Add interface for async texture processors.

Implementations of this interface will be able to drop or add frames,
change timestamps, accept multiple input frames before producing
output, and process frames on their own background thread.

A default implementation of this interface will be added to SingleFrameGlTextureProcessor in a follow-up.

PiperOrigin-RevId: 453159835
(cherry picked from commit 023d19c8c5aa54841aeec12657846ac6a889dddb)

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/GlTextureProcessor.java

@@ -0,0 +1,115 @@
+/*
+ * Copyright 2022 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.
+ */
+package com.google.android.exoplayer2.transformer;
+
+/**
+ * Processes frames from one OpenGL 2D texture to another.
+ *
+ * <p>The {@code GlTextureProcessor} consumes input frames it accepts via {@link
+ * #maybeQueueInputFrame(TextureInfo, long)} and surrenders each texture back to the caller via its
+ * {@linkplain Listener#onInputFrameProcessed(TextureInfo) listener} once the texture's contents
+ * have been processed.
+ *
+ * <p>The {@code GlTextureProcessor} produces output frames asynchronously and notifies its owner
+ * when they are available via its {@linkplain Listener#onOutputFrameAvailable(TextureInfo, long)
+ * listener}. The {@code GlTextureProcessor} instance's owner must surrender the texture back to the
+ * {@code GlTextureProcessor} via {@link #releaseOutputFrame(TextureInfo)} when it has finished
+ * processing it.
+ *
+ * <p>{@code GlTextureProcessor} implementations can choose to produce output frames before
+ * receiving input frames or process several input frames before producing an output frame. However,
+ * {@code GlTextureProcessor} implementations cannot assume that they will receive more than one
+ * input frame at a time, so they must process each input frame they accept even if they cannot
+ * produce output yet.
+ *
+ * <p>The methods in this interface must be called on the thread that owns the parent OpenGL
+ * context. If the implementation uses another OpenGL context, e.g., on another thread, it must
+ * configure it to share data with the context of thread the interface methods are called on.
+ */
+public interface GlTextureProcessor {
+
+  /**
+   * Listener for frame processing events.
+   *
+   * <p>This listener can be called from any thread.
+   */
+  interface Listener {
+    /**
+     * Called when the {@link GlTextureProcessor} has processed an input frame.
+     *
+     * @param inputTexture The {@link TextureInfo} that was used to {@linkplain
+     *     #maybeQueueInputFrame(TextureInfo, long) queue} the input frame.
+     */
+    void onInputFrameProcessed(TextureInfo inputTexture);
+
+    /**
+     * Called when the {@link GlTextureProcessor} has produced an output frame.
+     *
+     * <p>After the listener's owner has processed the output frame, it must call {@link
+     * #releaseOutputFrame(TextureInfo)}. The output frame should be released as soon as possible,
+     * as there is no guarantee that the {@link GlTextureProcessor} will produce further output
+     * frames before this output frame is released.
+     *
+     * @param outputTexture A {@link TextureInfo} describing the texture containing the output
+     *     frame.
+     * @param presentationTimeUs The presentation timestamp of the output frame, in microseconds.
+     */
+    void onOutputFrameAvailable(TextureInfo outputTexture, long presentationTimeUs);
+
+    /** Called when the {@link GlTextureProcessor} will not produce further output frames. */
+    void onOutputStreamEnded();
+
+    /**
+     * Called when an exception occurs during asynchronous frame processing.
+     *
+     * <p>If an error occurred, consuming and producing further frames will not work as expected and
+     * the {@link GlTextureProcessor} should be released.
+     */
+    void onFrameProcessingError(FrameProcessingException e);
+  }
+
+  /** Sets the {@link Listener} for frame processing events. */
+  void setListener(Listener listener);
+
+  /**
+   * Processes an input frame if possible.
+   *
+   * <p>If this method returns {@code true} the input frame has been accepted. The {@code
+   * GlTextureProcessor} owns the accepted frame until it calls {@link
+   * Listener#onInputFrameProcessed(TextureInfo)}. The caller should not overwrite or release the
+   * texture before the {@code GlTextureProcessor} has finished processing it.
+   *
+   * <p>If this method returns {@code false}, the input frame could not be accepted and the caller
+   * should decide whether to drop the frame or try again later.
+   *
+   * @param inputTexture A {@link TextureInfo} describing the texture containing the input frame.
+   * @param presentationTimeUs The presentation timestamp of the input frame, in microseconds.
+   * @return Whether the frame was accepted.
+   */
+  boolean maybeQueueInputFrame(TextureInfo inputTexture, long presentationTimeUs);
+
+  /**
+   * Notifies the texture processor that the frame on the given output texture is no longer used and
+   * can be overwritten.
+   */
+  void releaseOutputFrame(TextureInfo outputTexture);
+
+  /** Notifies the texture processor that no further input frames will become available. */
+  void signalEndOfInputStream();
+
+  /** Releases all resources. */
+  void release();
+}