Fill incomplete images in SkCodec parent class

src/codec/SkCodec.cpp

Index: src/codec/SkCodec.cpp
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index d12de21f515e45c861f6793cdd0b73b4bcc8055f..009db033cbbc32d1a38318636b9839d0d27be4f2 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -79,6 +79,7 @@ SkCodec::SkCodec(const SkImageInfo& info, SkStream* stream)
     : fInfo(info)
     , fStream(stream)
     , fNeedsRewind(false)
+    , fIncompleteScanlines(0)
 {}
 
 SkCodec::~SkCodec() {}
@@ -137,11 +138,26 @@ SkCodec::Result SkCodec::getPixels(const SkImageInfo& info, void* pixels, size_t
     if (nullptr == options) {
         options = &optsStorage;
     }
-    const Result result = this->onGetPixels(info, pixels, rowBytes, *options, ctable, ctableCount);
+
+    // On an incomplete decode, the subclass can specify the number of scanlines that it failed
+    // to decode.
+    int incompleteScanlines = 0;
+    const Result result = this->onGetPixels(info, pixels, rowBytes, *options, ctable, ctableCount,
+            &incompleteScanlines);
 
     if ((kIncompleteInput == result || kSuccess == result) && ctableCount) {
         SkASSERT(*ctableCount >= 0 && *ctableCount <= 256);
     }
+
+    // A return value of kIncompleteInput indicates a truncated image stream.
+    // In this case, we will fill any uninitialized memory with a default value.
+    if (kIncompleteInput == result && 0 != incompleteScanlines) {
+        void* fillDst = this->getFillDst(pixels, rowBytes, info.height() - incompleteScanlines);

[scroggo, 2015/09/25 15:55:05]

My mistake, you end up doing another subtract. If you just return the rows
decoded, you could avoid both, right?

[msarett, 2015/10/01 12:44:52]

Acknowledged.

+        const SkImageInfo fillInfo = info.makeWH(info.width(), incompleteScanlines);
+        const uint32_t fillValue = this->getFillValue(fillInfo);
+        SkSwizzler::Fill(fillDst, fillInfo, rowBytes, fillValue, options->fZeroInitialized);
+    }
+
     return result;
 }