Make SkPngCodec decode progressively.

src/codec/SkCodec.cpp

Index: src/codec/SkCodec.cpp
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index 8468f8a09996d1c7e79363970f9103e106049c7a..0f781642e40444eb6522cee07658b20411ec3502 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -154,6 +154,20 @@ bool SkCodec::rewindIfNeeded() {
     return this->onRewind();
 }
 
+#define CHECK_COLOR_TABLE                                   \
+    if (kIndex_8_SkColorType == info.colorType()) {      \

[msarett, 2016/05/20 18:21:38]

nit: line up slash?

[scroggo_chromium, 2016/05/20 18:58:37]

D'oh! edited this after putting the slash there. Done.

+        if (nullptr == ctable || nullptr == ctableCount) {  \
+            return SkCodec::kInvalidParameters;             \
+        }                                                   \
+    } else {                                                \
+        if (ctableCount) {                                  \
+            *ctableCount = 0;                               \
+        }                                                   \
+        ctableCount = nullptr;                              \
+        ctable = nullptr;                                   \
+    }
+
+
 SkCodec::Result SkCodec::getPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                                    const Options* options, SkPMColor ctable[], int* ctableCount) {
     if (kUnknown_SkColorType == info.colorType()) {
@@ -166,17 +180,7 @@ SkCodec::Result SkCodec::getPixels(const SkImageInfo& info, void* pixels, size_t
         return kInvalidParameters;
     }
 
-    if (kIndex_8_SkColorType == info.colorType()) {
-        if (nullptr == ctable || nullptr == ctableCount) {
-            return kInvalidParameters;
-        }
-    } else {
-        if (ctableCount) {
-            *ctableCount = 0;
-        }
-        ctableCount = nullptr;
-        ctable = nullptr;
-    }
+    CHECK_COLOR_TABLE;
 
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
@@ -228,23 +232,62 @@ SkCodec::Result SkCodec::getPixels(const SkImageInfo& info, void* pixels, size_t
     return this->getPixels(info, pixels, rowBytes, nullptr, nullptr, nullptr);
 }
 
-SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& dstInfo,
-        const SkCodec::Options* options, SkPMColor ctable[], int* ctableCount) {
-    // Reset fCurrScanline in case of failure.
-    fCurrScanline = -1;
+SkCodec::Result SkCodec::startIncrementalDecode(const SkImageInfo& info,
+        const SkCodec::Options* options, SkPMColor* ctable, int* ctableCount) {
+    fStartedIncrementalDecode = false;
+
     // Ensure that valid color ptrs are passed in for kIndex8 color type
-    if (kIndex_8_SkColorType == dstInfo.colorType()) {
-        if (nullptr == ctable || nullptr == ctableCount) {
-            return SkCodec::kInvalidParameters;
+    CHECK_COLOR_TABLE;
+
+    // FIXME: If the rows come after the rows of a previous incremental decode,
+    // we might be able to skip the rewind, but only the implementation knows
+    // that. (e.g. PNG will always need to rewind, since we called longjmp, but
+    // a bottom-up BMP could skip rewinding if the new rows are above the old
+    // rows.)
+    if (!this->rewindIfNeeded()) {
+        return kCouldNotRewind;
+    }
+
+    // Set options.
+    Options optsStorage;
+    if (nullptr == options) {
+        options = &optsStorage;
+    } else if (options->fSubset) {
+        SkIRect size = SkIRect::MakeSize(info.dimensions());
+        if (!size.contains(*options->fSubset)) {
+            return kInvalidParameters;
         }
-    } else {
-        if (ctableCount) {
-            *ctableCount = 0;
+
+        const int top = options->fSubset->top();
+        const int bottom = options->fSubset->bottom();
+        if (top < 0 || top >= info.height() || top >= bottom || bottom > info.height()) {
+            return kInvalidParameters;
         }
-        ctableCount = nullptr;
-        ctable = nullptr;
     }
 
+    if (!this->dimensionsSupported(info.dimensions())) {
+        return kInvalidScale;
+    }
+
+    fDstInfo = info;
+    fOptions = *options;
+
+    const Result result = this->onStartIncrementalDecode(info, fOptions, ctable,
+                                                         ctableCount);
+    if (kSuccess == result) {
+        fStartedIncrementalDecode = true;
+    }
+    return result;
+}
+
+
+SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& info,
+        const SkCodec::Options* options, SkPMColor ctable[], int* ctableCount) {
+    // Reset fCurrScanline in case of failure.
+    fCurrScanline = -1;
+    // Ensure that valid color ptrs are passed in for kIndex8 color type
+    CHECK_COLOR_TABLE;
+
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
     }
@@ -254,36 +297,38 @@ SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& dstInfo,
     if (nullptr == options) {
         options = &optsStorage;
     } else if (options->fSubset) {
-        SkIRect size = SkIRect::MakeSize(dstInfo.dimensions());
+        SkIRect size = SkIRect::MakeSize(info.dimensions());
         if (!size.contains(*options->fSubset)) {
             return kInvalidInput;
         }
 
         // We only support subsetting in the x-dimension for scanline decoder.
         // Subsetting in the y-dimension can be accomplished using skipScanlines().
-        if (options->fSubset->top() != 0 || options->fSubset->height() != dstInfo.height()) {
+        if (options->fSubset->top() != 0 || options->fSubset->height() != info.height()) {
             return kInvalidInput;
         }
     }
 
     // FIXME: Support subsets somehow?
-    if (!this->dimensionsSupported(dstInfo.dimensions())) {
+    if (!this->dimensionsSupported(info.dimensions())) {
         return kInvalidScale;
     }
 
-    const Result result = this->onStartScanlineDecode(dstInfo, *options, ctable, ctableCount);
+    const Result result = this->onStartScanlineDecode(info, *options, ctable, ctableCount);
     if (result != SkCodec::kSuccess) {
         return result;
     }
 
     fCurrScanline = 0;
-    fDstInfo = dstInfo;
+    fDstInfo = info;
     fOptions = *options;
     return kSuccess;
 }
 
-SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& dstInfo) {
-    return this->startScanlineDecode(dstInfo, nullptr, nullptr, nullptr);
+#undef CHECK_COLOR_TABLE
+
+SkCodec::Result SkCodec::startScanlineDecode(const SkImageInfo& info) {
+    return this->startScanlineDecode(info, nullptr, nullptr, nullptr);
 }
 
 int SkCodec::getScanlines(void* dst, int countLines, size_t rowBytes) {
@@ -331,7 +376,6 @@ int SkCodec::outputScanline(int inputScanline) const {
 int SkCodec::onOutputScanline(int inputScanline) const {
     switch (this->getScanlineOrder()) {
         case kTopDown_SkScanlineOrder:
-        case kNone_SkScanlineOrder:
             return inputScanline;
         case kBottomUp_SkScanlineOrder:
             return this->getInfo().height() - inputScanline - 1;
@@ -365,8 +409,7 @@ void SkCodec::fillIncompleteImage(const SkImageInfo& info, void* dst, size_t row
     }
 
     switch (this->getScanlineOrder()) {
-        case kTopDown_SkScanlineOrder:
-        case kNone_SkScanlineOrder: {
+        case kTopDown_SkScanlineOrder: {
             const SkImageInfo fillInfo = info.makeWH(fillWidth, linesRemaining);
             fillDst = SkTAddOffset<void>(dst, linesDecoded * rowBytes);
             fill_proc(fillInfo, fillDst, rowBytes, fillValue, zeroInit, sampler);