Merge SkCodec with SkScanlineDecoder

Benefits:
- This mimics other decoding APIs (including the ones SkCodec relies
on, e.g. a png_struct, which can be used to decode an entire image or
one line at a time).

- It allows a client to ask us to do what we can do efficiently - i.e.
start from encoded data and either decode the whole thing or scanlines.

- It removes the duplicate methods which appeared in both SkCodec and
SkScanlineDecoder (some of which, e.g. in SkJpegScanlineDecoder, just
call fCodec->sameMethod()).

- It simplifies moving more checks into the base class (e.g. the
examples in skbug.com/4284).

BUG=skia:4175
BUG=skia:4284

=====================================================================

SkScanlineDecoder.h/.cpp:
Removed.

SkCodec.h/.cpp:
Add methods, enums, and variables which were previously in
SkScanlineDecoder.
Default fCurrScanline to -1, as a sentinel that start has not been
called.

General changes:
Convert SkScanlineDecoders to SkCodecs.

General changes in SkCodec subclasses:
Merge SkScanlineDecoder implementation into SkCodec. Most (all?) owned
an SkCodec, so they now call this-> instead of fCodec->.

SkBmpCodec.h/.cpp:
Replace the unused rowOrder method with an override for
onGetScanlineOrder.
Make getDstRow const, since it is called by onGetY, which is const.

SkCodec_libpng.h/.cpp:
Make SkPngCodec an abstract class, with two subclasses which handle
scanline decoding separately (they share code for decoding the entire
image). Reimplement onReallyHasAlpha so that it can return the most
recent result (e.g. after a scanline decode which only decoded part
of the image) or a better answer (e.g. if the whole image is known to
be opaque).
Compute fNumberPasses early, so we know which subclass to instantiate.
Make SkPngInterlaceScanlineDecoder use the base class' fCurrScanline
rather than a separate variable.

CodexTest.cpp:
Add tests for the state changes in SkCodec (need to call start before
decoding scanlines; calling getPixels means that start will need to
be called again before decoding more scanlines).
Add a test which decodes in stripes, currently only used for an
interlaced PNG.

TODO: Add tests for onReallyHasAlpha.

Review URL: https://codereview.chromium.org/1365313002

1 files changed, 25 insertions, 41 deletions

diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 96a0ab1a3e..2e22556335 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -25,7 +25,6 @@
 #include "SkRecorder.h"
 #include "SkSVGCanvas.h"
 #include "SkScaledCodec.h"
-#include "SkScanlineDecoder.h"
 #include "SkStream.h"
 #include "SkTLogic.h"
 #include "SkXMLWriter.h"
@@ -238,18 +237,6 @@ bool CodecSrc::veto(SinkFlags flags) const {
         || flags.approach != SinkFlags::kDirect;
 }
 
-SkScanlineDecoder* start_scanline_decoder(SkData* encoded, const SkImageInfo& info,
-        SkPMColor* colorPtr, int* colorCountPtr) {
-    SkAutoTDelete<SkScanlineDecoder> scanlineDecoder(SkScanlineDecoder::NewFromData(encoded));
-    if (nullptr == scanlineDecoder) {
-        return nullptr;
-    }
-    if (SkCodec::kSuccess != scanlineDecoder->start(info, NULL, colorPtr, colorCountPtr)) {
-        return nullptr;
-    }
-    return scanlineDecoder.detach();
-}
-
 Error CodecSrc::draw(SkCanvas* canvas) const {
     SkAutoTUnref<SkData> encoded(SkData::NewFromFileName(fPath.c_str()));
     if (!encoded) {
@@ -348,25 +335,24 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
             break;
         }
         case kScanline_Mode: {
-            SkAutoTDelete<SkScanlineDecoder> scanlineDecoder(
-                    start_scanline_decoder(encoded.get(), decodeInfo, colorPtr, colorCountPtr));
-            if (nullptr == scanlineDecoder) {
+            if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
+                                                                colorCountPtr)) {
                 return Error::Nonfatal("Could not start scanline decoder");
             }
 
