图片复用

Android Bitmap inBitmap 可以复用图片，inBitmap指向缓存图片，c直接返回了inBitmap，配合内存缓存。

源码：http://androidxref.com/5.1.0_r1/xref/frameworks/base/core/jni/android/graphics/BitmapFactory.cpp

#define LOG_TAG "BitmapFactory"
#include "BitmapFactory.h"
#include "NinePatchPeeker.h"
#include "SkFrontBufferedStream.h"
#include "SkImageDecoder.h"
#include "SkMath.h"
#include "SkPixelRef.h"
#include "SkStream.h"
#include "SkTemplates.h"
#include "SkUtils.h"
#include "CreateJavaOutputStreamAdaptor.h"
#include "AutoDecodeCancel.h"
#include "Utils.h"
#include "JNIHelp.h"
#include "GraphicsJNI.h"
#include <android_runtime/AndroidRuntime.h>
#include <androidfw/Asset.h>
#include <androidfw/ResourceTypes.h>
#include <cutils/compiler.h>
#include <netinet/in.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/stat.h>
jfieldID gOptions_justBoundsFieldID;
jfieldID gOptions_sampleSizeFieldID;
jfieldID gOptions_configFieldID;
jfieldID gOptions_premultipliedFieldID;
jfieldID gOptions_mutableFieldID;
jfieldID gOptions_ditherFieldID;
jfieldID gOptions_preferQualityOverSpeedFieldID;
jfieldID gOptions_scaledFieldID;
jfieldID gOptions_densityFieldID;
jfieldID gOptions_screenDensityFieldID;
jfieldID gOptions_targetDensityFieldID;
jfieldID gOptions_widthFieldID;
jfieldID gOptions_heightFieldID;
jfieldID gOptions_mimeFieldID;
jfieldID gOptions_mCancelID;
jfieldID gOptions_bitmapFieldID;
jfieldID gBitmap_nativeBitmapFieldID;
jfieldID gBitmap_ninePatchInsetsFieldID;
jclass gInsetStruct_class;
jmethodID gInsetStruct_constructorMethodID;
using namespace android;
static inline int32_t validOrNeg1(bool isValid, int32_t value) {
//
return isValid ? value : -1;
SkASSERT((int)isValid == 0 || (int)isValid == 1);
return ((int32_t)isValid - 1) | value;
}
jstring getMimeTypeString(JNIEnv* env, SkImageDecoder::Format format) {
static const struct {
SkImageDecoder::Format fFormat;
const char*
fMimeType;
} gMimeTypes[] = {
{ SkImageDecoder::kBMP_Format,
"image/bmp" },
{ SkImageDecoder::kGIF_Format,
"image/gif" },
{ SkImageDecoder::kICO_Format,
"image/x-ico" },
{ SkImageDecoder::kJPEG_Format, "image/jpeg" },
{ SkImageDecoder::kPNG_Format,
"image/png" },
{ SkImageDecoder::kWEBP_Format, "image/webp" },
{ SkImageDecoder::kWBMP_Format, "image/vnd.wap.wbmp" }
};
const char* cstr = NULL;
for (size_t i = 0; i < SK_ARRAY_COUNT(gMimeTypes); i++) {
if (gMimeTypes[i].fFormat == format) {
cstr = gMimeTypes[i].fMimeType;
break;
}
}
jstring jstr = NULL;
if (cstr != NULL) {
// NOTE: Caller should env->ExceptionCheck() for OOM
// (can't check for NULL as it's a valid return value)
jstr = env->NewStringUTF(cstr);
}
return jstr;
}
static bool optionsJustBounds(JNIEnv* env, jobject options) {
return options != NULL && env->GetBooleanField(options, gOptions_justBoundsFieldID);
}
static void scaleDivRange(int32_t* divs, int count, float scale, int maxValue) {
for (int i = 0; i < count; i++) {
divs[i] = int32_t(divs[i] * scale + 0.5f);
if (i > 0 && divs[i] == divs[i - 1]) {
divs[i]++; // avoid collisions
}
}
if (CC_UNLIKELY(divs[count - 1] > maxValue)) {
// if the collision avoidance above put some divs outside the bounds of the bitmap,
// slide outer stretchable divs inward to stay within bounds
int highestAvailable = maxValue;
for (int i = count - 1; i >= 0; i--) {
divs[i] = highestAvailable;
if (i > 0 && divs[i] <= divs[i-1]){
// keep shifting
