Api Demo - .graphics(1)

//关键字：获取图片轮廓，Shader运用。文字垂直高度获取。

package com.example.android.apis.graphics;

import com.example.android.apis.R;

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

import java.io.InputStream;
import java.io.ByteArrayOutputStream;

public class AlphaBitmap extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }
    
    private static class SampleView extends View {
        private Bitmap mBitmap;
        private Bitmap mBitmap2;
        private Bitmap mBitmap3;
        private Shader mShader;
        
        private static void drawIntoBitmap(Bitmap bm) {
            float x = bm.getWidth();
            float y = bm.getHeight();
            Canvas c = new Canvas(bm);
            Paint p = new Paint();
            p.setAntiAlias(true);
            
            p.setAlpha(0x80);
            c.drawCircle(x/2, y/2, x/2, p);
            
            p.setAlpha(0x30);//透明度单传
            p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));//设置图像重叠模式
            p.setTextSize(60);
            p.setTextAlign(Paint.Align.CENTER);
            Paint.FontMetrics fm = p.getFontMetrics();
            c.drawText("Alpha", x/2, (y-fm.ascent)/2, p);//fm.ascent 文字垂直方向的关键点位置（相对于底线），
        }
        
        public SampleView(Context context) {
            super(context);
            setFocusable(true);
            
            InputStream is = context.getResources().openRawResource(R.drawable.frog);
            mBitmap = BitmapFactory.decodeStream(is);
            mBitmap2 = mBitmap.extractAlpha();//提取透明度，可以获得图像轮廓。
            mBitmap3 = Bitmap.createBitmap(200, 200, Bitmap.Config.ALPHA_8);//创建指定大小BMP
            drawIntoBitmap(mBitmap3);
            
            mShader = new LinearGradient(0, 0, 100, 70, new int[] {
                                         Color.RED, Color.GREEN, Color.BLUE },
                                         null, Shader.TileMode.MIRROR);//填充渲染效果，应用到Paint
        }
        
        @Override protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.WHITE);

            Paint p = new Paint();
            float y = 10;
            
            p.setColor(Color.BLUE);
            canvas.drawBitmap(mBitmap, 10, y, p);
            y += mBitmap.getHeight() + 10;
            canvas.drawBitmap(mBitmap2, 10, y, p);
            y += mBitmap2.getHeight() + 10;
            p.setShader(mShader);
            canvas.drawBitmap(mBitmap3, 10, y, p);
        }
    }
}