一、基本概念

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); }