/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "AnimationFrameBuffer.h"
#include "mozilla/Move.h" // for Move
namespace mozilla {
namespace image {
AnimationFrameBuffer::AnimationFrameBuffer()
: mThreshold(0),
mBatch(0),
mPending(0),
mAdvance(0),
mInsertIndex(0),
mGetIndex(0),
mSizeKnown(false) {}
void AnimationFrameBuffer::Initialize(size_t aThreshold, size_t aBatch,
size_t aStartFrame) {
MOZ_ASSERT(mThreshold == 0);
MOZ_ASSERT(mBatch == 0);
MOZ_ASSERT(mPending == 0);
MOZ_ASSERT(mAdvance == 0);
MOZ_ASSERT(mFrames.IsEmpty());
mThreshold = aThreshold;
mBatch = aBatch;
mAdvance = aStartFrame;
if (mBatch > SIZE_MAX / 4) {
// Batch size is so big, we will just end up decoding the whole animation.
mBatch = SIZE_MAX / 4;
} else if (mBatch < 1) {
// Never permit a batch size smaller than 1. We always want to be asking for
// at least one frame to start.
mBatch = 1;
}
// To simplify the code, we have the assumption that the threshold for
// entering discard-after-display mode is at least twice the batch size (since
// that is the most frames-pending-decode we will request) + 1 for the current
// frame. That way the redecoded frames being inserted will never risk
// overlapping the frames we will discard due to the animation progressing.
// That may cause us to use a little more memory than we want but that is an
// acceptable tradeoff for simplicity.
size_t minThreshold = 2 * mBatch + 1;
if (mThreshold < minThreshold) {
mThreshold = minThreshold;
}
// The maximum number of frames we should ever have decoded at one time is
// twice the batch. That is a good as number as any to start our decoding at.
mPending = mBatch * 2;
}
bool AnimationFrameBuffer::Insert(RawAccessFrameRef&& aFrame) {
// We should only insert new frames if we actually asked for them.
MOZ_ASSERT(mPending > 0);
if (mSizeKnown) {
// We only insert after the size is known if we are repeating the animation
// and we did not keep all of the frames. Replace whatever is there
// (probably an empty frame) with the new frame.
MOZ_ASSERT(MayDiscard());
MOZ_ASSERT(mInsertIndex < mFrames.Length());
if (mInsertIndex > 0) {
MOZ_ASSERT(!mFrames[mInsertIndex]);
mFrames[mInsertIndex] = Move(aFrame);
}
} else if (mInsertIndex == mFrames.Length()) {
// We are still on the first pass of the animation decoding, so this is
// the first time we have seen this frame.
mFrames.AppendElement(Move(aFrame));
if (mInsertIndex == mThreshold) {
// We just tripped over the threshold for the first time. This is our
// chance to do any clearing of already displayed frames. After this,
// we only need to release as we advance or force a restart.
MOZ_ASSERT(MayDiscard());
MOZ_ASSERT(mGetIndex < mInsertIndex);
for (size_t i = 1; i < mGetIndex; ++i) {
RawAccessFrameRef discard = Move(mFrames[i]);
}
}
} else if (mInsertIndex > 0) {
// We were forced to restart an animation before we decoded the last
// frame. If we were discarding frames, then we tossed what we had
// except for the first frame.
MOZ_ASSERT(mInsertIndex < mFrames.Length());
MOZ_ASSERT(!mFrames[mInsertIndex]);
MOZ_ASSERT(MayDiscard());
mFrames[mInsertIndex] = Move(aFrame);
} else { // mInsertIndex == 0
// We were forced to restart an animation before we decoded the last
// frame. We don't need the redecoded first frame because we always keep
// the original.
MOZ_ASSERT(MayDiscard());
}
MOZ_ASSERT(mFrames[mInsertIndex]);
++mInsertIndex;
// Ensure we only request more decoded frames if we actually need them. If we
// need to advance to a certain point in the animation on behalf of the owner,
// then do so. This ensures we keep decoding. If the batch size is really
// small (i.e. 1), it is possible advancing will request the decoder to
// "restart", but we haven't told it to stop yet. Note that we skip the first
// insert because we actually start "advanced" to the first frame anyways.
bool continueDecoding = --mPending > 0;
if (mAdvance > 0 && mInsertIndex > 1) {
continueDecoding |= AdvanceInternal();
--mAdvance;
}
return continueDecoding;
}
bool AnimationFrameBuffer::MarkComplete() {
// We reached the end of the animation, the next frame we get, if we get
// another, will be the first frame again.
MOZ_ASSERT(mInsertIndex == mFrames.Length());
mInsertIndex = 0;
// Since we only request advancing when we want to resume at a certain point
// in the animation, we should never exceed the number of frames.
