libs/hwui/DeferredDisplayList.cpp

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "OpenGLRenderer"
#define ATRACE_TAG ATRACE_TAG_VIEW

#include <SkCanvas.h>

#include <utils/Trace.h>
#include <ui/Rect.h>
#include <ui/Region.h>

#include "Caches.h"
#include "Debug.h"
#include "DeferredDisplayList.h"
#include "DisplayListOp.h"
#include "OpenGLRenderer.h"
#include "Properties.h"
#include "utils/MathUtils.h"

#if DEBUG_DEFER
    #define DEFER_LOGD(...) ALOGD(__VA_ARGS__)
#else
    #define DEFER_LOGD(...)
#endif

namespace android {
namespace uirenderer {

// Depth of the save stack at the beginning of batch playback at flush time
#define FLUSH_SAVE_STACK_DEPTH 2

#define DEBUG_COLOR_BARRIER          0x1f000000
#define DEBUG_COLOR_MERGEDBATCH      0x5f7f7fff
#define DEBUG_COLOR_MERGEDBATCH_SOLO 0x5f7fff7f

/////////////////////////////////////////////////////////////////////////////////
// Operation Batches
/////////////////////////////////////////////////////////////////////////////////

class Batch {
public:
    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) = 0;
    virtual ~Batch() {}
    virtual bool purelyDrawBatch() { return false; }
    virtual bool coversBounds(const Rect& bounds) { return false; }
};

class DrawBatch : public Batch {
public:
    DrawBatch(const DeferInfo& deferInfo) : mAllOpsOpaque(true),
            mBatchId(deferInfo.batchId), mMergeId(deferInfo.mergeId) {
        mOps.clear();
    }

    virtual ~DrawBatch() { mOps.clear(); }

    virtual void add(DrawOp* op, const DeferredDisplayState* state, bool opaqueOverBounds) {
        // NOTE: ignore empty bounds special case, since we don't merge across those ops
        mBounds.unionWith(state->mBounds);
        mAllOpsOpaque &= opaqueOverBounds;
        mOps.add(OpStatePair(op, state));
    }

    bool intersects(const Rect& rect) {
        if (!rect.intersects(mBounds)) return false;

        for (unsigned int i = 0; i < mOps.size(); i++) {
            if (rect.intersects(mOps[i].state->mBounds)) {
#if DEBUG_DEFER
                DEFER_LOGD("op intersects with op %p with bounds %f %f %f %f:", mOps[i].op,
                        mOps[i].state->mBounds.left, mOps[i].state->mBounds.top,
                        mOps[i].state->mBounds.right, mOps[i].state->mBounds.bottom);
                mOps[i].op->output(2);
#endif
                return true;
            }
        }
        return false;
    }

    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) override {
        DEFER_LOGD("%d  replaying DrawBatch %p, with %d ops (batch id %x, merge id %p)",
                index, this, mOps.size(), getBatchId(), getMergeId());

        for (unsigned int i = 0; i < mOps.size(); i++) {
            DrawOp* op = mOps[i].op;
            const DeferredDisplayState* state = mOps[i].state;
            renderer.restoreDisplayState(*state);

#if DEBUG_DISPLAY_LIST_OPS_AS_EVENTS
            renderer.eventMark(op->name());
#endif
            op->applyDraw(renderer, dirty);

#if DEBUG_MERGE_BEHAVIOR
            const Rect& bounds = state->mBounds;
            int batchColor = 0x1f000000;
            if (getBatchId() & 0x1) batchColor |= 0x0000ff;
            if (getBatchId() & 0x2) batchColor |= 0x00ff00;
            if (getBatchId() & 0x4) batchColor |= 0xff0000;
            renderer.drawScreenSpaceColorRect(bounds.left, bounds.top, bounds.right, bounds.bottom,
                    batchColor);
#endif
        }
    }

    virtual bool purelyDrawBatch() override { return true; }

    virtual bool coversBounds(const Rect& bounds) override {
        if (CC_LIKELY(!mAllOpsOpaque || !mBounds.contains(bounds) || count() == 1)) return false;

