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Asked: 2026-05-13T01:51:10+00:00

I want to draw some texts using Quartz. Now the app draws , but

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I want to draw some texts using Quartz. Now the app draws
alt text
, but I want it to show as “0123456789”. Is there any way to show its normal orientation?

Here is my code:

    //set image view
 drawImage = [[UIImageView alloc] initWithImage:nil];
 drawImage.frame = self.view.frame;
 [self.view addSubview:drawImage];

 UIGraphicsBeginImageContext(self.view.frame.size);  // begin
 // current context
 CGContextRef context = UIGraphicsGetCurrentContext();

 CGContextSelectFont(context, "Courier", 40,  kCGEncodingMacRoman);
 CGFloat white[] = {1.0, 1.0, 1.0, 1.0};
 CGContextSetFillColor(context, white);
 CGContextShowTextAtPoint(context, 0, 30, "0123456789", strlen("0123456789"));

 // get image
 drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
 UIGraphicsEndImageContext();    // end
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1 Answer

  1. Editorial Team

    In Quartz, the image will be upside down because its Y-Axis is inverted.

    iPhone’s Y axis goes positive from top to bottom i.e. origin is at top left while in Quartz and OpenGL, the co-ordinates are the same way as good old geometry i.e. origin at bottom left.

    Here is some code for solving Quartz inversion problem: 

    CGContextRef ctx = UIGraphicsGetCurrentContext();
// Tanslate and scale upside-down to compensate for Quartz's inverted coordinate system
CGContextTranslateCTM(ctx, 0.0, rect.size.height);
CGContextScaleCTM(ctx, 1.0, -1.0);

    Here is an interesting post about it where the author says a team in Singapore gave up an iPhone project due to this inversion problem which they could not figure out: http://trandangkhoa.blogspot.com/2009/07/iphone-os-drawing-image-and-stupid.html

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