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Unified Diff: src/core/SkMipMap.cpp

Issue 1639693002: Adding direct access to SkMipMap levels. (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Removing comparisons of ComputeLevelCoutn and Build's level coutn, since that comparison is already… Created 4 years, 10 months ago
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Index: src/core/SkMipMap.cpp
diff --git a/src/core/SkMipMap.cpp b/src/core/SkMipMap.cpp
index 7266dc6b21192c16019c0277ea4387244033d209..f3c152124dd2f0284435a52b6a049f9890308ef3 100644
--- a/src/core/SkMipMap.cpp
+++ b/src/core/SkMipMap.cpp
@@ -8,7 +8,9 @@
#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.
@@ -249,6 +251,8 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
return nullptr;
}
+ SkASSERT(countLevels == SkMipMap::ComputeLevelCount(src.width(), src.height()));
+
size_t storageSize = SkMipMap::AllocLevelsSize(countLevels, size);
if (0 == storageSize) {
return nullptr;
@@ -318,6 +322,46 @@ SkMipMap* SkMipMap::Build(const SkPixmap& src, SkDiscardableFactoryProc fact) {
return mipmap;
}
+int SkMipMap::ComputeLevelCount(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.
+ //
+ // This means it maintains isotropic space (both axes scaling down
+ // at the same rate) until one axis hits size 1.
+ // At that point, OpenGL continues to scale down into anisotropic space
+ // (where the scales are not the same between axes).
+ //
+ // Skia currently does not go into anisotropic space.
+ // Once an axis hits size 1 we stop.
+ // All this means is rather than use the largest axis we will use the
+ // smallest axis.
+
+ const int smallestAxis = SkTMin(baseWidth, baseHeight);
+ if (smallestAxis < 2) {
+ // SkMipMap::Build requires a minimum size of 2.
+ return 0;
+ }
+ const int leadingZeros = SkCLZ(static_cast<uint32_t>(smallestAxis));
+ // 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.
+ int mipLevelCount = significantBits;
+
+ // SkMipMap does not include the base mip level.
+ // For example, it contains levels 1-x instead of 0-x.
+ // This is because the image used to create SkMipMap is the base level.
+ // So subtract 1 from the mip level count.
+ if (mipLevelCount > 0) {
+ --mipLevelCount;
+ }
+
+ return mipLevelCount;
+}
+
///////////////////////////////////////////////////////////////////////////////
bool SkMipMap::extractLevel(const SkSize& scaleSize, Level* levelPtr) const {
@@ -371,3 +415,22 @@ SkMipMap* SkMipMap::Build(const SkBitmap& src, SkDiscardableFactoryProc fact) {
return Build(srcPixmap, fact);
}
+int SkMipMap::countLevels() const {
+ return fCount;
+}
+
+bool SkMipMap::getLevel(int index, Level* levelPtr) const {
+ if (NULL == fLevels) {
+ return false;
+ }
+ if (index < 0) {
+ return false;
+ }
+ if (index > fCount - 1) {
+ return false;
+ }
+ if (levelPtr) {
+ *levelPtr = fLevels[index];
+ }
+ return true;
+}
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