        Region uncovered(android::Rect(bounds.left, bounds.top, bounds.right, bounds.bottom));
        for (unsigned int i = 0; i < mOps.size(); i++) {
            const Rect &r = mOps[i].state->mBounds;
            uncovered.subtractSelf(android::Rect(r.left, r.top, r.right, r.bottom));
        }
        return uncovered.isEmpty();
    }

    inline int getBatchId() const { return mBatchId; }
    inline mergeid_t getMergeId() const { return mMergeId; }
    inline int count() const { return mOps.size(); }

protected:
    Vector<OpStatePair> mOps;
    Rect mBounds; // union of bounds of contained ops
private:
    bool mAllOpsOpaque;
    int mBatchId;
    mergeid_t mMergeId;
};

class MergingDrawBatch : public DrawBatch {
public:
    MergingDrawBatch(DeferInfo& deferInfo, int width, int height) :
            DrawBatch(deferInfo), mClipRect(width, height),
            mClipSideFlags(kClipSide_None) {}

    /*
     * Helper for determining if a new op can merge with a MergingDrawBatch based on their bounds
     * and clip side flags. Positive bounds delta means new bounds fit in old.
     */
    static inline bool checkSide(const int currentFlags, const int newFlags, const int side,
            float boundsDelta) {
        bool currentClipExists = currentFlags & side;
        bool newClipExists = newFlags & side;

        // if current is clipped, we must be able to fit new bounds in current
        if (boundsDelta > 0 && currentClipExists) return false;

        // if new is clipped, we must be able to fit current bounds in new
        if (boundsDelta < 0 && newClipExists) return false;

        return true;
    }

    /*
     * Checks if a (mergeable) op can be merged into this batch
     *
     * If true, the op's multiDraw must be guaranteed to handle both ops simultaneously, so it is
     * important to consider all paint attributes used in the draw calls in deciding both a) if an
     * op tries to merge at all, and b) if the op can merge with another set of ops
     *
     * False positives can lead to information from the paints of subsequent merged operations being
     * dropped, so we make simplifying qualifications on the ops that can merge, per op type.
     */
    bool canMergeWith(const DrawOp* op, const DeferredDisplayState* state) {
        bool isTextBatch = getBatchId() == DeferredDisplayList::kOpBatch_Text ||
                getBatchId() == DeferredDisplayList::kOpBatch_ColorText;

        // Overlapping other operations is only allowed for text without shadow. For other ops,
        // multiDraw isn't guaranteed to overdraw correctly
        if (!isTextBatch || op->hasTextShadow()) {
            if (intersects(state->mBounds)) return false;
        }
        const DeferredDisplayState* lhs = state;
        const DeferredDisplayState* rhs = mOps[0].state;

        if (!MathUtils::areEqual(lhs->mAlpha, rhs->mAlpha)) return false;

        // Identical round rect clip state means both ops will clip in the same way, or not at all.
        // As the state objects are const, we can compare their pointers to determine mergeability
        if (lhs->mRoundRectClipState != rhs->mRoundRectClipState) return false;

        /* Clipping compatibility check
         *
         * Exploits the fact that if a op or batch is clipped on a side, its bounds will equal its
         * clip for that side.
         */
        const int currentFlags = mClipSideFlags;
        const int newFlags = state->mClipSideFlags;
        if (currentFlags != kClipSide_None || newFlags != kClipSide_None) {
            const Rect& opBounds = state->mBounds;
            float boundsDelta = mBounds.left - opBounds.left;
            if (!checkSide(currentFlags, newFlags, kClipSide_Left, boundsDelta)) return false;
            boundsDelta = mBounds.top - opBounds.top;
            if (!checkSide(currentFlags, newFlags, kClipSide_Top, boundsDelta)) return false;

            // right and bottom delta calculation reversed to account for direction
            boundsDelta = opBounds.right - mBounds.right;
            if (!checkSide(currentFlags, newFlags, kClipSide_Right, boundsDelta)) return false;
            boundsDelta = opBounds.bottom - mBounds.bottom;
            if (!checkSide(currentFlags, newFlags, kClipSide_Bottom, boundsDelta)) return false;
        }

