add extractSubset and SkAutoPixmapStorage

src/core/SkPixmap.cpp

Index: src/core/SkPixmap.cpp
diff --git a/src/core/SkPixmap.cpp b/src/core/SkPixmap.cpp
index 3a0fad2a3936763cbd24f01da041d8be04bb2b55..9b7f993792dca69adf90a52fd716819198e3fea7 100644
--- a/src/core/SkPixmap.cpp
+++ b/src/core/SkPixmap.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "SkConfig8888.h"
+#include "SkMask.h"
 #include "SkPixmap.h"
 
 void SkAutoPixmapUnlock::reset(const SkPixmap& pm, void (*unlock)(void*), void* ctx) {
@@ -37,6 +38,37 @@ void SkPixmap::reset(const SkImageInfo& info, const void* addr, size_t rowBytes,
     fInfo = info;
 }
 
+bool SkPixmap::reset(const SkMask& src) {
+    if (SkMask::kA8_Format == src.fFormat) {
+        this->reset(SkImageInfo::MakeA8(src.fBounds.width(), src.fBounds.height()),
+                    src.fImage, src.fRowBytes, NULL);
+        return true;
+    }
+    this->reset();
+    return false;
+}
+
+bool SkPixmap::extractSubset(SkPixmap* result, const SkIRect& subset) const {
+    SkIRect srcRect, r;
+    srcRect.set(0, 0, this->width(), this->height());
+    if (!r.intersect(srcRect, subset)) {
+        return false;   // r is empty (i.e. no intersection)
+    }
+    
+    // If the upper left of the rectangle was outside the bounds of this SkBitmap, we should have
+    // exited above.
+    SkASSERT(static_cast<unsigned>(r.fLeft) < static_cast<unsigned>(this->width()));
+    SkASSERT(static_cast<unsigned>(r.fTop) < static_cast<unsigned>(this->height()));
+
+    const void* pixels = NULL;
+    if (fPixels) {
+        const size_t bpp = fInfo.bytesPerPixel();
+        pixels = (const uint8_t*)fPixels + r.fTop * fRowBytes + r.fLeft * bpp;
+    }
+    result->reset(fInfo.makeWH(r.width(), r.height()), pixels, fRowBytes, fCTable);
+    return true;
+}
+
 bool SkPixmap::readPixels(const SkImageInfo& requestedDstInfo, void* dstPixels, size_t dstRB,
                           int x, int y) const {
     if (kUnknown_SkColorType == requestedDstInfo.colorType()) {
@@ -72,3 +104,36 @@ bool SkPixmap::readPixels(const SkImageInfo& requestedDstInfo, void* dstPixels,
     return SkPixelInfo::CopyPixels(dstInfo, dstPixels, dstRB,
                                    srcInfo, srcPixels, this->rowBytes(), this->ctable());
 }
+
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
+SkAutoPixmapStorage::SkAutoPixmapStorage() : fStorage(NULL) {}
+
+SkAutoPixmapStorage::~SkAutoPixmapStorage() {
+    sk_free(fStorage);
+}
+
+bool SkAutoPixmapStorage::tryAlloc(const SkImageInfo& info) {
+    if (fStorage) {
+        sk_free(fStorage);
+        fStorage = NULL;
+    }
+    
+    size_t rb = info.minRowBytes();
+    size_t size = info.getSafeSize(rb);
+    if (0 == size) {
+        return false;
+    }
+    fStorage = sk_malloc_flags(size, 0);
+    if (NULL == fStorage) {
+        return false;
+    }
+    this->reset(info, fStorage, rb);
+    return true;
+}
+
+void SkAutoPixmapStorage::alloc(const SkImageInfo& info) {
+    if (!this->tryAlloc(info)) {
+        sk_throw();
+    }
+}