android/graphics/PostProcessor.java

/*
 * Copyright (C) 2017 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 android.graphics;

import android.annotation.NonNull;
import android.graphics.drawable.AnimatedImageDrawable;
import android.graphics.drawable.Drawable;

/**
 *  Helper interface for adding custom processing to an image.
 *
 *  <p>The image being processed may be a {@link Drawable}, a {@link Bitmap}, or
 *  a frame of an {@link AnimatedImageDrawable} produced by {@link ImageDecoder}.
 *  This is called before the requested object is returned.</p>
 *
 *  <p>This custom processing can even be applied to images that will be returned
 *  as immutable objects, such as a {@link Bitmap} with {@code Config}
 *  {@link Bitmap.Config#HARDWARE} returned by {@link ImageDecoder}.</p>
 *
 *  <p>On an {@link AnimatedImageDrawable}, the callback will only be called once,
 *  but the drawing commands will be applied to each frame, as if the {@link Canvas}
 *  had been returned by {@link Picture#beginRecording Picture.beginRecording}.<p>
 *
 *  <p>Supplied to ImageDecoder via {@link ImageDecoder#setPostProcessor setPostProcessor}.</p>
 */
public interface PostProcessor {
    /**
     *  Do any processing after (for example) decoding.
     *
     *  <p>Drawing to the {@link Canvas} will behave as if the initial processing
     *  (e.g. decoding) already exists in the Canvas. An implementation can draw
     *  effects on top of this, or it can even draw behind it using
     *  {@link PorterDuff.Mode#DST_OVER PorterDuff.Mode.DST_OVER}. A common
     *  effect is to add transparency to the corners to achieve rounded corners.
     *  That can be done with the following code:</p>
     *
     *  <pre class="prettyprint">
     *  Path path = new Path();
     *  path.setFillType(Path.FillType.INVERSE_EVEN_ODD);
     *  int width = canvas.getWidth();
     *  int height = canvas.getHeight();
     *  path.addRoundRect(0, 0, width, height, 20, 20, Path.Direction.CW);
     *  Paint paint = new Paint();
     *  paint.setAntiAlias(true);
     *  paint.setColor(Color.TRANSPARENT);
     *  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
     *  canvas.drawPath(path, paint);
     *  return PixelFormat.TRANSLUCENT;
     *  </pre>
     *
     *
     *  @param canvas The {@link Canvas} to draw to.
     *  @return Opacity of the result after drawing.
     *      {@link PixelFormat#UNKNOWN PixelFormat.UNKNOWN} means that the
     *      implementation did not change whether the image has alpha. Return
     *      this unless you added transparency (e.g. with the code above, in
     *      which case you should return
     *      {@link PixelFormat#TRANSLUCENT PixelFormat.TRANSLUCENT}) or you
     *      forced the image to be opaque (e.g. by drawing everywhere with an
     *      opaque color and {@link PorterDuff.Mode#DST_OVER PorterDuff.Mode.DST_OVER},
     *      in which case you should return {@link PixelFormat#OPAQUE PixelFormat.OPAQUE}).
     *      {@link PixelFormat#TRANSLUCENT PixelFormat.TRANSLUCENT} means that
     *      the implementation added transparency. This is safe to return even
     *      if the image already had transparency. This is also safe to return
     *      if the result is opaque, though it may draw more slowly.
     *      {@link PixelFormat#OPAQUE PixelFormat.OPAQUE} means that the
     *      implementation forced the image to be opaque. This is safe to return
     *      even if the image was already opaque.
     *      {@link PixelFormat#TRANSPARENT PixelFormat.TRANSPARENT} (or any other
     *      integer) is not allowed, and will result in throwing an
     *      {@link java.lang.IllegalArgumentException}.
     */
    @PixelFormat.Opacity
    public int onPostProcess(@NonNull Canvas canvas);
}