highestAvailable = divs[i] - 1;
} else {
break;
}
}
}
}
static void scaleNinePatchChunk(android::Res_png_9patch* chunk, float scale,
int scaledWidth, int scaledHeight) {
chunk->paddingLeft = int(chunk->paddingLeft * scale + 0.5f);
chunk->paddingTop = int(chunk->paddingTop * scale + 0.5f);
chunk->paddingRight = int(chunk->paddingRight * scale + 0.5f);
chunk->paddingBottom = int(chunk->paddingBottom * scale + 0.5f);
scaleDivRange(chunk->getXDivs(), chunk->numXDivs, scale, scaledWidth);
scaleDivRange(chunk->getYDivs(), chunk->numYDivs, scale, scaledHeight);
}
static SkColorType colorTypeForScaledOutput(SkColorType colorType) {
switch (colorType) {
case kUnknown_SkColorType:
case kIndex_8_SkColorType:
return kN32_SkColorType;
default:
break;
}
return colorType;
}
class ScaleCheckingAllocator : public SkBitmap::HeapAllocator {
public:
ScaleCheckingAllocator(float scale, int size)
: mScale(scale), mSize(size) {
}
virtual bool allocPixelRef(SkBitmap* bitmap, SkColorTable* ctable) {
// accounts for scale in final allocation, using eventual size and config
const int bytesPerPixel = SkColorTypeBytesPerPixel(
colorTypeForScaledOutput(bitmap->colorType()));
const int requestedSize = bytesPerPixel *
int(bitmap->width() * mScale + 0.5f) *
int(bitmap->height() * mScale + 0.5f);
if (requestedSize > mSize) {
ALOGW("bitmap for alloc reuse (%d bytes) can't fit scaled bitmap (%d bytes)",
mSize, requestedSize);
return false;
}
return SkBitmap::HeapAllocator::allocPixelRef(bitmap, ctable);
}
private:
const float mScale;
const int mSize;
};
class RecyclingPixelAllocator : public SkBitmap::Allocator {
public:
RecyclingPixelAllocator(SkPixelRef* pixelRef, unsigned int size)
: mPixelRef(pixelRef), mSize(size) {
SkSafeRef(mPixelRef);
}
~RecyclingPixelAllocator() {
SkSafeUnref(mPixelRef);
}
virtual bool allocPixelRef(SkBitmap* bitmap, SkColorTable* ctable) {
const SkImageInfo& info = bitmap->info();
if (info.fColorType == kUnknown_SkColorType) {
ALOGW("unable to reuse a bitmap as the target has an unknown bitmap configuration");
return false;
}
const int64_t size64 = info.getSafeSize64(bitmap->rowBytes());
if (!sk_64_isS32(size64)) {
ALOGW("bitmap is too large");
return false;
}
const size_t size = sk_64_asS32(size64);
if (size > mSize) {
ALOGW("bitmap marked for reuse (%d bytes) can't fit new bitmap (%d bytes)",
mSize, size);
return false;
}
// Create a new pixelref with the new ctable that wraps the previous pixelref
SkPixelRef* pr = new AndroidPixelRef(*static_cast<AndroidPixelRef*>(mPixelRef),
info, bitmap->rowBytes(), ctable);
bitmap->setPixelRef(pr)->unref();
// since we're already allocated, we lockPixels right away
// HeapAllocator/JavaPixelAllocator behaves this way too
bitmap->lockPixels();
return true;
}
private:
SkPixelRef* const mPixelRef;
const unsigned int mSize;
};
static jobject doDecode(JNIEnv* env, SkStreamRewindable* stream, jobject padding, jobject options) {
int sampleSize = 1;
SkImageDecoder::Mode decodeMode = SkImageDecoder::kDecodePixels_Mode;
SkColorType prefColorType = kN32_SkColorType;
bool doDither = true;
bool isMutable = false;
float scale = 1.0f;
bool preferQualityOverSpeed = false;
bool requireUnpremultiplied = false;
jobject javaBitmap = NULL;
if (options != NULL) {
sampleSize = env->GetIntField(options, gOptions_sampleSizeFieldID);
if (optionsJustBounds(env, options)) {
