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打开图片
图片的打开主要是把各种格式的图片转换为Bitmap对象，Android通过BitmapFactory类提供了一系列的静态方法来协助完成这个操作，如下所示：
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public class BitmapFactory {
public static Bitmap decodeFile(String pathName, Options opts);
public static Bitmap decodeFile(String pathName);
public static Bitmap decodeResourceStream(Resources res, TypedValue value,
InputStream is, Rect pad, Options opts) ;
public static Bitmap decodeResource(Resources res, int id, Options opts) ;
public static Bitmap decodeResource(Resources res, int id);
public static Bitmap decodeByteArray(byte[] data, int offset, int length, Options opts);
public static Bitmap decodeByteArray(byte[] data, int offset, int length);
public static Bitmap decodeStream(InputStream is, Rect outPadding, Options opts);
public static Bitmap decodeStream(InputStream is) ;
public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts);
public static Bitmap decodeFileDescriptor(FileDescriptor fd) ;
} |
通过这些静态方法，我们可以方便地从文件、资源、字节流等各种途径打开图片，生成Bitmap对象。下面给出一个从文件中打开图片的函数封装：
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public static Bitmap load( String filepath ) {
Bitmap bitmap = null;
try {
FileInputStream fin = new FileInputStream(filepath);
bitmap = BitmapFactory.decodeStream(fin);
fin.close();
}
catch (FileNotFoundException e) {
}
catch (IOException e) {
}
return bitmap;
} |
2. 保存图片
图片的保存则主要通过Bitmap的compress方法，该方法的原型如下：
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/** * Write a compressed version of the bitmap to the specified outputstream.
* @param format The format of the compressed image
* @param quality Hint to the compressor, 0-100. 0 meaning compress for
* small size, 100 meaning compress for max quality. Some
* formats, like PNG which is lossless, will ignore the
* quality setting
* @param stream The outputstream to write the compressed data.
* @return true if successfully compressed to the specified stream.
*/
public boolean compress(CompressFormat format, int quality, OutputStream stream)
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第一个参数是图片格式，只有JPEG、PNG和WEBP三种，第二个参数是压缩质量（0~100），数值越大图片信息损失越小，第三个参数则是文件流对象。
同样，这里给出一个保存图片的函数封装：
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public static void save( Bitmap bitmap, String filepath ) {
try {
FileOutputStream fos = new FileOutputStream(filepath);
bitmap.compress(CompressFormat.JPEG, 100, fos);
bitmap.recycle();
fos.close();
}
catch (FileNotFoundException e) {
}
catch (IOException e) {
}
}
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3. 剪裁图片
Android中剪裁图片主要有2种方法，一种通过Bitmap的createBitmap方法来生成剪裁的图片，另一种则是通过Canvas对象来“绘制”新的图片，这里先给出代码，再分析：
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public static Bitmap crop( Bitmap bitmap, Rect cropRect ) {
return Bitmap.createBitmap(bitmap,cropRect.left,cropRect.top,cropRect.width(),cropRect.height());
} public static Bitmap cropWithCanvas( Bitmap bitmap, Rect cropRect ) {
Rect destRect = new Rect(0,0,cropRect.width(),cropRect.height());
Bitmap cropped = Bitmap.createBitmap(cropRect.width(),cropRect.height(),Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(cropped);
canvas.drawBitmap(bitmap,cropRect,destRect,null);
return cropped;
} |
其实第一种方法内部实现也是利用了Canvas对象来“绘制”新的图片的，Canvas对象通过一个Bitmap对象来构建，该Bitmap即为“画布”，drawBitmap则是将源bitmap对象“画”到“画布”之中，这样就实现了数据的搬移，实现了图片的剪裁。
4. 旋转图片
Android中旋转图片同样是通过Bitmap的createBitmap方法来生成旋转后的图片，不过图片的旋转需要借助Matrix对象来协助完成，代码如下：
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public static Bitmap rotate( Bitmap bitmap, int degrees ) {
Matrix matrix = new Matrix();
matrix.postRotate(degrees);
return Bitmap.createBitmap(bitmap,0,0,bitmap.getWidth(),bitmap.getHeight(),matrix,true);
} |
当然，图片的旋转也是可以通过Canvas来“绘制”，由于图片旋转会导致边界坐标发生变化，所以需要以图片中心点坐标为中心来旋转，具体实现见如下代码：
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public static Bitmap rotateWithCanvas( Bitmap bitmap, int degrees ) {
int destWidth,destHeight;
float centerX = bitmap.getWidth()/2;
float centerY = bitmap.getHeight()/2;
// We want to do the rotation at origin, but since the bounding
// rectangle will be changed after rotation, so the delta values
// are based on old & new width/height respectively.
Matrix matrix = new Matrix();
matrix.preTranslate(-centerX,-centerY);
matrix.postRotate(degrees);
if( degrees/90%2 == 0 ) {
destWidth = bitmap.getWidth();
destHeight = bitmap.getHeight();
matrix.postTranslate(centerX,centerY);
}
else {
destWidth = bitmap.getHeight();
destHeight = bitmap.getWidth();
matrix.postTranslate(centerY,centerX);
}
Bitmap cropped = Bitmap.createBitmap(destWidth,destHeight,Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(cropped);
canvas.drawBitmap(bitmap, matrix, null);
return cropped;
} |
本文转自 Jhuster 51CTO博客，原文链接：http://blog.51cto.com/ticktick/1604074，如需转载请自行联系原作者