Enable DAA in the init-once phase of threaded backends

Bug: skia:
Change-Id: Idb856fe12f0f9fa1014e7d15ef40bd7b456634d6
Reviewed-on: https://skia-review.googlesource.com/107540
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

src/core/SkBlitter.cpp

@@ -92,7 +92,11 @@ void SkBlitter::blitCoverageDeltas(SkCoverageDeltaList* deltas, const SkIRect& c
     bool canUseMask = !deltas->forceRLE() &&
                       SkCoverageDeltaMask::CanHandle(SkIRect::MakeLTRB(0, 0, clip.width(), 1));
     const SkAntiRect& antiRect = deltas->getAntiRect();
-    for(int y = deltas->top(); y < deltas->bottom(); ++y) {
+
+    // Only access rows within our clip. Otherwise, we'll have data race in the threaded backend.
+    int top = SkTMax(deltas->top(), clip.fTop);
+    int bottom = SkTMin(deltas->bottom(), clip.fBottom);
+    for(int y = top; y < bottom; ++y) {
         // If antiRect is non-empty and we're at its top row, blit it and skip to the bottom
         if (antiRect.fHeight && y == antiRect.fY) {
             this->blitAntiRect(antiRect.fX, antiRect.fY, antiRect.fWidth, antiRect.fHeight,

src/core/SkDraw.cpp

@@ -1019,7 +1019,7 @@ void SkDraw::drawDevPath(const SkPath& devPath, const SkPaint& paint, bool drawC
 
     if (iData == nullptr) {
         proc(devPath, *fRC, blitter); // proceed directly if we're not in threaded init-once
-    } else if (true || !doFill || !paint.isAntiAlias()) {
+    } else if (!doFill || !paint.isAntiAlias()) {
         // TODO remove true in the if statement above so we can proceed to DAA.
 
         // We're in threaded init-once but we can't use DAA. Hence we'll stop here and hand all the
@@ -1033,7 +1033,15 @@ void SkDraw::drawDevPath(const SkPath& devPath, const SkPaint& paint, bool drawC
         });
     } else {
         // We can use DAA to do scan conversion in the init-once phase.
-        // TODO To be implemented
+        SkDAARecord* record = iData->fAlloc->make<SkDAARecord>(iData->fAlloc);
+        SkNullBlitter nullBlitter; // We don't want to blit anything during the init phase
+        SkScan::AntiFillPath(devPath, *fRC, &nullBlitter, record);
+        iData->fElement->setDrawFn([record, devPath, blitter](SkArenaAlloc* alloc,
+                    const SkThreadedBMPDevice::DrawState& ds, const SkIRect& tileBounds) {
+            SkASSERT(record->fType != SkDAARecord::Type::kToBeComputed);
+            SkThreadedBMPDevice::TileDraw tileDraw(ds, tileBounds);
+            SkScan::AntiFillPath(devPath, *tileDraw.fRC, blitter, record);
+        });
     }
 }
 

src/core/SkThreadedBMPDevice.cpp

@@ -156,7 +156,7 @@ void SkThreadedBMPDevice::drawPath(const SkPath& path, const SkPaint& paint,
         const SkMatrix* prePathMatrix, bool pathIsMutable) {
     SkRect drawBounds = path.isInverseFillType() ? SkRectPriv::MakeLargest()
                                                  : get_fast_bounds(path.getBounds(), paint);
-    if (path.countVerbs() < 100) { // when path is small, init-once has too much overhead
+    if (path.countVerbs() < 4) { // when path is small, init-once has too much overhead
         fQueue.push(drawBounds, [=](SkArenaAlloc*, const DrawState& ds, const SkIRect& tileBounds) {
             TileDraw(ds, tileBounds).drawPath(path, paint, prePathMatrix, false);
         });

src/core/SkThreadedBMPDevice.h

@@ -74,19 +74,26 @@ private:
                 , fDrawBounds(device->transformDrawBounds(rawDrawBounds)) {}
         DrawElement(SkThreadedBMPDevice* device, InitFn&& initFn, const SkRect& rawDrawBounds)
                 : fInitialized(false)
+                , fNeedInit(true)
                 , fInitFn(std::move(initFn))
                 , fDS(device)
                 , fDrawBounds(device->transformDrawBounds(rawDrawBounds)) {}
 
         SK_ALWAYS_INLINE bool tryInitOnce(SkArenaAlloc* alloc) {
-            if (fInitialized) {
+            bool t = true;
-                return false;
+            // If there are multiple threads reaching this point simutaneously,
-            }
+            // compare_exchange_strong ensures that only one thread can enter the if condition and
-            std::call_once(fNeedInit, [this, alloc]{
+            // do the initialization.
+            if (!fInitialized && fNeedInit && fNeedInit.compare_exchange_strong(t, false)) {
+#ifdef SK_DEBUG
+                fDrawFn = 0; // Invalidate fDrawFn
+#endif
                 fInitFn(alloc, this);
                 fInitialized = true;
-            });
+                SkASSERT(fDrawFn != 0); // Ensure that fInitFn does populate fDrawFn
-            return true;
+                return true;
+            }
+            return false;
         }
 
         SK_ALWAYS_INLINE bool tryDraw(const SkIRect& tileBounds, SkArenaAlloc* alloc) {
@@ -105,7 +112,7 @@ private:
 
     private:
         std::atomic<bool>   fInitialized;
-        std::once_flag      fNeedInit;
+        std::atomic<bool>   fNeedInit;
         InitFn              fInitFn;
         DrawFn              fDrawFn;
         DrawState           fDS;