decodeMode = SkImageDecoder::kDecodeBounds_Mode;
}
// initialize these, in case we fail later on
env->SetIntField(options, gOptions_widthFieldID, -1);
env->SetIntField(options, gOptions_heightFieldID, -1);
env->SetObjectField(options, gOptions_mimeFieldID, 0);
jobject jconfig = env->GetObjectField(options, gOptions_configFieldID);
prefColorType = GraphicsJNI::getNativeBitmapColorType(env, jconfig);
isMutable = env->GetBooleanField(options, gOptions_mutableFieldID);
doDither = env->GetBooleanField(options, gOptions_ditherFieldID);
preferQualityOverSpeed = env->GetBooleanField(options,
gOptions_preferQualityOverSpeedFieldID);
requireUnpremultiplied = !env->GetBooleanField(options, gOptions_premultipliedFieldID);
javaBitmap = env->GetObjectField(options, gOptions_bitmapFieldID);
if (env->GetBooleanField(options, gOptions_scaledFieldID)) {
const int density = env->GetIntField(options, gOptions_densityFieldID);
const int targetDensity = env->GetIntField(options, gOptions_targetDensityFieldID);
const int screenDensity = env->GetIntField(options, gOptions_screenDensityFieldID);
if (density != 0 && targetDensity != 0 && density != screenDensity) {
scale = (float) targetDensity / density;
}
}
}
const bool willScale = scale != 1.0f;
SkImageDecoder* decoder = SkImageDecoder::Factory(stream);
if (decoder == NULL) {
return nullObjectReturn("SkImageDecoder::Factory returned null");
}
decoder->setSampleSize(sampleSize);
decoder->setDitherImage(doDither);
decoder->setPreferQualityOverSpeed(preferQualityOverSpeed);
decoder->setRequireUnpremultipliedColors(requireUnpremultiplied);
SkBitmap* outputBitmap = NULL;
unsigned int existingBufferSize = 0;
if (javaBitmap != NULL) {
outputBitmap = (SkBitmap*) env->GetLongField(javaBitmap, gBitmap_nativeBitmapFieldID);
if (outputBitmap->isImmutable()) {
ALOGW("Unable to reuse an immutable bitmap as an image decoder target.");
javaBitmap = NULL;
outputBitmap = NULL;
} else {
existingBufferSize = GraphicsJNI::getBitmapAllocationByteCount(env, javaBitmap);
}
}
SkAutoTDelete<SkBitmap> adb(outputBitmap == NULL ? new SkBitmap : NULL);
if (outputBitmap == NULL) outputBitmap = adb.get();
NinePatchPeeker peeker(decoder);
decoder->setPeeker(&peeker);
JavaPixelAllocator javaAllocator(env);
RecyclingPixelAllocator recyclingAllocator(outputBitmap->pixelRef(), existingBufferSize);
ScaleCheckingAllocator scaleCheckingAllocator(scale, existingBufferSize);
SkBitmap::Allocator* outputAllocator = (javaBitmap != NULL) ?
(SkBitmap::Allocator*)&recyclingAllocator : (SkBitmap::Allocator*)&javaAllocator;
if (decodeMode != SkImageDecoder::kDecodeBounds_Mode) {
if (!willScale) {
// If the java allocator is being used to allocate the pixel memory, the decoder
// need not write zeroes, since the memory is initialized to 0.
decoder->setSkipWritingZeroes(outputAllocator == &javaAllocator);
decoder->setAllocator(outputAllocator);
} else if (javaBitmap != NULL) {
// check for eventual scaled bounds at allocation time, so we don't decode the bitmap
// only to find the scaled result too large to fit in the allocation
decoder->setAllocator(&scaleCheckingAllocator);
}
}
// Only setup the decoder to be deleted after its stack-based, refcounted
// components (allocators, peekers, etc) are declared. This prevents RefCnt
// asserts from firing due to the order objects are deleted from the stack.
