gecko-dev/mobile/android/base/gfx/OverscrollEdgeEffect.java

/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * 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/. */

package org.mozilla.gecko.gfx;

import org.mozilla.gecko.AppConstants.Versions;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PointF;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.widget.EdgeEffect;

import java.lang.reflect.Field;

public class OverscrollEdgeEffect implements Overscroll {
    // Used to index particular edges in the edges array
    private static final int TOP = 0;
    private static final int BOTTOM = 1;
    private static final int LEFT = 2;
    private static final int RIGHT = 3;

    // All four edges of the screen
    private final EdgeEffect[] mEdges = new EdgeEffect[4];

    // The view we're showing this overscroll on.
    private final LayerView mView;

    public OverscrollEdgeEffect(final LayerView v) {
        Field paintField = null;
        if (Versions.feature21Plus) {
            try {
                paintField = EdgeEffect.class.getDeclaredField("mPaint");
                paintField.setAccessible(true);
            } catch (NoSuchFieldException e) {
            }
        }

        mView = v;
        Context context = v.getContext();
        for (int i = 0; i < 4; i++) {
            mEdges[i] = new EdgeEffect(context);

            try {
                if (paintField != null) {
                    final Paint p = (Paint) paintField.get(mEdges[i]);

                    // The Android EdgeEffect class uses a mode of SRC_ATOP here, which means it will only
                    // draw the effect where there are non-transparent pixels in the destination. Since the LayerView
                    // itself is fully transparent, it doesn't display at all. We need to use SRC instead.
                    p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
                }
            } catch (IllegalAccessException e) {
            }
        }
    }

    @Override
    public void setSize(final int width, final int height) {
        mEdges[LEFT].setSize(height, width);
        mEdges[RIGHT].setSize(height, width);
        mEdges[TOP].setSize(width, height);
        mEdges[BOTTOM].setSize(width, height);
    }

    private EdgeEffect getEdgeForAxisAndSide(final Axis axis, final float side) {
        if (axis == Axis.Y) {
            if (side < 0) {
                return mEdges[TOP];
            } else {
                return mEdges[BOTTOM];
            }
        } else {
            if (side < 0) {
                return mEdges[LEFT];
            } else {
                return mEdges[RIGHT];
            }
        }
    }

    private void invalidate() {
        if (Versions.feature16Plus) {
            mView.postInvalidateOnAnimation();
        } else {
            mView.postInvalidateDelayed(10);
        }
    }

    @Override
    public void setVelocity(final float velocity, final Axis axis) {
        final EdgeEffect edge = getEdgeForAxisAndSide(axis, velocity);

        // If we're showing overscroll already, start fading it out.
        if (!edge.isFinished()) {
            edge.onRelease();
        } else {
            // Otherwise, show an absorb effect
            edge.onAbsorb((int)velocity);
        }

        invalidate();
    }

    @Override
    public void setDistance(final float distance, final Axis axis) {
        // The first overscroll event often has zero distance. Throw it out
        if (distance == 0.0f) {
            return;
        }

        final EdgeEffect edge = getEdgeForAxisAndSide(axis, (int)distance);
        edge.onPull(distance / (axis == Axis.X ? mView.getWidth() : mView.getHeight()));
        invalidate();
    }

    @Override
    public void draw(final Canvas canvas, final ImmutableViewportMetrics metrics) {
        if (metrics == null) {
            return;
        }

        float fillerSize = mView.getDynamicToolbarAnimator().getMaxTranslation();
        PointF visibleEnd = mView.getDynamicToolbarAnimator().getVisibleEndOfLayerView();

        // If we're pulling an edge, or fading it out, draw!
        boolean invalidate = false;
        if (!mEdges[TOP].isFinished()) {
            invalidate |= draw(mEdges[TOP], canvas, 0, fillerSize, 0);
        }

        if (!mEdges[BOTTOM].isFinished()) {
            invalidate |= draw(mEdges[BOTTOM], canvas, visibleEnd.x, fillerSize + visibleEnd.y, 180);
        }

        if (!mEdges[LEFT].isFinished()) {
            invalidate |= draw(mEdges[LEFT], canvas, 0, fillerSize + visibleEnd.y, 270);
        }

        if (!mEdges[RIGHT].isFinished()) {
            invalidate |= draw(mEdges[RIGHT], canvas, visibleEnd.x, fillerSize, 90);
        }

        // If the edge effect is animating off screen, invalidate.
        if (invalidate) {
            invalidate();
        }
    }

    private static boolean draw(final EdgeEffect edge, final Canvas canvas, final float translateX, final float translateY, final float rotation) {
        final int state = canvas.save();
        canvas.translate(translateX, translateY);
        canvas.rotate(rotation);
        boolean invalidate = edge.draw(canvas);
        canvas.restoreToCount(state);

        return invalidate;
    }
}