Simplify SkPdfTokenLooper behavior.

experimental/PdfViewer/inc/SkPdfTokenLooper.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPdfTokenLooper_DEFINED
 #define SkPdfTokenLooper_DEFINED
 
 #include "SkPdfNativeTokenizer.h"
 // For SkPdfResult
 #include "SkPdfUtils.h"
 
 class SkCanvas;
 class SkPdfContext;
 
+/**
+ *  An object which reads tokens from a tokenizer and draws it to an SkCanvas.
+ */
 class SkPdfTokenLooper {
-protected:
-    SkPdfTokenLooper* fParent;
-    SkPdfNativeTokenizer* fTokenizer;
-    SkPdfContext* fPdfContext;
-    SkCanvas* fCanvas;
+public:
+    /**
+     *  Create a looper with no parent.
+     *  @param tokenizer SkPdfNativeTokenizer for reading tokens.
+     *  @param pdfContext Context for drawing state.
+     *  @param canvas Target SkCanvas for drawing.
+     */
+    SkPdfTokenLooper(SkPdfNativeTokenizer* tokenizer,

[mtklein, 2013/12/02 21:28:08]

This has just occurred to me (I think, maybe I've asked this before...): why
does SkPdfTokenLooper have anything but

struct SkPdfTokenLooper {
  virtual ~SkPdfTokenLooper() {}

  virtual SkPdfResult consumeToken(PdfToken& token) = 0;
  virtual void loop() = 0;
};

I.e. can't it be an interface?  The members are just there for convenience
right?  Do all subclasses need all the members?

[scroggo, 2013/12/02 22:34:29]

All subclasses need fTokenizer, fPdfContext, and fCanvas. Only
PdfCompatibilitySectionLooper uses fParent (though PdfInlineImageLooper uses it
to set the other fields). As noted in a FIXME elsewhere, PdfInlineImageLooper
ONLY exists so it can have access to the protected fields of SkPdfTokenLooper.

Added a FIXME to continue investigating.

+                     SkPdfContext* pdfContext,
+                     SkCanvas* canvas)
+        : fParent(NULL)
+        , fTokenizer(tokenizer)
+        , fPdfContext(pdfContext)
+        , fCanvas(canvas) {}
 
-public:
-    SkPdfTokenLooper(SkPdfTokenLooper* parent,
-                   SkPdfNativeTokenizer* tokenizer,
-                   SkPdfContext* pdfContext,
-                   SkCanvas* canvas)
-        : fParent(parent), fTokenizer(tokenizer), fPdfContext(pdfContext), fCanvas(canvas) {}
+    /**
+     *  Create a looper as a child of parent. It will share the
+     *  SkPdfContext, SkPdfTokenizer, and SkCanvas with its parent.
+     */
+    explicit SkPdfTokenLooper(SkPdfTokenLooper* parent)
+        : fParent(parent)
+        , fTokenizer(parent->fTokenizer)
+        , fPdfContext(parent->fPdfContext)
+        , fCanvas(parent->fCanvas) {}
 
     virtual ~SkPdfTokenLooper() {}
 
+    /**
+     *  Consume a token, and draw to fCanvas as directed.
+     */
     virtual SkPdfResult consumeToken(PdfToken& token) = 0;
+
+    /**
+     *  Consume all the tokens this looper can handle.
+     */
     virtual void loop() = 0;
 
-    void setUp(SkPdfTokenLooper* parent) {
-        fParent = parent;
-        fTokenizer = parent->fTokenizer;
-        fPdfContext = parent->fPdfContext;
-        fCanvas = parent->fCanvas;
-    }
+protected:
+    // All are unowned pointers.
+    SkPdfTokenLooper*       fParent;
+    SkPdfNativeTokenizer*   fTokenizer;
+    SkPdfContext*           fPdfContext;
+    SkCanvas*               fCanvas;
 };
 
 #endif // SkPdfTokenLooper_DEFINED