Make SkPngCodec decode progressively.

tests/CodecPartial.cpp

Index: tests/CodecPartial.cpp
diff --git a/tests/CodecPartial.cpp b/tests/CodecPartial.cpp
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+++ b/tests/CodecPartial.cpp
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+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCodec.h"
+#include "SkData.h"
+#include "SkImageInfo.h"
+#include "SkRWBuffer.h"
+#include "SkString.h"
+
+#include "Resources.h"
+#include "Test.h"
+
+static sk_sp<SkData> make_from_resource(const char* name) {
+    SkString fullPath = GetResourcePath(name);
+    return SkData::MakeFromFileName(fullPath.c_str());
+}
+
+static SkImageInfo standardize_info(SkCodec* codec) {
+    return codec->getInfo().makeColorType(kN32_SkColorType).makeAlphaType(kPremul_SkAlphaType);
+}
+
+static bool create_truth(sk_sp<SkData> data, SkBitmap* dst) {
+    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromData(data.get()));
+    if (!codec) {
+        return false;
+    }
+
+    const SkImageInfo info = standardize_info(codec);
+    dst->allocPixels(info);
+    return SkCodec::kSuccess == codec->getPixels(info, dst->getPixels(), dst->rowBytes());
+}
+
+/*
+ *  Represents a stream without all of its data.
+ */
+class HaltingStream : public SkStream {
+public:
+    HaltingStream(sk_sp<SkData> data)
+        : fTotalSize(data->size())
+        , fLimit(fTotalSize / 2)
+        , fStream(std::move(data))
+    {}
+
+    void addNewData() {
+        // Arbitrary size, but deliberately different from
+        // the buffer size used by SkPngCodec.
+        fLimit = SkTMin(fTotalSize, fLimit + 1000);
+    }
+
+    size_t read(void* buffer, size_t size) override {
+        if (fStream.getPosition() + size > fLimit) {
+            size = fLimit - fStream.getPosition();
+        }
+
+        return fStream.read(buffer, size);
+    }
+
+    bool isAtEnd() const override {
+        return fStream.isAtEnd();
+    }
+
+    bool hasPosition() const override { return true; }
+    size_t getPosition() const override { return fStream.getPosition(); }
+    bool rewind() override { return fStream.rewind(); }
+
+private:
+    const size_t    fTotalSize;
+    size_t          fLimit;
+    SkMemoryStream  fStream;
+};
+
+static void test_partial(skiatest::Reporter* r, const char* name) {
+    sk_sp<SkData> file = make_from_resource(name);
+    if (!file) {
+        SkDebugf("missing resource %s\n", name);
+        return;
+    }
+
+    SkBitmap truth;
+    if (!create_truth(file, &truth)) {
+        ERRORF(r, "Failed to decode %s\n", name);
+        return;
+    }
+
+    const size_t fileSize = file->size();
+
+    // Now decode part of the file
+    HaltingStream* stream = new HaltingStream(file);
+
+    // Note that we cheat and hold on to a pointer to stream, though it is owned by
+    // partialCodec.
+    SkAutoTDelete<SkCodec> partialCodec(SkCodec::NewFromStream(stream));
+    if (!partialCodec) {
+        // Technically, this could be a small file where half the file is not
+        // enough.
+        ERRORF(r, "Failed to create codec for %s", name);
+        return;
+    }
+
+    const SkImageInfo info = standardize_info(partialCodec);
+    SkASSERT(info == truth.info());
+    SkBitmap incremental;
+    incremental.allocPixels(info);
+
+    const SkCodec::Result startResult = partialCodec->startIncrementalDecode(info);
+    if (startResult != SkCodec::kSuccess) {
+        ERRORF(r, "Failed to start scanline decode\n");
+        return;
+    }
+
+    while (true) {
+        const SkCodec::Result result = partialCodec->incrementalDecode(
+            [&incremental](int rowNum) {
+                return incremental.getAddr(0, rowNum);
+            });
+
+        if (stream->getPosition() == fileSize) {
+            REPORTER_ASSERT(r, result == SkCodec::kSuccess);
+            break;
+        }
+
+        SkASSERT(stream->getPosition() < fileSize);
+
+        REPORTER_ASSERT(r, result == SkCodec::kIncompleteInput);
+
+        // Append an arbitrary amount of data.
+        stream->addNewData();
+    }
+
+    // compare to original
+    for (int i = 0; i < info.height(); i++) {
+        REPORTER_ASSERT(r, !memcmp(truth.getAddr(0, 0), incremental.getAddr(0, 0),
+                                   info.minRowBytes()));
+    }
+}
+
+DEF_TEST(Codec_partial, r) {
+    test_partial(r, "plane.png");
+    test_partial(r, "plane_interlaced.png");
+    test_partial(r, "yellow_rose.png");
+    test_partial(r, "index8.png");
+    test_partial(r, "color_wheel.png");
+    test_partial(r, "mandrill_256.png");
+    test_partial(r, "mandrill_32.png");
+    test_partial(r, "arrow.png");
+    test_partial(r, "randPixels.png");
+    test_partial(r, "baby_tux.png");
+}