+}
+
+void SkTextBlob::internal_dispose() const {
+    // SkTextBlobs use externally-managed storage.
+    this->internal_dispose_restore_refcnt_to_1();
+    this->~SkTextBlob();
+    sk_free(const_cast<SkTextBlob*>(this));
+}
+
 uint32_t SkTextBlob::uniqueID() const {
     static int32_t  gTextBlobGenerationID; // = 0;
 
@@ -29,14 +143,8 @@ uint32_t SkTextBlob::uniqueID() const {
     return fUniqueID;
 }
 
-unsigned SkTextBlob::ScalarsPerGlyph(GlyphPositioning pos) {
-    // GlyphPositioning values are directly mapped to scalars-per-glyph.
-    SkASSERT(pos <= 2);
-    return pos;
-}
-
 void SkTextBlob::flatten(SkWriteBuffer& buffer) const {
-    int runCount = (NULL == fRuns.get()) ? 0 : fRuns->count();
+    int runCount = fRunCount;
 
     buffer.write32(runCount);
     buffer.writeRect(fBounds);
@@ -101,7 +209,8 @@ const SkTextBlob* SkTextBlob::CreateFromBuffer(SkReadBuffer& reader) {
         }
 
         if (!reader.readByteArray(buf->glyphs, glyphCount * sizeof(uint16_t)) ||
-            !reader.readByteArray(buf->pos, glyphCount * sizeof(SkScalar) * ScalarsPerGlyph(pos))) {
+            !reader.readByteArray(buf->pos,
+                                  glyphCount * sizeof(SkScalar) * ScalarsPerGlyph(pos))) {
             return NULL;
         }
     }
@@ -109,50 +218,61 @@ const SkTextBlob* SkTextBlob::CreateFromBuffer(SkReadBuffer& reader) {
     return blobBuilder.build();
 }
 
+unsigned SkTextBlob::ScalarsPerGlyph(GlyphPositioning pos) {
+    // GlyphPositioning values are directly mapped to scalars-per-glyph.
+    SkASSERT(pos <= 2);
+    return pos;
+}
+
 SkTextBlob::RunIterator::RunIterator(const SkTextBlob* blob)
-    : fBlob(blob)
-    , fIndex(0) {
-    SkASSERT(blob);
+    : fCurrentRun(RunRecord::First(blob))
+    , fRemainingRuns(blob->fRunCount) {
+    SkDEBUGCODE(fStorageTop = (uint8_t*)blob + blob->fStorageSize;)
 }
 
 bool SkTextBlob::RunIterator::done() const {
-    return NULL == fBlob->fRuns.get() || fIndex >= fBlob->fRuns->count();
+    return fRemainingRuns <= 0;
 }
 
 void SkTextBlob::RunIterator::next() {
     SkASSERT(!this->done());
-    fIndex++;
+
+    if (!this->done()) {
+        SkDEBUGCODE(fCurrentRun->validate(fStorageTop);)
+        fCurrentRun = RunRecord::Next(fCurrentRun);
+        fRemainingRuns--;
+    }
 }
 
 uint32_t SkTextBlob::RunIterator::glyphCount() const {
     SkASSERT(!this->done());
-    return (*fBlob->fRuns)[fIndex].count;
+    return fCurrentRun->glyphCount();
 }
 
 const uint16_t* SkTextBlob::RunIterator::glyphs() const {
     SkASSERT(!this->done());
-    return fBlob->fGlyphBuffer.get() + (*fBlob->fRuns)[fIndex].glyphStart;
+    return fCurrentRun->glyphBuffer();
 }
 
 const SkScalar* SkTextBlob::RunIterator::pos() const {
     SkASSERT(!this->done());
-    return fBlob->fPosBuffer.get() + (*fBlob->fRuns)[fIndex].posStart;
+    return fCurrentRun->posBuffer();
 }
 
 const SkPoint& SkTextBlob::RunIterator::offset() const {
     SkASSERT(!this->done());
-    return (*fBlob->fRuns)[fIndex].offset;
+    return fCurrentRun->offset();
 }
 
 SkTextBlob::GlyphPositioning SkTextBlob::RunIterator::positioning() const {
     SkASSERT(!this->done());
-    return (*fBlob->fRuns)[fIndex].positioning;
+    return fCurrentRun->positioning();
 }
 
 void SkTextBlob::RunIterator::applyFontToPaint(SkPaint* paint) const {
     SkASSERT(!this->done());
 
-    const SkPaint& font = (*fBlob->fRuns)[fIndex].font;
+    const SkPaint& font = fCurrentRun->font();
 
     paint->setTypeface(font.getTypeface());
     paint->setTextEncoding(font.getTextEncoding());
@@ -177,24 +297,25 @@ void SkTextBlob::RunIterator::applyFontToPaint(SkPaint* paint) const {
     paint->setFlags((paint->getFlags() & ~flagsMask) | (font.getFlags() & flagsMask));
 }
 
