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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) ;
}
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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;
}
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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;
}
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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
);
}
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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;
}
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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