        // if paints are equal, then modifiers + paint attribs don't need to be compared
        if (op->mPaint == mOps[0].op->mPaint) return true;

        if (op->getPaintAlpha() != mOps[0].op->getPaintAlpha()) return false;

        if (op->mPaint && mOps[0].op->mPaint &&
            op->mPaint->getColorFilter() != mOps[0].op->mPaint->getColorFilter()) {
            return false;
        }

        if (op->mPaint && mOps[0].op->mPaint &&
            op->mPaint->getShader() != mOps[0].op->mPaint->getShader()) {
            return false;
        }

        return true;
    }

    virtual void add(DrawOp* op, const DeferredDisplayState* state,
            bool opaqueOverBounds) override {
        DrawBatch::add(op, state, opaqueOverBounds);

        const int newClipSideFlags = state->mClipSideFlags;
        mClipSideFlags |= newClipSideFlags;
        if (newClipSideFlags & kClipSide_Left) mClipRect.left = state->mClip.left;
        if (newClipSideFlags & kClipSide_Top) mClipRect.top = state->mClip.top;
        if (newClipSideFlags & kClipSide_Right) mClipRect.right = state->mClip.right;
        if (newClipSideFlags & kClipSide_Bottom) mClipRect.bottom = state->mClip.bottom;
    }

    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) override {
        DEFER_LOGD("%d  replaying MergingDrawBatch %p, with %d ops,"
                " clip flags %x (batch id %x, merge id %p)",
                index, this, mOps.size(), mClipSideFlags, getBatchId(), getMergeId());
        if (mOps.size() == 1) {
            DrawBatch::replay(renderer, dirty, -1);
            return;
        }

        // clipping in the merged case is done ahead of time since all ops share the clip (if any)
        renderer.setupMergedMultiDraw(mClipSideFlags ? &mClipRect : nullptr);

        DrawOp* op = mOps[0].op;
#if DEBUG_DISPLAY_LIST_OPS_AS_EVENTS
        renderer.eventMark("multiDraw");
        renderer.eventMark(op->name());
#endif
        op->multiDraw(renderer, dirty, mOps, mBounds);

#if DEBUG_MERGE_BEHAVIOR
        renderer.drawScreenSpaceColorRect(mBounds.left, mBounds.top, mBounds.right, mBounds.bottom,
                DEBUG_COLOR_MERGEDBATCH);
#endif
    }

private:
    /*
     * Contains the effective clip rect shared by all merged ops. Initialized to the layer viewport,
     * it will shrink if an op must be clipped on a certain side. The clipped sides are reflected in
     * mClipSideFlags.
     */
    Rect mClipRect;
    int mClipSideFlags;
};

class StateOpBatch : public Batch {
public:
    // creates a single operation batch
    StateOpBatch(const StateOp* op, const DeferredDisplayState* state) : mOp(op), mState(state) {}

    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) override {
        DEFER_LOGD("replaying state op batch %p", this);
        renderer.restoreDisplayState(*mState);

        // use invalid save count because it won't be used at flush time - RestoreToCountOp is the
        // only one to use it, and we don't use that class at flush time, instead calling
        // renderer.restoreToCount directly
        int saveCount = -1;
        mOp->applyState(renderer, saveCount);
    }

private:
    const StateOp* mOp;
    const DeferredDisplayState* mState;
};

class RestoreToCountBatch : public Batch {
public:
    RestoreToCountBatch(const StateOp* op, const DeferredDisplayState* state, int restoreCount) :
            mState(state), mRestoreCount(restoreCount) {}

    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) override {
        DEFER_LOGD("batch %p restoring to count %d", this, mRestoreCount);

        renderer.restoreDisplayState(*mState);
        renderer.restoreToCount(mRestoreCount);
    }

private:
    // we use the state storage for the RestoreToCountOp, but don't replay the op itself
    const DeferredDisplayState* mState;

    /*
     * The count used here represents the flush() time saveCount. This is as opposed to the
     * DisplayList record time, or defer() time values (which are RestoreToCountOp's mCount, and
     * (saveCount + mCount) respectively). Since the count is different from the original
     * RestoreToCountOp, we don't store a pointer to the op, as elsewhere.
     */
    const int mRestoreCount;
};

#if DEBUG_MERGE_BEHAVIOR
class BarrierDebugBatch : public Batch {
    virtual void replay(OpenGLRenderer& renderer, Rect& dirty, int index) {
        renderer.drawScreenSpaceColorRect(0, 0, 10000, 10000, DEBUG_COLOR_BARRIER);
    }
};
#endif

