7

これが本当の謎です。

複雑な画像を画面外に描画する従来のプロセス（CGLayer）を実行していて、描画中に画面上で画像を断続的に更新していると想像してください。

ご存知のとおり、これを行う方法は次のとおりです。バックグラウンドで大規模な描画プロセスを実行し、必要に応じてフォアグラウンドでsetNeedsDisplaysを呼び出して、画像を更新します。これは簡単で、2行のコードで実現されます。

ただし、これを行うと、不思議な問題が発生します。各描画サイクルにかかる時間が毎回長くなり、使用できなくなります。さらに、時間は不規則に変化する可能性があります。

これは既知のiOSバグですか、それとも？誰かがこれを見たことがありますか？

これは非常に些細で非常に理解しやすいアプリで、問題をデモします。

http://www.fileswap.com/dl/p8lU3gAi/stepwiseDrawingV2.zip.html

以下の出力例。

なぜこれが起こるのか誰かが知っていますか？OSからは非常に奇妙な振る舞いです。

後で...驚くべき回避策がFELZによって理解されました。Felzは、ラウンドごとに1回CGLayerをコピーします。これにより、奇妙な動作が完全に停止します。

しかし、一体何が起こっているのかについての明確な理解はまだありません。したがって、文字通り、奇妙な問題が発生するときに使用されている時間はどこですか？

そして、これが出力の長い例です...

次のような「二重に奇妙な」結果が得られる場合があることに注意してください。これは「通常の」奇妙な動作を示しています。時間は毎回増加します。ただし、場合によっては、数ラウンドの間、時間が「信じられないほど速い」に低下し、その後戻ってくることがあります。変なハァッ？さらに、シミュレーターで実行している場合は、Mac上の無関係なアプリをクリックしてすばやく前に進み、「さらに奇妙な」結果を得ることができます。

Felzは完璧な答えを出しましたが、実際のメカニズムはまだ謎です。

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4

3 に答える 3

10

まず、これは面白いパズルだったと言わせてください。私はこれに取り組むのがとても楽しかったです。素敵な質問と素敵なサンプルコード。

考えられる答えについての私の見解は次のとおりです。

私が見る問題は次のとおりです。CGLayerは、レンダリングをフラットイメージにキャッシュするため、繰り返しペイントするのに最適です。追加の操作がコンテキストに追加されると、キャッシュは無効になります。これが発生すると、CGLayerが再度レンダリングされます。コードが単一のCGLayer（offscreenPrefabCGL ）を維持し、 paintActualGutsOfHugeImageのループのすべての反復でコンテキストが変更されるため、速度が低下します。offscreenPrefabCGLのコンテキストでの操作のシーケンスは花ごとに大きくなるため、レンダリングごとに時間がかかります。これは、各ディスプレイの時間の増加を説明しています。

私は2つの解決策を見ます：

  1. 新しいレンダリングをPaintViewの特定の場所にクリップします。ビュー全体を無効にする代わりに、実際に再描画が必要なCGRectのみを無効にします。これは、私が理解しているように、@v01dによって提案されたソリューションです。
  2. レイヤーをフラットにします。単一のCGLayerを保持する代わりに、反復ごとにCGLayerをコピーします。これにより、レンダリングが非常に高速なフラットな画像がレイヤーに維持されます。

（2）を実装しましたが、良い結果が得られました。最初の100の花はより速く、その後120msで安定します（デバイス内）。変更したバージョンを最大2000の花でテストしました。

私の変更したバージョンは次のとおりです。

http://dl.dropbox.com/u/9866261/felz_mod_stepwiseDrawingV2.zip

于 2011-01-25T11:37:59.940 に答える
3

EDIT2：

これが動作中の（減速なしの）デバッグプロジェクトです：http：//bit.ly/eukSgR

このプロジェクトは決して最適ではありません。

ここで興味深いのは、ビットマップコンテキストの必要性です。CGLayerは画像の描画をキャッシュし、進行性の速度低下を引き起こします。ビットマップコンテキストでは、レンダリングが強制されます。次に、これらのピクセルをdrawRect：のUIViewのCALayerにプッシュするだけです。

速度を上げるには、setNeedsDisplayInRect：を使用して、再描画する領域を最小限に抑えることができます。

ただし、あちこちで1つか2つの最適化を行う以外は、UIViewを介してピクセルをプッシュする方が、GPUでGLなどを介して完全にプッシュするよりも常に遅くなります。

于 2011-01-25T07:32:14.157 に答える
0

1つの実験として、進行中の未完成の大きな画像のビットマップまたはレイヤーの描画を使用して描画したり、そこから読み取ったりせずに、アニメーションの進行状況ビューを更新することをお勧めします。別の描画コンテキストからの読み取りまたは未完成の合成による描画は、GPUパイプラインまたは描画状態に興味深いことをしている可能性があります。ペッパーメソッドで何か他のものを描いてみてください。シンプルなカウンターか何か。

于 2011-01-25T04:08:26.780 に答える