Android中Bitmap和Drawable

一、相关概念

1、Drawable就是一个可画的对象，其可能是一张位图（BitmapDrawable），也可能是一个图形（ShapeDrawable），还有可能是一个图层（LayerDrawable），我们根据画图的需求，创建相应的可画对象

2、Canvas画布，绘图的目的区域，用于绘图

3、Bitmap位图，用于图的处理

4、Matrix矩阵

二、Bitmap

1、从资源中获取Bitmap

Resources res = getResources();  
Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.icon); 

2、Bitmap → byte[]

public byte[] Bitmap2Bytes(Bitmap bm) {  
    ByteArrayOutputStream baos = new ByteArrayOutputStream();  
    bm.compress(Bitmap.CompressFormat.PNG, 100, baos);  
    return baos.toByteArray();  
}  

 3、byte[] → Bitmap

public Bitmap Bytes2Bimap(byte[] b) {  
    if (b.length != 0) {  
        return BitmapFactory.decodeByteArray(b, 0, b.length);  
    } else {  
        return null;  
    }  
}  

4、Bitmap缩放

public static Bitmap zoomBitmap(Bitmap bitmap, int width, int height) {  
    int w = bitmap.getWidth();  
    int h = bitmap.getHeight();  
    Matrix matrix = new Matrix();  
    float scaleWidth = ((float) width / w);  
    float scaleHeight = ((float) height / h);  
    matrix.postScale(scaleWidth, scaleHeight);  
    Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, w, h, matrix, true);  
    return newbmp;  
}  

5、将Drawable转化为Bitmap

/** 
     * Drawable 转 bitmap 
     * @param drawable 
     * @return 
     */  
    public static Bitmap drawable2Bitmap(Drawable drawable){  
        if(drawable instanceof BitmapDrawable){  
            return ((BitmapDrawable)drawable).getBitmap() ;  
        }else if(drawable instanceof NinePatchDrawable){  
            Bitmap bitmap = Bitmap  
                    .createBitmap(  
                            drawable.getIntrinsicWidth(),  
                            drawable.getIntrinsicHeight(),  
                            drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888  
                                    : Bitmap.Config.RGB_565);  
            Canvas canvas = new Canvas(bitmap);  
            drawable.setBounds(0, 0, drawable.getIntrinsicWidth(),  
                    drawable.getIntrinsicHeight());  
            drawable.draw(canvas);  
            return bitmap;  
        }else{  
            return null ;  
        }  
    }  

6、获得圆角图片 

public static Bitmap getRoundedCornerBitmap(Bitmap bitmap, float roundPx) {  
    int w = bitmap.getWidth();  
    int h = bitmap.getHeight();  
    Bitmap output = Bitmap.createBitmap(w, h, Config.ARGB_8888);  
    Canvas canvas = new Canvas(output);  
    final int color = 0xff424242;  
    final Paint paint = new Paint();  
    final Rect rect = new Rect(0, 0, w, h);  
    final RectF rectF = new RectF(rect);  
    paint.setAntiAlias(true);  
    canvas.drawARGB(0, 0, 0, 0);  
    paint.setColor(color);  
    canvas.drawRoundRect(rectF, roundPx, roundPx, paint);  
    paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));  
    canvas.drawBitmap(bitmap, rect, rect, paint);  
  
    return output;  
}  

7、获得带倒影的图片

public static Drawable zoomDrawable(Drawable drawable, int w, int h) {
		int width = drawable.getIntrinsicWidth();
		int height = drawable.getIntrinsicHeight();
		// drawable转换成bitmap
		Bitmap oldbmp = drawableToBitmap(drawable);
		// 创建操作图片用的Matrix对象
		Matrix matrix = new Matrix();
		// 计算缩放比例
		float sx = ((float) w / width);
		float sy = ((float) h / height);
		// 设置缩放比例
		matrix.postScale(sx, sy);
		// 建立新的bitmap，其内容是对原bitmap的缩放后的图
		Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height,
				matrix, true);
		return new BitmapDrawable(newbmp);
	}

 三、Drawable

1、Bitmap转换成Drawable

Bitmap bm=xxx; //xxx根据你的情况获取
BitmapDrawable bd= new BitmapDrawable(getResource(), bm); 
因为BtimapDrawable是Drawable的子类，最终直接使用bd对象即可。

2、Drawable缩放

public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) {
		final int reflectionGap = 4;
		int w = bitmap.getWidth();
		int h = bitmap.getHeight();
		Matrix matrix = new Matrix();
		matrix.preScale(1, -1);
		Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, h / 2, w,
				h / 2, matrix, false);
		Bitmap bitmapWithReflection = Bitmap.createBitmap(w, (h + h / 2),
				Config.ARGB_8888);
		Canvas canvas = new Canvas(bitmapWithReflection);
		canvas.drawBitmap(bitmap, 0, 0, null);
		Paint deafalutPaint = new Paint();
		canvas.drawRect(0, h, w, h + reflectionGap, deafalutPaint);
		canvas.drawBitmap(reflectionImage, 0, h + reflectionGap, null);
		Paint paint = new Paint();
		LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
				bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
				0x00ffffff, TileMode.CLAMP);
		paint.setShader(shader);
		// Set the Transfer mode to be porter duff and destination in
		paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
		// Draw a rectangle using the paint with our linear gradient
		canvas.drawRect(0, h, w, bitmapWithReflection.getHeight()
				+ reflectionGap, paint);
		return bitmapWithReflection;
	}