Android中Bitmap和Drawable详解

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);
}