开始Android游戏-AndroidFastRenderView类代码说明

Question

我正在从这本书中学习Android游戏编程 - 开始Android游戏。我无法理解AndroidFastRenderView类run()方法中的代码。

Canvas canvas = holder.lockCanvas();
canvas.getClipBounds(dst);
canvas.drawBitmap(frameBuffer, null, dst, null);
holder.unlockCanvasAndPost(canvas);

代码如何：

canvas.drawBitmap(frameBuffer, null, dst, null); 

绘制位图？我理解drawBitmap()类中的AndroidGraphics方法是如何工作的（如下所示）。我不明白的是AndroidFastRenderView中的画布如何能够在AndroidGraphics中绘制使用Canvas绘制的位图？

AndroidGame类的代码：

public abstract class AndroidGame extends Activity implements Game {

AndroidFastRenderView renderView;
Graphics graphics;
Audio audio;
Input input;
FileIO fileIO;
Screen screen;
WakeLock wakeLock;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

    boolean isLandscape = getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE;
    int frameBufferWidth = isLandscape ? 480 : 320;
    int frameBufferHeight = isLandscape ? 320 : 480;
    Bitmap frameBuffer = Bitmap.createBitmap(frameBufferWidth,
            frameBufferHeight, Config.RGB_565);

    float scaleX = (float) frameBufferWidth
            / getWindowManager().getDefaultDisplay().getWidth();
    float scaleY = (float) frameBufferHeight
            / getWindowManager().getDefaultDisplay().getHeight();

    renderView = new AndroidFastRenderView(this, frameBuffer);
    graphics = new AndroidGraphics(getAssets(), frameBuffer);
    fileIO = new AndroidFileIO(this);
    audio = new AndroidAudio(this);
    input = new AndroidInput(this, renderView, scaleX, scaleY);
    screen = getStartScreen();
    setContentView(renderView);

    PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
    wakeLock = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK, "GLGame");
}

@Override
public void onResume() {
    super.onResume();
    wakeLock.acquire();
    screen.resume();
    renderView.resume();
}

@Override
public void onPause() {
    super.onPause();
    wakeLock.release();
    renderView.pause();
    screen.pause();

    if (isFinishing())
        screen.dispose();
}

public Input getInput() {
    return input;
}

public FileIO getFileIO() {
    return fileIO;
}

public Graphics getGraphics() {
    return graphics;
}

public Audio getAudio() {
    return audio;
}

public void setScreen(Screen screen) {
    if (screen == null)
        throw new IllegalArgumentException("Screen must not be null");

    this.screen.pause();
    this.screen.dispose();
    screen.resume();
    screen.update(0);
    this.screen = screen;
}

public Screen getCurrentScreen() {
    return screen;
}
}

AndrodFastRenderView的代码：

public class AndroidFastRenderView extends SurfaceView implements Runnable{
AndroidGame game;
Bitmap frameBuffer;
Thread renderThread = null;
SurfaceHolder holder;
private volatile boolean running = false;

public AndroidFastRenderView(AndroidGame game, Bitmap frameBuffer) {
    super(game);
    this.game = game;
    this.holder = getHolder();
    this.frameBuffer = frameBuffer;
}

public void resume() {
    running = true;
    renderThread = new Thread(this);
    renderThread.start();
}



@Override
public void run() {
    Log.d("ANDROIDFASTRENDERVIEW", "CREATING NEW THREAD");
    Rect dst = new Rect();
    long startTime = System.nanoTime();
    while(running) {
        if (!holder.getSurface().isValid()) {
            continue;
        }

        long deltaTime = startTime - System.nanoTime();
        startTime = System.nanoTime();

        game.getCurrentScreen().update(deltaTime);
        game.getCurrentScreen().present(deltaTime);


        Canvas canvas = holder.lockCanvas();
        canvas.getClipBounds(dst);
        canvas.drawBitmap(frameBuffer, null, dst, null);
        holder.unlockCanvasAndPost(canvas);
    }
}
}

AndroidGraphics的代码：

public class AndroidGraphics implements Graphics {
AssetManager assets;
Bitmap frameBuffer;
Canvas canvas;
Paint paint;
Rect srcRect = new Rect();
Rect dstRect = new Rect();

public AndroidGraphics(AssetManager assets, Bitmap frameBuffer) {
    this.assets = assets;
    this.frameBuffer = frameBuffer;
    canvas = new Canvas(frameBuffer);
    this.paint = new Paint();
}

@Override
public Pixmap newPixmap(String fileName, Pixmapformat format) {
    Bitmap.Config config = null;
    if (format == Pixmapformat.ARGB4444) {
        config = Bitmap.Config.ARGB_4444;
    } else if(format == Pixmapformat.ARGB8888) {
        config = Bitmap.Config.ARGB_8888;
    } else if(format == Pixmapformat.RGB565) {
        config = Bitmap.Config.RGB_565;
    }
    BitmapFactory.Options options = new BitmapFactory.Options();
    options.inPreferredConfig = config;

    InputStream in = null;
    Bitmap bitmap = null;

    try {
        in = assets.open(fileName);
        bitmap = BitmapFactory.decodeStream(in);
        if (bitmap == null)
            throw new RuntimeException("Couldn't load bitmap from asset '" + fileName + "'");
    } catch (IOException e) {
        throw new RuntimeException("Couldn't load bitmap from asset '" + fileName + "'");

    } finally {
        if (in != null) {
            try {
                in.close();
            } catch (IOException e) {

            }
        }
    }
    if (bitmap.getConfig() == Bitmap.Config.RGB_565) {
        format = Pixmapformat.RGB565;
    }
    else if (bitmap.getConfig() == Bitmap.Config.ARGB_4444) {
        format = Pixmapformat.ARGB4444;
    }
    else {
        format = Pixmapformat.ARGB8888;
    }
    return new AndroidPixmap(bitmap, format);

}

@Override
public void drawPixmap(Pixmap pixmap, int x, int y, int scrX, int srcY, int srcWidth, int srcHeight) {
    srcRect.top = srcY;
    srcRect.left = scrX;
    srcRect.right = x + srcWidth -1;
    srcRect.bottom = y + srcHeight -1;

    dstRect.left = x;
    dstRect.top = y;
    dstRect.right = x + srcWidth -1;
    dstRect.bottom = y + srcHeight -1;
    canvas.drawBitmap(((AndroidPixmap)(pixmap)).bitmap, srcRect, dstRect, null);
}

@Override
public void drawPixmap(Pixmap pixmap, int x, int y) {
    canvas.drawBitmap(((AndroidPixmap)(pixmap)).bitmap, x, y, null);
}


}