本文主要为大家分享一篇P关于Layer组件的同步以及减少GPU带宽的问题，具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧。

问题：

1) Layer 之间能否进行单独更新，比如其中video 层上面弹出的状态栏场景如何优化；

初步构想每次仅更新video layer或则将video layer 绕过BQ 进行处理。

2)FW 以及GPU对video layer 的常见处理；

3)几个变量的理解；

(1)mCurrentTexture ，nextTextureImage；

(2)BufferItem，BufferQueue,mslots；slot，mqueuedframe，mqueuedItem；

(3)syncForReleaseLocked，updateAndReleaseLocked，releaseBufferLocked，releaseBuffer

(4)/ 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// 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,

(5)mslots 与mframe 以及mframenumber 的区别

(6)onframavailable 和latchbuffer ，reject，updateteximage，的逻辑。

其中updateteximage；

(7)bufferitem 与mslots的区别

(8)bufferqueueconsumer 与bufferitemconsumer区别；

(9)acquirebuffer的fence 逻辑，fencefd是哪来的；

fence 相关接口定义参见ui/Fence.hstatus_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 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;

};

(10)updateAndReleaseLocked(item, &mPendingRelease)，updateAndReleaseLocked(item)，bindTextureImageLocked()