android开发之创建BMP位图

大体思路，首先Bitmap.createBitmap创建位图，然后自定义函数drawIntoBitmap,最后通过onDraw创建画布来实现绘制的位图

package com.example;

import java.io.InputStream;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader;
import android.os.Bundle;
import android.view.View;

public class AlphaBitmapActivity extends Activity {
 public Bitmap mBitmap1, mBitmap2, mBitmap3;
 public Shader mShader;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
       }
    public class SampleView extends View {
     public SampleView(Context context) {
      super(context);
      setFocusable(true);   //控件允许获取焦点
      InputStream is = context.getResources().openRawResource(R.drawable.sample);
      mBitmap1 = Bitmap.createBitmap(200, 200, Bitmap.Config.ALPHA_8);
      drawIntoBitmap(mBitmap3、1);
      /*生成 LinearGradient对象
          new LinearGradien(0,0,100,100,Color.RED,Color.BLUE,Shader.TileMode.MIRROR);
       参数一：为渐变起点坐标的x轴位置，
       参数二 ：为渐变起点坐标的y轴位置，
       参数三 ：为渐变终点坐标的x轴位置，
       参数四 ：为渐变终点坐标的y轴位置，
       参数五 ：平铺方式，这里设置为镜像
         */
      mShader = new LinearGradient(0, 0, 300, 500, new int[] {
        Color.RED, Color.GREEN, Color.BLUE}, null, Shader.TileMode.MIRROR);
     }

     /*绘制位图*/
     public 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(0x80);
      p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
      p.setTextSize(60);
      p.setTextAlign(Paint.Align.CENTER);
     Paint.FontMetrics fm = p.getFontMetrics();
      c.drawText("Alpha", x/2, y/2-fm.ascent/2, p);   //"Alpha"字符串在绘制的圆形中的文字
     }
    
     public void onDraw(Canvas canvas) {
         canvas.drawColor(Color.WHITE);                //画布底色设为白色
         Paint p = new Paint();
         p.setColor(Color.RED);                                 //设置文字颜色
         p.setTextSize(36);                                         //设置文字大小
         p.setShader(mShader);                                //设置图像阴影效果
         canvas.drawBitmap(mBitmap1, bw, bh, p);
         /*得到画布宽度高度*/
         float cw= canvas.getWidth();
         float ch = canvas.getHeight();
         canvas.drawText("宽度 "+cw+" 高度 "+ ch, 50, 50, p);
       }
    }

}

结果如图

另外说明的是 注意canvas.drawText()和canvas.drawBitmap()

drawText(String text, float x, float y, Paint paint) 中x，y是从字符串的左下角开始，y是字符串的baseline

drawBitmap(Bitmap bitmap, float left, float top, Paint paint)中x，y是生成位图的左上角的点到画布左边和上边的距离