already_AddRefed<gfx::DrawTarget>
PersistentBufferProviderShared::BorrowDrawTarget(const gfx::IntRect& aPersistedRect)
{
if (!mFwd->GetTextureForwarder()->IPCOpen()) {
return nullptr;
}
MOZ_ASSERT(!mSnapshot);
if (IsActivityTracked()) {
mFwd->GetActiveResourceTracker().MarkUsed(this);
} else {
mFwd->GetActiveResourceTracker().AddObject(this);
}
if (mDrawTarget) {
RefPtr<gfx::DrawTarget> dt(mDrawTarget);
return dt.forget();
}
mFront = Nothing();
auto previousBackBuffer = mBack;
TextureClient* tex = GetTexture(mBack);
// First try to reuse the current back buffer. If we can do that it means
// we can skip copying its content to the new back buffer.
if (tex && tex->IsReadLocked()) {
// The back buffer is currently used by the compositor, we can't draw
// into it.
tex = nullptr;
}
if (!tex) {
// Try to grab an already allocated texture if any is available.
for (uint32_t i = 0; i < mTextures.length(); ++i) {
if (!mTextures[i]->IsReadLocked()) {
mBack = Some(i);
tex = mTextures[i];
break;
}
}
}
if (!tex) {
// We have to allocate a new texture.
if (mTextures.length() >= 4) {
// We should never need to buffer that many textures, something's wrong.
MOZ_ASSERT(false);
// In theory we throttle the main thread when the compositor can't keep up,
// so we shoud never get in a situation where we sent 4 textures to the
// compositor and the latter as not released any of them.
// This seems to happen, however, in some edge cases such as just after a
// device reset (cf. Bug 1291163).
// It would be pretty bad to keep piling textures up at this point so we
// call NotifyInactive to remove some of our textures.
NotifyInactive();
// Give up now. The caller can fall-back to a non-shared buffer provider.
return nullptr;
}
RefPtr<TextureClient> newTexture = TextureClient::CreateForDrawing(
mFwd, mFormat, mSize,
BackendSelector::Canvas,
TextureFlags::DEFAULT,
TextureAllocationFlags::ALLOC_DEFAULT
);
MOZ_ASSERT(newTexture);
if (newTexture) {
if (mTextures.append(newTexture)) {
tex = newTexture;
mBack = Some<uint32_t>(mTextures.length() - 1);
}
}
}
if (!tex || !tex->Lock(OpenMode::OPEN_READ_WRITE)) {
return nullptr;
}
if (mBack != previousBackBuffer && !aPersistedRect.IsEmpty()) {
TextureClient* previous = GetTexture(previousBackBuffer);
if (previous && previous->Lock(OpenMode::OPEN_READ)) {
DebugOnly<bool> success = previous->CopyToTextureClient(tex, &aPersistedRect, nullptr);
MOZ_ASSERT(success);
previous->Unlock();
}
}
mDrawTarget = tex->BorrowDrawTarget();
RefPtr<gfx::DrawTarget> dt(mDrawTarget);
return dt.forget();
}
