com/android/internal/app/PlatLogoActivity.java

/*
 * Copyright (C) 2018 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.android.internal.app;

import android.animation.TimeAnimator;
import android.app.Activity;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.MotionEvent.PointerCoords;
import android.view.View;
import android.widget.FrameLayout;

public class PlatLogoActivity extends Activity {
    FrameLayout layout;
    TimeAnimator anim;
    PBackground bg;

    private class PBackground extends Drawable {
        private float maxRadius, radius, x, y, dp;
        private int[] palette;
        private int darkest;
        private float offset;

        public PBackground() {
            randomizePalette();
        }

        /**
         * set inner radius of "p" logo
         */
        public void setRadius(float r) {
            this.radius = Math.max(48*dp, r);
        }

        /**
         * move the "p"
         */
        public void setPosition(float x, float y) {
            this.x = x;
            this.y = y;
        }

        /**
         * for animating the "p"
         */
        public void setOffset(float o) {
            this.offset = o;
        }

        /**
         * rough luminance calculation
         * https://www.w3.org/TR/AERT/#color-contrast
         */
        public float lum(int rgb) {
            return ((Color.red(rgb) * 299f) + (Color.green(rgb) * 587f) + (Color.blue(rgb) * 114f)) / 1000f;
        }

        /**
         * create a random evenly-spaced color palette
         * guaranteed to contrast!
         */
        public void randomizePalette() {
            final int slots = 2 + (int)(Math.random() * 2);
            float[] color = new float[] { (float) Math.random() * 360f, 1f, 1f };
            palette = new int[slots];
            darkest = 0;
            for (int i=0; i<slots; i++) {
                palette[i] = Color.HSVToColor(color);
                color[0] += 360f/slots;
                if (lum(palette[i]) < lum(palette[darkest])) darkest = i;
            }

            final StringBuilder str = new StringBuilder();
            for (int c : palette) {
                str.append(String.format("#%08x ", c));
            }
            Log.v("PlatLogoActivity", "color palette: " + str);
        }

        @Override
        public void draw(Canvas canvas) {
            if (dp == 0) dp = getResources().getDisplayMetrics().density;
            final float width = canvas.getWidth();
            final float height = canvas.getHeight();
            if (radius == 0) {
                setPosition(width / 2, height / 2);
                setRadius(width / 6);
            }
            final float inner_w = radius * 0.667f;

            final Paint paint = new Paint();
            paint.setStrokeCap(Paint.Cap.BUTT);
            canvas.translate(x, y);

            Path p = new Path();
            p.moveTo(-radius, height);
            p.lineTo(-radius, 0);
            p.arcTo(-radius, -radius, radius, radius, -180, 270, false);
            p.lineTo(-radius, radius);

            float w = Math.max(canvas.getWidth(), canvas.getHeight())  * 1.414f;
            paint.setStyle(Paint.Style.FILL);

            int i=0;
            while (w > radius*2 + inner_w*2) {
                paint.setColor(0xFF000000 | palette[i % palette.length]);
                // for a slower but more complete version:
                // paint.setStrokeWidth(w);
                // canvas.drawPath(p, paint);
                canvas.drawOval(-w/2, -w/2, w/2, w/2, paint);
                w -= inner_w * (1.1f + Math.sin((i/20f + offset) * 3.14159f));
                i++;
            }

            // the innermost circle needs to be a constant color to avoid rapid flashing
            paint.setColor(0xFF000000 | palette[(darkest+1) % palette.length]);
            canvas.drawOval(-radius, -radius, radius, radius, paint);

            p.reset();
            p.moveTo(-radius, height);
            p.lineTo(-radius, 0);
            p.arcTo(-radius, -radius, radius, radius, -180, 270, false);
            p.lineTo(-radius + inner_w, radius);

            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(inner_w*2);
            paint.setColor(palette[darkest]);
            canvas.drawPath(p, paint);
            paint.setStrokeWidth(inner_w);
            paint.setColor(0xFFFFFFFF);
            canvas.drawPath(p, paint);
        }

        @Override
        public void setAlpha(int alpha) {

        }

        @Override
        public void setColorFilter(ColorFilter colorFilter) {

        }

        @Override
        public int getOpacity() {
            return 0;
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        layout = new FrameLayout(this);
        setContentView(layout);

        bg = new PBackground();
        layout.setBackground(bg);

        layout.setOnTouchListener(new View.OnTouchListener() {
            final PointerCoords pc0 = new PointerCoords();
            final PointerCoords pc1 = new PointerCoords();

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getActionMasked()) {
                    case MotionEvent.ACTION_DOWN:
                    case MotionEvent.ACTION_MOVE:
                        if (event.getPointerCount() > 1) {
                            event.getPointerCoords(0, pc0);
                            event.getPointerCoords(1, pc1);
                            bg.setRadius((float) Math.hypot(pc0.x - pc1.x, pc0.y - pc1.y) / 2f);
                        }
                        break;
                }
                return true;
            }
        });
    }

    @Override
    public void onStart() {
        super.onStart();

        bg.randomizePalette();

        anim = new TimeAnimator();
        anim.setTimeListener(
                new TimeAnimator.TimeListener() {
                    @Override
                    public void onTimeUpdate(TimeAnimator animation, long totalTime, long deltaTime) {
                        bg.setOffset((float) totalTime / 60000f);
                        bg.invalidateSelf();
                    }
                });

        anim.start();
    }

    @Override
    public void onStop() {
        if (anim != null) {
            anim.cancel();
            anim = null;
        }
        super.onStop();
    }
}