關於縮放的執行緒安全和非執行緒安全操作.
非執行緒安全的操作只能在主線程中進行操作,對於大的處理肯定會消耗大量的時間,
如下面的方法
方法1：使用uikit+
(uiimage
*)imagewithimage
uiimage
*)image scaledtosize
cgsize
)newsize;
cgcontextref bitmap;
if(sourceimage.imageorientation ==
uiimageorientationup
|| sourceimage.imageorientation ==
uiimageorientationdown
)else
if(sourceimage.imageorientation ==
uiimageorientationleft
)else
if(sourceimage.imageorientation ==
uiimageorientationright
)else
if(sourceimage.imageorientation ==
uiimageorientationup
)else
if(sourceimage.imageorientation ==
uiimageorientationdown)
cgcontextdrawimage
(bitmap,
cgrectmake(0
,0, targetwidth, targetheight), imageref);
cgimageref ref
= cgbitmapcontextcreateimage(
bitmap);
uiimage
* newimage =
[uiimage imagewithcgimage:
ref];
cgcontextrelease(
bitmap);
cgimagerelease(
ref);
return newimage; }
這種方法的好處是它是執行緒安全，加上它負責的 （使用正確的顏色空間和點陣圖資訊，處理影象方向）的小東西，uikit
版本不會。 如何
調整和保持長寬比
（如 aspectfill選項）？
它是非常類似於上述，方法，它看起來像這樣： +
(uiimage
*)imagewithimage
uiimage
*)sourceimagescaledtosizewithsameaspectratio
cgsize
)targetsize;
else
scaledwidth
= width * scalefactor;
scaledheight = height* scalefactor;
// center the image
if(widthfactor > heightfactor)
else
if(widthfactor < heightfactor) }
cgimageref imageref=
[sourceimage cgimage];
cgbitmapinfo bitmapinfo
=cgimagegetbitmapinfo(
imageref);
cgcolorspaceref colorspaceinfo
=cgimagegetcolorspace(
imageref);
if(bitmapinfo == kcgimagealphanone)
cgcontextref bitmap;
if(sourceimage.imageorientation ==
uiimageorientationup
|| sourceimage.imageorientation ==
uiimageorientationdown
)else
// in the right or left cases, we need to switch scaledwidth andscaledheight,
// and also the thumbnail point
if(sourceimage.imageorientation ==
uiimageorientationleft
)else
if(sourceimage.imageorientation ==
uiimageorientationright
)else
if(sourceimage.imageorientation ==
uiimageorientationup
)else
if(sourceimage.imageorientation ==
uiimageorientationdown)
cgcontextdrawimage
(bitmap,
cgrectmake
(thumbnailpoint.x,thumbnailpoint.y, scaledwidth, scaledheight), imageref);
cgimageref ref
= cgbitmapcontextcreateimage(
bitmap);
uiimage
* newimage =
[uiimage imagewithcgimage:
ref];
cgcontextrelease(
bitmap);
cgimagerelease(
ref);
return newimage;
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