How to rotate text drawn by Quartz on iPhone
I want to draw some texts using Quartz. Now the app draws
Here is my code:
//set image view
drawImage = [[UIImageView alloc] initWithImage:nil];
drawImage.frame =开发者_如何学Python 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
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
Another way to handle this would be to replace the Quartz text drawing code (from CGSelectFont() to CGContextShowTextAtPoint ()) with something like
[text drawAtPoint:CGPointMake(0.0f, 30.0f) withFont:[UIFont fontWithName:@"Courier" size:40.0f]];
where text is an NSString. On the iPhone, -drawAtPoint:withFont: automatically flips the text to account for the inverted Y axis of the UIViews.
This approach gives you the advantage of handling a wider character set than the MacRoman encoding in the pure Quartz text drawing can. However, it is slightly slower.
What do you mean, exactly, by "rotate them to the normal mode"?
Assuming you just mean rotation within a 2D space, you would typically use a transform matrix. Have a look at CGAffineTransformMakeRotation
.
You could apply it to the view itself (by setting the transform
property), or to the CG context you have.
Well this solved my problem
CGContextSetTextMatrix(context, CGAffineTransformMake(1.0,0.0, 0.0, -1.0, 0.0, 0.0));
精彩评论