截取uiimage指定大小区域
最近遇到这样的需求：从服务器获取到一张照片，只需要显示他的左半部分，或者中间部分等等。也就是截取uiimage指定大小区域。
uiimage扩展：
我的解决方案是对uiimage进行扩展。通过cgimageref和cgimage完成截取，调用的方法是：cgimagecreatewithimageinrect。扩展类叫uiimage+crop，具体代码如下：
uiimage+crop.h
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#import <uikit/uikit.h>
typedef ns_enum(nsinteger, xycropimagestyle){
xycropimagestyleright =0, // 右半部分
xycropimagestylecenter =1, // 中间部分
xycropimagestyleleft =2, // 左半部分
xycropimagestylerightoneofthird =3, // 右侧三分之一部分
xycropimagestylecenteroneofthird =4, // 中间三分之一部分
xycropimagestyleleftoneofthird =5, // 左侧三分之一部分
xycropimagestylerightquarter =6, // 右侧四分之一部分
xycropimagestylecenterrightquarter =7, // 中间右侧四分之一部分
xycropimagestylecenterleftquarter =8, // 中间左侧四分之一部分
xycropimagestyleleftquarter =9, // 左侧四分之一部分
};
@interface uiimage (crop)
- (uiimage *)imagebycroppingwithstyle:(xycropimagestyle)style;
@end
uiimage+crop.m
#import "uiimage+crop.h"
@implementation uiimage (crop)
- (uiimage *)imagebycroppingwithstyle:(xycropimagestyle)style
{
cgrect rect;
switch (style) {
case xycropimagestyleleft:
rect = cgrectmake(0, 0, self.size.width/2, self.size.height);
break;
case xycropimagestylecenter:
rect = cgrectmake(self.size.width/4, 0, self.size.width/2, self.size.height);
break;
case xycropimagestyleright:
rect = cgrectmake(self.size.width/2, 0, self.size.width/2, self.size.height);
break;
case xycropimagestyleleftoneofthird:
rect = cgrectmake(0, 0, self.size.width/3, self.size.height);
break;
case xycropimagestylecenteroneofthird:
rect = cgrectmake(self.size.width/3, 0, self.size.width/3, self.size.height);
break;
case xycropimagestylerightoneofthird:
rect = cgrectmake(self.size.width/3*2, 0, self.size.width/3, self.size.height);
break;
case xycropimagestyleleftquarter:
rect = cgrectmake(0, 0, self.size.width/4, self.size.height);
break;
case xycropimagestylecenterleftquarter:
rect = cgrectmake(self.size.width/4, 0, self.size.width/4, self.size.height);
break;
case xycropimagestylecenterrightquarter:
rect = cgrectmake(self.size.width/4*2, 0, self.size.width/4, self.size.height);
break;
case xycropimagestylerightquarter:
rect = cgrectmake(self.size.width/4*3, 0, self.size.width/4, self.size.height);
break;
default:
break;
}
cgimageref imageref = self.cgimage;
cgimageref imagepartref = cgimagecreatewithimageinrect(imageref, rect);
uiimage *cropimage = [uiimage imagewithcgimage:imagepartref];
cgimagerelease(imagepartref);
return cropimage;
}
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实际运用：
简单测试一下，看看有没有实现我们想要的效果。首先，先加载一个完整的uiimageview。这个应该不难。代码如下：
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uiimageview *imgview = [[uiimageview alloc] init];
imgview.frame = cgrectmake((screen.width - 226) / 2, 100, 226, 106);
uiimage *image = [uiimage imagenamed:@"ganggang"];
imgview.image = image;
[self.view addsubview:imgview];
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运行一下：
要对uiimage进行裁剪，首先导入头文件：
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#import "uiimage+crop.h"
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在上面uiimage *image = [uiimage imagenamed:@"ganggang"];这段代码之后加上下面这句：
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image = [image imagebycroppingwithstyle:xycropimagestyleleft];
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xycropimagestyleleft是截取照片的左半部分。效果如下：
截取成功，还可以截取其他区域的，只需要传入不同的xycropimagestyle即可实现。
uiimage等比缩放
前面讲了截取uiimage指定大小区域，很方便的截取uiimage。今天要和大家分享的是uiimage的缩放。
两种缩放:
1.缩放到指定大小
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- (uiimage*)imagecompresswithsimple:(uiimage*)image scaledtosize:(cgsize)size
{
uigraphicsbeginimagecontext(size);
[image drawinrect:cgrectmake(0,0,size.width,size.height)];
uiimage* newimage = uigraphicsgetimagefromcurrentimagecontext();
uigraphicsendimagecontext();
return newimage;
}
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2.等比缩放
（1）通过缩放系数：
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- (uiimage*)imagecompresswithsimple:(uiimage*)image scale:(float)scale
{
cgsize size = image.size;
cgfloat width = size.width;
cgfloat height = size.height;
cgfloat scaledwidth = width * scale;
cgfloat scaledheight = height * scale;
uigraphicsbeginimagecontext(size); // this will crop
[image drawinrect:cgrectmake(0,0,scaledwidth,scaledheight)];
uiimage* newimage= uigraphicsgetimagefromcurrentimagecontext();
uigraphicsendimagecontext();
return newimage;
}
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scale是缩放系数 。
（2）通过计算得到缩放系数
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- (uiimage*)imagebyscalingandcroppingforsize:(cgsize)targetsize
{
uiimage *sourceimage = [uiimage imagenamed:@"test.jpg"];
uiimage *newimage = nil;
cgsize imagesize = sourceimage.size;
cgfloat width = imagesize.width;
cgfloat height = imagesize.height;
cgfloat targetwidth = targetsize.width;
cgfloat targetheight = targetsize.height;
cgfloat scalefactor = 0.0;
cgfloat scaledwidth = targetwidth;
cgfloat scaledheight = targetheight;
cgpoint thumbnailpoint = cgpointmake(0.0,0.0);
if (cgsizeequaltosize(imagesize, targetsize) == no)
{
cgfloat widthfactor = targetwidth / width;
cgfloat heightfactor = targetheight / height;
if (widthfactor > heightfactor)
scalefactor = widthfactor; // scale to fit height
else
scalefactor = heightfactor; // scale to fit width
scaledwidth= width * scalefactor;
scaledheight = height * scalefactor;
// center the image
if (widthfactor > heightfactor)
{
thumbnailpoint.y = (targetheight - scaledheight) * 0.5;
}
else if (widthfactor < heightfactor)
{
thumbnailpoint.x = (targetwidth - scaledwidth) * 0.5;
}
}
uigraphicsbeginimagecontext(targetsize); // this will crop
cgrect thumbnailrect = cgrectzero;
thumbnailrect.origin = thumbnailpoint;
thumbnailrect.size.width= scaledwidth;
thumbnailrect.size.height = scaledheight;
[sourceimage drawinrect:thumbnailrect];
newimage = uigraphicsgetimagefromcurrentimagecontext();
if(newimage == nil)
nslog(@"could not scale image");
//pop the context to get back to the default
uigraphicsendimagecontext();
return newimage;
}
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