-SkTextBlobBuilder::SkTextBlobBuilder(unsigned runs)
-    : fRuns(NULL)
-    , fDeferredBounds(false) {
-
-    if (runs > 0) {
-        // if the number of runs is known, size our run storage accordingly.
-        fRuns = SkNEW(SkTArray<SkTextBlob::Run>(runs));
-    }
+SkTextBlobBuilder::SkTextBlobBuilder()
+    : fStorageSize(0)
+    , fStorageUsed(0)
+    , fRunCount(0)
+    , fDeferredBounds(false)
+    , fLastRun(0) {
     fBounds.setEmpty();
 }
 
 SkTextBlobBuilder::~SkTextBlobBuilder() {
-    // unused runs
-    SkDELETE(fRuns);
+    if (NULL != fStorage.get()) {
+        // We are abandoning runs and must destruct the associated font data.
+        // The easiest way to accomplish that is to use the blob destructor.
+        build()->unref();
+    }
 }
 
 void SkTextBlobBuilder::updateDeferredBounds() {
-    SkASSERT(!fDeferredBounds || (fRuns && !fRuns->empty()));
+    SkASSERT(!fDeferredBounds || fRunCount > 0);
 
     if (!fDeferredBounds) {
         return;
@@ -204,64 +325,103 @@ void SkTextBlobBuilder::updateDeferredBounds() {
     fDeferredBounds = false;
 }
 
-void SkTextBlobBuilder::ensureRun(const SkPaint& font, SkTextBlob::GlyphPositioning pos,
-                                  const SkPoint& offset) {
-    SkASSERT(SkPaint::kGlyphID_TextEncoding == font.getTextEncoding());
+void SkTextBlobBuilder::reserve(size_t size) {
+    // We don't currently pre-allocate, but maybe someday...
+    if (fStorageUsed + size <= fStorageSize) {
+        return;
+    }
+
+    if (0 == fRunCount) {
+        SkASSERT(NULL == fStorage.get());
+        SkASSERT(0 == fStorageSize);
+        SkASSERT(0 == fStorageUsed);
 
-    if (NULL == fRuns) {
-        fRuns = SkNEW(SkTArray<SkTextBlob::Run>());
+        // the first allocation also includes blob storage
+        fStorageUsed += sizeof(SkTextBlob);
+    }
+
+    fStorageSize = fStorageUsed + size;
+    fStorage.realloc(fStorageSize);

[mtklein, 2014/09/19 14:33:02]

// FYI: This relies on everything we store being relocatable, particularly
SkPaint.

[f(malita), 2014/09/19 15:42:36]

Done.

+}
+
+bool SkTextBlobBuilder::mergeRun(const SkPaint &font, SkTextBlob::GlyphPositioning positioning,
+                                 int count, SkPoint offset) {
+    if (0 == fLastRun) {
+        SkASSERT(0 == fRunCount);
+        return false;
+    }
+
+    SkASSERT(fLastRun >= sizeof(SkTextBlob));
+    SkTextBlob::RunRecord* run = reinterpret_cast<SkTextBlob::RunRecord*>(fStorage.get() +
+                                                                          fLastRun);
+    SkASSERT(run->glyphCount() > 0);
+
+    if (run->positioning() != positioning
+        || run->font() != font
+        || (run->glyphCount() + count < run->glyphCount())) {
+        return false;
     }
 
     // we can merge same-font/same-positioning runs in the following cases:
     //   * fully positioned run following another fully positioned run
     //   * horizontally postioned run following another horizontally positioned run with the same
     //     y-offset
-    if (!fRuns->empty()
-        && fRuns->back().positioning == pos
-        && fRuns->back().font == font
-        && (SkTextBlob::kFull_Positioning == fRuns->back().positioning
-            || (SkTextBlob::kHorizontal_Positioning == fRuns->back().positioning
-                && fRuns->back().offset.y() == offset.y()))){
-        return;
+    if (SkTextBlob::kFull_Positioning != positioning
+        && (SkTextBlob::kHorizontal_Positioning != positioning
+            || run->offset().y() != offset.y())) {
+        return false;
     }
 
-    this->updateDeferredBounds();
+    size_t sizeDelta = SkTextBlob::RunRecord::StorageSize(run->glyphCount() + count, positioning) -
+                       SkTextBlob::RunRecord::StorageSize(run->glyphCount(), positioning);
+    this->reserve(sizeDelta);
+
+    // reserve may have realloced
+    run = reinterpret_cast<SkTextBlob::RunRecord*>(fStorage.get() + fLastRun);
+    uint32_t preMergeCount = run->glyphCount();
+    run->grow(count);
+
+    // Callers expect the buffers to point at the newly added slice, ant not at the beginning.
+    fCurrentRunBuffer.glyphs = run->glyphBuffer() + preMergeCount;
+    fCurrentRunBuffer.pos = run->posBuffer()
+                          + preMergeCount * SkTextBlob::ScalarsPerGlyph(positioning);
+
+    fStorageUsed += sizeDelta;
+
+    SkASSERT(fStorageUsed <= fStorageSize);
+    run->validate(fStorage.get() + fStorageUsed);
 
