Home » Android » games » canvas » Displaying Images with Android

About Ilias Tsagklis

Ilias Tsagklis
Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.

Displaying Images with Android

With this example we are going to demonstrate how to display Images with Android using canvas.

In short, to create and use a Sprite Animation you should:

  • copy the image you want to display in one of the /res/drawable* resource folders of the Android Project
  • lock the canvas for exclusive pixel editing
  • model the image with a bitmap
  • use canvas.drawBitmap to draw the image into the canvas
  • create handlers to handle several touch events

as shown in the code snippets below:

package net.obviam.droidz;

import net.obviam.droidz.model.Droid;
import android.app.Activity;
import android.content.Context;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

public class MainGamePanel extends SurfaceView implements
  SurfaceHolder.Callback {

 private static final String TAG = MainGamePanel.class.getSimpleName();

 private MainThread thread;
 private Droid droid;

 public MainGamePanel(Context context) {
  super(context);
  // adding the callback (this) to the surface holder to intercept events
  getHolder().addCallback(this);

  // create droid and load bitmap
  droid = new Droid(BitmapFactory.decodeResource(getResources(), R.drawable.droid_1), 50, 50);

  // create the game loop thread
  thread = new MainThread(getHolder(), this);

  // make the GamePanel focusable so it can handle events
  setFocusable(true);
 }

 @Override
 public void surfaceChanged(SurfaceHolder holder, int format, int width,
   int height) {
 }

 @Override
 public void surfaceCreated(SurfaceHolder holder) {
  // at this point the surface is created and
  // we can safely start the game loop
  thread.setRunning(true);
  thread.start();
 }

 @Override
 public void surfaceDestroyed(SurfaceHolder holder) {
  Log.d(TAG, "Surface is being destroyed");
  // tell the thread to shut down and wait for it to finish
  // this is a clean shutdown
  boolean retry = true;
  while (retry) {
   try {
    thread.join();
    retry = false;
   } catch (InterruptedException e) {
    // try again shutting down the thread
   }
  }
  Log.d(TAG, "Thread was shut down cleanly");
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  if (event.getAction() == MotionEvent.ACTION_DOWN) {
   // delegating event handling to the droid
   droid.handleActionDown((int)event.getX(), (int)event.getY());

   // check if in the lower part of the screen we exit
   if (event.getY() > getHeight() - 50) {
    thread.setRunning(false);
    ((Activity)getContext()).finish();
   } else {
    Log.d(TAG, "Coords: x=" + event.getX() + ",y=" + event.getY());
   }
  } if (event.getAction() == MotionEvent.ACTION_MOVE) {
   // the gestures
   if (droid.isTouched()) {
    // the droid was picked up and is being dragged
    droid.setX((int)event.getX());
    droid.setY((int)event.getY());
   }
  } if (event.getAction() == MotionEvent.ACTION_UP) {
   // touch was released
   if (droid.isTouched()) {
    droid.setTouched(false);
   }
  }
  return true;
 }

 @Override
 protected void onDraw(Canvas canvas) {
  // fills the canvas with black
  canvas.drawColor(Color.BLACK);
  droid.draw(canvas);
 }
}
package net.obviam.droidz.model;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.view.MotionEvent;

public class Droid {

 private Bitmap bitmap; // the actual bitmap
 private int x;   // the X coordinate
 private int y;   // the Y coordinate
 private boolean touched; // if droid is touched/picked up

 public Droid(Bitmap bitmap, int x, int y) {
  this.bitmap = bitmap;
  this.x = x;
  this.y = y;
 }

 public Bitmap getBitmap() {
  return bitmap;
 }
 public void setBitmap(Bitmap bitmap) {
  this.bitmap = bitmap;
 }
 public int getX() {
  return x;
 }
 public void setX(int x) {
  this.x = x;
 }
 public int getY() {
  return y;
 }
 public void setY(int y) {
  this.y = y;
 }

 public boolean isTouched() {
  return touched;
 }

 public void setTouched(boolean touched) {
  this.touched = touched;
 }

 public void draw(Canvas canvas) {
  canvas.drawBitmap(bitmap, x - (bitmap.getWidth() / 2), y - (bitmap.getHeight() / 2), null);
 }

 public void handleActionDown(int eventX, int eventY) {
  if (eventX >= (x - bitmap.getWidth() / 2) && (eventX <= (x + bitmap.getWidth()/2))) {
   if (eventY >= (y - bitmap.getHeight() / 2) && (y <= (y + bitmap.getHeight() / 2))) {
    // droid touched
    setTouched(true);
   } else {
    setTouched(false);
   }
  } else {
   setTouched(false);
  }

 }
}
public void run() {
  Canvas canvas;
  Log.d(TAG, "Starting game loop");
  while (running) {
   canvas = null;
   // try locking the canvas for exclusive pixel editing on the surface
   try {
    canvas = this.surfaceHolder.lockCanvas();
    synchronized (surfaceHolder) {
     // update game state
     // draws the canvas on the panel
     this.gamePanel.onDraw(canvas);
    }
   } finally {
    // in case of an exception the surface is not left in
    // an inconsistent state
    if (canvas != null) {
     surfaceHolder.unlockCanvasAndPost(canvas);
    }
   } // end finally
  }
 }

 
This was an example of how to display Images in Android.

Related Article:

Reference: Displaying Images with Android from our JCG partner Tamas Jano at the “Against The Grain” blog.

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