Android系統截屏功能提取

Android在4.0版本之後同時按電源鍵和音量鍵可以截取當前屏幕，截圖後會有一個過渡動畫效果，這裡提取了將效果這部分提取出來，可以用於應用截圖分享功能。

截圖功能在源碼中的位置是com.android.systemui.screenshot，下面有四個類

其中主要工作都在GlobalScreenshot中，包括截圖後的動畫效果、保存到本地和顯示到通知欄。為了簡單，下面的代碼只保留了過渡動畫部分

class GlobalScreenshot {
    private static final String TAG = "GlobalScreenshot";

    private static final int SCREENSHOT_FLASH_TO_PEAK_DURATION = 130;
    private static final int SCREENSHOT_DROP_IN_DURATION = 430;
    private static final int SCREENSHOT_DROP_OUT_DELAY = 500;
    private static final int SCREENSHOT_DROP_OUT_DURATION = 430;
    private static final int SCREENSHOT_DROP_OUT_SCALE_DURATION = 370;
    private static final int SCREENSHOT_FAST_DROP_OUT_DURATION = 320;
    private static final float BACKGROUND_ALPHA = 0.5f;
    private static final float SCREENSHOT_SCALE = 1f;
    private static final float SCREENSHOT_DROP_IN_MIN_SCALE = SCREENSHOT_SCALE * 0.725f;
    private static final float SCREENSHOT_DROP_OUT_MIN_SCALE = SCREENSHOT_SCALE * 0.45f;
    private static final float SCREENSHOT_FAST_DROP_OUT_MIN_SCALE = SCREENSHOT_SCALE * 0.6f;
    private static final float SCREENSHOT_DROP_OUT_MIN_SCALE_OFFSET = 0f;

    private Context mContext;
    private WindowManager mWindowManager;
    private WindowManager.LayoutParams mWindowLayoutParams;
    private Display mDisplay;
    private DisplayMetrics mDisplayMetrics;

    private Bitmap mScreenBitmap;
    private View mScreenshotLayout;
    private ImageView mBackgroundView;
    private ImageView mScreenshotView;
    private ImageView mScreenshotFlash;

    private AnimatorSet mScreenshotAnimation;

    private float mBgPadding;
    private float mBgPaddingScale;

    private MediaActionSound mCameraSound;


    /**
     * @param context everything needs a context :(
     */
    public GlobalScreenshot(Context context) {
        Resources r = context.getResources();
        mContext = context;
        LayoutInflater layoutInflater = (LayoutInflater)
                context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        // Inflate the screenshot layout
        mScreenshotLayout = layoutInflater.inflate(R.layout.global_screenshot, null);
        mBackgroundView = (ImageView) mScreenshotLayout.findViewById(R.id.global_screenshot_background);
        mScreenshotView = (ImageView) mScreenshotLayout.findViewById(R.id.global_screenshot);
        mScreenshotFlash = (ImageView) mScreenshotLayout.findViewById(R.id.global_screenshot_flash);
        mScreenshotLayout.setFocusable(true);
        mScreenshotLayout.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                // Intercept and ignore all touch events
                return true;
            }
        });

        // Setup the window that we are going to use
        mWindowLayoutParams = new WindowManager.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT, 0, 0,
                WindowManager.LayoutParams.TYPE_SYSTEM_ALERT,
                WindowManager.LayoutParams.FLAG_FULLSCREEN
                        | WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED
                        | WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                        | WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED,
                PixelFormat.TRANSLUCENT);
        mWindowLayoutParams.setTitle("ScreenshotAnimation");
        mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

        mDisplay = mWindowManager.getDefaultDisplay();
        mDisplayMetrics = new DisplayMetrics();
        mDisplay.getRealMetrics(mDisplayMetrics);

        // Scale has to account for both sides of the bg
        mBgPadding = (float) r.getDimensionPixelSize(R.dimen.global_screenshot_bg_padding);
        mBgPaddingScale = mBgPadding / mDisplayMetrics.widthPixels;