SkAutoTDelete<SkImageDecoder> add(decoder);
AutoDecoderCancel adc(options, decoder);
// To fix the race condition in case "requestCancelDecode"
// happens earlier than AutoDecoderCancel object is added
// to the gAutoDecoderCancelMutex linked list.
if (options != NULL && env->GetBooleanField(options, gOptions_mCancelID)) {
return nullObjectReturn("gOptions_mCancelID");
}
SkBitmap decodingBitmap;
if (decoder->decode(stream, &decodingBitmap, prefColorType, decodeMode)
!= SkImageDecoder::kSuccess) {
return nullObjectReturn("decoder->decode returned false");
}
int scaledWidth = decodingBitmap.width();
int scaledHeight = decodingBitmap.height();
if (willScale && decodeMode != SkImageDecoder::kDecodeBounds_Mode) {
scaledWidth = int(scaledWidth * scale + 0.5f);
scaledHeight = int(scaledHeight * scale + 0.5f);
}
// update options (if any)
if (options != NULL) {
jstring mimeType = getMimeTypeString(env, decoder->getFormat());
if (env->ExceptionCheck()) {
return nullObjectReturn("OOM in getMimeTypeString()");
}
env->SetIntField(options, gOptions_widthFieldID, scaledWidth);
env->SetIntField(options, gOptions_heightFieldID, scaledHeight);
env->SetObjectField(options, gOptions_mimeFieldID, mimeType);
}
// if we're in justBounds mode, return now (skip the java bitmap)
if (decodeMode == SkImageDecoder::kDecodeBounds_Mode) {
return NULL;
}
jbyteArray ninePatchChunk = NULL;
if (peeker.mPatch != NULL) {
if (willScale) {
scaleNinePatchChunk(peeker.mPatch, scale, scaledWidth, scaledHeight);
}
size_t ninePatchArraySize = peeker.mPatch->serializedSize();
ninePatchChunk = env->NewByteArray(ninePatchArraySize);
if (ninePatchChunk == NULL) {
return nullObjectReturn("ninePatchChunk == null");
}
jbyte* array = (jbyte*) env->GetPrimitiveArrayCritical(ninePatchChunk, NULL);
if (array == NULL) {
return nullObjectReturn("primitive array == null");
}
memcpy(array, peeker.mPatch, peeker.mPatchSize);
env->ReleasePrimitiveArrayCritical(ninePatchChunk, array, 0);
}
jobject ninePatchInsets = NULL;
if (peeker.mHasInsets) {
ninePatchInsets = env->NewObject(gInsetStruct_class, gInsetStruct_constructorMethodID,
peeker.mOpticalInsets[0], peeker.mOpticalInsets[1], peeker.mOpticalInsets[2], peeker.mOpticalInsets[3],
peeker.mOutlineInsets[0], peeker.mOutlineInsets[1], peeker.mOutlineInsets[2], peeker.mOutlineInsets[3],
peeker.mOutlineRadius, peeker.mOutlineAlpha, scale);
if (ninePatchInsets == NULL) {
return nullObjectReturn("nine patch insets == null");
}
if (javaBitmap != NULL) {
env->SetObjectField(javaBitmap, gBitmap_ninePatchInsetsFieldID, ninePatchInsets);
}
}
if (willScale) {
// This is weird so let me explain: we could use the scale parameter
// directly, but for historical reasons this is how the corresponding
// Dalvik code has always behaved. We simply recreate the behavior here.
// The result is slightly different from simply using scale because of
// the 0.5f rounding bias applied when computing the target image size
const float sx = scaledWidth / float(decodingBitmap.width());
const float sy = scaledHeight / float(decodingBitmap.height());
// TODO: avoid copying when scaled size equals decodingBitmap size
SkColorType colorType = colorTypeForScaledOutput(decodingBitmap.colorType());
// FIXME: If the alphaType is kUnpremul and the image has alpha, the
// colors may not be correct, since Skia does not yet support drawing
// to/from unpremultiplied bitmaps.
