Fill incomplete images in SkCodec parent class

Rather than implementing some sort of "fill" in every
SkCodec subclass for incomplete images, let's make the
parent class handle this situation.

This includes an API change to SkCodec.h

SkCodec::getScanlines() now returns the number of lines it
read successfully, rather than an SkCodec::Result enum.
getScanlines() most often fails on an incomplete input, in
which case it is useful to know how many lines were
successfully decoded - this provides more information than
kIncomplete vs kSuccess.  We do lose information when the
API is used improperly, as we are no longer able to return
kInvalidParameter or kScanlineNotStarted.

Known Issues:
Does not work for incomplete fFrameIsSubset gifs.
Does not work for incomplete icos.

BUG=skia:

Review URL: https://codereview.chromium.org/1332053002

1 files changed, 11 insertions, 15 deletions

diff --git a/src/codec/SkCodec_wbmp.cpp b/src/codec/SkCodec_wbmp.cpp
index d7f446bb57..14b720988f 100644
--- a/src/codec/SkCodec_wbmp.cpp
+++ b/src/codec/SkCodec_wbmp.cpp
@@ -86,11 +86,8 @@ SkSwizzler* SkWbmpCodec::initializeSwizzler(const SkImageInfo& info,
                                       opts.fZeroInitialized);
 }
 
-SkCodec::Result SkWbmpCodec::readRow(uint8_t* row) {
-    if (this->stream()->read(row, fSrcRowBytes) != fSrcRowBytes) {
-        return kIncompleteInput;
-    }
-    return kSuccess;
+bool SkWbmpCodec::readRow(uint8_t* row) {
+    return this->stream()->read(row, fSrcRowBytes) == fSrcRowBytes;
 }
 
 SkWbmpCodec::SkWbmpCodec(const SkImageInfo& info, SkStream* stream)
@@ -109,7 +106,8 @@ SkCodec::Result SkWbmpCodec::onGetPixels(const SkImageInfo& info,
                                          size_t rowBytes,
                                          const Options& options,
                                          SkPMColor ctable[],
-                                         int* ctableCount) {
+                                         int* ctableCount,
+                                         int* rowsDecoded) {
     if (options.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
@@ -133,9 +131,9 @@ SkCodec::Result SkWbmpCodec::onGetPixels(const SkImageInfo& info,
     SkAutoTMalloc<uint8_t> src(fSrcRowBytes);
     void* dstRow = dst;
     for (int y = 0; y < size.height(); ++y) {
-        Result rowResult = this->readRow(src.get());
-        if (kSuccess != rowResult) {
-            return rowResult;
+        if (!this->readRow(src.get())) {
+            *rowsDecoded = y;
+            return kIncompleteInput;
         }
         swizzler->swizzle(dstRow, src.get());
         dstRow = SkTAddOffset<void>(dstRow, rowBytes);
@@ -158,17 +156,16 @@ SkCodec* SkWbmpCodec::NewFromStream(SkStream* stream) {
     return new SkWbmpCodec(info, streamDeleter.detach());
 }
 
-SkCodec::Result SkWbmpCodec::onGetScanlines(void* dst, int count, size_t dstRowBytes) {
+int SkWbmpCodec::onGetScanlines(void* dst, int count, size_t dstRowBytes) {
     void* dstRow = dst;
     for (int y = 0; y < count; ++y) {
-        Result rowResult = this->readRow(fSrcBuffer.get());
-        if (kSuccess != rowResult) {
-            return rowResult;
+        if (!this->readRow(fSrcBuffer.get())) {
+            return y;
         }
         fSwizzler->swizzle(dstRow, fSrcBuffer.get());
         dstRow = SkTAddOffset<void>(dstRow, dstRowBytes);
     }
-    return kSuccess;
+    return count;
 }
 
 SkCodec::Result SkWbmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
@@ -201,4 +198,3 @@ SkCodec::Result SkWbmpCodec::onStartScanlineDecode(const SkImageInfo& dstInfo,
 
     return kSuccess;
 }
-