mask text inside uitextview/uiwebview - iphone

Question

finally I choose to devote some time to find a way/implementation to
mask text inside UITextView/UIWebView.
By now what I'm able to do is:
- add some custom background
- add a uitextview/uiwebview with some text
- add an UIImageView (with a covering png) or a CAGradientLayer to
create a simple mask effect (*)
Of course this is not a magic bullet and require at least one more
layer (the one pointed out with *).
Furthermore it's not so good when you have a full transparent
background 'cause everyone can recognize the extra view/layer used to
fade away the text.
I searched all over google but still not found a good solution (I've
found about mask an image, blah blah)...
Any tips?
Thanks in advance,
marcio
PS maybe a screenshot will be more straightforward, here you're!
http://grab.by/KzS

Answer 1

Yes! I finally got it. I don't know if it's the Apple's way but it works. Maybe they have the opportunity to employ some private apis. Anyway this is a sort of pseudo-algorithm on how I got it works:
1) get a screenshot of the window
2) crop the desired rect with CGImageCreateWithImageInRect
3) apply a gradient mask (stolen from Apple' sample code on Reflections)
4) create an UIImageView with the freshly created image
I also noted that it doesn't affect the performances even on the lowest devices.
Hope it will be helpful!
And this is a crop of the result (link text)
I've promised to myself to implement a category just to make it better. Until now the code is quite spread in different classes.
Just to make a sample (supported only landscape orientation, see the transform below, supported only top mask). In this case I overrided didMoveToWindow of the table that needs to be masked:
- (void)didMoveToWindow {
if (self.window) {
UIImageView *reflected = (UIImageView *)[self.superview viewWithTag:TABLE_SHADOW_TOP];
if (!reflected) {
UIImage *image = [UIImage screenshot:self.window];
//
CGRect croppedRect = CGRectMake(480-self.frame.size.height, self.frame.origin.x, 16, self.frame.size.width);
CGImageRef cropImage = CGImageCreateWithImageInRect(image.CGImage, croppedRect);
UIImage *reflectedImage = [UIImage imageMaskedWithGradient:cropImage];
CGImageRelease(cropImage);
UIImageView *reflected = [[UIImageView alloc] initWithImage:reflectedImage];
reflected.transform = CGAffineTransformMakeRotation(-(M_PI/2));
reflected.tag = TABLE_SHADOW_TOP;
CGRect adjusted = reflected.frame;
adjusted.origin = self.frame.origin;
reflected.frame = adjusted;
[self.superview addSubview:reflected];
[reflected release];
}
}
}
and this is the uiimage category:
CGImageRef CreateGradientImage(int pixelsWide, int pixelsHigh)
{
CGImageRef theCGImage = NULL;
// gradient is always black-white and the mask must be in the gray colorspace
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
// create the bitmap context
CGContextRef gradientBitmapContext = CGBitmapContextCreate(NULL, pixelsWide, pixelsHigh,
8, 0, colorSpace, kCGImageAlphaNone);
// define the start and end grayscale values (with the alpha, even though
// our bitmap context doesn't support alpha the gradient requires it)
CGFloat colors[] = {0.0, 1.0, 1.0, 1.0};
// create the CGGradient and then release the gray color space
CGGradientRef grayScaleGradient = CGGradientCreateWithColorComponents(colorSpace, colors, NULL, 2);
CGColorSpaceRelease(colorSpace);
// create the start and end points for the gradient vector (straight down)
CGPoint gradientStartPoint = CGPointZero;
// CGPoint gradientStartPoint = CGPointMake(0, pixelsHigh);
CGPoint gradientEndPoint = CGPointMake(pixelsWide/1.75, 0);
// draw the gradient into the gray bitmap context
CGContextDrawLinearGradient(gradientBitmapContext, grayScaleGradient, gradientStartPoint,
gradientEndPoint, kCGGradientDrawsAfterEndLocation);
CGGradientRelease(grayScaleGradient);
// convert the context into a CGImageRef and release the context
theCGImage = CGBitmapContextCreateImage(gradientBitmapContext);
CGContextRelease(gradientBitmapContext);
// return the imageref containing the gradient
return theCGImage;
}
CGContextRef MyCreateBitmapContext(int pixelsWide, int pixelsHigh)
{
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create the bitmap context
CGContextRef bitmapContext = CGBitmapContextCreate (NULL, pixelsWide, pixelsHigh, 8,
0, colorSpace,
// this will give us an optimal BGRA format for the device:
(kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst));
CGColorSpaceRelease(colorSpace);
return bitmapContext;
}
+ (UIImage *)imageMaskedWithGradient:(CGImageRef)image {
UIDeviceOrientation deviceOrientation = [UIDevice currentDevice].orientation;
DEBUG(#"need to support deviceOrientation: %i", deviceOrientation);
float width = CGImageGetWidth(image);
float height = CGImageGetHeight(image);
// create a bitmap graphics context the size of the image
CGContextRef mainViewContentContext = MyCreateBitmapContext(width, height);
// create a 2 bit CGImage containing a gradient that will be used for masking the
// main view content to create the 'fade' of the reflection. The CGImageCreateWithMask
// function will stretch the bitmap image as required, so we can create a 1 pixel wide gradient
CGImageRef gradientMaskImage = CreateGradientImage(width, 1);
// create an image by masking the bitmap of the mainView content with the gradient view
// then release the pre-masked content bitmap and the gradient bitmap
CGContextClipToMask(mainViewContentContext, CGRectMake(0.0, 0.0, width, height), gradientMaskImage);
CGImageRelease(gradientMaskImage);
// draw the image into the bitmap context
CGContextDrawImage(mainViewContentContext, CGRectMake(0, 0, width, height), image);
// create CGImageRef of the main view bitmap content, and then release that bitmap context
CGImageRef reflectionImage = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);
// convert the finished reflection image to a UIImage
UIImage *theImage = [UIImage imageWithCGImage:reflectionImage];
// image is retained by the property setting above, so we can release the original
CGImageRelease(reflectionImage);
return theImage;
}
Hope it helps.