本文主要為大家分享一篇P關於Layer組件的同步以及減少GPU頻寬的問題，具有很好的參考價值，希望對大家有所幫助。一起跟著小編過來看看吧。
問題：
1) Layer 之間能否進行單獨更新，例如其中video 層上面彈出的狀態列場景如何優化；
初步構想每次僅更新video layer或則將video layer 繞過BQ 進行處理。
2）FW 以及GPU對video layer 的常見處理；
3）幾個變數的理解；
（1）mCurrentTexture ，nextTextureImage;
#（2）BufferItem，BufferQueue,mslots；slot，mqueuedframe，mqueuedItem；
（3）syncForReleaseLocked，updateAndReleaseLocked，releaseBufferLocked，releaseBuffer
##（4）##-r#（4）##-l#（4）##1#（4）##1#（4） ）mslots 與mframe 以及mframenumber 的差異（6）onframavailable 和latchbuffer ，reject，updateteximage，的邏輯。 其中updateteximage;(7)bufferitem 與mslots的區別(8)bufferqueueconsumer 與bufferitemconsumer區別；（9）acquirebuffer的fence 邏輯，fencefd是哪來的;
fence 相關介面定義參考ui
/Fence.h/ acquireBuffer attempts to acquire ownership of the next pending buffer in the BufferQueue.
// If no buffer is pending then it returns NO_BUFFER_AVAILABLE. If a buffer is successfully
// acquired, the information about the buffer is returned in BufferItem.
//
// If the buffer returned had previously been acquired then the BufferItem::mGraphicBuffer field
// of buffer is set to NULL and it is assumed that the consumer still holds a reference to the
// buffer.
//
// If presentWhen is non-zero, it indicates the time when the buffer will be displayed on
// screen. If the buffer's timestamp is farther in the future, the buffer won't be acquired, and
// PRESENT_LATER will be returned. The presentation time is in nanoseconds, and the time base
// is CLOCK_MONOTONIC.
//
// If maxFrameNumber is non-zero, it indicates that acquireBuffer should only return a buffer
// with a frame number less than or equal to maxFrameNumber. If no such frame is available
// (such as when a buffer has been replaced but the consumer has not received the
// onFrameReplaced callback), then PRESENT_LATER will be returned.
//
// Return of NO_ERROR means the operation completed as normal.
//
// Return of a positive value means the operation could not be completed at this time, but the
// user should try again later:
// * NO_BUFFER_AVAILABLE - no buffer is pending (nothing queued by producer)
// * PRESENT_LATER - the buffer's timestamp is farther in the future
//
// Return of a negative value means an error has occurred:
// * INVALID_OPERATION - too many buffers have been acquired
登入後複製 // Returned by releaseBuffer, after which the consumer must free any references to the
// just-released buffer that it might have.
STALE_BUFFER_SLOT = 1,
// Returned by dequeueBuffer if there are no pending buffers available.
NO_BUFFER_AVAILABLE,
// Returned by dequeueBuffer if it's too early for the buffer to be acquired.
PRESENT_LATER,
登入後複製
（10）
status_t Fence::waitForever(const char* logname) {64 ATRACE_CALL();
if (mFenceFd == -1) {
return NO_ERROR;
}
int warningTimeout = 3000;
int err = sync_wait(mFenceFd, warningTimeout);
if (err < 0 && errno == ETIME) {
ALOGE("%s: fence %d didn't signal in %u ms", logname, mFenceFd,
warningTimeout);
err = sync_wait(mFenceFd, TIMEOUT_NEVER);
}
return err < 0 ? -errno : status_t(NO_ERROR);
} struct EglSlot {
EglSlot() : mEglFence(EGL_NO_SYNC_KHR) {}
// mEglImage is the EGLImage created from mGraphicBuffer.
sp<EglImage> mEglImage;
// mFence is the EGL sync object that must signal before the buffer
// associated with this buffer slot may be dequeued. It is initialized
// to EGL_NO_SYNC_KHR when the buffer is created and (optionally, based
// on a compile-time option) set to a new sync object in updateTexImage.
EGLSyncKHR mEglFence;
};updateAndReleaseLocked(item, &mPendingRelease)，
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