add SkDeviceLooper to handle larger-than-fixedpoint

src/core/SkDeviceLooper.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 SkDeviceLooper_DEFINED
+#define SkDeviceLooper_DEFINED
+
+#include "SkBitmap.h"
+#include "SkMatrix.h"
+#include "SkRasterClip.h"
+
+class SkDeviceLooper {

[tomhudson, 2013/08/28 10:53:05]

Since this has state that changes the class semantics, can we get a little
documentation here about the lifecycle?

[reed1, 2013/08/28 12:35:07]

Yes indeed, I will add dox.

+public:
+    SkDeviceLooper(const SkBitmap& base, const SkRasterClip&,
+                   const SkIRect& bounds, bool aa);
+    ~SkDeviceLooper();
+
+    const SkBitmap& getBitmap() const {
+        SkASSERT(kDone_State != fState);
+        return *fCurrBitmap;
+    }
+
+    const SkRasterClip& getRC() const {
+        SkASSERT(kDone_State != fState);
+        return *fCurrRC;
+    }
+
+    void mapRect(SkRect* dst, const SkRect& src) const;
+    void mapMatrix(SkMatrix* dst, const SkMatrix& src) const;
+
+    bool next();
+
+private:
+    const SkBitmap&     fBaseBitmap;
+    const SkRasterClip& fBaseRC;
+
+    enum State {
+        kDone_State,    // iteration is complete, getters will assert
+        kSimple_State,  // no translate/clip mods needed
+        kComplex_State
+    };
+
+    // storage for our tiled versions. Perhaps could use SkTLazy
+    SkBitmap            fSubsetBitmap;
+    SkRasterClip        fSubsetRC;
+
+    const SkBitmap*     fCurrBitmap;
+    const SkRasterClip* fCurrRC;
+    SkIRect             fClippedBounds;
+    SkIPoint            fCurrOffset;
+    int                 fDelta;
+    State               fState;
+
+    enum Delta {
+        kBW_Delta = 1 << 14,        // 16K, gives room to spare for fixedpoint
+        kAA_Delta = kBW_Delta >> 2  // supersample 4x
+    };
+
+    bool fitsInDelta(const SkIRect& r) const {
+        return r.right() < fDelta && r.bottom() < fDelta;
+    }
+    
+    bool computeCurrBitmapAndClip();
+};
+
+#endif