深入理解Android Bitmap

// /home/yuxiang/repo_aosp/android-6.0.1_r79/frameworks/base/core/jni/android/graphics/Bitmap.cpp
static jobject Bitmap_creator(JNIEnv* env, jobject, jintArray jColors,
    jint offset, jint stride, jint width, jint height,
    jint configHandle, jboolean isMutable) {
 SkColorType colorType = GraphicsJNI::legacyBitmapConfigToColorType(configHandle);
 if (NULL != jColors) {
 size_t n = env->GetArrayLength(jColors);
 if (n < SkAbs32(stride) * (size_t)height) {
  doThrowAIOOBE(env);
  return NULL;
 }
 }
 // ARGB_4444 is a deprecated format, convert automatically to 8888
 if (colorType == kARGB_4444_SkColorType) {
 colorType = kN32_SkColorType;
 }
 SkBitmap bitmap;
 bitmap.setInfo(SkImageInfo::Make(width, height, colorType, kPremul_SkAlphaType));
 Bitmap* nativeBitmap = GraphicsJNI::allocateJavaPixelRef(env, &bitmap, NULL);
 if (!nativeBitmap) {
 return NULL;
 }
 if (jColors != NULL) {
 GraphicsJNI::SetPixels(env, jColors, offset, stride,
  0, 0, width, height, bitmap);
 }
 return GraphicsJNI::createBitmap(env, nativeBitmap,
  getPremulBitmapCreateFlags(isMutable));
}

// /home/yuxiang/repo_aosp/android-6.0.1_r79/external/skia/include/core/SkImageInfo.h
enum SkColorType {
 kUnknown_SkColorType,
 kAlpha_8_SkColorType,
 kRGB_565_SkColorType,
 kARGB_4444_SkColorType,
 kRGBA_8888_SkColorType,
 kBGRA_8888_SkColorType,
 kIndex_8_SkColorType,
 kGray_8_SkColorType,
 kLastEnum_SkColorType = kGray_8_SkColorType,
#if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
 kN32_SkColorType = kBGRA_8888_SkColorType,
#elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)
 kN32_SkColorType = kRGBA_8888_SkColorType,
#else
 #error "SK_*32_SHFIT values must correspond to BGRA or RGBA byte order"
#endif
};

public:
 SkImageInfo()
 : fWidth(0)
 , fHeight(0)
 , fColorType(kUnknown_SkColorType)
 , fAlphaType(kUnknown_SkAlphaType)
 , fProfileType(kLinear_SkColorProfileType)
 {}
 static SkImageInfo Make(int width, int height, SkColorType ct, SkAlphaType at,
    SkColorProfileType pt = kLinear_SkColorProfileType) {
 return SkImageInfo(width, height, ct, at, pt);
 }

int register_android_graphics_Graphics(JNIEnv* env)
{
 jmethodID m;
 jclass c;
 ...
 gVMRuntime = env->NewGlobalRef(env->CallStaticObjectMethod(gVMRuntime_class, m));
 gVMRuntime_newNonMovableArray = env->GetMethodID(gVMRuntime_class, "newNonMovableArray",
       "(Ljava/lang/Class;I)Ljava/lang/Object;");
 ...
}
env->CallObjectMethod(gVMRuntime, gVMRuntime_newNonMovableArray, gByte_class, size) 拿到虚拟机分配Heap对象， env->CallLongMethod(gVMRuntime, gVMRuntime_addressOf, arrayObj) 拿到分配对象的地址，调用 native 层构造函数 new android::Bitmap(env, arrayObj, (void*) addr, info, rowBytes, ctable)
// /home/yuxiang/repo_aosp/android-6.0.1_r79/frameworks/base/core/jni/android/graphics/Bitmap.cpp
Bitmap::Bitmap(JNIEnv* env, jbyteArray storageObj, void* address,
  const SkImageInfo& info, size_t rowBytes, SkColorTable* ctable)
 : mPixelStorageType(PixelStorageType::Java) {
 env->GetJavaVM(&mPixelStorage.java.jvm);
 mPixelStorage.java.jweakRef = env->NewWeakGlobalRef(storageObj);
 mPixelStorage.java.jstrongRef = nullptr;
 mPixelRef.reset(new WrappedPixelRef(this, address, info, rowBytes, ctable));
 // Note: this will trigger a call to onStrongRefDestroyed(), but
 // we want the pixel ref to have a ref count of 0 at this point
 mPixelRef->unref();
}
void Bitmap::getSkBitmap(SkBitmap* outBitmap) {
 assertValid();
 android::AutoMutex _lock(mLock);
 // Safe because mPixelRef is a WrappedPixelRef type, otherwise rowBytes()
 // would require locking the pixels first.
 outBitmap->setInfo(mPixelRef->info(), mPixelRef->rowBytes());
 outBitmap->setPixelRef(refPixelRefLocked())->unref();
 outBitmap->setHasHardwareMipMap(hasHardwareMipMap());
}
void Bitmap::pinPixelsLocked() {
 switch (mPixelStorageType) {
 case PixelStorageType::Invalid:
 LOG_ALWAYS_FATAL("Cannot pin invalid pixels!");
 break;
 case PixelStorageType::External:
 case PixelStorageType::Ashmem:
 // Nothing to do
 break;
 case PixelStorageType::Java: {
 JNIEnv* env = jniEnv();
 if (!mPixelStorage.java.jstrongRef) {
  mPixelStorage.java.jstrongRef = reinterpret_cast<jbyteArray>(
   env->NewGlobalRef(mPixelStorage.java.jweakRef));
  if (!mPixelStorage.java.jstrongRef) {
  LOG_ALWAYS_FATAL("Failed to acquire strong reference to pixels");
  }
 }
 break;
 }
 }
}
// /home/yuxiang/repo_aosp/android-6.0.1_r79/frameworks/base/core/jni/android/graphics/Bitmap.h
std::unique_ptr<WrappedPixelRef> mPixelRef;
PixelStorageType mPixelStorageType;
union {
 struct {
 void* address;
 void* context;
 FreeFunc freeFunc;
 } external;
 struct {
 void* address;
 int fd;
 size_t size;
 } ashmem;
 struct {
 JavaVM* jvm;
 jweak jweakRef;
 jbyteArray jstrongRef;
 } java;
} mPixelStorage;

