Android缩放drawable

Android缩放drawable

 

Android缩放drawable

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，绘制的目的区域，用于绘图

3.        Bitmap位图，用于图的处理

4.        Matrix矩阵，此例中用于操作图片

二、  步骤

1.        把drawable画到位图对象上

2.        对位图对象做缩放（或旋转等）操作

3.        把位图再转换成drawable

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

         static Drawable zoomDrawable(Drawable drawable, int w, int h)
         {
                   int width = drawable.getIntrinsicWidth();
                   int height= drawable.getIntrinsicHeight();
                   Bitmap oldbmp = drawableToBitmap(drawable); // drawable转换成bitmap
                   Matrix matrix = new Matrix();   // 创建操作图片用的Matrix对象
                   float scaleWidth = ((float)w / width);   // 计算缩放比例
                   float scaleHeight = ((float)h / height);
                   matrix.postScale(scaleWidth, scaleHeight);         // 设置缩放比例
                   Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height, matrix, true);       // 建立新的bitmap，其内容是对原bitmap的缩放后的图
                   return new BitmapDrawable(newbmp);       // 把bitmap转换成drawable并返回
         }
}