        // Setup the Camera shutter sound
        mCameraSound = new MediaActionSound();
        mCameraSound.load(MediaActionSound.SHUTTER_CLICK);
    }



    /**
     * Takes a screenshot of the current display and shows an animation.
     */
    void takeScreenshot(View view, Runnable finisher, boolean statusBarVisible, boolean navBarVisible) {
        // Take the screenshot
        mScreenBitmap = SurfaceControl.screenshot(view);
        if (mScreenBitmap == null) {
            notifyScreenshotError(mContext);
            finisher.run();
            return;
        }

        // Optimizations
        mScreenBitmap.setHasAlpha(false);
        mScreenBitmap.prepareToDraw();

        // Start the post-screenshot animation
        startAnimation(finisher, mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels,
                statusBarVisible, navBarVisible);
    }


    /**
     * Starts the animation after taking the screenshot
     */
    private void startAnimation(final Runnable finisher, int w, int h, boolean statusBarVisible,
                                boolean navBarVisible) {
        // Add the view for the animation
        mScreenshotView.setImageBitmap(mScreenBitmap);
        mScreenshotLayout.requestFocus();

        // Setup the animation with the screenshot just taken
        if (mScreenshotAnimation != null) {
            mScreenshotAnimation.end();
            mScreenshotAnimation.removeAllListeners();
        }

        mWindowManager.addView(mScreenshotLayout, mWindowLayoutParams);
        ValueAnimator screenshotDropInAnim = createScreenshotDropInAnimation();
        ValueAnimator screenshotFadeOutAnim = createScreenshotDropOutAnimation(w, h,
                statusBarVisible, navBarVisible);
        mScreenshotAnimation = new AnimatorSet();
        mScreenshotAnimation.playSequentially(screenshotDropInAnim, screenshotFadeOutAnim);
        mScreenshotAnimation.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                // Save the screenshot once we have a bit of time now
                saveScreenshotInWorkerThread(finisher);
                mWindowManager.removeView(mScreenshotLayout);

                // Clear any references to the bitmap
                mScreenBitmap = null;
                mScreenshotView.setImageBitmap(null);
            }
        });
        mScreenshotLayout.post(new Runnable() {
            @Override
            public void run() {
                // Play the shutter sound to notify that we've taken a screenshot
                mCameraSound.play(MediaActionSound.SHUTTER_CLICK);

                mScreenshotView.setLayerType(View.LAYER_TYPE_HARDWARE, null);
                mScreenshotView.buildLayer();
                mScreenshotAnimation.start();
            }
        });
    }

    private ValueAnimator createScreenshotDropInAnimation() {
        final float flashPeakDurationPct = ((float) (SCREENSHOT_FLASH_TO_PEAK_DURATION)
                / SCREENSHOT_DROP_IN_DURATION);
        final float flashDurationPct = 2f * flashPeakDurationPct;
        final Interpolator flashAlphaInterpolator = new Interpolator() {
            @Override
            public float getInterpolation(float x) {
                // Flash the flash view in and out quickly
                if (x <= flashDurationPct) {
                    return (float) Math.sin(Math.PI * (x / flashDurationPct));
                }
                return 0;
            }
        };
        final Interpolator scaleInterpolator = new Interpolator() {
            @Override
            public float getInterpolation(float x) {
                // We start scaling when the flash is at it's peak
                if (x < flashPeakDurationPct) {
                    return 0;
                }
                return (x - flashDurationPct) / (1f - flashDurationPct);
            }
        };
        ValueAnimator anim = ValueAnimator.ofFloat(0f, 1f);
        anim.setDuration(SCREENSHOT_DROP_IN_DURATION);
        anim.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationStart(Animator animation) {
                mBackgroundView.setAlpha(0f);
                mBackgroundView.setVisibility(View.VISIBLE);
                mScreenshotView.setAlpha(0f);
                mScreenshotView.setTranslationX(0f);
                mScreenshotView.setTranslationY(0f);
                mScreenshotView.setScaleX(SCREENSHOT_SCALE + mBgPaddingScale);
                mScreenshotView.setScaleY(SCREENSHOT_SCALE + mBgPaddingScale);
                mScreenshotView.setVisibility(View.VISIBLE);
                mScreenshotFlash.setAlpha(0f);
                mScreenshotFlash.setVisibility(View.VISIBLE);
            }

