SurfaceView繪圖機制

雖然前面都使用的View來進行繪圖，但View繪圖機制存在兩個缺陷：

1、缺乏雙緩沖機制

2、更新圖像時，必須更新View上的整張圖片，效率低。

所以在游戲繪制中推薦使用SurfaceView。它可以只對指定區域進行更新，可以提高效率。下面用一個簡單示例來演示SurfaceView的使用：

Activity：

package com.home.activity; 
 
import android.app.Activity; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Rect; 
import android.os.Bundle; 
import android.view.MotionEvent; 
import android.view.SurfaceHolder; 
import android.view.SurfaceHolder.Callback; 
import android.view.SurfaceView; 
import android.view.View; 
import android.view.View.OnTouchListener; 
 
import com.home.surfaceviewtest.R; 
 
public class SurfaceViewActivity extends Activity { 
    // SurfaceHolder負責維護SurfaceView上繪制的內容  
    private SurfaceHolder holder; 
    private Paint paint; 
 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
        paint = new Paint(); 
        // 獲取SurfaceView實例  
        SurfaceView surface = (SurfaceView) findViewById(R.id.main_sv); 
        // 初始化SurfaceHolder對象  
        holder = surface.getHolder(); 
        holder.addCallback(new Callback() { 
            //當surface將要被銷毀時回調該方法  
            @Override 
            public void surfaceDestroyed(SurfaceHolder holder) { 
 
            } 
            //當surface被創建時回調該方法  
            @Override 
            public void surfaceCreated(SurfaceHolder holder) { 
                // 鎖定整個SurfaceView  
                Canvas canvas = holder.lockCanvas(); 
                // 獲取背景資源  
                Bitmap bitmap = BitmapFactory.decodeResource( 
                        SurfaceViewActivity.this.getResources(), 
                        R.drawable.image2); 
                // 繪制背景  
                canvas.drawBitmap(bitmap, 0, 0, null); 
                // 繪制完成，釋放畫布，提交修改  
                holder.unlockCanvasAndPost(canvas); 
                // 重新鎖兩次，避免下次lockCanvas遮擋  
                holder.lockCanvas(new Rect(0, 0, 0, 0)); 
                holder.unlockCanvasAndPost(canvas); 
                holder.lockCanvas(new Rect(0, 0, 0, 0)); 
                holder.unlockCanvasAndPost(canvas); 
            } 
            //當一個surface的格式或大小發生改變時回調該方法  
            @Override 
            public void surfaceChanged(SurfaceHolder holder, int format, 
                    int width, int height) { 
 
            } 
        }); 
        surface.setOnTouchListener(new OnTouchListener() { 
 
            @Override 
            public boolean onTouch(View v, MotionEvent event) { 
                // 只處理按下事件  
                if (event.getAction() == MotionEvent.ACTION_DOWN) { 
                    int cx = (int) event.getX(); 
                    int cy = (int) event.getY(); 
                    // 鎖定SurfaceView的局部區域，只更新局部內容  
                    Canvas canvas = holder.lockCanvas(new Rect(cx - 60, 
                            cy - 60, cx + 60, cy + 60)); 
                    // 保存canvas的當前狀態  
                    canvas.save(); 
                    // 旋轉畫布  
                    canvas.rotate(30, cx, cy); 
                    paint.setColor(Color.RED); 
                    // 繪制紅色方塊  
                    canvas.drawRect(cx - 40, cy - 40, cx, cy, paint); 
                    // 恢復canvas之前的保存狀態  
                    canvas.restore(); 
                    paint.setColor(Color.GREEN); 
                    // 繪制綠色方塊  
                    canvas.drawRect(cx, cy, cx + 40, cy + 40, paint); 
                    // 繪制完成，釋放畫布，提交修改  
                    holder.unlockCanvasAndPost(canvas); 
                } 
                return false; 
            } 
        }); 
    } 
 
} 

package com.home.activity;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnTouchListener;

import com.home.surfaceviewtest.R;

public class SurfaceViewActivity extends Activity {
 // SurfaceHolder負責維護SurfaceView上繪制的內容
 private SurfaceHolder holder;
 private Paint paint;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  paint = new Paint();
  // 獲取SurfaceView實例
  SurfaceView surface = (SurfaceView) findViewById(R.id.main_sv);
  // 初始化SurfaceHolder對象
  holder = surface.getHolder();
  holder.addCallback(new Callback() {
   //當surface將要被銷毀時回調該方法
   @Override
   public void surfaceDestroyed(SurfaceHolder holder) {

   }
   //當surface被創建時回調該方法
   @Override
   public void surfaceCreated(SurfaceHolder holder) {
    // 鎖定整個SurfaceView
    Canvas canvas = holder.lockCanvas();
    // 獲取背景資源
    Bitmap bitmap = BitmapFactory.decodeResource(
      SurfaceViewActivity.this.getResources(),
      R.drawable.image2);
    // 繪制背景
    canvas.drawBitmap(bitmap, 0, 0, null);
    // 繪制完成，釋放畫布，提交修改
    holder.unlockCanvasAndPost(canvas);
    // 重新鎖兩次，避免下次lockCanvas遮擋
    holder.lockCanvas(new Rect(0, 0, 0, 0));
    holder.unlockCanvasAndPost(canvas);
    holder.lockCanvas(new Rect(0, 0, 0, 0));
    holder.unlockCanvasAndPost(canvas);
   }
   //當一個surface的格式或大小發生改變時回調該方法
   @Override
   public void surfaceChanged(SurfaceHolder holder, int format,
     int width, int height) {

   }
  });
  surface.setOnTouchListener(new OnTouchListener() {

   @Override
   public boolean onTouch(View v, MotionEvent event) {
    // 只處理按下事件
    if (event.getAction() == MotionEvent.ACTION_DOWN) {
     int cx = (int) event.getX();
     int cy = (int) event.getY();
     // 鎖定SurfaceView的局部區域，只更新局部內容
     Canvas canvas = holder.lockCanvas(new Rect(cx - 60,
       cy - 60, cx + 60, cy + 60));
     // 保存canvas的當前狀態
     canvas.save();
     // 旋轉畫布
     canvas.rotate(30, cx, cy);
     paint.setColor(Color.RED);
     // 繪制紅色方塊
     canvas.drawRect(cx - 40, cy - 40, cx, cy, paint);
     // 恢復canvas之前的保存狀態
     canvas.restore();
     paint.setColor(Color.GREEN);
     // 繪制綠色方塊
     canvas.drawRect(cx, cy, cx + 40, cy + 40, paint);
     // 繪制完成，釋放畫布，提交修改
     holder.unlockCanvasAndPost(canvas);
    }
    return false;
   }
  });
 }

}

 

布局XML：

LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical"> 
 
    <SurfaceView 
        android:id="@+id/main_sv" 
        android:layout_width="match_parent" 
        android:layout_height="match_parent"/> 
 
</LinearLayout> 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <SurfaceView
        android:id="@+id/main_sv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</LinearLayout>