SurfaceFlinger合成後就進行圖像的輸出的工作。在圖像輸出時，存在硬件合成器與不存在的情況有些差別。軟件合成時用到圖像緩衝區生產者與消費者模型。首先來看看圖像緩衝區的初始化。
void SurfaceFlinger::init() {
ALOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");
......
// initialize our non-virtual displays
for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {
DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);
// set-up the displays that are already connected
if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {
// All non-virtual displays are currently considered secure.
bool isSecure = true;
createBuiltinDisplayLocked(type);
wp<IBinder> token = mBuiltinDisplays[i];
sp<IGraphicBufferProducer> producer;
sp<IGraphicBufferConsumer> consumer;
BufferQueue::createBufferQueue(&producer, &consumer,
new GraphicBufferAlloc());
sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i,
consumer);
int32_t hwcId = allocateHwcDisplayId(type);
sp<DisplayDevice> hw = new DisplayDevice(this,
type, hwcId, mHwc->getFormat(hwcId), isSecure, token,
fbs, producer,
mRenderEngine->getEGLConfig());
if (i > DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: currently we don't get blank/unblank requests
// for displays other than the main display, so we always
// assume a connected display is unblanked.
ALOGD("marking display %zu as acquired/unblanked", i);
hw->setPowerMode(HWC_POWER_MODE_NORMAL);
}
mDisplays.add(token, hw);
}
}
......
}
- 調用BufferQueue::createBufferQueue創建圖像緩衝區，並得到其生產者和消費者接口
- 利用上面得到的consumer消費者接口創建FramebufferSurface
- 利用上面得到的producer生產者接口創建DisplayDevice
- DisplayDevice軟件合成的圖像在FramebufferSurface中得以消費處理
DisplayDevice::DisplayDevice(
const sp<SurfaceFlinger>& flinger,
DisplayType type,
int32_t hwcId,
int format,
bool isSecure,
const wp<IBinder>& displayToken,
const sp<DisplaySurface>& displaySurface,
const sp<IGraphicBufferProducer>& producer,
EGLConfig config)
: lastCompositionHadVisibleLayers(false),
mFlinger(flinger),
mType(type), mHwcDisplayId(hwcId),
mDisplayToken(displayToken),
mDisplaySurface(displaySurface),
mDisplay(EGL_NO_DISPLAY),
mSurface(EGL_NO_SURFACE),
mDisplayWidth(), mDisplayHeight(), mFormat(),
mFlags(),
mPageFlipCount(),
mIsSecure(isSecure),
mSecureLayerVisible(false),
mLayerStack(NO_LAYER_STACK),
mOrientation(),
mPowerMode(HWC_POWER_MODE_OFF),
mActiveConfig(0)
{
mNativeWindow = new Surface(producer, false);
ANativeWindow* const window = mNativeWindow.get();
/*
* Create our display's surface
*/
EGLSurface surface;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
if (config == EGL_NO_CONFIG) {
config = RenderEngine::chooseEglConfig(display, format);
}
surface = eglCreateWindowSurface(display, config, window, NULL);
eglQuerySurface(display, surface, EGL_WIDTH, &mDisplayWidth);
eglQuerySurface(display, surface, EGL_HEIGHT, &mDisplayHeight);
// Make sure that composition can never be stalled by a virtual display
// consumer that isn't processing buffers fast enough. We have to do this
// in two places:
// * Here, in case the display is composed entirely by HWC.
// * In makeCurrent(), using eglSwapInterval. Some EGL drivers set the
// window's swap interval in eglMakeCurrent, so they'll override the
// interval we set here.
if (mType >= DisplayDevice::DISPLAY_VIRTUAL)
window->setSwapInterval(window, 0);
mConfig = config;
mDisplay = display;
mSurface = surface;
mFormat = format;
mPageFlipCount = 0;
mViewport.makeInvalid();
mFrame.makeInvalid();
// virtual displays are always considered enabled
mPowerMode = (mType >= DisplayDevice::DISPLAY_VIRTUAL) ?
HWC_POWER_MODE_NORMAL : HWC_POWER_MODE_OFF;
// Name the display. The name will be replaced shortly if the display
// was created with createDisplay().
switch (mType) {
case DISPLAY_PRIMARY:
mDisplayName = "Built-in Screen";
break;
case DISPLAY_EXTERNAL:
mDisplayName = "HDMI Screen";
break;
default:
mDisplayName = "Virtual Screen"; // e.g. Overlay #n
break;
}
// initialize the display orientation transform.