outputBitmap->setInfo(SkImageInfo::Make(scaledWidth, scaledHeight,
colorType, decodingBitmap.alphaType()));
if (!outputBitmap->allocPixels(outputAllocator, NULL)) {
return nullObjectReturn("allocation failed for scaled bitmap");
}
// If outputBitmap's pixels are newly allocated by Java, there is no need
// to erase to 0, since the pixels were initialized to 0.
if (outputAllocator != &javaAllocator) {
outputBitmap->eraseColor(0);
}
SkPaint paint;
paint.setFilterLevel(SkPaint::kLow_FilterLevel);
SkCanvas canvas(*outputBitmap);
canvas.scale(sx, sy);
canvas.drawBitmap(decodingBitmap, 0.0f, 0.0f, &paint);
} else {
outputBitmap->swap(decodingBitmap);
}
if (padding) {
if (peeker.mPatch != NULL) {
GraphicsJNI::set_jrect(env, padding,
peeker.mPatch->paddingLeft, peeker.mPatch->paddingTop,
peeker.mPatch->paddingRight, peeker.mPatch->paddingBottom);
} else {
GraphicsJNI::set_jrect(env, padding, -1, -1, -1, -1);
}
}
// if we get here, we're in kDecodePixels_Mode and will therefore
// already have a pixelref installed.
if (outputBitmap->pixelRef() == NULL) {
return nullObjectReturn("Got null SkPixelRef");
}
if (!isMutable && javaBitmap == NULL) {
// promise we will never change our pixels (great for sharing and pictures)
outputBitmap->setImmutable();
}
// detach bitmap from its autodeleter, since we want to own it now
adb.detach();
if (javaBitmap != NULL) {
bool isPremultiplied = !requireUnpremultiplied;
GraphicsJNI::reinitBitmap(env, javaBitmap, outputBitmap, isPremultiplied);
outputBitmap->notifyPixelsChanged();
// If a java bitmap was passed in for reuse, pass it back
return javaBitmap;
}
int bitmapCreateFlags = 0x0;
if (isMutable) bitmapCreateFlags |= GraphicsJNI::kBitmapCreateFlag_Mutable;
if (!requireUnpremultiplied) bitmapCreateFlags |= GraphicsJNI::kBitmapCreateFlag_Premultiplied;
// now create the java bitmap
return GraphicsJNI::createBitmap(env, outputBitmap, javaAllocator.getStorageObj(),
bitmapCreateFlags, ninePatchChunk, ninePatchInsets, -1);
}
// Need to buffer enough input to be able to rewind as much as might be read by a decoder
// trying to determine the stream's format. Currently the most is 64, read by
// SkImageDecoder_libwebp.
// FIXME: Get this number from SkImageDecoder
#define BYTES_TO_BUFFER 64
static jobject nativeDecodeStream(JNIEnv* env, jobject clazz, jobject is, jbyteArray storage,
jobject padding, jobject options) {
jobject bitmap = NULL;
SkAutoTUnref<SkStream> stream(CreateJavaInputStreamAdaptor(env, is, storage));
if (stream.get()) {
SkAutoTUnref<SkStreamRewindable> bufferedStream(
SkFrontBufferedStream::Create(stream, BYTES_TO_BUFFER));
SkASSERT(bufferedStream.get() != NULL);
bitmap = doDecode(env, bufferedStream, padding, options);
}
return bitmap;
}
static jobject nativeDecodeFileDescriptor(JNIEnv* env, jobject clazz, jobject fileDescriptor,
jobject padding, jobject bitmapFactoryOptions) {
NPE_CHECK_RETURN_ZERO(env, fileDescriptor);
int descriptor = jniGetFDFromFileDescriptor(env, fileDescriptor);
struct stat fdStat;
if (fstat(descriptor, &fdStat) == -1) {
doThrowIOE(env, "broken file descriptor");
return nullObjectReturn("fstat return -1");
}
// Restore the descriptor's offset on exiting this function. Even though
// we dup the descriptor, both the original and dup refer to the same open
// file description and changes to the file offset in one impact the other.
AutoFDSeek autoRestore(descriptor);
// Duplicate the descriptor here to prevent leaking memory. A leak occurs
// if we only close the file descriptor and not the file object it is used to
// create.
