PDF: Add (low-memory) SkPDFBitmap class

src/pdf/SkPDFBitmap.cpp

Index: src/pdf/SkPDFBitmap.cpp
diff --git a/src/pdf/SkPDFBitmap.cpp b/src/pdf/SkPDFBitmap.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..26410d7fa3f0342bb4494ad4ce8fe2fdaa6ba94c
--- /dev/null
+++ b/src/pdf/SkPDFBitmap.cpp
@@ -0,0 +1,333 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkColorPriv.h"
+#include "SkDeflateWStream.h"
+#include "SkPDFBitmap.h"
+#include "SkPDFCanon.h"
+#include "SkPDFCatalog.h"
+#include "SkPDFDocument.h"
+#include "SkStream.h"
+#include "SkUnPreMultiply.h"
+
+////////////////////////////////////////////////////////////////////////////////
+
+static void pdf_stream_begin(SkWStream* stream) {
+    static const char streamBegin[] = " stream\n";
+    stream->write(streamBegin, strlen(streamBegin));
+}
+
+static void pdf_stream_end(SkWStream* stream) {
+    static const char streamEnd[] = "\nendstream";
+    stream->write(streamEnd, strlen(streamEnd));
+}
+
+static size_t pixel_count(const SkBitmap& bm) {
+    return SkToSizeT(bm.width()) * SkToSizeT(bm.height());
+}
+
+static bool skip_compression(SkPDFDocument::Flags flag) {
+#ifndef SK_NO_FLATE
+    return SkToBool(flag & SkPDFDocument::kFavorSpeedOverSize_Flags);
+#else
+    return true;
+#endif  // SK_NO_FLATE
+}
+
+// write a single byte to a stream n times.
+static void fill_stream(SkWStream* out, char value, size_t n) {
+    char buffer[4096];
+    memset(buffer, value, sizeof(buffer));
+    while (n) {
+        size_t k = SkTMin(n, sizeof(buffer));
+        out->write(buffer, k);
+        n -= k;
+    }
+}
+
+static SkPMColor get_pmcolor_neighbor_avg_color(const SkBitmap& bitmap,
+                                                int xOrig,
+                                                int yOrig) {
+    SkASSERT(kN32_SkColorType == bitmap.colorType());
+    SkASSERT(bitmap.getPixels());
+    uint8_t count = 0;
+    unsigned r = 0;
+    unsigned g = 0;
+    unsigned b = 0;
+    for (int y = yOrig - 1; y <= yOrig + 1; ++y) {
+        if (y < 0 || y >= bitmap.height()) {
+            continue;
+        }
+        uint32_t* src = bitmap.getAddr32(0, y);
+        for (int x = xOrig - 1; x <= xOrig + 1; ++x) {
+            if (x < 0 || x >= bitmap.width()) {
+                continue;
+            }
+            SkPMColor pmColor = src[x];
+            U8CPU alpha = SkGetPackedA32(pmColor);
+            if (alpha != SK_AlphaTRANSPARENT) {
+                uint32_t s = SkUnPreMultiply::GetScale(alpha);
+                r += SkUnPreMultiply::ApplyScale(s, SkGetPackedR32(pmColor));
+                g += SkUnPreMultiply::ApplyScale(s, SkGetPackedG32(pmColor));
+                b += SkUnPreMultiply::ApplyScale(s, SkGetPackedB32(pmColor));
+                ++count;
+            }
+        }
+    }
+    if (count == 0) {
+        return SkPackARGB32NoCheck(SK_AlphaOPAQUE, 0, 0, 0);
+    } else {
+        return SkPackARGB32NoCheck(
+                SK_AlphaOPAQUE, r / count, g / count, b / count);
+    }
+}
+
+static void pmcolor_to_rgb24(const SkBitmap& bm, SkWStream* out) {
+    SkASSERT(kN32_SkColorType == bm.colorType());
+    if (!bm.getPixels()) {
+        fill_stream(out, '\xFF', 3 * pixel_count(bm));
+        return;
+    }
+    size_t scanlineLength = 3 * bm.width();
+    SkAutoTMalloc<uint8_t> scanline(scanlineLength);
+    for (int y = 0; y < bm.height(); ++y) {
+        uint8_t* dst = scanline.get();
+        const SkPMColor* src = bm.getAddr32(0, y);
+        for (int x = 0; x < bm.width(); ++x) {
+            SkPMColor color = *src++;
+            U8CPU alpha = SkGetPackedA32(color);
+            if (alpha != SK_AlphaTRANSPARENT) {
+                uint32_t s = SkUnPreMultiply::GetScale(alpha);
+                *dst++ = SkUnPreMultiply::ApplyScale(s, SkGetPackedR32(color));
+                *dst++ = SkUnPreMultiply::ApplyScale(s, SkGetPackedG32(color));
+                *dst++ = SkUnPreMultiply::ApplyScale(s, SkGetPackedB32(color));
+            } else {
+                /* It is necessary to average the color component of
+                   transparent pixels with their surrounding neighbors
+                   since the PDF renderer may separately re-sample the
+                   alpha and color channels when the image is not
+                   displayed at its native resolution. Since an alpha
+                   of zero gives no information about the color
+                   component, the pathological case is a white image
+                   with sharp transparency bounds - the color channel
+                   goes to black, and the should-be-transparent pixels
+                   are rendered as grey because of the separate soft
+                   mask and color resizing. e.g.: gm/bitmappremul.cpp */
+                color = get_pmcolor_neighbor_avg_color(bm, x, y);
+                *dst++ = SkGetPackedR32(color);
+                *dst++ = SkGetPackedG32(color);
+                *dst++ = SkGetPackedB32(color);
+            }
+        }
+        out->write(scanline.get(), scanlineLength);
+    }
+}
+
+static void pmcolor_alpha_to_a8(const SkBitmap& bm, SkWStream* out) {
+    SkASSERT(kN32_SkColorType == bm.colorType());
+    if (!bm.getPixels()) {
+        fill_stream(out, '\xFF', pixel_count(bm));
+        return;
+    }
+    size_t scanlineLength = bm.width();
+    SkAutoTMalloc<uint8_t> scanline(scanlineLength);
+    for (int y = 0; y < bm.height(); ++y) {
+        uint8_t* dst = scanline.get();
+        const SkPMColor* src = bm.getAddr32(0, y);
+        for (int x = 0; x < bm.width(); ++x) {
+            *dst++ = SkGetPackedA32(*src++);
+        }
+        out->write(scanline.get(), scanlineLength);
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+namespace {
+// This SkPDFObject only outputs the alpha layer of the given bitmap.
+class PDFAlphaBitmap : public SkPDFObject {
+public:
+    PDFAlphaBitmap(const SkBitmap& bm) : fBitmap(bm) {}
+    ~PDFAlphaBitmap() {}
+    void emitObject(SkWStream*, SkPDFCatalog*) SK_OVERRIDE;
+    void addResources(SkTSet<SkPDFObject*>*, SkPDFCatalog*) const SK_OVERRIDE {}
+
+private:
+    const SkBitmap fBitmap;
+    void emitDict(SkWStream*, SkPDFCatalog*, size_t, bool) const;
+};
+
+void PDFAlphaBitmap::emitObject(SkWStream* stream, SkPDFCatalog* catalog) {
+    SkAutoLockPixels autoLockPixels(fBitmap);
+
+    if (skip_compression(catalog->getDocumentFlags())) {
+        this->emitDict(stream, catalog, pixel_count(fBitmap),
+                       /*deflate=*/false);
+        pdf_stream_begin(stream);
+        pmcolor_alpha_to_a8(fBitmap, stream);
+        pdf_stream_end(stream);
+        return;
+    }
+#ifndef SK_NO_FLATE
+    // Write to a temporary buffer to get the compressed length.
+    SkDynamicMemoryWStream buffer;
+    SkDeflateWStream deflateWStream(&buffer);
+    pmcolor_alpha_to_a8(fBitmap, &deflateWStream);
+    deflateWStream.finalize();  // call before detachAsStream().
+    SkAutoTDelete<SkStreamAsset> asset(buffer.detachAsStream());
+
+    this->emitDict(stream, catalog, asset->getLength(), /*deflate=*/true);
+    pdf_stream_begin(stream);
+    stream->writeStream(asset.get(), asset->getLength());
+    pdf_stream_end(stream);
+#endif  // SK_NO_FLATE
+}
+
+void PDFAlphaBitmap::emitDict(SkWStream* stream,
+                              SkPDFCatalog* catalog,
+                              size_t length,
+                              bool deflate) const {
+    SkPDFDict pdfDict("XObject");
+    pdfDict.insertName("Subtype", "Image");
+    pdfDict.insertInt("Width", fBitmap.width());
+    pdfDict.insertInt("Height", fBitmap.height());
+    pdfDict.insertName("ColorSpace", "DeviceGray");
+    pdfDict.insertInt("BitsPerComponent", 8);
+    if (deflate) {
+        pdfDict.insertName("Filter", "FlateDecode");
+    }
+    pdfDict.insertInt("Length", length);
+    pdfDict.emitObject(stream, catalog);
+}
+}  // namespace
+
+////////////////////////////////////////////////////////////////////////////////
+
+void SkPDFBitmap::addResources(SkTSet<SkPDFObject*>* resourceSet,
+                               SkPDFCatalog* catalog) const {
+    if (fSMask.get()) {
+        resourceSet->add(fSMask.get());
+    }
+}
+
+void SkPDFBitmap::emitObject(SkWStream* stream, SkPDFCatalog* catalog) {
+    SkAutoLockPixels autoLockPixels(fBitmap);
+
+    if (skip_compression(catalog->getDocumentFlags())) {
+        this->emitDict(stream, catalog, 3 * pixel_count(fBitmap),
+                       /*deflate=*/false);
+        pdf_stream_begin(stream);
+        pmcolor_to_rgb24(fBitmap, stream);
+        pdf_stream_end(stream);
+        return;
+    }
+#ifndef SK_NO_FLATE
+    // Write to a temporary buffer to get the compressed length.
+    SkDynamicMemoryWStream buffer;
+    SkDeflateWStream deflateWStream(&buffer);
+    pmcolor_to_rgb24(fBitmap, &deflateWStream);
+    deflateWStream.finalize();  // call before detachAsStream().
+    SkAutoTDelete<SkStreamAsset> asset(buffer.detachAsStream());
+
+    this->emitDict(stream, catalog, asset->getLength(), /*deflate=*/true);
+    pdf_stream_begin(stream);
+    stream->writeStream(asset.get(), asset->getLength());
+    pdf_stream_end(stream);
+#endif  // SK_NO_FLATE
+}
+
+void SkPDFBitmap::emitDict(SkWStream* stream,
+                           SkPDFCatalog* catalog,
+                           size_t length,
+                           bool deflate) const {
+    SkPDFDict pdfDict("XObject");
+    pdfDict.insertName("Subtype", "Image");
+    pdfDict.insertInt("Width", fBitmap.width());
+    pdfDict.insertInt("Height", fBitmap.height());
+    pdfDict.insertName("ColorSpace", "DeviceRGB");
+    pdfDict.insertInt("BitsPerComponent", 8);
+    if (fSMask) {
+        pdfDict.insert("SMask", new SkPDFObjRef(fSMask))->unref();
+    }
+    if (deflate) {
+        pdfDict.insertName("Filter", "FlateDecode");
+    }
+    pdfDict.insertInt("Length", length);
+    pdfDict.emitObject(stream, catalog);
+}
+
+SkPDFBitmap::SkPDFBitmap(const SkBitmap& bm, SkPDFObject* smask)
+    : fBitmap(bm), fSMask(smask) {}
+
+SkPDFBitmap::~SkPDFBitmap() {
+    SkAutoMutexAcquire autoMutexAcquire(SkPDFCanon::GetBitmapMutex());
+    SkPDFCanon::GetCanon().removeBitmap(this);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+static bool is_transparent(const SkBitmap& bm) {
+    SkAutoLockPixels autoLockPixels(bm);
+    if (NULL == bm.getPixels()) {
+        return true;
+    }
+    SkASSERT(kN32_SkColorType == bm.colorType());
+    for (int y = 0; y < bm.height(); ++y) {
+        U8CPU alpha = 0;
+        const SkPMColor* src = bm.getAddr32(0, y);
+        for (int x = 0; x < bm.width(); ++x) {
+            alpha |= SkGetPackedA32(*src++);
+        }
+        if (alpha) {
+            return false;
+        }
+    }
+    return true;
+}
+
+// TODO(halcanary): SkPDFBitmap::Create should take a SkPDFCanon* parameter.
+SkPDFBitmap* SkPDFBitmap::Create(const SkBitmap& bitmap,
+                                 const SkIRect& subset) {
+    if (kN32_SkColorType != bitmap.colorType()) {
+        // TODO(halcanary): support other colortypes.
+        return NULL;
+    }
+    SkBitmap bm;
+    // Should extractSubset be done by the SkPDFDevice?
+    if (!bitmap.extractSubset(&bm, subset)) {
+        return NULL;
+    }
+    if (bm.drawsNothing()) {
+        return NULL;
+    }
+    if (!bm.isImmutable()) {
+        SkBitmap copy;
+        if (!bm.copyTo(&copy)) {
+            return NULL;
+        }
+        copy.setImmutable();
+        bm = copy;
+    }
+
+    SkAutoMutexAcquire autoMutexAcquire(SkPDFCanon::GetBitmapMutex());
+    SkPDFCanon& canon = SkPDFCanon::GetCanon();
+    SkPDFBitmap* pdfBitmap = canon.findBitmap(bm);
+    if (pdfBitmap) {
+        return SkRef(pdfBitmap);
+    }
+    SkPDFObject* smask = NULL;
+    if (!bm.isOpaque() && !SkBitmap::ComputeIsOpaque(bm)) {
+        if (is_transparent(bm)) {
+            return NULL;
+        }
+        // PDFAlphaBitmaps do not get directly canonicalized (they
+        // are refed by the SkPDFBitmap).
+        smask = SkNEW_ARGS(PDFAlphaBitmap, (bm));
+    }
+    pdfBitmap = SkNEW_ARGS(SkPDFBitmap, (bm, smask));
+    canon.addBitmap(pdfBitmap);
+    return pdfBitmap;
+}