/////////////////////////////////////////////////////////////////////////////////
// DeferredDisplayList
/////////////////////////////////////////////////////////////////////////////////

void DeferredDisplayList::resetBatchingState() {
    for (int i = 0; i < kOpBatch_Count; i++) {
        mBatchLookup[i] = nullptr;
        mMergingBatches[i].clear();
    }
#if DEBUG_MERGE_BEHAVIOR
    if (mBatches.size() != 0) {
        mBatches.add(new BarrierDebugBatch());
    }
#endif
    mEarliestBatchIndex = mBatches.size();
}

void DeferredDisplayList::clear() {
    resetBatchingState();
    mComplexClipStackStart = -1;

    for (unsigned int i = 0; i < mBatches.size(); i++) {
        delete mBatches[i];
    }
    mBatches.clear();
    mSaveStack.clear();
    mEarliestBatchIndex = 0;
    mEarliestUnclearedIndex = 0;
}

/////////////////////////////////////////////////////////////////////////////////
// Operation adding
/////////////////////////////////////////////////////////////////////////////////

int DeferredDisplayList::getStateOpDeferFlags() const {
    // For both clipOp and save(Layer)Op, we don't want to save drawing info, and only want to save
    // the clip if we aren't recording a complex clip (and can thus trust it to be a rect)
    return recordingComplexClip() ? 0 : kStateDeferFlag_Clip;
}

int DeferredDisplayList::getDrawOpDeferFlags() const {
    return kStateDeferFlag_Draw | getStateOpDeferFlags();
}

/**
 * When an clipping operation occurs that could cause a complex clip, record the operation and all
 * subsequent clipOps, save/restores (if the clip flag is set). During a flush, instead of loading
 * the clip from deferred state, we play back all of the relevant state operations that generated
 * the complex clip.
 *
 * Note that we don't need to record the associated restore operation, since operations at defer
 * time record whether they should store the renderer's current clip
 */
void DeferredDisplayList::addClip(OpenGLRenderer& renderer, ClipOp* op) {
    if (recordingComplexClip() || op->canCauseComplexClip() || !renderer.hasRectToRectTransform()) {
        DEFER_LOGD("%p Received complex clip operation %p", this, op);

        // NOTE: defer clip op before setting mComplexClipStackStart so previous clip is recorded
        storeStateOpBarrier(renderer, op);

        if (!recordingComplexClip()) {
            mComplexClipStackStart = renderer.getSaveCount() - 1;
            DEFER_LOGD("    Starting complex clip region, start is %d", mComplexClipStackStart);
        }
    }
}

/**
 * For now, we record save layer operations as barriers in the batch list, preventing drawing
 * operations from reordering around the saveLayer and it's associated restore()
 *
 * In the future, we should send saveLayer commands (if they can be played out of order) and their
 * contained drawing operations to a seperate list of batches, so that they may draw at the
 * beginning of the frame. This would avoid targetting and removing an FBO in the middle of a frame.
 *
 * saveLayer operations should be pulled to the beginning of the frame if the canvas doesn't have a
 * complex clip, and if the flags (kClip_SaveFlag & kClipToLayer_SaveFlag) are set.
 */
void DeferredDisplayList::addSaveLayer(OpenGLRenderer& renderer,
        SaveLayerOp* op, int newSaveCount) {
    DEFER_LOGD("%p adding saveLayerOp %p, flags %x, new count %d",
            this, op, op->getFlags(), newSaveCount);

    storeStateOpBarrier(renderer, op);
    mSaveStack.push(newSaveCount);
}

/**
 * Takes save op and it's return value - the new save count - and stores it into the stream as a
 * barrier if it's needed to properly modify a complex clip
 */
void DeferredDisplayList::addSave(OpenGLRenderer& renderer, SaveOp* op, int newSaveCount) {
    int saveFlags = op->getFlags();
    DEFER_LOGD("%p adding saveOp %p, flags %x, new count %d", this, op, saveFlags, newSaveCount);

    if (recordingComplexClip() && (saveFlags & SkCanvas::kClip_SaveFlag)) {
        // store and replay the save operation, as it may be needed to correctly playback the clip
        DEFER_LOGD("    adding save barrier with new save count %d", newSaveCount);
        storeStateOpBarrier(renderer, op);
        mSaveStack.push(newSaveCount);
    }
}

