Creating functions for uploading a mipmapped texture.

src/core/SkMipMapLevel.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#include "SkMath.h"
+#include "SkMipMapLevel.h"
+#include "SkTypes.h"
+
+SkMipMapLevel::SkMipMapLevel(const void* texelsOrOffset, size_t rowBytes, int width, int height)
+    : fTexelsOrOffset(texelsOrOffset)
+    , fRowBytes(rowBytes)
+    , fWidth(width)
+    , fHeight(height)
+{
+}
+
+SkMipMapLevel::SkMipMapLevel(SkMipMapLevel&& rhs)
+    : fTexelsOrOffset(rhs.fTexelsOrOffset)
+    , fRowBytes(rhs.fRowBytes)
+    , fWidth(rhs.fWidth)
+    , fHeight(rhs.fHeight)
+{
+    rhs.fTexelsOrOffset = nullptr;
+    rhs.fRowBytes = 0;
+    rhs.fWidth = 0;
+    rhs.fHeight = 0;
+}
+
+SkMipMapLevel& SkMipMapLevel::operator =(SkMipMapLevel&& rhs) {
+    fTexelsOrOffset = rhs.fTexelsOrOffset;
+    fRowBytes = rhs.fRowBytes;
+    fWidth = rhs.fWidth;
+    fHeight = rhs.fHeight;
+
+    rhs.fTexelsOrOffset = nullptr;
+    rhs.fRowBytes = 0;
+    rhs.fWidth = 0;
+    rhs.fHeight = 0;
+
+    return *this;
+}
+
+int SkMipMapLevelCount(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;
+}