Andrews - multimedia programming

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Multimedia concept

• writing 、 picture 、 Audio 、 video Calculate the size of the computer image Image size = Total image pixels * The size of each pixel occupies
• Monochromatic graph ： Every pixel takes up 1/8 Bytes
• 16 Color map ： Every pixel takes up 1/2 Bytes
• 256 Color map ： Every pixel takes up 1 Bytes
• 24 Bitmap ： Every pixel takes up 3 Bytes

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Load large pictures into memory

Android System to ARGB Represents each pixel , So each pixel occupies 4 Bytes , very easy out of memory

Scale the image

• Get screen width and height

Display dp = getWindowManager().getDefaultDisplay();
int screenWidth = dp.getWidth();
int screenHeight = dp.getHeight();

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• Get the width and height of the picture

Options opts = new Options();
// Request image attributes but not memory 
opts.inJustDecodeBounds = true;
BitmapFactory.decodeFile("sdcard/dog.jpg", opts);
int imageWidth = opts.outWidth;
int imageHeight = opts.outHeight;

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• Divide the width and height of the picture by the width and height of the screen , Calculate the scale of width and height , Take a larger value as the zoom ratio of the picture

int scale = 1;
int scaleX = imageWidth / screenWidth;
int scaleY = imageHeight / screenHeight;
if(scaleX >= scaleY && scaleX > 1){
    scale = scaleX;
}
else if(scaleY > scaleX && scaleY > 1){
    scale = scaleY;
}

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• Load pictures in scale

// Set scaling 
opts.inSampleSize = scale;
// Apply for memory for pictures 
opts.inJustDecodeBounds = false;
Bitmap bm = BitmapFactory.decodeFile("sdcard/dog.jpg", opts);
iv.setImageBitmap(bm);

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Create a copy of the picture in memory

Directly loaded bitmap Objects are only read . Unable to change . To change an image, you can only create an identical one in memory bitmap copy . Then change the copy

    // Load original 
    Bitmap srcBm = BitmapFactory.decodeFile("sdcard/photo3.jpg");
    iv_src.setImageBitmap(srcBm);

    // Create a blank that is the same size as the original bitmap
    Bitmap copyBm = Bitmap.createBitmap(srcBm.getWidth(), srcBm.getHeight(), srcBm.getConfig());
    // Define the brush 
    Paint paint = new Paint();
    // Lay the paper on the drawing board 
    Canvas canvas = new Canvas(copyBm);
    // hold srcBm The content of is drawn in copyBm On 
    canvas.drawBitmap(srcBm, new Matrix(), paint);

    iv_copy.setImageBitmap(copyBm);

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Create a copy of the picture in memory Directly loaded bitmap Objects are only read . Unable to change . To change an image, you can only create an identical one in memory bitmap copy . Then change the copy

    // Load original 
    Bitmap srcBm = BitmapFactory.decodeFile("sdcard/photo3.jpg");
    iv_src.setImageBitmap(srcBm);

    // Create a blank that is the same size as the original bitmap
    Bitmap copyBm = Bitmap.createBitmap(srcBm.getWidth(), srcBm.getHeight(), srcBm.getConfig());
    // Define the brush 
    Paint paint = new Paint();
    // Lay the paper on the drawing board 
    Canvas canvas = new Canvas(copyBm);
    // hold srcBm The content of is drawn in copyBm On 
    canvas.drawBitmap(srcBm, new Matrix(), paint);

    iv_copy.setImageBitmap(copyBm);

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Special effect the picture

• First define a matrix object

Matrix mt = new Matrix(); 

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• Zoom effect

//x Axis zoom 1 times ,y Axis zoom 0.5 times 
mt.setScale(1, 0.5f);

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• Rotation effect

// With copyBm.getWidth() / 2, copyBm.getHeight() / 2 The point is the pivot point , Rotate in time 30 degree 
mt.setRotate(30, copyBm.getWidth() / 2, copyBm.getHeight() / 2);

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• translation

//x Axis coordinates +10,y Axis coordinates +20
mt.setTranslate(10, 20);

