Api Demo - .graphics(15)

package com.example.android.apis.graphics;

import android.app.Activity;
import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.*;

public class Layers extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }
    
    private static class SampleView extends View {
        private static final int LAYER_FLAGS = Canvas.MATRIX_SAVE_FLAG |
                                            Canvas.CLIP_SAVE_FLAG |
                                            Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                                            Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                                            Canvas.CLIP_TO_LAYER_SAVE_FLAG; 
                 //ALL_SAVE_FLAG; 
        //该参数当画布执行restore 操作时，需要restore的状态属性分别对应：matrix，clip，alpha，color，越界的clip,everything
        private Paint mPaint;

        public SampleView(Context context) {
            super(context);
            setFocusable(true);
            
            mPaint = new Paint();
            mPaint.setAntiAlias(true);
        }
        
        @Override protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.WHITE);            
            
            canvas.translate(10, 10);
            
            mPaint.setColor(Color.RED);
            canvas.drawCircle(75, 75, 75, mPaint);
            canvas.saveLayerAlpha(0, 0, 200, 200, 0x20, LAYER_FLAGS);//新建图层并指定透明度，图层位于栈顶，所以直到restore以前的操作都只作用于此图层
            mPaint.setColor(Color.BLUE);
            canvas.drawCircle(125, 125, 75, mPaint);
            
            canvas.restore();//将新建的图层合并到画布上
        }
    }
}