CODEWITHSUNDEEP
iosquartz-2dcore-image
Teddy
Teddy

Reputation: 1095

CGContextRef => CGImageRef => CIImage => CGImageRef => CGContextDrawImage chain turns image upside down

This issue kills me. I do not know what is going wrong. But the following code turns the image upside down. It does a vertical flip in fact and I do not know why.

UIFont *font = [UIFont fontWithName:fontName size:fontSize];

NSMutableDictionary *attributes = [[NSMutableDictionary alloc] init];
[attributes setObject:font forKey:NSFontAttributeName];
[attributes setObject:[NSNumber numberWithFloat:kStrokeWidth] forKey:NSStrokeWidthAttributeName];
[attributes setObject:[UIColor redColor] forKey:NSStrokeColorAttributeName];
[attributes setObject:style forKey:NSParagraphStyleAttributeName];

[text drawInRect:drawRect withAttributes:attributes];

[attributes removeObjectForKey:NSStrokeWidthAttributeName];
[attributes removeObjectForKey:NSStrokeColorAttributeName];
[attributes setObject:[UIColor blueColor] forKey:NSForegroundColorAttributeName];
[text drawInRect:drawRect withAttributes:attributes];

CGImageRef cgImg = CGBitmapContextCreateImage(context);
CIImage *beginImage = [CIImage imageWithCGImage:cgImg];

CIContext *cicontext = [CIContext contextWithOptions:nil];
CGImageRef cgimg = [cicontext createCGImage:beginImage fromRect:[beginImage extent]];
CGContextDrawImage(context, [beginImage extent] , cgimg);
CGImageRelease(cgImg);
CGImageRelease(cgimg);


UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

This will result in this:

enter image description here

Why, oh why?

Upvotes: 1

Views: 1528

Answers (1)

Aaron Golden
Aaron Golden

Reputation: 7102

This might be more appropriate as a comment than as an answer, but it's too long for a comment.

As @Andrea noted, it's a little weird that you are creating both a CGContext and CIContext. If you just want to extract a UIImage from a CGImageRef you can use

UIImage *newImage = [[UIImage alloc] initWithCGImage:cgImg]

The resulting newImage will still be flipped. The coordinate systems used by UIImages and CGContextRefs have oppositely oriented vertical axes. I recommend that you flip your initial CGContextRef vertically while drawing:

CGContextSaveGState(context);
CGContextTranslateCTM(context, 0, CGBitmapContextGetHeight(context));
CGContextScaleCTM(context, 1, -1);
// All your drawing code goes here.
CGContextRestoreGState(context);

Upvotes: 2

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