Make SkPngCodec decode progressively.

src/codec/SkIcoCodec.cpp

Index: src/codec/SkIcoCodec.cpp
diff --git a/src/codec/SkIcoCodec.cpp b/src/codec/SkIcoCodec.cpp
index 45000b636fe4b04700633cbb0cb947de61607d3b..63b72c40391ac2654eeef3a7bdbf3d3e2d73ae93 100644
--- a/src/codec/SkIcoCodec.cpp
+++ b/src/codec/SkIcoCodec.cpp
@@ -185,6 +185,7 @@ SkIcoCodec::SkIcoCodec(int width, int height, const SkEncodedInfo& info,
     : INHERITED(width, height, info, nullptr)
     , fEmbeddedCodecs(codecs)
     , fCurrScanlineCodec(nullptr)
+    , fCurrIncrementalCodec(nullptr)
 {}
 
 /*
@@ -288,6 +289,7 @@ SkCodec::Result SkIcoCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
         result = embeddedCodec->startScanlineDecode(dstInfo, &options, colorTable, colorCount);
         if (kSuccess == result) {
             fCurrScanlineCodec = embeddedCodec;
+            fCurrIncrementalCodec = nullptr;
             return result;
         }
 
@@ -308,13 +310,82 @@ bool SkIcoCodec::onSkipScanlines(int count) {
     return fCurrScanlineCodec->skipScanlines(count);
 }
 
+SkCodec::Result SkIcoCodec::onStartIncrementalDecode(const SkImageInfo& dstInfo,
+        void* pixels, size_t rowBytes, const SkCodec::Options& options,
+        SkPMColor* colorTable, int* colorCount) {
+    int index = 0;
+    while (true) {
+        index = this->chooseCodec(dstInfo.dimensions(), index);
+        if (index < 0) {
+            break;
+        }
+
+        SkCodec* embeddedCodec = fEmbeddedCodecs->operator[](index);
+        switch (embeddedCodec->startIncrementalDecode(dstInfo,
+                pixels, rowBytes, &options, colorTable, colorCount)) {
+            case kSuccess:
+                fCurrIncrementalCodec = embeddedCodec;
+                fCurrScanlineCodec = nullptr;
+                return kSuccess;
+            case kUnimplemented:
+                // FIXME: embeddedCodec is a BMP. If scanline decoding would work,
+                // return kUnimplemented so that SkSampledCodec will fall through
+                // to use the scanline decoder.
+                // Note that calling startScanlineDecode will require an extra
+                // rewind. The embedded codec has an SkMemoryStream, which is
+                // cheap to rewind, though it will do extra work re-reading the
+                // header.
+                // Also note that we pass nullptr for Options. This is because
+                // Options that are valid for incremental decoding may not be
+                // valid for scanline decoding.
+                // Once BMP supports incremental decoding this workaround can go
+                // away.
+                if (embeddedCodec->startScanlineDecode(dstInfo, nullptr,
+                        colorTable, colorCount) == kSuccess) {
+                    return kUnimplemented;
+                }
+                // Move on to the next embedded codec.
+                break;
+            default:
+                break;
+        }
+
+        index++;
+    }
+
+    SkCodecPrintf("Error: No matching candidate image in ico.\n");
+    return kInvalidScale;
+}
+
+SkCodec::Result SkIcoCodec::onIncrementalDecode(int* rowsDecoded) {
+    SkASSERT(fCurrIncrementalCodec);
+    return fCurrIncrementalCodec->incrementalDecode(rowsDecoded);
+}
+
 SkCodec::SkScanlineOrder SkIcoCodec::onGetScanlineOrder() const {
     // FIXME: This function will possibly return the wrong value if it is called
-    //        before startScanlineDecode().
-    return fCurrScanlineCodec ? fCurrScanlineCodec->getScanlineOrder() :
-            INHERITED::onGetScanlineOrder();
+    //        before startScanlineDecode()/startIncrementalDecode().
+    if (fCurrScanlineCodec) {
+        SkASSERT(!fCurrIncrementalCodec);
+        return fCurrScanlineCodec->getScanlineOrder();
+    }
+
+    if (fCurrIncrementalCodec) {
+        return fCurrIncrementalCodec->getScanlineOrder();
+    }
+
+    return INHERITED::onGetScanlineOrder();
 }
 
 SkSampler* SkIcoCodec::getSampler(bool createIfNecessary) {
-    return fCurrScanlineCodec ? fCurrScanlineCodec->getSampler(createIfNecessary) : nullptr;
+    if (fCurrScanlineCodec) {
+        SkASSERT(!fCurrIncrementalCodec);
+        return fCurrScanlineCodec->getSampler(createIfNecessary);
+    }
+
+    if (fCurrIncrementalCodec) {
+        return fCurrIncrementalCodec->getSampler(createIfNecessary);
+    }
+
+    return nullptr;
 }