If we don't explicitly clean up the file (which in turn closes the
// descriptor) the buffers allocated internally by fseek will be leaked.
int dupDescriptor = dup(descriptor);
FILE* file = fdopen(dupDescriptor, "r");
if (file == NULL) {
// cleanup the duplicated descriptor since it will not be closed when the
// file is cleaned up (fclose).
close(dupDescriptor);
return nullObjectReturn("Could not open file");
}
SkAutoTUnref<SkFILEStream> fileStream(new SkFILEStream(file,
SkFILEStream::kCallerPasses_Ownership));
// Use a buffered stream. Although an SkFILEStream can be rewound, this
// ensures that SkImageDecoder::Factory never rewinds beyond the
// current position of the file descriptor.
SkAutoTUnref<SkStreamRewindable> stream(SkFrontBufferedStream::Create(fileStream,
BYTES_TO_BUFFER));
return doDecode(env, stream, padding, bitmapFactoryOptions);
}
static jobject nativeDecodeAsset(JNIEnv* env, jobject clazz, jlong native_asset,
jobject padding, jobject options) {
Asset* asset = reinterpret_cast<Asset*>(native_asset);
// since we know we'll be done with the asset when we return, we can
// just use a simple wrapper
SkAutoTUnref<SkStreamRewindable> stream(new AssetStreamAdaptor(asset,
AssetStreamAdaptor::kNo_OwnAsset, AssetStreamAdaptor::kNo_HasMemoryBase));
return doDecode(env, stream, padding, options);
}
static jobject nativeDecodeByteArray(JNIEnv* env, jobject, jbyteArray byteArray,
jint offset, jint length, jobject options) {
AutoJavaByteArray ar(env, byteArray);
SkMemoryStream* stream = new SkMemoryStream(ar.ptr() + offset, length, false);
SkAutoUnref aur(stream);
return doDecode(env, stream, NULL, options);
}
static void nativeRequestCancel(JNIEnv*, jobject joptions) {
(void)AutoDecoderCancel::RequestCancel(joptions);
}
static jboolean nativeIsSeekable(JNIEnv* env, jobject, jobject fileDescriptor) {
jint descriptor = jniGetFDFromFileDescriptor(env, fileDescriptor);
return ::lseek64(descriptor, 0, SEEK_CUR) != -1 ? JNI_TRUE : JNI_FALSE;
}
///
static JNINativeMethod gMethods[] = {
{
"nativeDecodeStream",
"(Ljava/io/InputStream;[BLandroid/graphics/Rect;Landroid/graphics/BitmapFactory$Options;)Landroid/graphics/Bitmap;",
(void*)nativeDecodeStream
},
{
"nativeDecodeFileDescriptor",
"(Ljava/io/FileDescriptor;Landroid/graphics/Rect;Landroid/graphics/BitmapFactory$Options;)Landroid/graphics/Bitmap;",
(void*)nativeDecodeFileDescriptor
},
{
"nativeDecodeAsset",
"(JLandroid/graphics/Rect;Landroid/graphics/BitmapFactory$Options;)Landroid/graphics/Bitmap;",
(void*)nativeDecodeAsset
},
{
"nativeDecodeByteArray",
"([BIILandroid/graphics/BitmapFactory$Options;)Landroid/graphics/Bitmap;",
(void*)nativeDecodeByteArray
},
{
"nativeIsSeekable",
"(Ljava/io/FileDescriptor;)Z",
(void*)nativeIsSeekable
},
};
static JNINativeMethod gOptionsMethods[] = {
{
"requestCancel", "()V", (void*)nativeRequestCancel }
};
static jfieldID getFieldIDCheck(JNIEnv* env, jclass clazz,
const char fieldname[], const char type[]) {
jfieldID id = env->GetFieldID(clazz, fieldname, type);
SkASSERT(id);
return id;
}
int register_android_graphics_BitmapFactory(JNIEnv* env) {
