上图为WMS, SurfaceFlinger, app如何同步buffer大小,总结下来有如下6 个步骤
1 Window宽度高度发生变化,如转屏或者window动画.
2 WMS更新SurfaceControl大小,这一步要通过事务来完成
3 SurfaceFlinger到下一个vsync周期处理事务翻转,这时候会设置该Layer的mDefaultWidth和mDefaultHeight
4 为客户端这边的动作,客户端会进行下一帧的绘制,绘制完成后进行queueBuffer, queueBuffer的过程会返回sf中关于
该layout的mDefaultWidth和mDefaultHeight,使用这个宽度高度更新request height和request width
5 客户端使用新的request height ,request width去dequeueBuffer(注意这里会尽量不改变dequeueBuffer的大小,如果发生转屏的话是不用改变reques大小的,只需要queueBuffer进行旋转buffer就可以)
6 下次queueBuffer前根据宽度高度去旋转buffer的角度. 然后queueBuffer
7 sf收到queueBuffer和Layer的mDefaultWidth,mDefaultHeight相等后,开始使用新的宽度高度渲染.
所以这里第四步还是渲染在旧的大小的buffer上. 这就算是一个过度过程.
const bool resizePending = ((c.requested.w != c.active.w) || (c.requested.h != c.active.h)) &&
(getBE().compositionInfo.mBuffer != nullptr) ;
if (!isFixedSize()) {
if (resizePending && getBE().compositionInfo.hwc.sidebandStream == nullptr) {
flags |= eDontUpdateGeometryState;
}
}
// Here we apply various requested geometry states, depending on our
// latching configuration. See Layer.h for a detailed discussion of
// how geometry latching is controlled.
if (!(flags & eDontUpdateGeometryState)) {
Layer::State& editCurrentState(getCurrentState());
// If mFreezeGeometryUpdates is true we are in the setGeometryAppliesWithResize
// mode, which causes attributes which normally latch regardless of scaling mode,
// to be delayed. We copy the requested state to the active state making sure
// to respect these rules (again see Layer.h for a detailed discussion).
//
// There is an awkward asymmetry in the handling of the crop states in the position
// states, as can be seen below. Largely this arises from position and transform
// being stored in the same data structure while having different latching rules.
// b/38182305
//
// Careful that "c" and editCurrentState may not begin as equivalent due to
// applyPendingStates in the presence of deferred transactions.
if (mFreezeGeometryUpdates) {
float tx = c.active.transform.tx();
float ty = c.active.transform.ty();
c.active = c.requested;
c.active.transform.set(tx, ty);
editCurrentState.active = c.active;
} else {
editCurrentState.active = editCurrentState.requested;
c.active = c.requested;
}
}
if (s.active != c.active) {
// invalidate and recompute the visible regions if needed
flags |= Layer::eVisibleRegion;
}
if (c.sequence != s.sequence) {
// invalidate and recompute the visible regions if needed
flags |= eVisibleRegion;
this->contentDirty = true;
// we may use linear filtering, if the matrix scales us
const uint8_t type = c.active.transform.getType();
mNeedsFiltering = (!c.active.transform.preserveRects() || (type >= Transform::SCALE));
}SurfaceFlinger在事务翻转的时候并不基于去改变active的宽度高度,只是会锁存起来.
关键的语句就是这个
const bool resizePending = ((c.requested.w != c.active.w) || (c.requested.h != c.active.h)) &&
(getBE().compositionInfo.mBuffer != nullptr) ;
这个条件.
再来看看何时翻转
bool LayerRejecter::reject(const sp<GraphicBuffer>& buf, const BufferItem& item) {
if (buf == nullptr) {
return false;
}
uint32_t bufWidth = buf->getWidth();
uint32_t bufHeight = buf->getHeight();
// check that we received a buffer of the right size
// (Take the buffer's orientation into account)
if (item.mTransform & Transform::ROT_90) {
swap(bufWidth, bufHeight);
}
int actualScalingMode = mOverrideScalingMode >= 0 ? mOverrideScalingMode : item.mScalingMode;
bool isFixedSize = actualScalingMode != NATIVE_WINDOW_SCALING_MODE_FREEZE;
if (mFront.active != mFront.requested) {
if (isFixedSize || (bufWidth == mFront.requested.w && bufHeight == mFront.requested.h)) {
// Here we pretend the transaction happened by updating the
// current and drawing states. Drawing state is only accessed
// in this thread, no need to have it locked
mFront.active = mFront.requested;
// We also need to update the current state so that
// we don't end-up overwriting the drawing state with
// this stale current state during the next transaction
//
// NOTE: We don't need to hold the transaction lock here
// because State::active is only accessed from this thread.
mCurrent.active = mFront.active;
mCurrent.modified = true;
// recompute visible region
mRecomputeVisibleRegions = true;
mFreezeGeometryUpdates = false;
if (mFront.crop != mFront.requestedCrop) {
mFront.crop = mFront.requestedCrop;
mCurrent.crop = mFront.requestedCrop;
mRecomputeVisibleRegions = true;
}
if (mFront.finalCrop != mFront.requestedFinalCrop) {
mFront.finalCrop = mFront.requestedFinalCrop;
mCurrent.finalCrop = mFront.requestedFinalCrop;
mRecomputeVisibleRegions = true;
}
}
ALOGD_IF(DEBUG_RESIZE,
"[%s] latchBuffer/reject: buffer (%ux%u, tr=%02x), scalingMode=%d\n"
" drawing={ active ={ wh={%4u,%4u} crop={%4d,%4d,%4d,%4d} (%4d,%4d) "
"}\n"
" requested={ wh={%4u,%4u} }}\n",
mName, bufWidth, bufHeight, item.mTransform, item.mScalingMode, mFront.active.w,
mFront.active.h, mFront.crop.left, mFront.crop.top, mFront.crop.right,
mFront.crop.bottom, mFront.crop.getWidth(), mFront.crop.getHeight(),
mFront.requested.w, mFront.requested.h);
}
if (!isFixedSize && !mStickyTransformSet) {
if (mFront.active.w != bufWidth || mFront.active.h != bufHeight) {
// reject this buffer
ALOGE("[%s] rejecting buffer: "
"bufWidth=%d, bufHeight=%d, front.active.{w=%d, h=%d}",
mName, bufWidth, bufHeight, mFront.active.w, mFront.active.h);
return true;
}
}
// if the transparent region has changed (this test is
// conservative, but that's fine, worst case we're doing
// a bit of extra work), we latch the new one and we
// trigger a visible-region recompute.
//
// We latch the transparent region here, instead of above where we latch
// the rest of the geometry because it is only content but not necessarily
// resize dependent.
if (!mFront.activeTransparentRegion.isTriviallyEqual(mFront.requestedTransparentRegion)) {
mFront.activeTransparentRegion = mFront.requestedTransparentRegion;
// We also need to update the current state so that
// we don't end-up overwriting the drawing state with
// this stale current state during the next transaction
//
// NOTE: We don't need to hold the transaction lock here
// because State::active is only accessed from this thread.
mCurrent.activeTransparentRegion = mFront.activeTransparentRegion;
// recompute visible region
mRecomputeVisibleRegions = true;
}
return false;
}接下来要进行合成的buffer的宽度高度和request的一样的时候,就可以使用新的高度渲染了.