Android中Bitmap、Drawable 、Canvas和Matrix

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

public static Bitmap drawableToBitmap(Drawable drawable) {   
        // 取 drawable 的长宽   
        int w = drawable.getIntrinsicWidth();   
        int h = drawable.getIntrinsicHeight();   
  
        // 取 drawable 的颜色格式   
        Bitmap.Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888   
                : Bitmap.Config.RGB_565;   
        // 建立对应 bitmap   
        Bitmap bitmap = Bitmap.createBitmap(w, h, config);   
        // 建立对应 bitmap 的画布   
        Canvas canvas = new Canvas(bitmap);   
        drawable.setBounds(0, 0, w, h);   
        // 把 drawable 内容画到画布中   
        drawable.draw(canvas);   
        return bitmap;   
    }  

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 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;   
}  

 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 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);   
}