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• The mirror

// hold X Coordinates become negative 
mt.setScale(-1, 1);
// The picture moves to the right as a whole 
mt.postTranslate(copyBm.getWidth(), 0);

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• inverted reflection in water

// hold Y Coordinates become negative 
mt.setScale(1, -1);
// The picture moves down as a whole 
mt.postTranslate(0, copyBm.getHeight());

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Sketchpad

Record user touch events XY coordinate , Draw a straight line

• to ImageView Set touch listening , Get the user's touch event , And know that the user touches ImageView Coordinates of

    iv.setOnTouchListener(new OnTouchListener() {

        @Override
        public boolean onTouch(View v, MotionEvent event) {
            // TODO Auto-generated method stub
            switch (event.getAction()) {
            // Touch the screen 
            case MotionEvent.ACTION_DOWN:
                // Get the coordinates of your fingers when touching the screen 
                startX = (int) event.getX();
                startY = (int) event.getY();
                break;
            // Slide on screen 
            case MotionEvent.ACTION_MOVE:
                // The user slides his finger . The coordinates are constantly changing , Get the latest coordinates 
                int newX = (int) event.getX();
                int newY = (int) event.getY();
                // Use last time onTouch Draw a straight line with the coordinates obtained by the method and the coordinates obtained this time 
                canvas.drawLine(startX, startY, newX, newY, paint);
                iv.setImageBitmap(copyBm);
                startX = newX;
                startY = newY;
                break;

            }
            return true;
        }
    });

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• Brush effect , Bold brush

paint.setStrokeWidth(8);

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• palette . Change the brush color

paint.setColor(Color.GREEN);

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• Save the picture to SD card

FileOutputStream fos = null;
try {
    fos = new FileOutputStream(new File("sdcard/dazuo.png"));
} catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
// Save the picture 
copyBm.compress(CompressFormat.PNG, 100, fos);

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• Every time the system receives SD When the card is ready to broadcast . Will traverse sd All files and directories of the card , Put all the multimedia files traversed in MediaStore The database holds an index . This index includes the file names of multimedia files 、 route 、 size
• Every time the gallery is opened . I won't traverse sd Card to get pictures . Instead, it is through the content provider from MediaStore Get the information of pictures in the database , Then read the picture
• Start the system or click load sd card button when , The system will send sd Card ready broadcast , We can also send ready broadcasts manually

Intent intent = new Intent();
intent.setAction(Intent.ACTION_MEDIA_MOUNTED);
intent.setData(Uri.fromFile(Environment.getExternalStorageDirectory()));
sendBroadcast(intent);

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heartbeat

• principle ： Overlay the photos of wearing underwear and clothes . Underwear is shown below , When the user swipes the screen . What you touch is a coat photo . Set the pixels passed by your fingers to be transparent . Underwear photos show up

 iv.setOnTouchListener(new OnTouchListener() {

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
        case MotionEvent.ACTION_MOVE:
            int newX = (int) event.getX();
            int newY = (int) event.getY();
            // Make the specified pixel transparent 
            copyBm.setPixel(newX, newY, Color.TRANSPARENT);
            iv.setImageBitmap(copyBm);
            break;

        }
        return true;
    }
});

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• Setting just one pixel at a time is too slow , Take the touched pixel as the center of the circle . The radius is 5 A circle , All pixels in the circle are made transparent

for (int i = -5; i < 6; i++) {
    for (int j = -5; j < 6; j++) {
        if(Math.sqrt(i * i + j * j) <= 5)
            copyBm.setPixel(newX + i, newY + j, Color.TRANSPARENT);
    }
}

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Music player

Broadcast service

• The code for playing audio should be executed in the service . Define a playback service MusicService
• The definition of service is play、stop、pause、continuePlay Other methods

    private void play() {
        // TODO Auto-generated method stub
        player.reset();
        try {
            player.setDataSource("sdcard/bzj.mp3");
            player.prepare();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        player.start();

    }
    private void pause() {
        player.pause();
    }
    private void stop() {
        player.stop();
    }
    private void continuePlay() {
        player.start();
    }