// /home/yuxiang/repo_aosp/android-6.0.1_r79/frameworks/base/core/jni/android/graphics/Bitmap.cpp
jobject GraphicsJNI::createBitmap(JNIEnv* env, android::Bitmap* bitmap,
 int bitmapCreateFlags, jbyteArray ninePatchChunk, jobject ninePatchInsets,
 int density) {
 bool isMutable = bitmapCreateFlags & kBitmapCreateFlag_Mutable;
 bool isPremultiplied = bitmapCreateFlags & kBitmapCreateFlag_Premultiplied;
 // The caller needs to have already set the alpha type properly, so the
 // native SkBitmap stays in sync with the Java Bitmap.
 assert_premultiplied(bitmap->info(), isPremultiplied);

 jobject obj = env->NewObject(gBitmap_class, gBitmap_constructorMethodID,
  reinterpret_cast<jlong>(bitmap), bitmap->javaByteArray(),
  bitmap->width(), bitmap->height(), density, isMutable, isPremultiplied,
  ninePatchChunk, ninePatchInsets);
 hasException(env); // For the side effect of logging.
 return obj;
}

// /home/yuxiang/repo_aosp/android-6.0.1_r79/frameworks/base/core/jni/android/graphics/Bitmap.cpp
void Bitmap::freePixels() {
 AutoMutex _lock(mLock);
 if (mPinnedRefCount == 0) {
 doFreePixels();
 mPixelStorageType = PixelStorageType::Invalid;
 }
}
void Bitmap::doFreePixels() {
 switch (mPixelStorageType) {
 case PixelStorageType::Invalid:
 // already free'd, nothing to do
 break;
 case PixelStorageType::External:
 mPixelStorage.external.freeFunc(mPixelStorage.external.address,
  mPixelStorage.external.context);
 break;
 case PixelStorageType::Ashmem:
 munmap(mPixelStorage.ashmem.address, mPixelStorage.ashmem.size);
 close(mPixelStorage.ashmem.fd);
 break;
 case PixelStorageType::Java:
 JNIEnv* env = jniEnv();
 LOG_ALWAYS_FATAL_IF(mPixelStorage.java.jstrongRef,
  "Deleting a bitmap wrapper while there are outstanding strong "
  "references! mPinnedRefCount = %d", mPinnedRefCount);
 env->DeleteWeakGlobalRef(mPixelStorage.java.jweakRef);
 break;
 }
 if (android::uirenderer::Caches::hasInstance()) {
 android::uirenderer::Caches::getInstance().textureCache.releaseTexture(
  mPixelRef->getStableID());
 }
}

// /home/yuxiang/repo_aosp/android-6.0.1_r79/art/runtime/jni_internal.cc
static void DeleteWeakGlobalRef(JNIEnv* env, jweak obj) {
 JavaVMExt* vm = down_cast<JNIEnvExt*>(env)->vm;
 Thread* self = down_cast<JNIEnvExt*>(env)->self;
 vm->DeleteWeakGlobalRef(self, obj);
}
// /home/yuxiang/repo_aosp/android-6.0.1_r79/art/runtime/java_vm_ext.cc
void JavaVMExt::DeleteWeakGlobalRef(Thread* self, jweak obj) {
 if (obj == nullptr) {
 return;
 }
 MutexLock mu(self, weak_globals_lock_);
 if (!weak_globals_.Remove(IRT_FIRST_SEGMENT, obj)) {
 LOG(WARNING) << "JNI WARNING: DeleteWeakGlobalRef(" << obj << ") "
   << "failed to find entry";
 }
}

// BitmapFactory.java
private static native Bitmap nativeDecodeStream(InputStream is, byte[] storage, Rect padding, Options opts);
private static native Bitmap nativeDecodeFileDescriptor(FileDescriptor fd, Rect padding, Options opts);
private static native Bitmap nativeDecodeAsset(long nativeAsset, Rect padding, Options opts);
private static native Bitmap nativeDecodeByteArray(byte[] data, int offset, int length, Options opts);
private static native boolean nativeIsSeekable(FileDescriptor fd);

// BitmapFactory.cpp
static jobject nativeDecodeStream(JNIEnv* env, jobject clazz, jobject is, jbyteArray storage,
 jobject padding, jobject options) {
 jobject bitmap = NULL;
 SkAutoTDelete<SkStream> stream(CreateJavaInputStreamAdaptor(env, is, storage));
 if (stream.get()) {
 SkAutoTDelete<SkStreamRewindable> bufferedStream(
  SkFrontBufferedStream::Create(stream.detach(), BYTES_TO_BUFFER));
 SkASSERT(bufferedStream.get() != NULL);
 bitmap = doDecode(env, bufferedStream, padding, options);
 }
 return bitmap;
}

// BitmapFactory.cpp
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;
  }
 }
 ...
}

// BitmapFactory.cpp
static jobject doDecode(JNIEnv* env, SkStreamRewindable* stream, jobject padding, jobject options) {
 ...
 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)
 ...
}
// SkImageDecoder_FactoryDefault.cpp
SkImageDecoder* SkImageDecoder::Factory(SkStreamRewindable* stream) {
 return image_decoder_from_stream(stream);
}
// SkImageDecoder_FactoryRegistrar.cpp
SkImageDecoder* image_decoder_from_stream(SkStreamRewindable* stream) {
 SkImageDecoder* codec = NULL;
 const SkImageDecoder_DecodeReg* curr = SkImageDecoder_DecodeReg::Head();
 while (curr) {
 codec = curr->factory()(stream);
 // we rewind here, because we promise later when we call "decode", that
 // the stream will be at its beginning.
 bool rewindSuceeded = stream->rewind();
 // our image decoder's require that rewind is supported so we fail early
 // if we are given a stream that does not support rewinding.
 if (!rewindSuceeded) {
  SkDEBUGF(("Unable to rewind the image stream."));
  SkDELETE(codec);
  return NULL;
 }
 if (codec) {
  return codec;
 }
 curr = curr->next();
 }
 return NULL;
}
// SkImageDecoder.cpp
const char* SkImageDecoder::GetFormatName(Format format) {
 switch (format) {
 case kUnknown_Format:
  return "Unknown Format";
 case kBMP_Format:
  return "BMP";
 case kGIF_Format:
  return "GIF";
 case kICO_Format:
  return "ICO";
 case kPKM_Format:
  return "PKM";
 case kKTX_Format:
  return "KTX";
 case kASTC_Format:
  return "ASTC";
 case kJPEG_Format:
  return "JPEG";
 case kPNG_Format:
  return "PNG";
 case kWBMP_Format:
  return "WBMP";
 case kWEBP_Format:
  return "WEBP";
 default:
  SkDEBUGFAIL("Invalid format type!");
 }
 return "Unknown Format";
}

// BitmapFactory.cpp
static jobject doDecode(JNIEnv* env, SkStreamRewindable* stream, jobject padding, jobject options) {
 ...
 SkBitmap outputBitmap;
 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.tryAllocPixels(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.setFilterQuality(kLow_SkFilterQuality);
 SkCanvas canvas(outputBitmap);
 canvas.scale(sx, sy);
 canvas.drawARGB(0x00, 0x00, 0x00, 0x00);
 canvas.drawBitmap(decodingBitmap, 0.0f, 0.0f, &paint);
 }
 ...
 // now create the java bitmap
 return GraphicsJNI::createBitmap(env, javaAllocator.getStorageObjAndReset(),
  bitmapCreateFlags, ninePatchChunk, ninePatchInsets, -1);
}