MOZ_ASSERT(mAdvance == 0);
if (!mSizeKnown) {
// We just received the last frame in the animation. Compact the frame array
// because we know we won't need to grow beyond here.
mSizeKnown = true;
mFrames.Compact();
if (!MayDiscard()) {
// If we did not meet the threshold, then we know we want to keep all of
// the frames. If we also hit the last frame, we don't want to ask for
// more.
mPending = 0;
}
}
return mPending > 0;
}
DrawableFrameRef AnimationFrameBuffer::Get(size_t aFrame) {
// We should not have asked for a frame if we never inserted.
if (mFrames.IsEmpty()) {
MOZ_ASSERT_UNREACHABLE("Calling Get() when we have no frames");
return DrawableFrameRef();
}
// If we don't have that frame, return an empty frame ref.
if (aFrame >= mFrames.Length()) {
return DrawableFrameRef();
}
// We've got the requested frame because we are not discarding frames. While
// we typically should have not run out of frames since we ask for more before
// we want them, it is possible the decoder is behind.
if (!mFrames[aFrame]) {
MOZ_ASSERT(MayDiscard());
return DrawableFrameRef();
}
// If we are advancing on behalf of the animation, we don't expect it to be
// getting any frames (besides the first) until we get the desired frame.
MOZ_ASSERT(aFrame == 0 || mAdvance == 0);
return mFrames[aFrame]->DrawableRef();
}
bool AnimationFrameBuffer::AdvanceTo(size_t aExpectedFrame) {
// The owner should only be advancing once it has reached the requested frame
// in the animation.
MOZ_ASSERT(mAdvance == 0);
bool restartDecoder = AdvanceInternal();
// Advancing should always be successful, as it should only happen after the
// owner has accessed the next (now current) frame.
MOZ_ASSERT(mGetIndex == aExpectedFrame);
return restartDecoder;
}
bool AnimationFrameBuffer::AdvanceInternal() {
// We should not have advanced if we never inserted.
if (mFrames.IsEmpty()) {
MOZ_ASSERT_UNREACHABLE("Calling Advance() when we have no frames");
return false;
}
// We only want to change the current frame index if we have advanced. This
// means either a higher frame index, or going back to the beginning.
size_t framesLength = mFrames.Length();
// We should never have advanced beyond the frame buffer.
MOZ_ASSERT(mGetIndex < framesLength);
// We should never advance if the current frame is null -- it needs to know
// the timeout from it at least to know when to advance.
MOZ_ASSERT(mFrames[mGetIndex]);
if (++mGetIndex == framesLength) {
MOZ_ASSERT(mSizeKnown);
mGetIndex = 0;
}
// The owner should have already accessed the next frame, so it should also
// be available.
MOZ_ASSERT(mFrames[mGetIndex]);
// If we moved forward, that means we can remove the previous frame, assuming
// that frame is not the first frame. If we looped and are back at the first
// frame, we can remove the last frame.
if (MayDiscard()) {
RawAccessFrameRef discard;
if (mGetIndex > 1) {
discard = Move(mFrames[mGetIndex - 1]);
} else if (mGetIndex == 0) {
MOZ_ASSERT(mSizeKnown && framesLength > 1);
discard = Move(mFrames[framesLength - 1]);
}
}
if (!mSizeKnown || MayDiscard()) {
// Calculate how many frames we have requested ahead of the current frame.
size_t buffered = mPending;
if (mGetIndex > mInsertIndex) {
// It wrapped around and we are decoding the beginning again before the
// the display has finished the loop.
MOZ_ASSERT(mSizeKnown);
buffered += mInsertIndex + framesLength - mGetIndex - 1;
} else {
buffered += mInsertIndex - mGetIndex - 1;
}
if (buffered < mBatch) {
// If we have fewer frames than the batch size, then ask for more. If we
// do not have any pending, then we know that there is no active decoding.
mPending += mBatch;
return mPending == mBatch;
}
}
return false;
}
bool AnimationFrameBuffer::Reset() {
// The animation needs to start back at the beginning.
mGetIndex = 0;
mAdvance = 0;
if (!MayDiscard()) {
// If we haven't crossed the threshold, then we know by definition we have
// not discarded any frames. If we previously requested more frames, but
// it would have been more than we would have buffered otherwise, we can
// stop the decoding after one more frame.
if (mPending > 1 && mInsertIndex - 1 >= mBatch * 2) {
MOZ_ASSERT(!mSizeKnown);
mPending = 1;
}
// Either the decoder is still running, or we have enough frames already.
// No need for us to restart it.
return false;
}
// If we are over the threshold, then we know we will have missing frames in
// our buffer. The easiest thing to do is to drop everything but the first
// frame and go back to the initial state.
bool restartDecoder = mPending == 0;
mInsertIndex = 0;
mPending = 2 * mBatch;
// Discard all frames besides the first, because the decoder always expects
// that when it re-inserts a frame, it is not present. (It doesn't re-insert
// the first frame.)
for (size_t i = 1; i < mFrames.Length(); ++i) {
RawAccessFrameRef discard = Move(mFrames[i]);
}
return restartDecoder;
}
} // namespace image
} // namespace mozilla