            @Override
            public void onAnimationEnd(android.animation.Animator animation) {
                mScreenshotFlash.setVisibility(View.GONE);
            }
        });
        anim.addUpdateListener(new AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                float t = (Float) animation.getAnimatedValue();
                float scaleT = (SCREENSHOT_SCALE + mBgPaddingScale)
                        - scaleInterpolator.getInterpolation(t)
                        * (SCREENSHOT_SCALE - SCREENSHOT_DROP_IN_MIN_SCALE);
                mBackgroundView.setAlpha(scaleInterpolator.getInterpolation(t) * BACKGROUND_ALPHA);
                mScreenshotView.setAlpha(t);
                mScreenshotView.setScaleX(scaleT);
                mScreenshotView.setScaleY(scaleT);
                mScreenshotFlash.setAlpha(flashAlphaInterpolator.getInterpolation(t));
            }
        });
        return anim;
    }

    private ValueAnimator createScreenshotDropOutAnimation(int w, int h, boolean statusBarVisible,
                                                           boolean navBarVisible) {
        ValueAnimator anim = ValueAnimator.ofFloat(0f, 1f);
        anim.setStartDelay(SCREENSHOT_DROP_OUT_DELAY);
        anim.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                mBackgroundView.setVisibility(View.GONE);
                mScreenshotView.setVisibility(View.GONE);
                mScreenshotView.setLayerType(View.LAYER_TYPE_NONE, null);
            }
        });

        if (!statusBarVisible || !navBarVisible) {
            // There is no status bar/nav bar, so just fade the screenshot away in place
            anim.setDuration(SCREENSHOT_FAST_DROP_OUT_DURATION);
            anim.addUpdateListener(new AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    float t = (Float) animation.getAnimatedValue();
                    float scaleT = (SCREENSHOT_DROP_IN_MIN_SCALE + mBgPaddingScale)
                            - t * (SCREENSHOT_DROP_IN_MIN_SCALE - SCREENSHOT_FAST_DROP_OUT_MIN_SCALE);
                    mBackgroundView.setAlpha((1f - t) * BACKGROUND_ALPHA);
                    mScreenshotView.setAlpha(1f - t);
                    mScreenshotView.setScaleX(scaleT);
                    mScreenshotView.setScaleY(scaleT);
                }
            });
        } else {
            // In the case where there is a status bar, animate to the origin of the bar (top-left)
            final float scaleDurationPct = (float) SCREENSHOT_DROP_OUT_SCALE_DURATION
                    / SCREENSHOT_DROP_OUT_DURATION;
            final Interpolator scaleInterpolator = new Interpolator() {
                @Override
                public float getInterpolation(float x) {
                    if (x < scaleDurationPct) {
                        // Decelerate, and scale the input accordingly
                        return (float) (1f - Math.pow(1f - (x / scaleDurationPct), 2f));
                    }
                    return 1f;
                }
            };

            // Determine the bounds of how to scale
            float halfScreenWidth = (w - 2f * mBgPadding) / 2f;
            float halfScreenHeight = (h - 2f * mBgPadding) / 2f;
            final float offsetPct = SCREENSHOT_DROP_OUT_MIN_SCALE_OFFSET;
            final PointF finalPos = new PointF(
                    -halfScreenWidth + (SCREENSHOT_DROP_OUT_MIN_SCALE + offsetPct) * halfScreenWidth,
                    -halfScreenHeight + (SCREENSHOT_DROP_OUT_MIN_SCALE + offsetPct) * halfScreenHeight);

            // Animate the screenshot to the status bar
            anim.setDuration(SCREENSHOT_DROP_OUT_DURATION);
            anim.addUpdateListener(new AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    float t = (Float) animation.getAnimatedValue();
                    float scaleT = (SCREENSHOT_DROP_IN_MIN_SCALE + mBgPaddingScale)
                            - scaleInterpolator.getInterpolation(t)
                            * (SCREENSHOT_DROP_IN_MIN_SCALE - SCREENSHOT_DROP_OUT_MIN_SCALE);
                    mBackgroundView.setAlpha((1f - t) * BACKGROUND_ALPHA);
                    mScreenshotView.setAlpha(1f - scaleInterpolator.getInterpolation(t));
                    mScreenshotView.setScaleX(scaleT);
                    mScreenshotView.setScaleY(scaleT);
                    mScreenshotView.setTranslationX(t * finalPos.x);
                    mScreenshotView.setTranslationY(t * finalPos.y);
                }
            });
        }
        return anim;
    }

    private void notifyScreenshotError(Context context) {

    }

    private void saveScreenshotInWorkerThread(Runnable runnable) {

    }


}

看一下效果

下面是下面就分析一下相關原理：<喎?/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+MaGivdjNvMjnus7P1Mq+PC9wPgo8cD692M28uvO3tbvYttTTprXEYml0bWFwo6zTw1dpbmRvd01hbmFnZXLWsb3T1NrGwcS7yc+9q2JpdG1hcM/Uyr6z9sC0o6zSsr7Nyse9q2JpdG1hcLfFtb3Su7j2aW1hZ2VWaWV31tCjrFdpbmRvd01hbmFnZXIgYWRkdmlld77Nv8nS1M/Uyr7By6GjPC9wPgo8cD7OqsHL09DS9dOwtcTQp7n7o6zV4sDvtu7N4rao0uXBy9K7uPZsYXlvdXSjumdsb2JhbF9zY3JlZW5zaG90LnhtbKOsyOfPwjwvcD4KPHA+PHByZSBjbGFzcz0="brush:java;"><frameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> </frameLayout>
上面的布局一共有三層，最下面的background用於遮蓋，中間的screenshot用於放截圖，最上邊還有一層flash，主要是用於做一個反光的效果。

截圖的bitmap就放在global_screenshot這個imageview中。對應的代碼

mScreenshotView.setImageBitmap(mScreenBitmap);
        mScreenshotLayout.requestFocus();

        // Setup the animation with the screenshot just taken
        if (mScreenshotAnimation != null) {
            mScreenshotAnimation.end();
            mScreenshotAnimation.removeAllListeners();
        }

        mWindowManager.addView(mScreenshotLayout, mWindowLayoutParams);

這樣就可以在屏幕上看到截圖了，之後還有一個過渡動畫效果，分別是

        ValueAnimator screenshotDropInAnim = createScreenshotDropInAnimation();
        ValueAnimator screenshotFadeOutAnim = createScreenshotDropOutAnimation(w, h,
                statusBarVisible, navBarVisible);

這兩個屬性動畫完成了顯示-縮放-消失這個過程，具體就是對上面三層view進行變換了。

在Activity中調用

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final GlobalScreenshot screenshot = new GlobalScreenshot(this);
        findViewById(R.id.main_btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                screenshot.takeScreenshot(getWindow().getDecorView(), new Runnable() {
                    @Override
                    public void run() {

                    }
                }, true, true);
            }
        });
    }

後面的兩個boolean參數是表示是否有狀態欄，用於顯示不同的淡出動畫，如果有一個為false，就會直接淡出，而不會向上偏移到狀態欄上。