/**
 * saveLayer() commands must be associated with a restoreToCount batch that will clean up and draw
 * the layer in the deferred list
 *
 * other save() commands which occur as children of a snapshot with complex clip will be deferred,
 * and must be restored
 *
 * Either will act as a barrier to draw operation reordering, as we want to play back layer
 * save/restore and complex canvas modifications (including save/restore) in order.
 */
void DeferredDisplayList::addRestoreToCount(OpenGLRenderer& renderer, StateOp* op,
        int newSaveCount) {
    DEFER_LOGD("%p addRestoreToCount %d", this, newSaveCount);

    if (recordingComplexClip() && newSaveCount <= mComplexClipStackStart) {
        mComplexClipStackStart = -1;
        resetBatchingState();
    }

    if (mSaveStack.isEmpty() || newSaveCount > mSaveStack.top()) {
        return;
    }

    while (!mSaveStack.isEmpty() && mSaveStack.top() >= newSaveCount) mSaveStack.pop();

    storeRestoreToCountBarrier(renderer, op, mSaveStack.size() + FLUSH_SAVE_STACK_DEPTH);
}

void DeferredDisplayList::addDrawOp(OpenGLRenderer& renderer, DrawOp* op) {
    /* 1: op calculates local bounds */
    DeferredDisplayState* const state = createState();
    if (op->getLocalBounds(state->mBounds)) {
        if (state->mBounds.isEmpty()) {
            // valid empty bounds, don't bother deferring
            tryRecycleState(state);
            return;
        }
    } else {
        state->mBounds.setEmpty();
    }

    /* 2: renderer calculates global bounds + stores state */
    if (renderer.storeDisplayState(*state, getDrawOpDeferFlags())) {
        tryRecycleState(state);
        return; // quick rejected
    }

    /* 3: ask op for defer info, given renderer state */
    DeferInfo deferInfo;
    op->onDefer(renderer, deferInfo, *state);

    // complex clip has a complex set of expectations on the renderer state - for now, avoid taking
    // the merge path in those cases
    deferInfo.mergeable &= !recordingComplexClip();
    deferInfo.opaqueOverBounds &= !recordingComplexClip() && mSaveStack.isEmpty();

    if (CC_LIKELY(mAvoidOverdraw) && mBatches.size() &&
            state->mClipSideFlags != kClipSide_ConservativeFull &&
            deferInfo.opaqueOverBounds && state->mBounds.contains(mBounds)) {
        // avoid overdraw by resetting drawing state + discarding drawing ops
        discardDrawingBatches(mBatches.size() - 1);
        resetBatchingState();
    }

    if (CC_UNLIKELY(Properties::drawReorderDisabled)) {
        // TODO: elegant way to reuse batches?
        DrawBatch* b = new DrawBatch(deferInfo);
        b->add(op, state, deferInfo.opaqueOverBounds);
        mBatches.add(b);
        return;
    }

    // find the latest batch of the new op's type, and try to merge the new op into it
    DrawBatch* targetBatch = nullptr;

    // insertion point of a new batch, will hopefully be immediately after similar batch
    // (eventually, should be similar shader)
    int insertBatchIndex = mBatches.size();
    if (!mBatches.isEmpty()) {
        if (state->mBounds.isEmpty()) {
            // don't know the bounds for op, so add to last batch and start from scratch on next op
            DrawBatch* b = new DrawBatch(deferInfo);
            b->add(op, state, deferInfo.opaqueOverBounds);
            mBatches.add(b);
            resetBatchingState();
#if DEBUG_DEFER
            DEFER_LOGD("Warning: Encountered op with empty bounds, resetting batches");
            op->output(2);
#endif
            return;
        }

        if (deferInfo.mergeable) {
            // Try to merge with any existing batch with same mergeId.
            if (mMergingBatches[deferInfo.batchId].get(deferInfo.mergeId, targetBatch)) {
                if (!((MergingDrawBatch*) targetBatch)->canMergeWith(op, state)) {
                    targetBatch = nullptr;
                }
            }
        } else {
            // join with similar, non-merging batch
            targetBatch = (DrawBatch*)mBatchLookup[deferInfo.batchId];
        }

        if (targetBatch || deferInfo.mergeable) {
            // iterate back toward target to see if anything drawn since should overlap the new op
            // if no target, merging ops still interate to find similar batch to insert after
            for (int i = mBatches.size() - 1; i >= mEarliestBatchIndex; i--) {
                DrawBatch* overBatch = (DrawBatch*)mBatches[i];

                if (overBatch == targetBatch) break;

