如何绘制UIImage图像，例如装修样式

Question

我想从jpg文件中获取缩略图并显示为UIImage。显示样式为装修模式，例如 UIViewContentModeScaleAspectFill。下面是示例代码，但它太复杂了。

-(UIImage*)scaleToSize:(CGSize)size   
{  
    CGFloat width = CGImageGetWidth(self.CGImage);  
    CGFloat height = CGImageGetHeight(self.CGImage);    
    NSLog(@"size w=%f, h=%f, image w=%f, h=%f", size.width, size.height, width, height);
    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;  
    NSLog(@"width=%f, height=%f", width, height);
    int xPos = (size.width - width)/2;  
    int yPos = (size.height-height)/2;  
    NSLog(@"xpos=%d, ypos=%d", xPos, yPos);
    CGSize sz = CGSizeMake(width, height);  
    UIGraphicsBeginImageContext(sz);    
    //  
    [self drawInRect:CGRectMake(0, 0, width, height)];    
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();    
    CGRect rt = CGRectMake(-xPos, -yPos, size.width, size.height);
    UIImage* thub = [scaledImage getSubImage:rt];
    scaledImage = nil;
    return thub;  
} 
    - (UIImage *)getSubImage:(CGRect) rect{
    CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
    CGRect smallBounds = CGRectMake(rect.origin.x, rect.origin.y,       CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));
    NSLog(@"small bounds x=%f, y=%f, w=%f, h=%f", smallBounds.origin.x, smallBounds.origin.y, smallBounds.size.width, smallBounds.size.height);
    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage* smallImg = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();
    return smallImg;
}

Answer 1

我已经更新了该方法：

-(UIImage*)getSubImage:(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;  
    radio = verticalRadio < horizontalRadio ? horizontalRadio : verticalRadio;
    CGRect displayRect = CGRectMake((size.width - width*radio)/2.0f, 
                                (size.height-height*radio)/2.0f, 
                                width*radio, 
                                height*radio);

    // create a bitmap context and then set the context to current using     
    UIGraphicsBeginImageContext(size);    
    //clip
    UIRectClip(displayRect);
    //draw the bitmap in rect    
    [self drawInRect:displayRect];    
    // from context to get a UIIMage  
    UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();    
    // move context out of buffer
    UIGraphicsEndImageContext();   
    NSLog(@"getSubImage ---->");
    // return. 
    return scaledImage;  
}