How can I use the animation framework inside the canvas?

Question

I want to use certain animations such as bounce inside my canvas. Is it possible to use the animation interpolators inside?

In my case I want to rotate an image from 0 to 180 degrees with a bounce at the end.

How is it possible?

Answer 1

The Android animation class applies to objects such as views and layouts. The canvas is just a surface for drawing which is either part of a View or linked to a bitmap. In onDraw in a custom view only one frame is drawn at the time until next invalidate is called, which means that you have to draw your animation frame by frame. Here is an example of bouncing ball which rotates, which you may find useful.

import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.os.Bundle; import android.text.format.Time; import android.view.View;  public class StartActivity extends Activity {      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(new BallBounce(this));     } }   class BallBounce extends View {     int screenW;     int screenH;     int X;     int Y;     int initialY ;     int ballW;     int ballH;     int angle;     float dY;     float acc;     Bitmap ball, bgr;      public BallBounce(Context context) {         super(context);         ball = BitmapFactory.decodeResource(getResources(),R.drawable.football); //load a ball image         bgr = BitmapFactory.decodeResource(getResources(),R.drawable.sky_bgr); //load a background         ballW = ball.getWidth();         ballH = ball.getHeight();         acc = 0.2f; //acceleration         dY = 0; //vertical speed         initialY = 100; //Initial vertical position.         angle = 0; //Start value for rotation angle.     }      @Override     public void onSizeChanged (int w, int h, int oldw, int oldh) {         super.onSizeChanged(w, h, oldw, oldh);         screenW = w;         screenH = h;         bgr = Bitmap.createScaledBitmap(bgr, w, h, true); //Resize background to fit the screen.         X = (int) (screenW /2) - (ballW / 2) ; //Centre ball into the centre of the screen.         Y = initialY;     }      @Override     public void onDraw(Canvas canvas) {         super.onDraw(canvas);          //Draw background.         canvas.drawBitmap(bgr, 0, 0, null);          //Compute roughly ball speed and location.         Y+= (int) dY; //Increase or decrease vertical position.         if (Y > (screenH - ballH)) {             dY=(-1)*dY; //Reverse speed when bottom hit.         }         dY+= acc; //Increase or decrease speed.          //Increase rotating angle.         if (angle++ >360)             angle =0;          //Draw ball         canvas.save(); //Save the position of the canvas.         canvas.rotate(angle, X + (ballW / 2), Y + (ballH / 2)); //Rotate the canvas.         canvas.drawBitmap(ball, X, Y, null); //Draw the ball on the rotated canvas.         canvas.restore(); //Rotate the canvas back so that it looks like ball has rotated.          //Call the next frame.         invalidate();     } } 

This is just a simple illustration but I would use surfaceView and drive frames from another thread, which is a bit more complicated but a proper way to do when making interactive animations like games etc. Here is an example with a scrolling backround and the user can move the ball with his finger:

import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Matrix; import android.graphics.Paint; import android.graphics.Rect; import android.os.Bundle; import android.view.MotionEvent; import android.view.SurfaceHolder; import android.view.SurfaceView;  public class SurfaceViewActivity extends Activity {     BallBounces ball;      @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         ball = new BallBounces(this);         setContentView(ball);     } }   class BallBounces extends SurfaceView implements SurfaceHolder.Callback {     GameThread thread;     int screenW; //Device's screen width.     int screenH; //Devices's screen height.     int ballX; //Ball x position.     int ballY; //Ball y position.     int initialY ;     float dY; //Ball vertical speed.     int ballW;     int ballH;     int bgrW;     int bgrH;     int angle;     int bgrScroll;     int dBgrY; //Background scroll speed.     float acc;     Bitmap ball, bgr, bgrReverse;     boolean reverseBackroundFirst;     boolean ballFingerMove;      //Measure frames per second.     long now;     int framesCount=0;     int framesCountAvg=0;     long framesTimer=0;     Paint fpsPaint=new Paint();      //Frame speed     long timeNow;     long timePrev = 0;     long timePrevFrame = 0;     long timeDelta;       public BallBounces(Context context) {         super(context);         ball = BitmapFactory.decodeResource(getResources(),R.drawable.football); //Load a ball image.         bgr = BitmapFactory.decodeResource(getResources(),R.drawable.sky_bgr); //Load a background.         ballW = ball.getWidth();         ballH = ball.getHeight();          //Create a flag for the onDraw method to alternate background with its mirror image.         reverseBackroundFirst = false;          //Initialise animation variables.         acc = 0.2f; //Acceleration         dY = 0; //vertical speed         initialY = 100; //Initial vertical position         angle = 0; //Start value for the rotation angle         bgrScroll = 0;  //Background scroll position         dBgrY = 1; //Scrolling background speed          fpsPaint.setTextSize(30);          //Set thread         getHolder().addCallback(this);          setFocusable(true);     }      @Override     public void onSizeChanged (int w, int h, int oldw, int oldh) {         super.onSizeChanged(w, h, oldw, oldh);         //This event-method provides the real dimensions of this custom view.         screenW = w;         screenH = h;          bgr = Bitmap.createScaledBitmap(bgr, w, h, true); //Scale background to fit the screen.         bgrW = bgr.getWidth();         bgrH = bgr.getHeight();          //Create a mirror image of the background (horizontal flip) - for a more circular background.         Matrix matrix = new Matrix();  //Like a frame or mould for an image.         matrix.setScale(-1, 1); //Horizontal mirror effect.         bgrReverse = Bitmap.createBitmap(bgr, 0, 0, bgrW, bgrH, matrix, true); //Create a new mirrored bitmap by applying the matrix.          ballX = (int) (screenW /2) - (ballW / 2) ; //Centre ball X into the centre of the screen.         ballY = -50; //Centre ball height above the screen.     }      //***************************************     //*************  TOUCH  *****************     //***************************************     @Override     public synchronized boolean onTouchEvent(MotionEvent ev) {          switch (ev.getAction()) {             case MotionEvent.ACTION_DOWN: {                 ballX = (int) ev.getX() - ballW/2;                 ballY = (int) ev.getY() - ballH/2;                  ballFingerMove = true;                 break;             }              case MotionEvent.ACTION_MOVE: {                 ballX = (int) ev.getX() - ballW/2;                 ballY = (int) ev.getY() - ballH/2;                  break;             }              case MotionEvent.ACTION_UP:                 ballFingerMove = false;                 dY = 0;                 break;             }         return true;     }      @Override     public void onDraw(Canvas canvas) {         super.onDraw(canvas);          //Draw scrolling background.         Rect fromRect1 = new Rect(0, 0, bgrW - bgrScroll, bgrH);         Rect toRect1 = new Rect(bgrScroll, 0, bgrW, bgrH);          Rect fromRect2 = new Rect(bgrW - bgrScroll, 0, bgrW, bgrH);         Rect toRect2 = new Rect(0, 0, bgrScroll, bgrH);          if (!reverseBackroundFirst) {             canvas.drawBitmap(bgr, fromRect1, toRect1, null);             canvas.drawBitmap(bgrReverse, fromRect2, toRect2, null);         }         else{             canvas.drawBitmap(bgr, fromRect2, toRect2, null);             canvas.drawBitmap(bgrReverse, fromRect1, toRect1, null);         }          //Next value for the background's position.         if ( (bgrScroll += dBgrY) >= bgrW) {             bgrScroll = 0;             reverseBackroundFirst = !reverseBackroundFirst;         }          //Compute roughly the ball's speed and location.         if (!ballFingerMove) {             ballY += (int) dY; //Increase or decrease vertical position.             if (ballY > (screenH - ballH)) {                 dY=(-1)*dY; //Reverse speed when bottom hit.             }             dY+= acc; //Increase or decrease speed.         }          //Increase rotating angle         if (angle++ >360)             angle =0;          //DRAW BALL         //Rotate method one         /*         Matrix matrix = new Matrix();         matrix.postRotate(angle, (ballW / 2), (ballH / 2)); //Rotate it.         matrix.postTranslate(ballX, ballY); //Move it into x, y position.         canvas.drawBitmap(ball, matrix, null); //Draw the ball with applied matrix.          */// Rotate method two          canvas.save(); //Save the position of the canvas matrix.         canvas.rotate(angle, ballX + (ballW / 2), ballY + (ballH / 2)); //Rotate the canvas matrix.         canvas.drawBitmap(ball, ballX, ballY, null); //Draw the ball by applying the canvas rotated matrix.         canvas.restore(); //Rotate the canvas matrix back to its saved position - only the ball bitmap was rotated not all canvas.          //*/          //Measure frame rate (unit: frames per second).          now=System.currentTimeMillis();          canvas.drawText(framesCountAvg+" fps", 40, 70, fpsPaint);          framesCount++;          if(now-framesTimer>1000) {                  framesTimer=now;                  framesCountAvg=framesCount;                  framesCount=0;          }     }      @Override     public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {     }      @Override     public void surfaceCreated(SurfaceHolder holder) {         thread = new GameThread(getHolder(), this);         thread.setRunning(true);         thread.start();     }      @Override     public void surfaceDestroyed(SurfaceHolder holder) {         boolean retry = true;         thread.setRunning(false);         while (retry) {             try {                 thread.join();                 retry = false;             } catch (InterruptedException e) {              }         }     }       class GameThread extends Thread {         private SurfaceHolder surfaceHolder;         private BallBounces gameView;         private boolean run = false;          public GameThread(SurfaceHolder surfaceHolder, BallBounces gameView) {             this.surfaceHolder = surfaceHolder;             this.gameView = gameView;         }          public void setRunning(boolean run) {             this.run = run;         }          public SurfaceHolder getSurfaceHolder() {             return surfaceHolder;         }          @Override         public void run() {             Canvas c;             while (run) {                 c = null;                  //limit frame rate to max 60fps                 timeNow = System.currentTimeMillis();                 timeDelta = timeNow - timePrevFrame;                 if ( timeDelta < 16) {                     try {                         Thread.sleep(16 - timeDelta);                     }                     catch(InterruptedException e) {                      }                 }                 timePrevFrame = System.currentTimeMillis();                  try {                     c = surfaceHolder.lockCanvas(null);                     synchronized (surfaceHolder) {                        //call methods to draw and process next fame                         gameView.onDraw(c);                     }                 } finally {                     if (c != null) {                         surfaceHolder.unlockCanvasAndPost(c);                     }                 }             }         }     } } 

Here are the images: