src/pdf/SkPDFDocument.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkPDFDocument.h"

#include "SkCanvas.h"
#include "SkMakeUnique.h"
#include "SkPDFCanon.h"
#include "SkPDFDevice.h"
#include "SkPDFUtils.h"
#include "SkStream.h"

SkPDFObjectSerializer::SkPDFObjectSerializer() : fBaseOffset(0), fNextToBeSerialized(0) {}

SkPDFObjectSerializer::~SkPDFObjectSerializer() {
    for (int i = 0; i < fObjNumMap.objects().count(); ++i) {
        fObjNumMap.objects()[i]->drop();
    }
}
SkPDFObjectSerializer::SkPDFObjectSerializer(SkPDFObjectSerializer&&) = default;
SkPDFObjectSerializer& SkPDFObjectSerializer::operator=(SkPDFObjectSerializer&&) = default;


void SkPDFObjectSerializer::addObjectRecursively(const sk_sp<SkPDFObject>& object) {
    fObjNumMap.addObjectRecursively(object.get());
}

#define SKPDF_MAGIC "\xD3\xEB\xE9\xE1"
#ifndef SK_BUILD_FOR_WIN
static_assert((SKPDF_MAGIC[0] & 0x7F) == "Skia"[0], "");
static_assert((SKPDF_MAGIC[1] & 0x7F) == "Skia"[1], "");
static_assert((SKPDF_MAGIC[2] & 0x7F) == "Skia"[2], "");
static_assert((SKPDF_MAGIC[3] & 0x7F) == "Skia"[3], "");
#endif
void SkPDFObjectSerializer::serializeHeader(SkWStream* wStream,
                                            const SkDocument::PDFMetadata& md) {
    fBaseOffset = wStream->bytesWritten();
    static const char kHeader[] = "%PDF-1.4\n%" SKPDF_MAGIC "\n";
    wStream->writeText(kHeader);
    // The PDF spec recommends including a comment with four
    // bytes, all with their high bits set.  "\xD3\xEB\xE9\xE1" is
    // "Skia" with the high bits set.
    fInfoDict = SkPDFMetadata::MakeDocumentInformationDict(md);
    this->addObjectRecursively(fInfoDict);
    this->serializeObjects(wStream);
}
#undef SKPDF_MAGIC

// Serialize all objects in the fObjNumMap that have not yet been serialized;
void SkPDFObjectSerializer::serializeObjects(SkWStream* wStream) {
    const SkTArray<sk_sp<SkPDFObject>>& objects = fObjNumMap.objects();
    while (fNextToBeSerialized < objects.count()) {
        SkPDFObject* object = objects[fNextToBeSerialized].get();
        int32_t index = fNextToBeSerialized + 1;  // Skip object 0.
        // "The first entry in the [XREF] table (object number 0) is
        // always free and has a generation number of 65,535; it is
        // the head of the linked list of free objects."
        SkASSERT(fOffsets.count() == fNextToBeSerialized);
        fOffsets.push(this->offset(wStream));
        wStream->writeDecAsText(index);
        wStream->writeText(" 0 obj\n");  // Generation number is always 0.
        object->emitObject(wStream, fObjNumMap);
        wStream->writeText("\nendobj\n");
        object->drop();
        ++fNextToBeSerialized;
    }
}

// Xref table and footer
void SkPDFObjectSerializer::serializeFooter(SkWStream* wStream,
                                            const sk_sp<SkPDFObject> docCatalog,
                                            sk_sp<SkPDFObject> id) {
    this->serializeObjects(wStream);
    int32_t xRefFileOffset = this->offset(wStream);
    // Include the special zeroth object in the count.
    int32_t objCount = SkToS32(fOffsets.count() + 1);
    wStream->writeText("xref\n0 ");
    wStream->writeDecAsText(objCount);
    wStream->writeText("\n0000000000 65535 f \n");
    for (int i = 0; i < fOffsets.count(); i++) {
        wStream->writeBigDecAsText(fOffsets[i], 10);
        wStream->writeText(" 00000 n \n");
    }
    SkPDFDict trailerDict;
    trailerDict.insertInt("Size", objCount);
    SkASSERT(docCatalog);
    trailerDict.insertObjRef("Root", docCatalog);
    SkASSERT(fInfoDict);
    trailerDict.insertObjRef("Info", std::move(fInfoDict));
    if (id) {
        trailerDict.insertObject("ID", std::move(id));
    }
    wStream->writeText("trailer\n");
    trailerDict.emitObject(wStream, fObjNumMap);
    wStream->writeText("\nstartxref\n");
    wStream->writeBigDecAsText(xRefFileOffset);
    wStream->writeText("\n%%EOF");
}

int32_t SkPDFObjectSerializer::offset(SkWStream* wStream) {
    size_t offset = wStream->bytesWritten();
    SkASSERT(offset > fBaseOffset);
    return SkToS32(offset - fBaseOffset);
}


