Android中的bitmap，drawable，canvas以及paint

1，Bitmap，位图也就是位的数组，扩展名为.bmp的不带压缩的点阵图，也就是一种图片信息存储对象。

2，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。实际上它是android平台的通用对象，用来装载png，jpg，gif，bmp等各种常见的图片资源。

3，Canvas，绘图的目的区域，任何要展现的形状或效果都需要它作为背景。可以通过它来对bitmap进行裁剪转化等操作。一般draw这个动作由canvas发起：canvas.drawCircle

4，Paint，画笔，设置颜色抗锯齿什么的。

二，Bitmap

1，从资源中获取bitmap

Resources res = getResources();

Bitmap bmp = BitmapFactory.decodeResource(res, R.drawable.ic_launcher);

2，bitmap -> byte[]

public byte[] BitmapToBytes(Bitmap bitmap) {

ByteArrayOutputStream mByteArrayOutputStream= new ByteArrayOutputStream();

bitmap.compress(Bitmap.CompressFormat.PNG, 100, mByteArrayOutputStream);

return mByteArrayOutputStream.toByteArray();

}

3，byte[] -> bitmap

public Bitmap BytesToBimap(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，drawable -> 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 -> 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);

}