UIImage扩展

//
//  UIImage+Scale.h
//  CloudShopping
//
//  Created by sixiaobo on 14-7-8.
//  Copyright (c) 2014年 com.Uni2uni. All rights reserved.
//

#import <UIKit/UIKit.h>

/*!
 * @brief
 * @author huangyibiao
 */
@interface UIImage (Scale)

/*!
 * @brief 根据指定的Rect来截取图片，返回截取后的图片
 * @param rect 指定的Rect，如果大小超过图片大小，就会返回原图片
 * @return 返回截取后的图片
 */
- (UIImage *)subImageWithRect:(CGRect)rect;

/*!
 * @brief 把图片等比例缩放到指定的size
 * @param size 缩放后的图片的大小
 * @return 返回缩放后的图片
 */
- (UIImage *)scaleToSize:(CGSize)size;

@end

//
//  UIImage+Scale.m
//  CloudShopping
//
//  Created by sixiaobo on 14-7-8.
//  Copyright (c) 2014年 com.Uni2uni. All rights reserved.
//

#import "UIImage+Scale.h"

@implementation UIImage (Scale)

#pragma mark - 截取部分图像
- (UIImage *)subImageWithRect:(CGRect)rect {
    CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    CGRect smallBounds = CGRectMake(0, 0, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));

    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();

    return smallImage;
}

#pragma mark - 等比例缩放
- (UIImage *)scaleToSize:(CGSize)size {
    CGFloat width = CGImageGetWidth(self.CGImage);
    CGFloat height = CGImageGetHeight(self.CGImage);

    float verticalRadio = size.height * 1.0 / height;
    float horizontalRadio = size.width * 1.0 / width;
    float radio = 1;

    if(verticalRadio > 1 && horizontalRadio > 1) {
        radio = verticalRadio > horizontalRadio ? horizontalRadio : verticalRadio;
    } else {
        radio = verticalRadio < horizontalRadio ? verticalRadio : horizontalRadio;
    }

    width = width * radio;
    height = height * radio;
    int xPos = (size.width - width) / 2;
    int yPos = (size.height - height) / 2;

    // 创建一个bitmap的context
    // 并把它设置成为当前正在使用的context
    UIGraphicsBeginImageContext(size);
    // 绘制改变大小的图片
    [self drawInRect:CGRectMake(xPos, yPos, width, height)];
    // 从当前context中创建一个改变大小后的图片
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    // 使当前的context出堆栈
    UIGraphicsEndImageContext();
    // 返回新的改变大小后的图片
    return scaledImage;
}

@end