objective c - Scaling UITextView using contentScaleFactor property

Question

I am trying to create a higher resolution image of a UIView, specifically UITextView.

This question and answer is exactly what I am trying to figure out:

• Retain the resolution of the label after scaling in iphone

But, when I do the same, my text is still blurry:

self.view.transform = CGAffineTransformMakeScale(2.f, 2.f);
[myText setContentScaleFactor:2.f]; // myText is a subview of self.view object

I have also tried the same in the Apple sample project "UICatalog" to UILabel and it is also blurry.

I can't understand why it would work for Warrior from the other question and not for me. I would have asked there — but I can't seem to leave a comment or a question there.

Answer 1

Setting the contentScaleFactor and contentsScale is in fact the key, as @dbotha pointed out, however you have to walk the view and layer hierarchies separately in order to reach every internal CATiledLayer that actually does the text rendering. Adding the screen scale might also make sense.

So the correct implementation would be something like this:

- (void)updateForZoomScale:(CGFloat)zoomScale {
    CGFloat screenAndZoomScale = zoomScale * [UIScreen mainScreen].scale;
    // Walk the layer and view hierarchies separately. We need to reach all tiled layers.
    [self applyScale:(zoomScale * [UIScreen mainScreen].scale) toView:self.textView];
    [self applyScale:(zoomScale * [UIScreen mainScreen].scale) toLayer:self.textView.layer];
}

- (void)applyScale:(CGFloat)scale toView:(UIView *)view {
    view.contentScaleFactor = scale;
    for (UIView *subview in view.subviews) {
        [self applyScale:scale toView:subview];
    }
}

- (void)applyScale:(CGFloat)scale toLayer:(CALayer *)layer {
    layer.contentsScale = scale;
    for (CALayer *sublayer in layer.sublayers) {
        [self applyScale:scale toLayer:sublayer];
    }
}