// return root node.
static sk_sp<SkPDFDict> generate_page_tree(SkTArray<sk_sp<SkPDFDict>>* pages) {
    // PDF wants a tree describing all the pages in the document.  We arbitrary
    // choose 8 (kNodeSize) as the number of allowed children.  The internal
    // nodes have type "Pages" with an array of children, a parent pointer, and
    // the number of leaves below the node as "Count."  The leaves are passed
    // into the method, have type "Page" and need a parent pointer. This method
    // builds the tree bottom up, skipping internal nodes that would have only
    // one child.
    static const int kNodeSize = 8;

    // curNodes takes a reference to its items, which it passes to pageTree.
    int totalPageCount = pages->count();
    SkTArray<sk_sp<SkPDFDict>> curNodes;
    curNodes.swap(pages);

    // nextRoundNodes passes its references to nodes on to curNodes.
    int treeCapacity = kNodeSize;
    do {
        SkTArray<sk_sp<SkPDFDict>> nextRoundNodes;
        for (int i = 0; i < curNodes.count(); ) {
            if (i > 0 && i + 1 == curNodes.count()) {
                SkASSERT(curNodes[i]);
                nextRoundNodes.emplace_back(std::move(curNodes[i]));
                break;
            }

            auto newNode = sk_make_sp<SkPDFDict>("Pages");
            auto kids = sk_make_sp<SkPDFArray>();
            kids->reserve(kNodeSize);

            int count = 0;
            for (; i < curNodes.count() && count < kNodeSize; i++, count++) {
                SkASSERT(curNodes[i]);
                curNodes[i]->insertObjRef("Parent", newNode);
                kids->appendObjRef(std::move(curNodes[i]));
            }

            // treeCapacity is the number of leaf nodes possible for the
            // current set of subtrees being generated. (i.e. 8, 64, 512, ...).
            // It is hard to count the number of leaf nodes in the current
            // subtree. However, by construction, we know that unless it's the
            // last subtree for the current depth, the leaf count will be
            // treeCapacity, otherwise it's what ever is left over after
            // consuming treeCapacity chunks.
            int pageCount = treeCapacity;
            if (i == curNodes.count()) {
                pageCount = ((totalPageCount - 1) % treeCapacity) + 1;
            }
            newNode->insertInt("Count", pageCount);
            newNode->insertObject("Kids", std::move(kids));
            nextRoundNodes.emplace_back(std::move(newNode));
        }
        SkDEBUGCODE( for (const auto& n : curNodes) { SkASSERT(!n); } );

        curNodes.swap(&nextRoundNodes);
        nextRoundNodes.reset();
        treeCapacity *= kNodeSize;
    } while (curNodes.count() > 1);
    return std::move(curNodes[0]);
}

////////////////////////////////////////////////////////////////////////////////

SkPDFDocument::SkPDFDocument(SkWStream* stream,
                             const SkDocument::PDFMetadata& metadata)
    : SkDocument(stream)
    , fMetadata(metadata) {
}

SkPDFDocument::~SkPDFDocument() {
    // subclasses of SkDocument must call close() in their destructors.
    this->close();
}

void SkPDFDocument::serialize(const sk_sp<SkPDFObject>& object) {
    fObjectSerializer.addObjectRecursively(object);
    fObjectSerializer.serializeObjects(this->getStream());
}

SkCanvas* SkPDFDocument::onBeginPage(SkScalar width, SkScalar height) {
    SkASSERT(!fCanvas.get());  // endPage() was called before this.
    if (fPages.empty()) {
        // if this is the first page if the document.
        fObjectSerializer.serializeHeader(this->getStream(), fMetadata);
        fDests = sk_make_sp<SkPDFDict>();
        if (fMetadata.fPDFA) {
            SkPDFMetadata::UUID uuid = SkPDFMetadata::CreateUUID(fMetadata);
            // We use the same UUID for Document ID and Instance ID since this
            // is the first revision of this document (and Skia does not
            // support revising existing PDF documents).
            // If we are not in PDF/A mode, don't use a UUID since testing
            // works best with reproducible outputs.
            fID = SkPDFMetadata::MakePdfId(uuid, uuid);
            fXMP = SkPDFMetadata::MakeXMPObject(fMetadata, uuid, uuid);
            fObjectSerializer.addObjectRecursively(fXMP);
            fObjectSerializer.serializeObjects(this->getStream());
        }
    }
    SkISize pageSize = SkISize::Make(
            SkScalarRoundToInt(width), SkScalarRoundToInt(height));
    fPageDevice = sk_make_sp<SkPDFDevice>(pageSize, this);
    fPageDevice->setFlip();  // Only the top-level device needs to be flipped.
    fCanvas.reset(new SkCanvas(fPageDevice));
    return fCanvas.get();
}

void SkPDFDocument::onEndPage() {
    SkASSERT(fCanvas.get());
    fCanvas->flush();
    fCanvas.reset(nullptr);
    SkASSERT(fPageDevice);
    auto page = sk_make_sp<SkPDFDict>("Page");
    page->insertObject("Resources", fPageDevice->makeResourceDict());
    page->insertObject("MediaBox", fPageDevice->copyMediaBox());
    auto annotations = sk_make_sp<SkPDFArray>();
    fPageDevice->appendAnnotations(annotations.get());
    if (annotations->size() > 0) {
        page->insertObject("Annots", std::move(annotations));
    }
    auto contentObject = sk_make_sp<SkPDFStream>(fPageDevice->content());
    this->serialize(contentObject);
    page->insertObjRef("Contents", std::move(contentObject));
    fPageDevice->appendDestinations(fDests.get(), page.get());
    fPages.emplace_back(std::move(page));
    fPageDevice.reset(nullptr);
}

