fix state machine so we know simple only loops once, but we can call maprect in debug mode

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"
+
+/**
+ *  Helper class to manage "tiling" are large coordinate space into managable

[tomhudson, 2013/08/28 14:27:50]

Nit: are?

[reed1, 2013/08/28 14:38:33]

Done.

+ *  chunks, where managable means areas that are <= some max critical coordinate
+ *  size.
+ *
+ *  The constructor takes an antialiasing bool, which affects what this maximum
+ *  allowable size is: If we're drawing BW, then we need coordinates to stay
+ *  safely within fixed-point range (we use +- 16K, to give ourselves room to
+ *  add/subtract two fixed values and still be in range. If we're drawing AA,
+ *  then we reduce that size by the amount that the supersampler scan converter
+ *  needs (at the moment, that is 4X, so the effect "safe" range is +- 4K).

[tomhudson, 2013/08/28 14:27:50]

Nit: effect -> effective
Or just drop that word, and the quotes around safe.

[reed1, 2013/08/28 14:38:33]

Done.

+ *
+ *  For performance reasons, the class first checks to see if any help is needed
+ *  at all, and if not (i.e. the specified bounds and base bitmap area already
+ *  in the safe-zone, then the class does nothing (effectively).
+ */
+class SkDeviceLooper {
+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();

[tomhudson, 2013/08/28 14:27:50]

Even after reading the code I don't know what the return value of this function
means or how I should use it.

[reed1, 2013/08/28 14:38:33]

Same as all of skia's interators that just use a next() method. But I definitely
need to document it.

+
+private:
+    const SkBitmap&     fBaseBitmap;
+    const SkRasterClip& fBaseRC;
+
+    enum State {
+        kDone_State,    // iteration is complete, getters will assert
+        kPreSimple_State,  // no translate/clip mods needed
+        kPostSimple_State,
+        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