jclass options_class = env->FindClass("android/graphics/BitmapFactory$Options");
SkASSERT(options_class);
gOptions_bitmapFieldID = getFieldIDCheck(env, options_class, "inBitmap",
"Landroid/graphics/Bitmap;");
gOptions_justBoundsFieldID = getFieldIDCheck(env, options_class, "inJustDecodeBounds", "Z");
gOptions_sampleSizeFieldID = getFieldIDCheck(env, options_class, "inSampleSize", "I");
gOptions_configFieldID = getFieldIDCheck(env, options_class, "inPreferredConfig",
"Landroid/graphics/Bitmap$Config;");
gOptions_premultipliedFieldID = getFieldIDCheck(env, options_class, "inPremultiplied", "Z");
gOptions_mutableFieldID = getFieldIDCheck(env, options_class, "inMutable", "Z");
gOptions_ditherFieldID = getFieldIDCheck(env, options_class, "inDither", "Z");
gOptions_preferQualityOverSpeedFieldID = getFieldIDCheck(env, options_class,
"inPreferQualityOverSpeed", "Z");
gOptions_scaledFieldID = getFieldIDCheck(env, options_class, "inScaled", "Z");
gOptions_densityFieldID = getFieldIDCheck(env, options_class, "inDensity", "I");
gOptions_screenDensityFieldID = getFieldIDCheck(env, options_class, "inScreenDensity", "I");
gOptions_targetDensityFieldID = getFieldIDCheck(env, options_class, "inTargetDensity", "I");
gOptions_widthFieldID = getFieldIDCheck(env, options_class, "outWidth", "I");
gOptions_heightFieldID = getFieldIDCheck(env, options_class, "outHeight", "I");
gOptions_mimeFieldID = getFieldIDCheck(env, options_class, "outMimeType", "Ljava/lang/String;");
gOptions_mCancelID = getFieldIDCheck(env, options_class, "mCancel", "Z");
jclass bitmap_class = env->FindClass("android/graphics/Bitmap");
SkASSERT(bitmap_class);
gBitmap_nativeBitmapFieldID = getFieldIDCheck(env, bitmap_class, "mNativeBitmap", "J");
gBitmap_ninePatchInsetsFieldID = getFieldIDCheck(env, bitmap_class, "mNinePatchInsets",
"Landroid/graphics/NinePatch$InsetStruct;");
gInsetStruct_class = (jclass) env->NewGlobalRef(env->FindClass("android/graphics/NinePatch$InsetStruct"));
gInsetStruct_constructorMethodID = env->GetMethodID(gInsetStruct_class, "<init>", "(IIIIIIIIFIF)V");
int ret = AndroidRuntime::registerNativeMethods(env,
"android/graphics/BitmapFactory$Options",
gOptionsMethods,
SK_ARRAY_COUNT(gOptionsMethods));
if (ret) {
return ret;
}
return android::AndroidRuntime::registerNativeMethods(env, "android/graphics/BitmapFactory",
gMethods, SK_ARRAY_COUNT(gMethods));
}

主要就是指的复用内存块，不需要在重新给这个bitmap申请一块新的内存,避免了一次内存的分配和回收，从而改善了运行效率。
需要注意的是inBitmap只能在3.0以后使用。2.3上，bitmap的数据是存储在native的内存区域，并不是在Dalvik的内存堆上。
使用inBitmap，在4.4之前，只能重用相同大小的bitmap的内存区域，而4.4之后你可以重用任何bitmap的内存区域，只要这块内存比将要分配内存的bitmap大就可以。这里最好的方法就是使用LRUCache来缓存bitmap，后面来了新的bitmap，可以从cache中按照api版本找到最适合重用的bitmap，来重用它的内存区域。
Google官方文档已经给出了一个非常棒的教程Managing Bitmap Memory
Google官方文档的 Displaying Bitmaps Efficiently 绝对帮你精通bitmap的操作

点9图的使用

为了适配不同的分辨率，首先考虑用 XML 实现。不能用 XML 轻松的写出来的时候就用一套至少包含 hdpi 到 xxxdpi 的素材；需要拉伸的时候就要 .9，.9 也要做到每个 DPI 各一套。

服务端动态返回的图片尺寸处理方法

静态资源一般通过准备多份图片文件(hdpi mdpi ldpi等)来适应不同分辨率,如果在应用中有动态图片资源要处理,一般在服务端返回统一尺寸图片,然后在客户端缩放;也可以由客户端传递宽高，由服务端裁剪。

最后

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