Adding direct access to SkMipMap levels.

src/core/SkMipMap.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMipMap.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
+#include "SkMath.h"
 #include "SkNx.h"
+#include "SkTypes.h"
 
 //
 // ColorTypeFilter is the "Type" we pass to some downsample template functions.
 // It controls how we expand a pixel into a large type, with space between each component,
 // so we can then perform our simple filter (either box or triangle) and store the intermediates
 // in the expanded type.
 //
 
 struct ColorTypeFilter_8888 {
     typedef uint32_t Type;
@@ skipping 343 matching lines @@
         return nullptr;
     }
     const SkPixmap& srcPixmap = srcUnlocker.pixmap();
     // Try to catch where we might have returned nullptr for src crbug.com/492818
     if (nullptr == srcPixmap.addr()) {
         sk_throw();
     }
     return Build(srcPixmap, fact);
 }
 
+int SkMipMap::countLevels() const {
+    return fCount;
+}
+
+void SkMipMap::getLevel(int index, Level* levelPtr) const {
+    if (NULL == fLevels) {
+        return;
+    }
+    if (index < 0) {
+        return;
+    }
+    if (index > fCount - 1) {
+        return;
+    }
+    if (levelPtr) {
+        *levelPtr = fLevels[index];
+    }
+}
+
+int SkGetMipMapLevelCount(int baseWidth, int baseHeight) {
+    // OpenGL's spec requires that each mipmap level have height/width equal to
+    // max(1, floor(original_height / 2^i)
+    // (or original_width) where i is the mipmap level.
+    // Continue scaling down until both axes are size 1.
+
+    const int largestAxis = SkTMax(baseWidth, baseHeight);
+    if (largestAxis < 0) {
+        return 0;
+    }
+    const int leadingZeros = SkCLZ(static_cast<uint32_t>(largestAxis));
+    // If the value 00011010 has 3 leading 0s then it has 5 significant bits
+    // (the bits which are not leading zeros)
+    const int significantBits = (sizeof(uint32_t) * 8) - leadingZeros;
+    // This is making the assumption that the size of a byte is 8 bits
+    // and that sizeof(uint32_t)'s implementation-defined behavior is 4.
+    const int mipLevelCount = significantBits;
+
+    return mipLevelCount;
+}