Simplify reference management in SkPDF

Prior to this change, SkPDFObject subclasses were required
to track their resources separately from the document
structure.  (An object has a resource if it depends, via an
indirect reference, on another object).  This led to a lot
of extra code to duplicate effort.  I replace the
getResources() function with the much simpler addResources()
function.  I only define a non-trivial addResources() method
on arrays, dictionaries, and indirect object references.
All other specialized classes simply rely on their parent
class's implementation.

SkPDFObject::addResources() works by recursively walking the
directed graph of object (direct and indirect) references
and adding resources to a set.  It doesn't matter that there
are closed loops in the graph, since we check the set before
walking down a branch.

-  Add SkPDFObject::addResources() virtual function, with
   four implementations
-  Remove SkPDFObject::getResources() virtual function and
   all implementations.
-  Remove SkPDFObject::GetResourcesHelper()
-  Remove SkPDFObject::AddResourceHelper()
-  In SkPDFCatalog::findObjectIndex(), add an object to the
   catalog if it doesn't exist yet.
-  SkPDFCatalog::setSubstitute() no longer sets up resources
-  SkPDFDocument.cpp no longer needs the Streamer object
-  SkPDFDocument.cpp calls fDocCatalog->addResources to build
   the resource list.
-  SkPDFFont::addResource() removed
-  All SkPDF-::fResource sets removed (they are redundant).
-  removed SkPDFImage::addSMask() function
-  SkPDFResourceDict::getReferencedResources() removed.

Motivation: this removes quite a bit of code and makes the
objects slightly slimmer in memory.  Most importantly, this
will lead the way towards removing SkPDFObject's inheritance
from SkRefCnt, which will greatly simplify everything.

Testing: I usually test changes to the PDF backend by
comparing checksums of PDF files rendered from GMs and SKPs
before and after the change.  This change both re-orders and
re-numbers the indirect PDF objects.  I used the qpdf
program to normalize the PDFs and then compared the
normalized outputs from before and after the change; they
matched.

Review URL: https://codereview.chromium.org/870333002

1 files changed, 30 insertions, 32 deletions

diff --git a/src/pdf/SkPDFTypes.cpp b/src/pdf/SkPDFTypes.cpp
index b0763a3c59..7902e599ce 100644
--- a/src/pdf/SkPDFTypes.cpp
+++ b/src/pdf/SkPDFTypes.cpp
@@ -17,36 +17,6 @@
     #define SNPRINTF    snprintf
 #endif
 
-///////////////////////////////////////////////////////////////////////////////
-
-void SkPDFObject::getResources(const SkTSet<SkPDFObject*>& knownResourceObjects,
-                               SkTSet<SkPDFObject*>* newResourceObjects) {}
-
-void SkPDFObject::AddResourceHelper(SkPDFObject* resource,
-                                    SkTDArray<SkPDFObject*>* list) {
-    list->push(resource);
-    resource->ref();
-}
-
-void SkPDFObject::GetResourcesHelper(
-        const SkTDArray<SkPDFObject*>* resources,
-        const SkTSet<SkPDFObject*>& knownResourceObjects,
-        SkTSet<SkPDFObject*>* newResourceObjects) {
-    if (resources->count()) {
-        newResourceObjects->setReserve(
-            newResourceObjects->count() + resources->count());
-        for (int i = 0; i < resources->count(); i++) {
-            if (!knownResourceObjects.contains((*resources)[i]) &&
-                    !newResourceObjects->contains((*resources)[i])) {
-                newResourceObjects->add((*resources)[i]);
-                (*resources)[i]->ref();
-                (*resources)[i]->getResources(knownResourceObjects,
-                                              newResourceObjects);
-            }
-        }
-    }
-}
-
 ////////////////////////////////////////////////////////////////////////////////
 
 SkPDFObjRef::SkPDFObjRef(SkPDFObject* obj) : fObj(obj) {
@@ -56,8 +26,17 @@ SkPDFObjRef::SkPDFObjRef(SkPDFObject* obj) : fObj(obj) {
 SkPDFObjRef::~SkPDFObjRef() {}
 
 void SkPDFObjRef::emitObject(SkWStream* stream, SkPDFCatalog* catalog) {
-    catalog->emitObjectNumber(stream, fObj.get());
-    stream->writeText(" R");
+    stream->writeDecAsText(catalog->getObjectNumber(fObj.get()));
+    stream->writeText(" 0 R");  // Generation number is always 0.
+}
+
+void SkPDFObjRef::addResources(SkTSet<SkPDFObject*>* resourceSet,
+                               SkPDFCatalog* catalog) const {
+    SkPDFObject* obj = catalog->getSubstituteObject(fObj);
+    SkASSERT(obj);
+    if (resourceSet->add(obj)) {
+        obj->addResources(resourceSet, catalog);
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -277,6 +256,14 @@ void SkPDFArray::emitObject(SkWStream* stream, SkPDFCatalog* catalog) {
     stream->writeText("]");
 }
 
+void SkPDFArray::addResources(SkTSet<SkPDFObject*>* resourceSet,
+                              SkPDFCatalog* catalog) const {
+    for (int i = 0; i < fValue.count(); i++) {
+        catalog->getSubstituteObject(fValue[i])
+                ->addResources(resourceSet, catalog);
+    }
+}
+
 void SkPDFArray::reserve(int length) {
     SkASSERT(length <= kMaxLen);
     fValue.setReserve(length);
@@ -347,6 +334,17 @@ void SkPDFDict::emitObject(SkWStream* stream, SkPDFCatalog* catalog) {
     stream->writeText(">>");
 }
 
+void SkPDFDict::addResources(SkTSet<SkPDFObject*>* resourceSet,
+                             SkPDFCatalog* catalog) const {
+    for (int i = 0; i < fValue.count(); i++) {
+        SkASSERT(fValue[i].key);
+        SkASSERT(fValue[i].value);
+        fValue[i].key->addResources(resourceSet, catalog);
+        catalog->getSubstituteObject(fValue[i].value)
+                ->addResources(resourceSet, catalog);
+    }
+}
+
 SkPDFObject*  SkPDFDict::append(SkPDFName* key, SkPDFObject* value) {
     SkASSERT(key);
     SkASSERT(value);