                // TODO: also consider shader shared between batch types
                if (deferInfo.batchId == overBatch->getBatchId()) {
                    insertBatchIndex = i + 1;
                    if (!targetBatch) break; // found insert position, quit
                }

                if (overBatch->intersects(state->mBounds)) {
                    // NOTE: it may be possible to optimize for special cases where two operations
                    // of the same batch/paint could swap order, such as with a non-mergeable
                    // (clipped) and a mergeable text operation
                    targetBatch = nullptr;
#if DEBUG_DEFER
                    DEFER_LOGD("op couldn't join batch %p, was intersected by batch %d",
                            targetBatch, i);
                    op->output(2);
#endif
                    break;
                }
            }
        }
    }

    if (!targetBatch) {
        if (deferInfo.mergeable) {
            targetBatch = new MergingDrawBatch(deferInfo,
                    renderer.getViewportWidth(), renderer.getViewportHeight());
            mMergingBatches[deferInfo.batchId].put(deferInfo.mergeId, targetBatch);
        } else {
            targetBatch = new DrawBatch(deferInfo);
            mBatchLookup[deferInfo.batchId] = targetBatch;
        }

        DEFER_LOGD("creating %singBatch %p, bid %x, at %d",
                deferInfo.mergeable ? "Merg" : "Draw",
                targetBatch, deferInfo.batchId, insertBatchIndex);
        mBatches.insertAt(targetBatch, insertBatchIndex);
    }

    targetBatch->add(op, state, deferInfo.opaqueOverBounds);
}

void DeferredDisplayList::storeStateOpBarrier(OpenGLRenderer& renderer, StateOp* op) {
    DEFER_LOGD("%p adding state op barrier at pos %d", this, mBatches.size());

    DeferredDisplayState* state = createState();
    renderer.storeDisplayState(*state, getStateOpDeferFlags());
    mBatches.add(new StateOpBatch(op, state));
    resetBatchingState();
}

void DeferredDisplayList::storeRestoreToCountBarrier(OpenGLRenderer& renderer, StateOp* op,
        int newSaveCount) {
    DEFER_LOGD("%p adding restore to count %d barrier, pos %d",
            this, newSaveCount, mBatches.size());

    // store displayState for the restore operation, as it may be associated with a saveLayer that
    // doesn't have kClip_SaveFlag set
    DeferredDisplayState* state = createState();
    renderer.storeDisplayState(*state, getStateOpDeferFlags());
    mBatches.add(new RestoreToCountBatch(op, state, newSaveCount));
    resetBatchingState();
}

/////////////////////////////////////////////////////////////////////////////////
// Replay / flush
/////////////////////////////////////////////////////////////////////////////////

static void replayBatchList(const Vector<Batch*>& batchList,
        OpenGLRenderer& renderer, Rect& dirty) {

    for (unsigned int i = 0; i < batchList.size(); i++) {
        if (batchList[i]) {
            batchList[i]->replay(renderer, dirty, i);
        }
    }
    DEFER_LOGD("--flushed, drew %d batches", batchList.size());
}

void DeferredDisplayList::flush(OpenGLRenderer& renderer, Rect& dirty) {
    ATRACE_NAME("flush drawing commands");
    Caches::getInstance().fontRenderer->endPrecaching();

    if (isEmpty()) return; // nothing to flush
    renderer.restoreToCount(1);

    DEFER_LOGD("--flushing");
    renderer.eventMark("Flush");

    // save and restore so that reordering doesn't affect final state
    renderer.save(SkCanvas::kMatrix_SaveFlag | SkCanvas::kClip_SaveFlag);

    if (CC_LIKELY(mAvoidOverdraw)) {
        for (unsigned int i = 1; i < mBatches.size(); i++) {
            if (mBatches[i] && mBatches[i]->coversBounds(mBounds)) {
                discardDrawingBatches(i - 1);
            }
        }
    }
    // NOTE: depth of the save stack at this point, before playback, should be reflected in
    // FLUSH_SAVE_STACK_DEPTH, so that save/restores match up correctly
    replayBatchList(mBatches, renderer, dirty);

    renderer.restoreToCount(1);

    DEFER_LOGD("--flush complete, returning %x", status);
    clear();
}

void DeferredDisplayList::discardDrawingBatches(const unsigned int maxIndex) {
    for (unsigned int i = mEarliestUnclearedIndex; i <= maxIndex; i++) {
        // leave deferred state ops alone for simplicity (empty save restore pairs may now exist)
        if (mBatches[i] && mBatches[i]->purelyDrawBatch()) {
            delete mBatches[i];
            mBatches.replaceAt(nullptr, i);
        }
    }
    mEarliestUnclearedIndex = maxIndex + 1;
}

}; // namespace uirenderer
}; // namespace android