Android Canvas drawing using SurfaceView SurfaceView with drawing thread
Example
This example describes how to create a SurfaceView with a dedicated drawing thread. This implementation also handles edge cases such as manufacture specific issues as well as starting/stopping the thread to save cpu time.
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
/**
* Defines a custom SurfaceView class which handles the drawing thread
**/
public class BaseSurface extends SurfaceView implements SurfaceHolder.Callback, View.OnTouchListener, Runnable
{
/**
* Holds the surface frame
*/
private SurfaceHolder holder;
/**
* Draw thread
*/
private Thread drawThread;
/**
* True when the surface is ready to draw
*/
private boolean surfaceReady = false;
/**
* Drawing thread flag
*/
private boolean drawingActive = false;
/**
* Paint for drawing the sample rectangle
*/
private Paint samplePaint = new Paint();
/**
* Time per frame for 60 FPS
*/
private static final int MAX_FRAME_TIME = (int) (1000.0 / 60.0);
private static final String LOGTAG = "surface";
public BaseSurface(Context context, AttributeSet attrs)
{
super(context, attrs);
SurfaceHolder holder = getHolder();
holder.addCallback(this);
setOnTouchListener(this);
// red
samplePaint.setColor(0xffff0000);
// smooth edges
samplePaint.setAntiAlias(true);
}
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
{
if (width == 0 || height == 0)
{
return;
}
// resize your UI
}
@Override
public void surfaceCreated(SurfaceHolder holder)
{
this.holder = holder;
if (drawThread != null)
{
Log.d(LOGTAG, "draw thread still active..");
drawingActive = false;
try
{
drawThread.join();
} catch (InterruptedException e)
{ // do nothing
}
}
surfaceReady = true;
startDrawThread();
Log.d(LOGTAG, "Created");
}
@Override
public void surfaceDestroyed(SurfaceHolder holder)
{
// Surface is not used anymore - stop the drawing thread
stopDrawThread();
// and release the surface
holder.getSurface().release();
this.holder = null;
surfaceReady = false;
Log.d(LOGTAG, "Destroyed");
}
@Override
public boolean onTouch(View v, MotionEvent event)
{
// Handle touch events
return true;
}
/**
* Stops the drawing thread
*/
public void stopDrawThread()
{
if (drawThread == null)
{
Log.d(LOGTAG, "DrawThread is null");
return;
}
drawingActive = false;
while (true)
{
try
{
Log.d(LOGTAG, "Request last frame");
drawThread.join(5000);
break;
} catch (Exception e)
{
Log.e(LOGTAG, "Could not join with draw thread");
}
}
drawThread = null;
}
/**
* Creates a new draw thread and starts it.
*/
public void startDrawThread()
{
if (surfaceReady && drawThread == null)
{
drawThread = new Thread(this, "Draw thread");
drawingActive = true;
drawThread.start();
}
}
@Override
public void run()
{
Log.d(LOGTAG, "Draw thread started");
long frameStartTime;
long frameTime;
/*
* In order to work reliable on Nexus 7, we place ~500ms delay at the start of drawing thread
* (AOSP - Issue 58385)
*/
if (android.os.Build.BRAND.equalsIgnoreCase("google") && android.os.Build.MANUFACTURER.equalsIgnoreCase("asus") && android.os.Build.MODEL.equalsIgnoreCase("Nexus 7"))
{
Log.w(LOGTAG, "Sleep 500ms (Device: Asus Nexus 7)");
try
{
Thread.sleep(500);
} catch (InterruptedException ignored)
{
}
}
try
{
while (drawingActive)
{
if (holder == null)
{
return;
}
frameStartTime = System.nanoTime();
Canvas canvas = holder.lockCanvas();
if (canvas != null)
{
// clear the screen using black
canvas.drawARGB(255, 0, 0, 0);
try
{
// Your drawing here
canvas.drawRect(0, 0, getWidth() / 2, getHeight() / 2, samplePaint);
} finally
{
holder.unlockCanvasAndPost(canvas);
}
}
// calculate the time required to draw the frame in ms
frameTime = (System.nanoTime() - frameStartTime) / 1000000;
if (frameTime < MAX_FRAME_TIME) // faster than the max fps - limit the FPS
{
try
{
Thread.sleep(MAX_FRAME_TIME - frameTime);
} catch (InterruptedException e)
{
// ignore
}
}
}
} catch (Exception e)
{
Log.w(LOGTAG, "Exception while locking/unlocking");
}
Log.d(LOGTAG, "Draw thread finished");
}
}
This layout only contains the custom SurfaceView and maximizes it to the screen size.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="sample.devcore.org.surfaceviewsample.MainActivity">
<sample.devcore.org.surfaceviewsample.BaseSurface
android:id="@+id/baseSurface"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>
The activity which uses the SurfaceView is responsible for starting and stopping the drawing thread. This approach saves battery as the drawing is stopped as soon as the activity gets in the background.
import android.app.Activity;
import android.os.Bundle;
public class MainActivity extends Activity
{
/**
* Surface object
*/
private BaseSurface surface;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
surface = (BaseSurface) findViewById(R.id.baseSurface);
}
@Override
protected void onResume()
{
super.onResume();
// start the drawing
surface.startDrawThread();
}
@Override
protected void onPause()
{
// stop the drawing to save cpu time
surface.stopDrawThread();
super.onPause();
}
}
