Android 2D绘图小技巧

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

个人常用：

Drawable drawable=activity.getResources().getDrawable(R.drawable.sg1);        BitmapDrawable bd=(BitmapDrawable) drawable;        Bitmap bitmap=bd.getBitmap();

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);    }