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• Extract these methods into an interface MusicInterface
• Define an intermediate human , Inherit Binder, Realization MusicInterface
• First start start-up MusicService, Again bind

Intent intent = new Intent(this, MusicService.class);
startService(intent);
bindService(intent, conn, BIND_AUTO_CREATE);

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• Set the progress bar according to the playback progress
• Get the current playback time and the maximum time of the current audio

int currentPosition = player.getCurrentPosition();
int duration = player.getDuration();

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• The playback progress needs to be obtained constantly . Keep refreshing the progress bar . Use a timer every 500 Get a playback progress in milliseconds
• Send a message to Handler. Put the playback progress into Message In the object , stay Handler In the update SeekBar Progress

Timer timer = new Timer();
timer.schedule(new TimerTask() {

    @Override
    public void run() {
        int currentPosition = player.getCurrentPosition();
        int duration = player.getDuration();
        Message msg = Message.obtain();
        // Save the playback progress into Message in 
        Bundle data = new Bundle();
        data.putInt("currentPosition", currentPosition);
        data.putInt("duration", duration);
        msg.setData(data);
        MainActivity.handler.sendMessage(msg);
    }
}, 5, 500);

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• stay Activity In the definition of Handler

static Handler handler = new Handler(){
    public void handleMessage(android.os.Message msg) {
        // Take out the data carried by the message 
        Bundle data = msg.getData();
        int currentPosition = data.getInt("currentPosition");
        int duration = data.getInt("duration");

        // Set the playback schedule 
        sb.setMax(duration);
        sb.setProgress(currentPosition);
    };
};

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• Drag the progress bar to change the playback progress

 // to sb Set up a drag listening 
 sb.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
    // Call when dragging stops 
    @Override
    public void onStopTrackingTouch(SeekBar seekBar) {
        // TODO Auto-generated method stub
        int progress = seekBar.getProgress();
        mi.seekTo(progress);
    }
    // Call when you start dragging          
    @Override
    public void onStartTrackingTouch(SeekBar seekBar) {
        // TODO Auto-generated method stub

    }
    // Call constantly when dragging            
    @Override
    public void onProgressChanged(SeekBar seekBar, int progress,
            boolean fromUser) {
        // TODO Auto-generated method stub

    }
}); 

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Video player

SurfaceView

• The real-time update of the picture is highly required
• Double buffering technology ： There are two canvases in memory ,A Canvas display to screen ,B Canvas draws the next frame in memory . After drawing B Show to screen ,A Continue to draw the next frame in memory
• Playing video is also used MediaPlayer. It's just different from audio , To set which SurfaceView

SurfaceView sv = (SurfaceView) findViewById(R.id.sv);
SurfaceHolder sh = sv.getHolder();

MediaPlayer player = new MediaPlayer();
player.reset();
try {
    player.setDataSource("sdcard/2.3gp");
    player.setDisplay(sh);
    player.prepare();
} catch (Exception e) {
    e.printStackTrace();
}
player.start();

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• SurfaceView It's a heavyweight component , Only when visible
• to SurfaceHolder Set up CallBack. Similar to listening . To know SurfaceView The state of

sh.addCallback(new Callback() {
    //SurfaceView Called on destroy 
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        // TODO Auto-generated method stub

    }
    //SurfaceView Call... On creation 
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
        // TODO Auto-generated method stub

    }
});

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• SurfaceView Once invisible . Will be destroyed , Once visible . Will be created . Stop playing when destroying . Play again when you create it again

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camera

• Start the camera program provided by the system

// Implicitly start the camera provided by the system Activity
Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
// Set the path to save photos 
File file = new File(Environment.getExternalStorageDirectory(), "haha.jpg"); 
intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(file)); 
startActivityForResult(intent, 0);

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• Start the camera program provided by the system

Intent intent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);

File file = new File(Environment.getExternalStorageDirectory(), "haha.3gp"); 
intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(file)); 
// Set the quality of the saved video file 
intent.putExtra(MediaStore.EXTRA_VIDEO_QUALITY, 1);
startActivityForResult(intent, 0);

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