Android
सरफेस व्यू का उपयोग करके कैनवस ड्राइंग

टिप्पणियों

सतह धागा ड्राइंग के साथ

यह उदाहरण बताता है कि एक समर्पित ड्राइंग थ्रेड के साथ एक सरफेस व्यू कैसे बनाया जाए। यह कार्यान्वयन धार मामलों को भी संभालता है जैसे कि विशिष्ट मुद्दों के निर्माण के साथ-साथ सीपीयू समय बचाने के लिए थ्रेड को शुरू करना / रोकना।

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");
    }
}

इस लेआउट में केवल कस्टम सरफेस व्यू होता है और इसे स्क्रीन के आकार तक बढ़ाता है।

<?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>

भूतल दृश्य का उपयोग करने वाली गतिविधि ड्राइंग थ्रेड को शुरू करने और रोकने के लिए जिम्मेदार है। बैकग्राउंड में एक्टिविटी मिलते ही यह एप्रोच बैटरी बचा लेती है।

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();
    }
}