void SkPDFDocument::onAbort() {
    this->reset();
}

void SkPDFDocument::reset() {
    fCanvas.reset(nullptr);
    fPages.reset();
    fCanon = SkPDFCanon();
    fObjectSerializer = SkPDFObjectSerializer();
    fFonts.reset();
}

static sk_sp<SkData> SkSrgbIcm() {
    // Source: http://www.argyllcms.com/icclibsrc.html
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        "S\342\333\343c\343\353\344s\344\374\345\204\346\r\346\226\347\37\347"
        "\251\3502\350\274\351F\351\320\352[\352\345\353p\353\373\354\206\355"
        "\21\355\234\356(\356\264\357@\357\314\360X\360\345\361r\361\377\362"
        "\214\363\31\363\247\3644\364\302\365P\365\336\366m\366\373\367\212"
        "\370\31\370\250\3718\371\307\372W\372\347\373w\374\7\374\230\375)\375"
        "\272\376K\376\334\377m\377\377";
    const size_t kProfileLength = 3212;
    static_assert(kProfileLength == sizeof(kProfile) - 1, "");
    return SkData::MakeWithoutCopy(kProfile, kProfileLength);
}

static sk_sp<SkPDFStream> make_srgb_color_profile() {
    sk_sp<SkPDFStream> stream = sk_make_sp<SkPDFStream>(SkSrgbIcm());
    stream->dict()->insertInt("N", 3);
    sk_sp<SkPDFArray> array = sk_make_sp<SkPDFArray>();
    array->appendScalar(0.0f);
    array->appendScalar(1.0f);
    array->appendScalar(0.0f);
    array->appendScalar(1.0f);
    array->appendScalar(0.0f);
    array->appendScalar(1.0f);
    stream->dict()->insertObject("Range", std::move(array));
    return stream;
}

static sk_sp<SkPDFArray> make_srgb_output_intents() {
    // sRGB is specified by HTML, CSS, and SVG.
    auto outputIntent = sk_make_sp<SkPDFDict>("OutputIntent");
    outputIntent->insertName("S", "GTS_PDFA1");
    outputIntent->insertString("RegistryName", "http://www.color.org");
    outputIntent->insertString("OutputConditionIdentifier",
                               "Custom");
    outputIntent->insertString("Info","sRGB IEC61966-2.1");
    outputIntent->insertObjRef("DestOutputProfile",
                               make_srgb_color_profile());
    auto intentArray = sk_make_sp<SkPDFArray>();
    intentArray->appendObject(std::move(outputIntent));
    return intentArray;
}

void SkPDFDocument::onClose(SkWStream* stream) {
    SkASSERT(!fCanvas.get());
    if (fPages.empty()) {
        this->reset();
        return;
    }
    auto docCatalog = sk_make_sp<SkPDFDict>("Catalog");
    if (fMetadata.fPDFA) {
        SkASSERT(fXMP);
        docCatalog->insertObjRef("Metadata", fXMP);
        // Don't specify OutputIntents if we are not in PDF/A mode since
        // no one has ever asked for this feature.
        docCatalog->insertObject("OutputIntents", make_srgb_output_intents());
    }
    SkASSERT(!fPages.empty());
    docCatalog->insertObjRef("Pages", generate_page_tree(&fPages));
    SkASSERT(fPages.empty());

    if (fDests->size() > 0) {
        docCatalog->insertObjRef("Dests", std::move(fDests));
    }

    // Build font subsetting info before calling addObjectRecursively().
    SkPDFCanon* canon = &fCanon;
    fFonts.foreach([canon](SkPDFFont* p){ p->getFontSubset(canon); });
    fObjectSerializer.addObjectRecursively(docCatalog);
    fObjectSerializer.serializeObjects(this->getStream());
    fObjectSerializer.serializeFooter(this->getStream(), docCatalog, fID);
    this->reset();
}

///////////////////////////////////////////////////////////////////////////////

sk_sp<SkDocument> SkPDFMakeDocument(SkWStream* stream,
                                    const SkDocument::PDFMetadata& metadata) {
    SkDocument::PDFMetadata meta = metadata;
    if (meta.fRasterDPI <= 0) {
        meta.fRasterDPI = 72.0f;
    }
    if (meta.fEncodingQuality < 0) {
        meta.fEncodingQuality = 0;
    }
    return stream ? sk_make_sp<SkPDFDocument>(stream, meta) : nullptr;
}

sk_sp<SkDocument> SkDocument::MakePDF(SkWStream* stream, const PDFMetadata& metadata) {
    return SkPDFMakeDocument(stream, metadata);
}

sk_sp<SkDocument> SkDocument::MakePDF(SkWStream* stream) {
    return SkPDFMakeDocument(stream, PDFMetadata());
}