高效能繪圖桌布-Canvas

SurfaceView為高效能繪圖介面, 也是邁向遊戲設計之路的起點. 從前都是在Activity中放入R.layout.xxx的畫面設定. 如今, 只是在Activity中放入一個SurfaceView, 再由SurfaceView的holder.lockCanvas()取得一張圖畫紙(canvas), 然後在這張圖畫紙上畫上想要畫的圖形.

使用Surface元件, 需繼承SurfaceView並實作SurfaceHolder.Callback的三個方法
surfaceCreated(), surfaceChanged(), surfaceDestroyed()

在Canvas圖畫紙上, 可以畫線, 畫圓, 畫圖檔

public class MyCanvas extends SurfaceView implements SurfaceHolder.Callback {
    SurfaceHolder holder=getHolder();
    Canvas canvas;
    Paint paint;
    public MyCanvas(Context context) {
        super(context);
        holder.addCallback(this);
    }
    @Override
    public void surfaceCreated(SurfaceHolder surfaceHolder) {
        canvas=holder.lockCanvas();
        paint=new Paint();
        paint.setColor(Color.RED);
        canvas.drawCircle(500,500,250, paint);
        paint.setColor(Color.BLUE);
        paint.setStrokeWidth(10);
        canvas.drawLine(200,500,800,500, paint);
        canvas.drawLine(500, 200, 500, 800, paint);
        holder.unlockCanvasAndPost(canvas);
    }
    @Override
    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {}
    @Override
    public void surfaceDestroyed(SurfaceHolder surfaceHolder) {}
}

然後在MainActivity的onCreate()更改setContentView即可

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(
                WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN );
        setContentView(new MyCanvas(this));
    }
}

清空畫布

canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);

反彈球

下面代碼, 畫了一顆球, 並在Canvas持續的移動反彈

public class MyCanvas extends SurfaceView implements SurfaceHolder.Callback {
    SurfaceHolder holder=getHolder();
    Canvas canvas;
    Paint paint=new Paint();
    int r=30;
    int cx=r, cy=r;
    int xdir=1, ydir=1;
    int xspeed=10, yspeed=10;
    public MyCanvas(Context context) {
        super(context);
        holder.addCallback(this);
    }
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        new Thread(()->{
            while(true) {
                canvas = holder.lockCanvas();
                canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
                Log.d("Thomas", String.format("%d, %d", canvas.getWidth(), canvas.getHeight()));
                paint.setColor(Color.RED);
                cx+=xdir*xspeed;cy+=ydir*yspeed;
                if(cx>canvas.getWidth()-r){
                    cx=canvas.getWidth()-r;
                    xdir=-xdir;
                }
                if(cx<r){ cx=r; xdir=-xdir; } if(cy>canvas.getHeight()-r){
                    cy=canvas.getHeight()-r;
                    ydir=-ydir;
                }
                if(cy<r){
                    cy=r;
                    ydir=-ydir;
                }
                canvas.drawCircle(cx, cy, r, paint);
                holder.unlockCanvasAndPost(canvas);
            }
        }).start();
    }
    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {}
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {}
}