setProjection(DisplayState::eOrientationDefault, mViewport, mFrame);
}
- 使用生產者接口初始化egl圖形庫
- 軟件繪製圖層時就會調用EGL圖形庫，間接調用生產者接口
在SurfaceFlinger::doDisplayComposition函數中調用doComposeSurfaces函數合成圖層，然後調用hw->swapBuffers。對於沒有HWComper存在時，直接提交顯示。若存在HWComper時，將軟件合成的圖層交由HWComper處理。
void DisplayDevice::swapBuffers(HWComposer& hwc) const {
// We need to call eglSwapBuffers() if:
// (1) we don't have a hardware composer, or
// (2) we did GLES composition this frame, and either
// (a) we have framebuffer target support (not present on legacy
// devices, where HWComposer::commit() handles things); or
// (b) this is a virtual display
if (hwc.initCheck() != NO_ERROR ||
(hwc.hasGlesComposition(mHwcDisplayId) &&
(hwc.supportsFramebufferTarget() || mType >= DISPLAY_VIRTUAL))) {
EGLBoolean success = eglSwapBuffers(mDisplay, mSurface);
if (!success) {
EGLint error = eglGetError();
if (error == EGL_CONTEXT_LOST ||
mType == DisplayDevice::DISPLAY_PRIMARY) {
LOG_ALWAYS_FATAL("eglSwapBuffers(%p, %p) failed with 0x%08x",
mDisplay, mSurface, error);
} else {
ALOGE("eglSwapBuffers(%p, %p) failed with 0x%08x",
mDisplay, mSurface, error);
}
}
}
status_t result = mDisplaySurface->advanceFrame();
if (result != NO_ERROR) {
ALOGE("[%s] failed pushing new frame to HWC: %d",
mDisplayName.string(), result);
}
}
- 在不存在HWComposer或存在HWComposer但使用gles合成時調用eglSwapBuffers提交gles合成的緩衝區
- 其它情況對圖層合層不作處理
eglSwapBuffers提交gles合成的緩衝區後交由圖層消費者去處理，前文中提到消費者是FramebufferSurface。看看其處理函數：
void FramebufferSurface::onFrameAvailable(const BufferItem& /* item */) {
sp<GraphicBuffer> buf;
sp<Fence> acquireFence;
status_t err = nextBuffer(buf, acquireFence);
if (err != NO_ERROR) {
ALOGE("error latching nnext FramebufferSurface buffer: %s (%d)",
strerror(-err), err);
return;
}
err = mHwc.fbPost(mDisplayType, acquireFence, buf);
if (err != NO_ERROR) {
ALOGE("error posting framebuffer: %d", err);
}
}
- 調用mHwc.fbPost提交buffer到HWComposer函數
int HWComposer::fbPost(int32_t id,
const sp<Fence>& acquireFence, const sp<GraphicBuffer>& buffer) {
if (mHwc && hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
return setFramebufferTarget(id, acquireFence, buffer);
} else {
acquireFence->waitForever("HWComposer::fbPost");
return mFbDev->post(mFbDev, buffer->handle);
}
}
- 存在硬件合成器時，調用setFramebufferTarget函數將軟件合成的結果提交給硬件合成器去混合圖層輸出
- 不存在硬件合成器時，直接調用mFbDev->post將軟件合成的結果提交到framebuffer進去輸出
在SurfaceFlinger中執行完doDisplayComposition進行圖層處理後會調用postFramebuffer提交圖層到HWComposer中。
void SurfaceFlinger::postFramebuffer()
{
ATRACE_CALL();
......
HWComposer& hwc(getHwComposer());
if (hwc.initCheck() == NO_ERROR) {
if (!hwc.supportsFramebufferTarget()) {
// EGL spec says:
// "surface must be bound to the calling thread's current context,
// for the current rendering API."
getDefaultDisplayDevice()->makeCurrent(mEGLDisplay, mEGLContext);
}
hwc.commit();
}
......
}
- 存在HWComposer時調用hwc.commit()提交圖層。
status_t HWComposer::commit() {
int err = NO_ERROR;
if (mHwc) {
if (!hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
// On version 1.0, the OpenGL ES target surface is communicated
// by the (dpy, sur) fields and we are guaranteed to have only
// a single display.
mLists[0]->dpy = eglGetCurrentDisplay();
mLists[0]->sur = eglGetCurrentSurface(EGL_DRAW);
}
for (size_t i=VIRTUAL_DISPLAY_ID_BASE; i<mNumDisplays; i++) {
DisplayData& disp(mDisplayData[i]);
if (disp.outbufHandle) {
mLists[i]->outbuf = disp.outbufHandle;
mLists[i]->outbufAcquireFenceFd =
disp.outbufAcquireFence->dup();
}
}
err = mHwc->set(mHwc, mNumDisplays, mLists);
for (size_t i=0 ; i<mNumDisplays ; i++) {
DisplayData& disp(mDisplayData[i]);
disp.lastDisplayFence = disp.lastRetireFence;
disp.lastRetireFence = Fence::NO_FENCE;
if (disp.list) {
if (disp.list->retireFenceFd != -1) {
disp.lastRetireFence = new Fence(disp.list->retireFenceFd);
disp.list->retireFenceFd = -1;
}
disp.list->flags &= ~HWC_GEOMETRY_CHANGED;
}
}
}
return (status_t)err;
}
- 調用mHwc->set使用硬件對層圖進行合成並輸出到顯示設備