-    // start a new run
-    SkTextBlob::Run& newRun = fRuns->push_back();
-    newRun.count = 0;
-    newRun.glyphStart = fGlyphBuffer.count();
-    newRun.posStart = fPosBuffer.count();
-    newRun.offset = offset;
-    newRun.font = font;
-    newRun.positioning = pos;
+    return true;
 }
 
 void SkTextBlobBuilder::allocInternal(const SkPaint &font,
                                       SkTextBlob::GlyphPositioning positioning,
                                       int count, SkPoint offset, const SkRect* bounds) {
     SkASSERT(count > 0);
+    SkASSERT(SkPaint::kGlyphID_TextEncoding == font.getTextEncoding());
+
+    if (!this->mergeRun(font, positioning, count, offset)) {
+        updateDeferredBounds();
 
-    this->ensureRun(font, positioning, offset);
+        size_t runSize = SkTextBlob::RunRecord::StorageSize(count, positioning);
+        this->reserve(runSize);
 
-    unsigned posScalarsPerGlyph = SkTextBlob::ScalarsPerGlyph(positioning);
+        SkASSERT(fStorageUsed >= sizeof(SkTextBlob));
+        SkASSERT(fStorageUsed + runSize <= fStorageSize);
 
-    fGlyphBuffer.append(count);
-    fPosBuffer.append(count * posScalarsPerGlyph);
+        SkTextBlob::RunRecord* run = new (fStorage.get() + fStorageUsed)
+                                         SkTextBlob::RunRecord(count, offset, font, positioning);
 
-    SkASSERT(fRuns && !fRuns->empty());
-    SkTextBlob::Run& run = fRuns->back();
+        fCurrentRunBuffer.glyphs = run->glyphBuffer();
+        fCurrentRunBuffer.pos = run->posBuffer();
 
-    run.count += count;
+        fLastRun = fStorageUsed;
+        fStorageUsed += runSize;
+        fRunCount++;
 
-    // The current run might have been merged, so the start offset may point to prev run data.
-    // Start from the back (which always points to the end of the current run buffers) instead.
-    fCurrentRunBuffer.glyphs = fGlyphBuffer.isEmpty()
-            ? NULL : fGlyphBuffer.end() - count;
-    SkASSERT(NULL == fCurrentRunBuffer.glyphs || fCurrentRunBuffer.glyphs >= fGlyphBuffer.begin());
-    fCurrentRunBuffer.pos = fPosBuffer.isEmpty()
-            ? NULL : fPosBuffer.end() - count * posScalarsPerGlyph;
-    SkASSERT(NULL == fCurrentRunBuffer.pos || fCurrentRunBuffer.pos >= fPosBuffer.begin());
+        SkASSERT(fStorageUsed <= fStorageSize);
+        run->validate(fStorage.get() + fStorageUsed);
+    }
 
     if (!fDeferredBounds) {
         if (bounds) {
@@ -297,29 +457,24 @@ const SkTextBlobBuilder::RunBuffer& SkTextBlobBuilder::allocRunPos(const SkPaint
 }
 
 const SkTextBlob* SkTextBlobBuilder::build() {
-    const SkTextBlob* blob;
-
-    if (fGlyphBuffer.count() > 0) {
-        // we have some glyphs, construct a real blob
-        SkASSERT(fRuns && !fRuns->empty());
-
-        this->updateDeferredBounds();
-
-        // ownership of all buffers is transferred to the blob
-        blob = SkNEW_ARGS(SkTextBlob, (fGlyphBuffer.detach(),
-                                       fPosBuffer.detach(),
-                                       fRuns,
-                                       fBounds));
-        fRuns = NULL;
-        fBounds.setEmpty();
-    } else {
-        // empty blob
-        SkASSERT(NULL == fRuns || fRuns->empty());
-        SkASSERT(fBounds.isEmpty());
-
-        blob = SkNEW_ARGS(SkTextBlob, (NULL, NULL, NULL, SkRect::MakeEmpty()));
+    SkASSERT((fRunCount > 0) == (NULL != fStorage.get()));
+
+    this->updateDeferredBounds();
+
+    if (0 == fRunCount) {
+        SkASSERT(NULL == fStorage.get());
+        fStorage.realloc(sizeof(SkTextBlob));
     }
 
+    const SkTextBlob* blob = new (fStorage.detach()) SkTextBlob(fRunCount, fBounds);
+    SkDEBUGCODE(const_cast<SkTextBlob*>(blob)->fStorageSize = fStorageSize;)
+
+    fStorageUsed = 0;
+    fStorageSize = 0;
+    fRunCount = 0;
+    fLastRun = 0;
+    fBounds.setEmpty();
+
     return blob;
 }