使用 UIImage drawInRect 仍然将其呈现为上下颠倒

发布于 2024-10-09 04:02:19 字数 1037 浏览 6 评论 0原文

我在这个网站上读过一些关于使用 drawInRect 而不是 CGContext 绘制方法的帖子。它仍然把它画得颠倒吗？我认为使用 drawInRect 会将其正面朝上打印，坐标系起始于左上角？

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
[image drawInRect:CGRectMake(x, size.height-y-height, width, height)];
UIGraphicsPopContext();
}

请注意，我正在执行 size.height-y-height ，如果我不这样做，它就不会到达我期望的位置（假设 drawInRect 使用左上角坐标系））。它使用上面的代码呈现在正确的位置，但仍然颠倒。帮助！！！！！！

更新

感谢下面的答案，这是工作方法

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
CGContextSaveGState(context); 
CGContextTranslateCTM(context, 0, size.height);
CGContextScaleCTM(context, 1.0, -1.0);
[image drawInRect:CGRectMake(x, y, width, height)];
CGContextRestoreGState(context);
UIGraphicsPopContext();
}

原文

I have read some posts on this website about using drawInRect instead of the CGContext draw methods. It still draws it upside down? I thought using drawInRect would print it right side up with the coordinate system originating at the top left?

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
[image drawInRect:CGRectMake(x, size.height-y-height, width, height)];
UIGraphicsPopContext();
}

Notice I'm doing size.height-y-height and if I don't do that it doesn't go where I expect (assuming drawInRect using a topleft coordinate system). It renders in the correct spot with the above code but still upside down. HELP!!!!!!

UPDATE

Thanks to the answer below this is the working method

-(void) drawImage:(UIImage*) image atX:(float) x andY:(float) y withWidth:(float) width andHeight:(float) height onContext:(CGContextRef) context{
UIGraphicsPushContext(context);
CGContextSaveGState(context); 
CGContextTranslateCTM(context, 0, size.height);
CGContextScaleCTM(context, 1.0, -1.0);
[image drawInRect:CGRectMake(x, y, width, height)];
CGContextRestoreGState(context);
UIGraphicsPopContext();
}

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简美 2024-10-16 04:02:19

    UIGraphicsBeginImageContext(imageViewSize);
CGContextRef imageContext = UIGraphicsGetCurrentContext();

// Draw the image in the upper left corner (0,0) with its actual size
CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

//  As it draws the image from lower right corner, 
//  following code will flip it up side down vertically.


CGContextTranslateCTM(imageContext, 0.0, 0.0);
CGContextScaleCTM(imageContext, 1.0, -1.0);

CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

    UIGraphicsBeginImageContext(imageViewSize);
CGContextRef imageContext = UIGraphicsGetCurrentContext();

// Draw the image in the upper left corner (0,0) with its actual size
CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

//  As it draws the image from lower right corner, 
//  following code will flip it up side down vertically.


CGContextTranslateCTM(imageContext, 0.0, 0.0);
CGContextScaleCTM(imageContext, 1.0, -1.0);

CGContextDrawImage(imageContext, imageViewRect, oldImage.CGImage);

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