             SkCodec::Result result = SkCodec::kUnimplemented;
-            switch (scanlineDecoder->getScanlineOrder()) {
-                case SkScanlineDecoder::kTopDown_SkScanlineOrder:
-                case SkScanlineDecoder::kBottomUp_SkScanlineOrder:
-                case SkScanlineDecoder::kNone_SkScanlineOrder:
-                    result = scanlineDecoder->getScanlines(bitmap.getAddr(0, 0),
+            switch (codec->getScanlineOrder()) {
+                case SkCodec::kTopDown_SkScanlineOrder:
+                case SkCodec::kBottomUp_SkScanlineOrder:
+                case SkCodec::kNone_SkScanlineOrder:
+                    result = codec->getScanlines(bitmap.getAddr(0, 0),
                             decodeInfo.height(), bitmap.rowBytes());
                     break;
-                case SkScanlineDecoder::kOutOfOrder_SkScanlineOrder: {
+                case SkCodec::kOutOfOrder_SkScanlineOrder: {
                     for (int y = 0; y < decodeInfo.height(); y++) {
-                        int dstY = scanlineDecoder->getY();
+                        int dstY = codec->nextScanline();
                         void* dstPtr = bitmap.getAddr(0, dstY);
-                        result = scanlineDecoder->getScanlines(dstPtr, 1, bitmap.rowBytes());
+                        result = codec->getScanlines(dstPtr, 1, bitmap.rowBytes());
                         if (SkCodec::kSuccess != result && SkCodec::kIncompleteInput != result) {
                             return SkStringPrintf("%s failed with error message %d",
                                                   fPath.c_str(), (int) result);
@@ -432,11 +418,10 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                             subsetHeight + extraY : subsetHeight;
                     const int y = row * subsetHeight;
                     //create scanline decoder for each subset
-                    SkAutoTDelete<SkScanlineDecoder> decoder(start_scanline_decoder(encoded.get(),
-                            decodeInfo, colorPtr, colorCountPtr));
-                    // TODO (msarett): Support this mode for all scanline orderings.
-                    if (nullptr == decoder || SkScanlineDecoder::kTopDown_SkScanlineOrder !=
-                            decoder->getScanlineOrder()) {
+                    if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
+                                                                        colorCountPtr)
+                            // TODO (msarett): Support this mode for all scanline orderings.
+                            || SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
                         if (x == 0 && y == 0) {
                             //first try, image may not be compatible
                             return Error::Nonfatal("Could not start top-down scanline decoder");
@@ -445,7 +430,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                         }
                     }
                     //skip to first line of subset
-                    const SkCodec::Result skipResult = decoder->skipScanlines(y);
+                    const SkCodec::Result skipResult = codec->skipScanlines(y);
                     switch (skipResult) {
                         case SkCodec::kSuccess:
                         case SkCodec::kIncompleteInput:
@@ -461,7 +446,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                     SkAssertResult(largestSubsetBm.extractSubset(&subsetBm, bounds));
                     SkAutoLockPixels autlockSubsetBm(subsetBm, true);
                     const SkCodec::Result subsetResult =
-                            decoder->getScanlines(buffer, currentSubsetHeight, rowBytes);
+                            codec->getScanlines(buffer, currentSubsetHeight, rowBytes);
                     switch (subsetResult) {
                         case SkCodec::kSuccess:
                         case SkCodec::kIncompleteInput:
@@ -501,10 +486,9 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
             const int numStripes = (height + stripeHeight - 1) / stripeHeight;
 
             // Decode odd stripes
-            SkAutoTDelete<SkScanlineDecoder> decoder(
-                    start_scanline_decoder(encoded.get(), decodeInfo, colorPtr, colorCountPtr));
-            if (nullptr == decoder ||
-                    SkScanlineDecoder::kTopDown_SkScanlineOrder != decoder->getScanlineOrder()) {
+            if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
+                                                                colorCountPtr)
+                    || SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
                 // This mode was designed to test the new skip scanlines API in libjpeg-turbo.
                 // Jpegs have kTopDown_SkScanlineOrder, and at this time, it is not interesting
                 // to run this test for image types that do not have this scanline ordering.
@@ -513,7 +497,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
             for (int i = 0; i < numStripes; i += 2) {
                 // Skip a stripe
                 const int linesToSkip = SkTMin(stripeHeight, height - i * stripeHeight);
-                SkCodec::Result result = decoder->skipScanlines(linesToSkip);
+                SkCodec::Result result = codec->skipScanlines(linesToSkip);
                 switch (result) {
                     case SkCodec::kSuccess:
                     case SkCodec::kIncompleteInput:
@@ -526,7 +510,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                 const int startY = (i + 1) * stripeHeight;
                 const int linesToRead = SkTMin(stripeHeight, height - startY);
                 if (linesToRead > 0) {
-                    result = decoder->getScanlines(bitmap.getAddr(0, startY),
+                    result = codec->getScanlines(bitmap.getAddr(0, startY),
                             linesToRead, bitmap.rowBytes());
                     switch (result) {
                         case SkCodec::kSuccess:
@@ -539,8 +523,8 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
             }
 
             // Decode even stripes
-            const SkCodec::Result startResult = decoder->start(decodeInfo, nullptr, colorPtr,
-                                                               colorCountPtr);
+            const SkCodec::Result startResult = codec->startScanlineDecode(decodeInfo, nullptr,
+                    colorPtr, colorCountPtr);
             if (SkCodec::kSuccess != startResult) {
                 return "Failed to restart scanline decoder with same parameters.";
             }
@@ -548,7 +532,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                 // Read a stripe
                 const int startY = i * stripeHeight;
                 const int linesToRead = SkTMin(stripeHeight, height - startY);
-                SkCodec::Result result = decoder->getScanlines(bitmap.getAddr(0, startY),
+                SkCodec::Result result = codec->getScanlines(bitmap.getAddr(0, startY),
                         linesToRead, bitmap.rowBytes());
                 switch (result) {
                     case SkCodec::kSuccess:
@@ -561,7 +545,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                 // Skip a stripe
                 const int linesToSkip = SkTMin(stripeHeight, height - (i + 1) * stripeHeight);
                 if (linesToSkip > 0) {
-                    result = decoder->skipScanlines(linesToSkip);
+                    result = codec->skipScanlines(linesToSkip);
                     switch (result) {
                         case SkCodec::kSuccess:
                         case SkCodec::kIncompleteInput: